Abstract:
The present invention provides sheet feeding apparatus comprises a sheet stacking means, a sheet feeding rotary member, conveying means, leading edge detecting means, driving means, and control means, and the control means controls a conveying amount of the sheet by the normal and reverse rotations of the conveying means, in accordance with a sheet leading edge blank amount and a normal rotation convey amount of the sheet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet feeding apparatus for feeding sheets one by one, and more particularly, it relates to a sheet feeding apparatus used with a recording apparatus such as a copying machine, a printer and the like. 
     2. Related Background Art 
     In the past, there has been proposed a sheet feeding apparatus used with a recording apparatus such as a copying machine, a printer and the like, in which, for example, sheets are fed out one by one by means of a semi-circular feed roller one rotation of which is controlled, and the fed sheet is supplied to a recording portion by a convey roller. The feed roller is provided with a flag in order to stop the feed roller after one rotation, and, by detecting the flag by a sensor (photo-interrupter or the like), completion of one rotation of the feed roller is detected. Further, in a drive system, a driving force of a convey roller rotatable normally and reversely is switched by a pendulum gear to effect connection or disconnection of transmission of the driving force. That is to say, when the convey roller is rotated in a normal direction, the driving force is transmitted to the feed roller by the pendulum gear; whereas, when the convey roller is rotated in a reverse direction, the transmission of the driving force is released. Incidentally, in the released position, a slide lever can be fitted into a support member of the pendulum gear to fixedly keep the posture of the gear, and, when the convey roller is rotated in the normal direction, only the convey roller can be rotated. The slide lever is disengaged from the support member of the pendulum gear when a carriage on which a recording head is mounted is shifted up to an end of the apparatus, with the result that the pendulum gear can freely be moved. In the condition that the fixing of the pendulum gear is released, when the convey roller is rotated in the normal direction, the feed roller is rotated together with the convey roller. 
     In a fundamental flow of the sheet in the sheet feeding, first of all, the carriage is shifted up to the end of the apparatus to rotate the convey roller and the feed roller, thereby feeding out a single sheet. When the completion of one rotation of the feed roller is detected by the sensor, the convey roller is rotated in the reverse direction by a predetermined amount, thereby releasing the transmission of the driving force to the feed roller. Here, when the carriage is returned toward a center of the apparatus, the slide lever is fitted into the support member of the pendulum gear to fix the posture of the gear, and only the convey roller is rotated, with the result that the sheet is conveyed to the recording portion only by the convey roller. 
     However, due to dispersion in sheet features, since a time period from when the rotation of the feed roller is started to when a leading edge of the sheet reaches a sheet leading edge detecting sensor (referred to as “PE sensor” hereinafter) is varied from sheet to sheet, when one rotation of the feed roller is completed, a distance from the convey roller (sheet leading edge detecting sensor) to the leading edge of the sheet is also varied from sheet to sheet. Thus, a dispersion correcting operation, i.e., a feeding operation of the leading edge to an initial position in which, as shown in FIGS. 9A to  9 D, after one rotation of the feed roller is completed, the sheet is set at an image leading portion recording position by reverse and normal rotations of the convey roller is required. 
     In FIGS. 9A to  9 D, “P” indicates the sheet;  100  denotes the convey roller;  101  denotes the PE sensor (sheet leading edge detecting sensor); and  102  denotes the recording head. Further, “β” indicates a normal convey distance of the sheet P from when the leading edge of the sheet is detected by the PE sensor  101  to when one rotation of the feed roller is completed; “ε” indicates a distance from the PE sensor  101  to a recording position of the recording head  102 ; “γ” indicates a reverse rotation amount required for the above-mentioned drive switching; “σ” indicates a backlash correction amount when the normal rotation is effected again; “δ1” indicates a blank amount from the leading edge of the sheet to a leading portion of a record permitting area; and “δ2” indicates a blank amount from the leading portion of the record permitting area to an image leading end portion based upon image data. 
     FIG. 9A shows a condition that the sheet P is fed out by the distance β after one rotation of the feed roller was completed. FIG. 9B shows a condition that the sheet is returned by rotating the convey roller reversely by an amount corresponding to by the sum of the reverse rotation amount γ required for the drive switching, an excessive fed amount in FIG.  9 A and the backlash correction amount σ of the drive switching portion. In this case, the reverse rotation amount of the convey roller is defined as (β−ε+σ−δ1), and diameters of the rollers are designed so that this reverse rotation amount becomes greater than the reverse rotation amount γ required for the drive switching without fail. FIG. 9C shows a condition that the sheet is fed out by rotating the convey roller in the normal direction by the backlash correction amount σ. As a result, the leading portion of the record permitting area is fed to the recording position (record starting position) of the recording head. FIG. 9D shows a condition that the sheet is fed out by rotating the convey roller in the normal direction by the blank amount δ2 with reference to the blank amount δ2 to the image leading portion based upon the image data. From this condition, the recording is started. 
