Patent Publication Number: US-2022229390-A1

Title: Image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus for forming an image on a sheet. 
     In the image forming apparatus of an electrophotographic type or the like, a constitution in which different images are formed on a first surface (front surface) and a second surface (black surface), respectively, of the sheet is employed. In such an image forming apparatus, the image is formed on a first surface, and thereafter, and leading and trailing ends of the sheet are reversed, and the image is formed on the second surface. By this sheet reversing operation, the trailing end of the sheet becomes the leading end of the sheet. That is, in the case where the image is formed on the first surface of the sheet, the image is formed on the sheet by being aligned with a sheet leading end position on the first surface of the sheet. On the other hand, in the case where the image is formed on the sheet, the image is formed on the second surface of the sheet, the image is formed on the sheet by being aligned with a sheet leading end position (sheet trailing end position on the first surface of the sheet) on the second surface of the sheet. 
     In order to accurately align an image forming position of the first surface of the sheet with an image forming position of the second surface of the sheet, in Japanese Laid-Open Patent Application 2018-72538, a technique such that a plurality of reference images for adjusting the positions are formed on the sheet and are read by a scanner, and then the positions where the images are formed are adjusted depending on a difference between the positions of these reference images is disclosed. 
     However, for example, in the case where the sheet fed is a thin sheet and a leading end of the sheet is curled, even when the reference image positions are adjusted in the above, there is a liability that a distance from the leading end to the image position varies by an amount of the curl. For that reason, in order to suppress the amount of the curl, when a thickness (distance between guiding members) of a sheet feeding passage is set at a small value, a thick sheet causes a jam, and therefore, there is a problem that such setting cannot meet the thick sheet. On the other hand, in order to prevent the occurrence of the jam of the thick sheet, when the thickness of the sheet feeding passage is set at a large value in conformity to the thick sheet, there arises a problem that accuracy of the positional alignment of the thin sheet becomes unsatisfactory. 
     SUMMARY OF THE INVENTION 
     A principal object of the present invention is to provide an image forming apparatus capable of detecting a position of a thin sheet with accuracy while enabling even a thick sheet to be subjected to image formation. 
     According to an aspect of the present invention is to provide an image forming apparatus comprising: an image forming portion configured to form an image on a sheet; a sheet feeding portion configured to feed the sheet toward the image forming portion; a first guiding member provided between the sheet feeding portion and the image forming portion and including a first guiding surface for guiding the sheet; a second guiding member configured to form a sheet feeding passage in which the sheet passes, by being provided opposed to the first guiding member and including a second guiding surface for guiding the sheet; a driving portion configured to movably drive the first guiding portion so that a distance in the sheet feeding passage with respect to a thickness direction of the sheet changes; a detecting portion provided downstream of the sheet feeding portion with respect to the feeding direction and configured to detect a leading end of the sheet at a detecting position; and a controller configured to control a time until the leading end of the sheet reaches from the detecting position of the detecting portion to the image forming portion by controlling the sheet feeding portion on the basis of a detection result of the leading end of the sheet by the detecting portion, wherein when the leading end of the sheet is detected by the detecting portion, in a case that information on a thickness of the sheet fed by the sheet feeding portion is a first thickness, the controller controls the driving portion so that the distance in the sheet feeding passage with respect to the thickness direction is a first distance, and in a case that the information on the thickness of the sheet fed by the sheet feeding portion is a second thickness thinner than the first thickness, the controller controls the driving portion so that the distance in the sheet feeding passage with respect to the thickness direction is a second distance shorter than the first distance. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an image forming system according to a first embodiment. 
         FIG. 2  is an enlarged sectional view showing a feeding passage, in which a timing sensor is provided, from a registration roller pair to a transfer portion. 
         FIG. 3  is an enlarged schematic view showing the feeding passage in which the timing sensor is disposed and the registration roller pair. 
         FIG. 4A  is a schematic view showing a state in which a thin sheet which is not curled is fed in a state in which a moving feeding guide is kept at a longest distance from a fixed feeding guide. 
         FIG. 4B  is a schematic view showing a state in which a thin sheet which is curled is fed in the state in which the moving feeding guide is kept at the longest distance from the fixed feeding guide. 
         FIG. 4C  is a schematic view showing a state in which the thin sheet is fed in a state in which the moving feeding guide is brought near to the fixed feeding guide for the thin sheet. 
         FIG. 5  is a sectional view showing the fixed feeding guide and the moving feeding guide in a position of the timing sensor according to the first embodiment. 
         FIG. 6  is a block diagram showing a control system of the image forming apparatus according to the first embodiment. 
         FIG. 7  is a flowchart showing feeding passage thickness control according to the first embodiment. 
         FIG. 8A  is a sectional view showing a fixed feeding guide and a moving feeding guide in a position of a timing sensor according to a second embodiment. 
         FIG. 8B  is an enlarged schematic view showing a driving mechanism according to the second embodiment. 
         FIG. 9  is a sectional view showing a fixed feeding guide and a moving feeding guide in a position of a timing sensor according to a third embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, an image reading apparatus and an image forming system according to respective embodiments will be described while making reference to the drawings. As regards dimensions, materials, shapes, and relative arrangements of constituent elements described in the following embodiments, an application range of the present invention is not intended to be limited only thereto unless otherwise specified. 