     However, in the above-mentioned conventional apparatus, as mentioned above, since the leading edge of the sheet is returned up to the recording position of the recording head and then is fed out by the blank amount regardless of the image data, the shifting amount and time of the sheet required for the heading to the recording position become great, thereby worsening the record processing speed of the recording apparatus. 
     Concretely, for example, when β=20 mm, ε=8 mm, γ=5 mm, σ=1 mm, δ1=2 mm and δ2=4 mm, the shifting amount of the sheet required for the heading will be (β−ε+σ−δ1+σ−δ2)=16 mm. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide reduce a shifting amount of a sheet required for heading to a recording position, thereby improving a processing speed of an apparatus. 
     The present invention provides a sheet feeding apparatus comprising a sheet stacking means for supporting a sheet, a sheet feeding rotary member for feeding out the sheet from the sheet stacking means by one rotation control, a conveying means for conveying the sheet fed out by the sheet feeding rotary member to a recording means, a leading edge detecting means for detecting a leading edge of the sheet fed out by the sheet feeding rotary member, a driving means for rotating the conveying means in normal and reverse directions, and a control means for controlling the driving means, and wherein the control means controls a conveying amount of the sheet by the normal and reverse rotations of the conveying means, in accordance with a sheet leading edge blank amount obtained by adding a blank amount between the leading edge of the sheet and a leading portion of a record permitting area to a blank amount at a leading edge of image data, and, a normal rotation conveying amount of the sheet from when the leading edge of the sheet is detected by the leading edge detecting means to when one rotation of the sheet feeding rotary member is completed, referring to the blank amount at the leading edge of image data prior to initiation of feeding of the leading edge of the sheet to an initial position, when the sheet is conveyed to feed the leading edge of the sheet to an initial position after the sheet is fed out by one rotation of the sheet feeding rotary member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a schematic construction of a recording apparatus having an automatic sheet feeding apparatus; 
     FIGS. 2A and 2B are explanatory views showing a gear switching portion between a conveying roller and a sheet feeding roller; 
     FIG. 3 is a plan view of the automatic sheet feeding apparatus; 
     FIGS. 4A and 4B are side views of the automatic sheet feeding apparatus; 
     FIGS. 5A and 5B are side views of a sheet feeding roller portion of the automatic sheet feeding apparatus; 
     FIG. 6 is a flow chart showing control in a sheet feeding operation; 
     FIGS. 7A,  7 B and  7 C are explanatory views of a feeding operation of a leading edge to an initial position; 
     FIGS. 8A,  8 B and  8 C are explanatory views of a feeding operation of a leading edge to an initial position; and 
     FIGS. 9A,  9 B,  9 C and  9 D are views of for explaining a conventional technique. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be fully explained in connection with a sheet feeding apparatus and a recording apparatus according to an embodiment with reference to the accompanying drawings. 
     Now, a sheet feeding apparatus and a recording apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Incidentally, in this embodiment, an ink jet recording apparatus having an automatic sheet feeding apparatus as the sheet feeding apparatus will be explained as an example. 
     FIG. 1 is a perspective view showing a schematic construction of the recording apparatus having the automatic sheet feeding apparatus in this embodiment. In FIG. 1, a sheet feeding portion  11  as the automatic. sheet feeding apparatus is attached to a main body  3  of the apparatus at an angle of 30 to 60 degrees. Sheets P set in the sheet feeding portion  11  are to be discharged horizontally after recording. The sheet feeding portion  11  includes a sheet feeding roller  5 , a separation claw  17 , a movable side guide  19 , a base  20 , a pressure plate  21  (all are shown in FIG.  3 ), pressure plate springs  22  (FIGS.  5 A and  5 B), gears  25  to  30 , a release cam  31 , a claw spring  32 , a releasing lever  33  and a releasing cam  35  (all are shown in FIGS.  4 A and  4 B). Normally, the pressure plate  21  is lowered to a position shown in FIG. 5A by the release cam  31 , with the result that the sheet P is spaced apart from the sheet feeding roller  5 . 
     In a condition that the sheets P are set, a driving force of a convey roller  36  (FIGS. 7A to  7 C and FIGS. 8A to  8 C) is transmitted to the sheet feeding roller  5  and the release cam  31  through the gears  25  to  30 . When the release cam  31  is separated from the pressure plate  21 , the pressure plate  21  is lifted up to a position shown in FIG. 5B, with the result that the sheet P contacts with the sheet feeding roller  5 . The sheets P are picked up by rotation of the sheet feeding roller  5  and are separated one by one by the separation claw  17 . The separated sheet P is sent to a sheet convey portion  12 . The sheet feeding roller  5  and the release cam  31  are rotated by one rotation until the sheet P is sent to the sheet convey portion, and, in the condition that the pressure plate  21  is released from the sheet feeding roller  5  is restored again, the driving force from the convey roller  36  is disconnected, and this initial condition is maintained. 
     The sheet convey portion includes the convey roller  36 , a pinch roller  37 , a PE sensor  42  (all are shown in FIGS. 7A to  7 C and FIGS. 8A to  8 C), and a platen  46  (FIG.  1 ). The sheet P sent to the sheet convey portion is guided by the platen  46 , a pinch roller guide (not shown) and an upper guide (not shown) and is sent to a pair of rollers comprised of the convey roller  36  and the pinch roller  37 . The PE sensor  42  is disposed in front of the pair of rollers. When a leading edge of the sheet P is detected by the PE sensor  42 , a printing position on the sheet P is determined by the PE sensor  42 . The pinch roller  37  is biased by a pinch roller spring (not shown) via the pinch roller guide so that the pinch roller is urged against the convey roller  36 , thereby providing a conveying force for the sheet P. 
     The sheet P sent by the pair of rollers  36 ,  37  is advanced on the platen  46  by the pair of rollers  36 ,  37  rotated by an LF motor (convey motor)  47 ; meanwhile, the recording is effected by a recording head  49  on the basis of predetermined image information. Incidentally, the recording head  49  is of ink jet recording type for effecting the recording by discharging ink, and in the illustrated embodiment, the recording head is integrally formed with an ink tank to form an easy replaceable ink jet recording head. The recording head has electrical/thermal converters so that ink is discharged from a discharge port by growth and contraction of a bubble generated in the ink by film-boiling caused by thermal energy created by energizing the electrical/thermal converter in response to a record signal, thereby effecting the recording. 
     In FIGS. 2A and 2B, a switching output gear  81  is integrally formed with the convey roller  36  and is reversibly rotated by the LF motor  47 . A switching arm  82  has a base portion rotatably mounted on a support shaft  36   a  integral with the convey roller  36 . A switching output gear  83  is rotatably mounted on a free end of the switching arm  82  and can be engaged with the input gear  25  by rotation of the switching arm  82  to transmit normal rotation of the convey roller  36  to the input gear  25  and the associated sheet feeding roller  5 . A control apparatus  80  controls rotations of the LF motor  47  and the convey roller  36  in a manner which will be described later. 
     A carriage portion (recording portion)  15  includes a carriage  50  to which the recording head  49  is attached, a guide shaft  51  for guiding reciprocal scan of the carriage  50  in a direction perpendicular to a conveying direction of the sheet P, a guide  52  for holding a rear end (at an upper part of the apparatus) of the carriage  50  to maintain a predetermined gap between the recording head  49  and the sheet P, a timing belt  55  for transmitting drive of a carriage motor  53  to the carriage  50 , an idle pulley  56  for applying tension to the timing belt  55 , and a flexible cable  57  for transmitting a head drive signal from an electric substrate to the recording head  49 . The recording head  49  is scanned together with the carriage  50  in the direction perpendicular to the sheet conveying direction, so that the image is formed on the sheet P being conveyed on the platen  46 . 
     A sheet discharge portion includes sheet discharge rollers  59 , transmission rollers  60  for transmitting the driving force of the convey roller  36  to the sheet discharge rollers  59 , spurs  61  for aiding sheet discharging, and a sheet discharge tray  62 . The sheet P is discharged onto the sheet discharge tray  62  by the sheet discharge rollers  59  and the spurs  61  without distorting the image on the sheet P. Incidentally, the spurs are so designed as to have small contact area with the sheet, so that, even when the spurs are contacted with the imaged surface of the sheet, the image on the sheet is not distorted. 
     A cleaning portion  16  includes a pump  63  for cleaning the recording head  49 , a cap  65  for preventing drying of the recording head  49 , and a drive switching lever  66  for switching the driving force of the convey roller  36  between the sheet feeding portion  11  and the pump  63 . When the sheet is fed, except for cleaning, the drive switching lever  66  is in a condition that the lever is entered into a hole  82   c  of the switching arm  82  shown in FIG. 2A, so that, since the switching output gear  83  to be rotated around a center of the convey roller  36  is fixed or secured at a predetermined position, the driving force of the convey roller  36  is not transmitted to the pump  63  and the sheet feeding portion  11 . 