     First Embodiment 
     [General Structure of Image Forming System] 
       FIG. 1  is a schematic view of an image forming system  100 S according to a first embodiment. The image forming system  100 S includes an image forming apparatus  100  and a finisher  200 . In this embodiment, as the image forming apparatus, the image forming apparatus  100  which is a laser beam printer of an electrophotographic type will be described as an example, but is not limited thereto. The image forming apparatus may also be a printer of an ink jet type or a printer of a sublimation type. 
     In a casing  101  of the image forming apparatus  100 , an image forming engine  102 , a controller  900  for controlling an operation of the image forming system  100 S, and a control board accommodating portion for accommodating a storing portion  901  (see  FIG. 6 ) which is a data storing area are mounted. The image forming engine  102  as an image forming portion includes an optical processing mechanism  10  and a fixing processing mechanism  20  which are used for forming an image on a recording material by an image forming process, and includes a feeding processing mechanism  30  and a conveying processing mechanism  40  which are used for feeding and conveying a rectangular sheet  110  used as the recording material. As the recording material, it is possible to use sheets including papers such as plain paper and thick paper, surface-treated papers such as coated paper and embossed paper, a plastic film, a cloth, and the like. 
     The optical processing mechanism  10  includes stations  120 ,  121 ,  122  and  123  for forming toner images of colors of yellow, magenta, cyan and black, respectively, and an intermediary transfer belt  106 . In each of the stations  120 - 123 , a surface of a photosensitive member  105  which is a drum-shaped photosensitive member is electrically charged by a primary charger  111 . A laser scanner portion  107  performs an exposure processing of the photosensitive member  105  on the basis of an instruction signal which is generated based on image data and which is sent to the laser scanner portion  107 . The laser scanner portion  107  includes a laser driver for turning on and off laser light emitted from a semiconductor laser. The laser scanner portion  107  guides the laser light from the semiconductor laser toward the photosensitive member  105  via a reflecting mirror  109  while dividing the laser light (beams) in a main scan direction (widthwise direction of the sheet) by a rotatable polygonal mirror. By this, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive member  105 . 
     A depending device  112  accommodates there is a developer containing toner and supplies charged toner particles to the photosensitive member  105 . The toner particles are deposited on the drum surface depending on a surface potential distribution, so that the electrostatic latent image carried on the photosensitive member  105  is visualized as a toner image. The toner image carried on the photosensitive member  105  is transferred (primary-transferred) onto the intermediary transfer belt  106  to which a voltage of a polarity opposite to a normal charge polarity of the toner is applied. In the case where a color image is formed, the toner images formed by the four stations  120 - 123  are multiple-transferred so as to be superposed on each other on the intermediary transfer belt  106 , so that a full-color toner image is formed on the belt. 
     On the other hand, the feeding processing mechanism  30  feeds sheets  110  one by one from a sheet accommodating portion  113 , inserted into the casing  101  of the image forming apparatus  100  so as to be capable of being pulled out of the casing, toward a transfer portion  330  formed by a transfer roller  114  and an inner transfer roller  331 . As described later specifically, a leading end of the sheet  110  fed is detected by a timing sensor  116  as a detecting portion. The controller  900  controls a timing when a feeding (conveying) speed of the sheet  110  by a registration roller pair  301  on the basis of detection of a leading end of the sheet  110  as a detection result of the timing sensor  116  is lowered, and thus adjusts a timing when the leading end of the sheet  110  reaches the transfer portion  330 . Then, the toner image carried on the intermediary transfer belt  106  which is an intermediary transfer member is transferred (secondary-transferred) onto the sheet  110 . 
     Around the intermediary transfer belt  106 , an image formation start position detecting sensor  115  for determining a print start position when image formation is performed, the timing sensor  116  for establishing a timing when the sheet  110  is fed, and a density sensor  117  are provided. The density sensor  117  measures a density of a patch image for a test carried on the intermediary transfer belt  106 . The controller  900  adjusts an operation condition (for example, setting of a target charging potential of the primary charger  111  and a bias voltage of the developing device  112 ) of the optical processing mechanism  10  on the basis of a detection result of the density sensor  117 . 
     The fixing processing mechanism  20  as a fixing portion in this embodiment is constituted by a first fixing device  150  and a second fixing device  160 . The first fixing device  150  includes a fixing roller  151 , a pressing belt  152  for causing the sheet  110  to press-contact the fixing roller  151 , and a first post-fixing sensor  153  for detecting completion of fixing processing by the first fixing device  150 . The fixing roller  151  is a hollow roller and includes a heater therein. The first fixing provided  150  applies heat and pressure to the toner image on the sheet  110  while nipping and feeding the sheet  110  by the fixing roller  151  and the pressing belt  152  which are a rotatable member pair. By this, the toner particles are melted and then are fixed, so that the image is fixed on the sheet  110 . 
     The second fixing device  160  is disposed on a side downstream of the first fixing device  150  with respect to a feeding passage of the sheet  110 . The second fixing device  160  has a function of enhancing glossiness of the image subjected to the fixing processing by the first fixing device  150  and of ensuring a fixing property of the image on the sheet  110 . The second fixing device  160  includes a fixing roller  161  and a pressing roller  162  which are a rotatable member pair for heating and pressing the sheet  110  while feeding the sheet  110  similarly as the first fixing device  150 , and a second post-fixing sensor  163  for detecting completion of fixing processing by the second fixing device  160 . 
     Incidentally, there is a case that there is no need to pass the sheet  110  through the second fixing device  160  depending on a kind of the sheet  110 . In such a case, the image forming apparatus  100  includes a detour feeding passage  130  for discharging the sheet  110  without via the second fixing device  160  for the purpose of reducing energy consumption. The sheet  110  sent from the first fixing device  150  is derived to either one of the second fixing device  160  and the detour feeding passage  130  by a first switching flapper  131 . 