     By shifting the carriage  50 , when the drive switching lever  66  is shifted in a direction shown by the arrow A in FIG. 1, the drive switching lever  66  is disengaged from the hole  82   c  of the switching arm  82 , and the switching output gear  83  is shifted as shown in FIGS. 2A and 2B by the normal or reverse rotation of the convey roller  36 . In a condition that the carriage  50  is secured at the shifted position in the direction A, when the convey roller  36  is rotated normally, the driving force of the LF motor  47  is transmitted to the sheet feeding portion  11 ; whereas, when the convey roller  36  is rotated reversely, the driving force of the LF motor  47  is transmitted to the pump  63 . 
     Further, as the LF motor for driving the convey roller  36  and the carriage motor  53  for driving the carriage  50 , stepping motors rotated by predetermined angles in response to signals sent from drivers (not shown) are used. 
     As shown in FIG. 3, the sheet feeding roller  5  is provided with a sensor plate  69  having a diameter smaller than a diameter of a sheet feeding rubber  67  attached to the sheet feeding roller  5 . The sensor plate  69  has a cut-out portion so that, only when the sheet feeding roller  5  and the release cam  31  are located at their initial positions (FIG. 5A) where the pressure plate  21  is released, light from a roller sensor comprised of a photo-interrupter directly attached to the electric substrate (not shown) is not interrupted. By detecting the condition of the sensor plate  69 , an angular position of the sheet feeding roller  5  and an angular position of the release cam  31  operated in synchronous with the sheet feeding roller  5  with the same phase can be detected, thereby providing a control timing of the sheet P in a sheet feeding sequence. 
     Next, main parts of the sheet feeding portion  11  will be described. Various parts of the sheet feeding portion  11  are attached to the base  20  to form a unit. As shown in FIG. 3, in the illustrated embodiment, the sheet feeding portion  11  serves to feed the sheet by utilizing one lateral edge of the sheet P as a reference, and a sheet standard (reference) surface is constituted by an inner wall of a right side plate of the base  20 . As shown in FIG. 5A, the base  20  has a shape so that the pressure plate  21  can be retarded as shown in FIG.  5 A. Further, the base is provided with recessed portions for positioning the pressure plate springs  22  at positions substantially opposed to roller portions  5   c  of the sheet feeding roller  5 . 
     The pressure plate  21  is connected to the base  20  via pressure plate shafts  21   b  provided on both upper end portions of the pressure plate so that the pressure plate can be rotated around the pressure plate shafts  21   b . As shown in FIG. 3, separation pads  73  made of material having relatively high frictional coefficient such as synthetic leather are adhered to the pressure plate  21  at positions opposed to the roller portions  5   c  of the sheet feeding roller  5 , so that, when the number of the sheets on the pressure plate becomes few, double-feeding is prevented. Further, the movable side guide  19  slidable in a left-and-right direction is attached onto the pressure plate  21 , so that, even when different size sheets P are used, one lateral edges of the sheets can be aligned by utilizing the sheet standard surface. 
     The sheet feeding roller  5  is rotatably supported by the base  20  at its both ends. The sheet feeding roller  5  is a integrally molded plastic part including a shaft portion  5   b  and the roller portions  5   c , and the sheet feeding rubbers  67  for conveying the sheet P are provided on outer peripheral surfaces of the roller portions  5   c . Each roller portion  5   c  has a D-cut (semicircular) shape. Further, sub-rollers  75  each having a radius smaller than a radius of the sheet feeding rubber  67  attached to the sheet feeding roller  5  by 0.5 mm to 3.0 mm are provided on both sides of the roller portion  5   c , so that contamination of the image or positional deviation of the sheet feeding roller  5  is prevented by not contacting the sheet P with the roller rubbers  67  of the sheet feeding roller  5  other than the sheet feeding. 
     Further, in the illustrated embodiment, there are two roller portions  5   c  along the axial direction, which are spaced apart from the sheet standard surface by about 40 mm and about 170 mm, respectively. Accordingly, a recording sheet having A4 size is conveyed by the two roller portions  5   c , and a post card is conveyed by only the single roller portion  5   c  near the sheet standard surface. 