     The sheet  110  passed through the second fixing device  160  or the detour feeding passage  130  is derived to either one of a discharging feeding passage  139  and a reverse sheet  135  by a second switching flapper  132 . The sheet  110  conveyed to the reverse feeding passage  135  is subjected to detection of a position of the sheet  110  by a reversing sensor  137 , so that a downstream end (leading end) and an upstream end (trailing end) of the sheet  110  with respect to a sub-scan direction (sheet feeding direction) are switched to each other by a switch-back operation performed by a reversing portion  136 . In the case of double-side printing, the sheet  110  on which the image is formed on the front surface is conveyed again toward the transfer roller  114  via a re-feeding (conveying) passage  138  by a third switching flap  133  in a state in which leading end trailing ends of the sheet  110  are changed to each other by the reversing portion  136 , so that an image is formed on a back surface of the sheet  110  opposite from the front surface of the sheet  110 . 
     The sheet  110  on which the image formation in one-side printing is ended or the sheet  110  on which the image formation on the back surface in the double-side printing is ended is discharged to an outside of the image forming apparatus  100  by a discharging roller  139   a  provided in a discharging feeding passage  139  and then is fed to the finisher  200 . Between the reversing feeding passage  135  and the discharging feeding passage  139 , a fourth flapper  134  capable of deriving the sheet  110 , switched back by the reversing portion  136 , toward the discharging feeding passage  139  is provided. That is, by this fourth flapper  134 , the front and back surfaces (sides) of the sheet  110  when the sheet  110  is discharged from the image forming apparatus  100  is made selectable. Incidentally, at an upper portion of the image forming apparatus  100 , an image reading device  190  for reading image information from an original is provided. Further, the finisher  200  carries out processing such that a plurality of the sheets  110  which are fed successively from the image forming apparatus  100  are discharged while being aligned and stored in bundles or are discharged after being subjected to stapling processing. Then, the sheets  110  are discharged to the outside of the finisher  200 , so that the sheet discharging as the image forming system  100 S is completed. 
     [General Structure of Feeding Passage from Registration Roller Pair to Transfer Portion] 
     General structures of sheet feeding passages P 1 , P 2  and P 3  of the sheets, from the registration roller pair  301  to the transfer portion  330 , in which the timing sensor  116  is disposed will be described using  FIG. 2 .  FIG. 2  is an enlarged sectional view showing the feeding passages, from the registration roller pair  301  to the transfer potion  330 , in which the timing sensor  116  is disposed. The sheet  110  fed from the sheet accommodating portion  113  or the reversing portion  136  passes through the feeding passage P 1  formed between a feeding guide  311  including a guide surface  311   a  and a feeding guide  312  including a guide surface  312   a  and is fed to the registration roller pair  301 . The registration roller pair  301  as a sheet feeding portion is constituted by including a driving roller  301   a  which is a first roller driven by a driving motor and a follower roller  301   b  which is a second roller driven by the driving roller  301   a . The sheet  110  fed by a feeding force of the registration roller pair  301  is disposed on a downstream side of the sheet feeding direction and is fed to the feeding passage P 2  in which the timing sensor  116  is disposed. 
     The feeding passage P 2  is constituted by a fixed feeding guide  303  including a guide surface  303   a  constituting a second guiding surface and a moving feeding guide  304  including a guide surface  304   a  constituting a first guiding surface. That is, the feeding passage P 2  is formed as a space in which the sheet  110  is capable of passing through between the guide surface  303   a  and the guide surface  304   a  disposed opposed to each other, and the fixed feeding guide  303  is disposed below the feeding passage P 2  and the moving feeding guide  304  is disposed above the feeding passage P 2 . In the first embodiment, each of the guide surfaces  303   a  and  304   a  is larger in distance with respect to the widthwise direction than a maximum width size of the sheet with respect to the widthwise direction in which the image is capable of being formed in the image forming apparatus  100 , in other words, in which the sheet is capable of being fed by the respective rollers. Accordingly, a constitution in which even when the maximum width size sheet is fed, the sheet falls within a range with respect to the widthwise direction, without projecting in the widthwise direction of the feeding passage P 2 , between the guide surface  303   a  and the guide surface  304   a  is employed. 
     The timing sensor  116  is constituted by including a sensor main body  116   a  as an element for emitting and receiving light and a prism  116   b  as a reflecting member for reflecting the light from the sensor main body  116   a  and for returning the light to the fixed feeding guide  303 . The sensor main body  116   a  is fixed and supported by the fixed feeding guide  303 . The prism  116   b  is fixed and supported by the moving feeding guide  304 . Further, in the first embodiment, the fixed feeding guide  303  is fixed to a frame fixed to the casing  101 , and the moving feeding guide  304  is supported movably by the frame. 
     Further, on a side downstream, with respect to the sheet feeding direction, of the feeding passage P 2  formed by the fixed feeding guide  303  and the moving feeding guide  304 , the feeding passage P 3  is disposed. The feeding passage P 3  is formed by a feeding guide  321  including a guide surface  321   a  and a feeding guide  322  including a guide surface  322   a . That is, the feeding passage P 3  is formed between the guide surface  321   a  and the guide surface  322   a , and the feeding guide  321  is disposed below the feeding passage P 3  and the feeding guide  322  is disposed above the feeding passage P 3 . This feeding passage P 3  is disposed between the feeding passage P 2  and the transfer portion  330  and is constituted so that the sheet  110  fed by the registration roller pair  301  is guided to the transfer portion  330 . For that reason, the feeding passage P 3  is formed so as to be curved as viewed in the widthwise direction of the sheet so that the sheet  110  is guided upward and is caused to approach the intermediary transfer belt  106  and then so that an angle between the intermediary transfer belt  106  and an advancing direction of the leading end of the sheet  110  is made small and then the sheet  110  reaches the transfer portion  330 . 
     Incidentally, the widthwise direction of the sheet refers to a direction perpendicular to the sheet feeding direction and a sheet thickness direction, and refers to a direction parallel to axial directions of the various rollers. 
     [Cause of Detection Error by Timing Sensor and Reduction of Error] 
     Next, a cause of an occurrence of an error of a timing (sheet feeding distance) when the leading end of the sheet  110  is detected by the timing sensor  116 , and an error reducing constitution will be described using  FIG. 3 ,  FIG. 4A ,  FIG. 4B  and  FIG. 4C .  FIG. 3  is an enlarged schematic view showing the feeding passage in which the timing sensor is disposed and showing the registration roller pair.  FIG. 4A  is a schematic view showing a state in which a thin sheet which is not curled is fed in a state in which the moving feeding guide is kept at a longest distance from the fixed feeding guide.  FIG. 4B  is a schematic view showing a state in which a thin sheet which is curled is fed in the state in which the moving feeding guide is kept at the longest distance from the fixed feeding guide.  FIG. 4C  is a schematic view showing a state in which the thin sheet is fed in a state in which the moving feeding guide is brought near to the fixed feeding guide for the thin sheet. 
     As shown in  FIG. 3 , in the registration roller pair  301 , a nip  301 N is formed at a position where the driving roller  301   a  and the follower roller  301   b  are in contact with each other. In other words, the nip  301 N is formed at a point of intersection of a line connecting centers of the driving roller  301   a  and the follower roller and an outer periphery of each of these rollers. A distance from the nip  301 N to a detecting position  116   p  where the timing sensor  116  detects the leading end of the sheet  110  is a length L. 
     A tangential line T passing through the nip  301 N and contacting the driving roller  301   a  or the follower roller  301   b  is referred to as a phantom line. On the other hand, the guide surface  303   a  of the above-described fixed feeding guide  303  includes an upstream-side end portion  303   b  and a downstream-side end portion  303   c  with respect to the feeding direction. In the image forming apparatus  100  of this embodiment, the transfer portion  330  is disposed on one side (upper side) relative to the tangential line T (see  FIG. 2 ). For that reason, as viewed in the widthwise direction, the downstream-side end portion  303   c  with respect to the feeding direction is positioned on one side (upper side) relative to the tangential line T, and the upstream-side end portion  303   b  with respect to the feeding direction is positioned on the other side (lower side) relative to the tangential line T. Further, the guide surface  303   a  is inclined relative to the tangential line T so that the nip  301 N is positioned on a feeding passage P 2  side. In summary, the guide surface  303   a  of the fixed feeding guide  303  is guided so that the leading end of the sheet  110  moves toward the transfer portion  330  positioned on one side (upper side) relative to the tangential line L. By this, as shown in  FIG. 4A , if the sheet  110  is not curled, the leading end of the sheet  110  fed from the registration roller pair  301  is to be fed so as to contact and follow the guide surface  303   a.    
     A state shown in  FIG. 4A  is a state in which a distance between the fixed feeding guide  303  and the moving feeding guide  304  is determined in conformity to a thickest sheet. In this state, a distance in the feeding passage P 2  with respect to the thickness direction of the sheet, which is a distance between the guide surface  303   a  and the guide surface  304   a  (hereinafter, this distance is referred to as a “path interval”) is 1.5 mm. Here, for example, it is assumed that the surface  110  is thin paper and is 0.1 mm in thickness and that the sheet  110  does not cause curl, crease, and the like. When such a sheet  110  is fed by the registration roller pair  301 , the leading end of the sheet  110  passes through a linear shortest passage along the above-described tangential line T and passes through the detecting position  116   p  of the timing sensor  116 , and is detected by the timing sensor  116 . At this time, an arrival distance from the nip  301 N to the detecting position  116   p  of the timing sensor  116  is 25.02 mm. 
     A state shown in  FIG. 4B  is the same as the state shown in  FIG. 4A  in the path interval in the feeding passage P 2 , and is a state in which the sheet  110  is curled upward. In this state, it is assumed that the curl occurs at a position of 10 mm from the leading end of the sheet  110  toward the upstream side of the feeding direction. In this case, in a state in which the leading end of the sheet  110  reaches the detecting position  116   p , the sheet  110  is fed from the nip  301 N of the registration roller pair  301  by 25.15 mm. That is, at this point of time, a length of the sheet actually existing from the nip  301 N to the detecting position  116   p  is 25.15 mm. The timing sensor  116  (controller  900  (see  FIG. 6 )) discriminates that the sheet  110  is linearly fed as shown in  FIG. 4A  and detects that the length is 25.02 mm as a value set in advance, so that an actual advance amount of the paper (sheet) is deviated by 0.13 mm at the maximum. For example, in the image forming apparatus in which offset printing is performed, printing can be performed in an error tolerable range for alignment of front and back surfaces (sides) of 0.2 mm. As regards such an error level, when an occurrence of a variation in alignment of front and back surfaces due to another factor such as moisture absorption of the paper or the like factor is taken into consideration, the error of 0.13 mm in detection of the leading end of the sheet is large as the error. 
     Therefore, in the first embodiment, as shown in  FIG. 4C , the moving feeding guide  304  is moved depending on the thickness of the sheet  110 , so that the path interval in the feeding passage P 2  is adjusted. In the state shown in  FIG. 4C , the sheet  110  is thin paper and the path interval in the feeding passage P 2  is set at 0.3 mm. By this, even when the sheet  110  is curled, the curl is rectified by the fixed feeding guide  303  and the moving feeding guide  304 . For that reason, at the point of time when the leading end of the sheet  110  reaches the detecting position  116   p , the length of the sheet actually existing from the nip  301 N to the detecting position  116   p  becomes 25.04 mm. Compared with the length of the sheet  110  in the case where the sheet  110  is not curled as shown in  FIG. 4A , the deviation amount is 0.02 mm, so that the error can be reduced. That is, a variation in position of the leading end of the sheet  110  when the sheet  110  is detected can be made small. In other words, the position of the leading end of the sheet  110  can be detected with accuracy. 
     [Constitution of Driving Mechanism of Feeding Guide and Control System] 
     Then, a constitution of a control system of the image forming apparatus  100  will be described using  FIG. 5  and  FIG. 6 .  FIG. 5  is a sectional view showing the fixed feeding guide and the moving feeding guide in the position of the timing sensor according to the first embodiment.  FIG. 6  is a block diagram showing the control system of the image forming apparatus according to the first embodiment. 
     As shown in  FIG. 6 , the image forming apparatus  100  includes the controller  900  for carrying out integrated control of an operation of the image forming apparatus  100  or the image forming system  100 S (see  FIG. 1 ) and the storing portion  901  for storing various data by being connected to the controller  900 . Further, to the controller  900 , an operating portion  180  (see  FIG. 1 ), an external interface (I/F)  189 , a sheet thickness sensor  118 , a driving motor  400 M of a driving mechanism  400 , the above-described timing sensor  116 , a registration motor  301 M for the registration roller pair  301 , and the like are connected. 
     The operating portion  180  is provided with a display as a displaying means for displaying information to a user. Further, the operating portion  180  is provided with, as a receiving potion capable of receiving instructions and data from the user to the image forming system  100 S, for example, physical keys such as numerical keys and a print execution button and a touch panel function of the display. By an operation of the operating portion  180 . The user is capable of inputting, to the storing portion  901  via the controller  900 , information indicating sheet attributes such as a name, a basis weight execution or non-execution of surface treatment of the sheets set in a certain sheet accommodating portion  113 . 
     Further, the controller  900  is connected to an external wired or wireless communication network via the interface (I/F)  189  as the receiving portion, and is capable of communicating with an external computer. That is, instead of the information inputted through the above-described operating portion  180 , input of information from the external computer can be received by the controller  900 . Further, the controller  900  is also connected to a control circuit for an apparatus (the finisher  200  in this embodiment) which is connected to the image forming apparatus  100  and which constitutes the image forming system  100 S. The controller  900  establishes communication with these devices (apparatus) and causes the image forming apparatus  100  and the respective devices to be in cooperation with each other. 
     The sheet thickness sensor  118  as a thickness detecting portion is disposed on a sheet feeding passage connecting the sheet accommodating portion  113  or the reversing portion  136  with the registration roller pair  301  as shown in  FIG. 1 . The sheet thickness sensor  118  detects the thickness of the sheet  110  fed to the registration roller pair  301  (i.e., to the above-described feeding passage P 2 ). Specifically, as the sheet thickness sensor  118 , for example, an ultrasonic sensor for applying ultrasonic wave to the sheet  110  and for detecting attenuation of the ultrasonic wave can be used, but the sheet thickness sensor  118  is not limited thereto, and for example, one for measuring a displacement of the sheet  110  by bringing a movable member into contact with the sheet  110  may also be used. 
     Incidentally, the timing sensor  116  is a sensor for detecting that the leading end of the sheet  110  reaches the timing sensor  116  between the registration roller pair  301  and the transfer portion  330  with respect to the sheet feeding direction. Further, the registration motor  301 M is a motor for driving the driving roller  301   a  of the registration roller pair  301 . The controller  900  is capable of changing a feeding speed of the sheet  110  by controlling this registration motor  301 M. 
     The driving mechanism  400  as a driving portion is a mechanism for moving the moving feeding guide  304  toward and away from the fixed feeding guide  303 , i.e., for enabling drive of the moving feeding guide  304  so as to move in the widthwise direction of the sheet. The driving mechanism  400  is provided with a driving motor  400 M (see  FIG. 6 ) and direct-acting mechanisms  401  and  402  which are ball spring mechanisms each constituted by a ball spring. The direct-acting mechanisms are constituted by including screw shafts  401   a  and  402   a , respectively, and nuts  401   b  and  402   b , respectively. The nut  401   b  is fixed to one end portion  304 A of the moving feeding guide  304  with respect to the widthwise direction of the sheet, and the nut  402   b  is fixed to the other end portion  304 B of the moving feeding guide  304  with respect to the widthwise direction of the sheet. Each of the one end portion  304 A and the other end portion  304 B of the moving feeding guide  304  is positioned outside of widthwise ends of the fixed feeding guide  303 , i.e., is disposed outside a passing region of the above-described maximum width size sheet. Accordingly, the moving feeding guide  304  is constituted so as not to prevent passing of the maximum width size sheet. Further, the driving motor  400 M rotationally drives the spring shafts  401   a  and  401   b  and moves and drives the moving feeding guide  304  in the sheet thickness direction via the nuts  401   b  and  402   b . By this, the controller  900  is constituted so as to be capable of controlling the driving mechanism  400  so that the path interval of the feeding passage P 2  changes. 
     [Control of Feeding Passage Thickness] 
     Next, control of the feeding passage thickness which is executed by the controller  900  and which is set by changing the thickness of the feeding passage P 2  will be described along  FIG. 7 .  FIG. 7  is a flowchart showing the feeding passage thickness control according to the first embodiment. 
     When the feeding passage thickness control according to the first embodiment is started, first, the controller  900  acquires sheet thickness information which is information on the thickness of the sheet  110  (S 1 ). This sheet thickness information is acquired by detecting the thickness of the sheet  110  when the sheet  110  passes through a detecting position of the above-described sheet thickness sensor  118 . 
     Next, the controller  900  determines the thickness of the feeding passage P 2  (target position of the moving feeding guide  304 ) which is a target, depending on the sheet thickness information (S 2 ). Then, the controller  900  drives the driving motor  400 M of the driving mechanism  400 , and thus moves the moving feeding guide  304  to the target position (S 3 ). Thus, if the sheet  110  is, for example, thin paper of 0.1 mm in thickness, the thickness of the feeding passage P 2  is set at 1.5 mm corresponding to an initial position as shown in  FIG. 4B . Further, if the sheet  110  is, for example, thick paper of 1.0 mm in thickness, the thickness of the feeding passage P 2  is narrowed from 1.5 mm, which corresponds to the initial position, to 0.3 mm, i.e., is set at a small value as shown in  FIG. 4C . Then, when the leading end of the sheet  110  reaches the detecting position of the timing sensor  116 , the sheet  110  is detected by the timing sensor  116  (S 4 ). 
     At this time, even when the sheet  110  is, for example, the thin paper and is curled, an error between a length of the sheet  110  fed until the leading end of the sheet  110  reaches from the nip  301 N of the registration roller pair  301  to the detecting position  116   p  of the timing sensor  116  and the distance L between the nip  301 N and the detecting position  116   p  is suppressed to a small value. The controller  900  controls the registration motor  301 M on the basis of a detection timing of this sheet  110 , and adjusts a timing when the feeding speed of the sheet  110  by the registration roller pair  301  is lowered. That is, a timing when the leading end (image formation start position) of the sheet  110  reaches the transfer portion  330  is conformed to a timing when the toner image formed on the intermediary transfer belt  106  reaches the transfer portion  330 . 
     Thereafter, the controller  900  discriminates whether or not the sheet  110  of which leading end is detected by the timing sensor  116  is final sheet of a job (S 5 ), and when the sheet  110  is not the final sheet (No of S 5 ), the sequence is returned to the step S 1 , and the above-described control is repeated. Further, when the sheet  110  of which leading end is detected by the timing sensor  116  is the final sheet (Yes of S 5 ), the feeding passage thickness control is ended. 
     Summary of First Embodiment 
     As described above, in the case where the sheet input information is a thickness (first thickness) of the thick paper, the path interval (distance with respect to the thickness direction) of the feeding passage P 2  is made a large distance (first distance). On the other hand, in the case where the sheet input information is a thickness (second thickness) of the thin paper thinner than the thickness (first thickness) of the thick paper, the path interval of the feeding passage P 2  is made a small distance (second distance). By this, although even when the sheet is a thick sheet, a jam is not readily caused to occur and the image formation is enabled, even when the sheet is a thin sheet, the position of the leading end of the sheet can be detected with accuracy. 
     Incidentally, in the image forming apparatus  100  of this embodiment, there is a place where the sheet feeding passage is curved, and in order to reduce a feeding resistance when the thick sheet such as the thick paper high in rigidity is fed, basis setting of the path interval is made not less than 1.5 mm which is sufficiently larger than the sheet thickness. Thereafter, in order to increase the number of kinds of sheets which can be met by the image forming apparatus  100 , in the case where a sheet which is further thick and which is further high in rigidity is fed, there is a need to further increase the path interval. Further, when the path interval is made larger than 1.5 mm even in the feeding passage P 2  between the detecting position  116   p  of the timing sensor  116  and the nip  301 N of the registration roller pair  301 , the influence of flexure and curl of the thin sheet becomes large. For that reason, there is a liability that a positional deviation between the toner image and the sheet becomes large. However, as in the first embodiment, in the case where the path interval of the feeding passage P 2  is changed depending on the thickness of the sheet, the path interval is made small particularly when the sheet is the thin sheet, whereby the above-described positional deviation can be made small. Further, particularly when the sheet is the thick sheet, by increasing the path interval, a degree of the occurrence of the jam is reduced, so that feeding of the sheet is enabled. In summary, the image forming apparatus  100  is capable of meeting either of the thick sheet and the thin sheet. 
     Further, in the first embodiment, continuous and accurate positioning is enabled by supporting the moving feeding guide  304  by the direct-acting mechanisms  401  and  402  which are the ball screw mechanisms and then by stopping the moving feeding guide  304  at the target position by driving the moving feeding guide  304  with the driving motor  400 M. Enabling of the continuous positioning means that an optimum path interval is always set continuously when the thickness of the sheets can be detected one by one. For example, in this case, a variation in detection accuracy of the position of the leading end of the sheet can be further reduced than in the case where the path interval is set stepwise on the basis of a sheet basis weight range of print setting set by the image forming apparatus  100 . Incidentally, the use of the ball screw mechanisms requires many accurate component parts, and therefore is liable to become expensive, but allows positioning with accuracy. In the first embodiment, the direct-acting mechanisms  401  and  402  which are the ball spring mechanisms are provided at two positions, but a single direct-acting mechanism is provided, or direct-acting mechanisms may also be disposed at three or more positions. 
     Incidentally, a method in which the path interval is narrowed by using a thin member (flexible member) made of a resin material or in which a variation in attitude of paper would be considered as an alternate technique. However, in general, compared with a zinc-plated steel plate or a stainless plate which form a feeding surface, the resin member is low in durability and is not suitable particularly for a purpose of commercial printing in which the number of sheets printed is large. Further, the flexible member can only rectify the sheet only at a part of the path interval, and thus is not suitable for the case where the sheet is intended to be widely rectified in a region on a side upstream of the detecting position  116   p  of the timing sensor  116  with respect to the sheet feeding direction. In the first embodiment, on the side upstream of the detecting position  116   p  with respect to the feeding direction, the sheet can be rectified long particularly with respect to the feeding direction, so that accuracy when the timing sensor  116  detects the leading end of the sheet  110  can be made satisfactory. 
     Further, in the first embodiment, the sheet thickness information is acquired by the sheet thickness sensor  118 , and the path interval is adjusted by using the information, but a thickness detecting method is not limited to the detection with the use of the sheet thickness sensor  118 . That is, the sheet thickness information may also be acquired on the basis of input of information on the kind of the sheet by the user through the operating portion  180  or on the basis of input of information on the kind of the sheet by the user in the external computer via the external interface (I/F)  189 . Specifically, for example, a set value of the sheet basis weight range set during printing may also be utilized. 
     In this case, a relationship between the thickness and the basis weight of the sheet is set in advance, and then the path interval is set depending on the inputted basis weight. 
     Second Embodiment 
     Then, a second embodiment in which the first embodiment is partially changed will be described using  FIGS. 8A and 8B .  FIG. 8A  is a sectional view showing a state in which a fixed feeding guide and a moving feeding guide in a position of a timing sensor according to the second embodiment are viewed in the sheet feeding direction.  FIG. 8B  is an enlarged schematic view showing a state in which a driving mechanism according to the second embodiment is viewed on the widthwise direction of the sheet. Incidentally, in the description of the second embodiment, portions similar to those in the above-described first embodiment are represented by using the same reference numerals or symbols, and description thereof will be omitted. 
     In the second embodiment, compared with the above-described first embodiment, the driving mechanism for the moving feeding guide  304  is changed. Specifically, as shown in  FIG. 8A  and  FIG. 8B , a driving mechanism  500  as the driving portion includes cams  501  and  501  rotatably supported by one end portion  304 A and the other end portion  304 B, respectively, of the moving feeding guide  304  and includes springs  502  and  502  as urging portions. each of the springs  502  and  502  is compressedly provided between a frame  101 F and the moving feeding guide  304  and urges the moving feeding guide  304  toward the fixed feeding guide  303 . Further, each of the cams  501  and  501  driven by the driving motor  400 M is formed in an elliptical shape at an outer peripheral surface thereof contacting the fixed feeding guide  303 . That is, the cams  501  and  501  are positioned while being rotationally driven by the driving motor  400 M, so that the moving feeding guide  304  is moved away from the fixed feeding guide  303  against the urging force of the springs  502  and  502 . 
     In summary, the driving motor  400 M and the cams  501  and  501  move and drive the guide surface  304   a  relative to the guide surface  303   a , so that the guide surface  304   a  is driven in a direction away from the guide surface  303   a.    
     The controller  900  designates a rotation angle of the cams  501  and  501  by controlling the driving motor  400 M. Then, in conformity to a diameter of the cams  501  and  501 , the position of the guide surface  304   a  of the moving feeding guide  304  relative to the guide surface  303   a  of the guide surface  303   a , i.e., the path interval is set so as to be freely changed. The cams  501  and  501  are processed with accuracy, so that the path interval can be positioned with accuracy. Incidentally, compared with the driving mechanism  400  according to the first embodiment, there is a limit to formation of the cams  501  and  501  in a for stably positioning the cams  501  and  501  in height, and further, there is a liability that the cam shafts and the moving feeding guide  304  themselves are flexed by the springs  502  and  502  or the like. However, a constitution which is more inexpensive than in the case where the mechanism such as the ball screws is used. 
     Incidentally, constitutions, actions, and effects other than this in the second embodiment are similar to those in the above-described first embodiment, and therefore, will be omitted from description. 
     Third Embodiment 
     Then, a third embodiment in which the second embodiment is partially changed will be described using  FIG. 9 .  FIG. 9  is a sectional view showing a state in which a fixed feeding guide and a moving feeding guide in a position of a timing sensor according to the third embodiment are viewed in the sheet feeding direction. Incidentally, in the description of the third embodiment, portions similar to those in the above-described first and second embodiments are represented by using the same reference numerals or symbols, and description thereof will be omitted. 
     In the third embodiment, compared with the above-described second embodiment, as shown in  FIG. 9 , a length of the moving feeding guide  304  with respect to the widthwise direction of the sheet is made smaller than the above-described maximum width size. Further, on opposite sides of the moving feeding guides  304  with respect to the widthwise direction, fixed feeding guides  305 A and  305 B each including a guide surface  305   a  which is disposed opposed to the guide surface  303   a  and which is a third guiding surface forming the feeding passage P 2  are provided, respectively. These fixed feeding guides  305 A and  305 B are fixed immovably to the frame  101 F on an inside of the image forming apparatus  100 . Further, outer peripheral surfaces of the cams  501  and  501  of the driving mechanism  500  are constituted so as to contact outer surfaces  305   b  and  305   b  opposite from the guide surfaces  305   a  and  305   a  of the fixed feeding guides  305 A and  305 B, not the fixed feeding guide  303 . 
     In summary, the driving motor  400 M and the cams  501  and  501  move and drive the guide surface  304   a  relative to the guide surface  303   a , so that the guide surface  304   a  is driven in a direction away from the guide surface  303   a , so that the path interval is set so as to be freely changed. 
     For example, in the first and second embodiments, the path interval is set in an entire area with respect to the widthwise direction of the sheet. For this reason, for example, in the case where a narrow path interval such as 0.3 mm is set in conformity to the thin paper, the feeding resistance of the sheet  110  is increased. Further, there is a possibility that the path interval is easily changed by the influence of flatness, distortion during installation, and the like of component parts constituting the guide surfaces  303   a  and  304   a  and the path interval becomes excessively narrow, and thus non-feeding of the sheet, scars on the sheet, and the like occur. 
     In the third embodiment, an attitude of a portion of the sheet  110  overlapping with the detecting position  116   p  of the timing sensor  116  with respect to the widthwise direction of the sheet as viewed in the sheet feeding direction may only be required to be rectified (regulated). In other words, the attitude of the portion of the sheet  110  along the sheet feeding direction may only be required to be rectified. For that reason, there is no need to move the guide surface  304   a  in the entire area with respect to the widthwise direction, and as shown in  FIG. 9 , the guide surface  304   a  is moved in a range of a peripheral region (a width of about 70 mm including the detecting position  116   p  in this embodiment) in which the detecting position  116   p  of the timing sensor  116  exists. On the other hand, the guide surfaces  305   a  and  305   a  are fixed in the large path interval as they are. By this, it is possible to improve the detection accuracy of the timing sensor  116  at the same level as the level in the case where the guide surface  304   a  is moved in the entire area (region of not less than the maximum width size) with respect to the widthwise direction as in, for example, the second embodiment). Further, as in this embodiment (third embodiment), narrowing of the path interval at a part of the widthwise direction is capable of reducing the feeding resistance because the path interval (at the guide surfaces  305   a  and  305   a ) in other regions is large. Further, for example, compared with the second embodiment, a reference (surface) for positioning the guide surface  304   a  is changed from the guide surface  303   a  to the outer surfaces  305   b , and therefore, although there is a liability that the positioning accuracy of the path interval lowers, downsizing can be realized. 
     Incidentally, constitutions, actions, and effects other than this in the third embodiment are similar to those in the above-described first and second embodiments, and therefore, will be omitted from description. 
     Other Embodiments 
     Incidentally, in the above-described first to third embodiments, the constitutions in which the detection accuracy of the timing sensor  116  for detecting the timing when the leading end of the sheet  110  reaches the transfer portion  330  is improved were described. However, the present invention is not limited thereto, and if a place where there is a need to accurately detect the position of the leading end of the sheet exists inside the image forming apparatus, the moving feeding guide may also be provided in any place. For example, a constitution in which oblique movement correction is made by abutting the sheet against the registration roller pair and thus by forming flexure of the sheet and in which the timing sensor is disposed upstream of the registration roller pair with respect to the sheet feeding direction for detecting the rotation start timing of the registration roller pair may also be employed. 
     In this case, a structure for adjusting the path interval of the feeding passage by the moving feeding guide may only be required to be disposed on a side upstream of the timing sensor with respect to the sheet feeding direction. 
     Further, in the detecting first to third embodiments, the constitutions in which the structure for adjusting the path interval of the feeding passage by the moving feeding guide is disposed on the side upstream of the timing sensor with respect to the sheet feeding direction and accurately detects the leading end of the sheet were described. However, the present invention is not limited thereto, and the structure for adjusting the path interval of the feeding passage by the moving feeding guide is disposed on a side downstream of the timing sensor with respect to the sheet feeding direction and may also accurately detect the trailing end of the sheet. In this case, an accuracy-improving effect is achieved for the sheet which causes the curl at the trailing end of the sheet. 
     Further, in the above-described first to third embodiments, the constitutions in which the image forming apparatus is the so-called laser printer in which the image forming portion forms the image in the electrophotographic type were described. However, the present invention is not limited thereto, and for example, the image forming apparatus may also be an ink jet printer or the like, in which the image forming portion forms the image in any manner. 
     Further, in the above-described first to third embodiments, the constitutions in which in order to adjust the path interval of the feeding passage P 2 , the moving feeding guide is moved in the sheet thickness direction relative to the fixed feeding guide  303  were described. However, the present invention is not limited thereto, and a constitution in which both feeding guides are movable may also be employed. Further, the direction of the movable feeding guide is not required to be a direction perpendicular to the guide surface, and for example, a constitution in which the path interval is adjusted by linearly moving the feeding guide in a direction inclined relative to the guide surface or by moving the feeding guide along an arcuate portion may also be employed. 
     Further, in the above-described first to third embodiments, the constitutions in which the timing sensor  116  detects the leading end of the sheet  110  fed by the registration roller pair  301  were described. However, the present invention is not limited thereto, and the sheet feeding portion may also be any sheet feeding portion for feeding the sheet, such as a conveying roller, a feeding roller, a transfer roller, and a fixing roller. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-005876 filed on Jan. 18, 2021, which is hereby incorporated by reference herein in its entirety.