     When the drive switching lever  66  of the cleaning portion  16  is shifted in the direction A in FIG. 1 by the carriage  50  to rotate the convey roller  36  normally, the switching output gear  83  is shifted to be engaged by the input gear  25 , thereby transmitting the driving force to the sheet feeding portion  11  (refer to FIG.  2 B). In this case, since the switching output gear  83  is rocked toward the direction engaging with the input gear  25  to engage by the latter, so long as these gears once meshed with each other, even when the carriage  50  is retarded to a direction opposite to the direction A, the engagement between the gears is maintained to continue the transmission of the driving force. 
     The input gear  25  transmits the driving force to a sheet feeding roller gear  28  coupled to the sheet feeding roller  5  through idler gears  26 ,  27 . The sheet feeding roller  5  is rotated by the sheet feeding roller gear  28  to convey the sheet P. 
     Further, as shown in FIGS. 4A and 4B, the sheet feeding roller gear  28  transmits the driving force to the release cam  31  through a clutch gear  29  and an idler gear  30 . In this case, the sheet feeding roller  5  and the release cam  31  are designed and arranged so that phases thereof are aligned with each other for each rotation. As a result, as shown in FIG. 4B, in the condition that the pressure plate  21  is released, as shown in FIG. 5A, the sheet feeding roller  5  is designed and arranged so that the semi-circular portions are opposed to the pressure plate  21 . 
     The release cam  31  is so shaped that it releases the pressure plate  21  only between the angle of about 120 degrees of semi-circular portions of the sheet feeding roller  5  and that it contacts with the sheet P or the pressure plate  21  with an urging force of about 200 g to about 500 g when portion of the sheet feeding roller  5  other than the semi-circular portions is opposed to the pressure plate  21 . Further, the release cam  31  releases the pressure plate  21  by depressing a depressed portion  21   c  of the pressure plate  21  protruded from a hole formed in the right side plate of the base  20  (refer to FIG.  4 B). 
     In this case, the pressure plate cam  76  attached to the base  20  is depressed by a cam  21   d  near the depressed portion  21   c  of the pressure plate  21 , with the result that the pressure plate cam  76  is rotated around a center  76   b . And, a cam (not shown) outside of the left roller portion  5   c  is lowered by the pressure plate cam  76 . As a result, even when the depressed portion  21   c  of the pressure plate  21  is depressed, the pressure plate  21  is not inclined with respect to the base  20 , so that the pressure plate is released substantially horizontally. 
     The clutch gear  29  is provided at its interior with a clutch spring  77  (FIG. 3) so that the clutch spring  77  is tightened in a direction B in FIG. 4A, thereby preventing reverse rotation. Thus, when the switching from the sheet feeding portion  11  to the sheet convey portion is effected by the reverse rotation of the LF motor  47  or when the jammed sheet is removed or pulled by the operator, the sheet feeding roller  5  is not subjected to reverse rotation. 
     The separation claw  17  can be rotated around a center  17   b  and is biased by the claw spring  32  against the sheet P or the pressure plate  21  with an elastic force of about 20 g to about 100 g. The separation claw  17  serves to separate recording sheets P comprised of normal sheets and is positioned near the sheet standard surface as shown in FIGS. 4A and 4B to cover a corner of the sheet P in a triangular fashion. Since the sheets P are subjected to resistance from the triangular claw, the sheets can be separated one by one. Further, separation of thick sheets other than normal sheet is effected by abutting the sheets against a lower guide portion  20   b  (FIGS. 5A and 5B) of the base  20  (without engaging the separation claw  17  with the sheets) to utilize frictional resistance of the lower guide portion  20   b , thereby separating the sheets one by one. 
     The releasing lever  33  and the releasing cam  35 . (FIG. 4A) are provided in coaxial with the release cam  31  (FIG.  4 B). The releasing lever  33  and the releasing cam  35  are not synchronous with the release cam  31  but are operated independently and aid to set the sheets P by the operator. The releasing lever  33  and the releasing cam  35  are interconnected through a gear. 
     The releasing lever  33  assumes (1) a feed position, (2) a thick sheet set position and (3) a normal sheet set position. An angle between these positions is selected to about 20 degrees to about 50 degrees. A ratio between the gears are set so that the releasing cam  35  is rotated by about 90 degrees in correspondence to three positions of the releasing lever  33 . 
     (1) In the feed position, the releasing cam  35  does not act on the depressed portion  21   c  of the pressure plate  21  and a depressed portion  17   c  of the separation claw  17 . This position is selected during normal sheet feeding. 
     (2) In the thick sheet set position, since the releasing cam  35  depresses only the depressed portion  21   c  of the pressure plate  21 , the separation claw  17  is lowered to follow the pressure plate  21 , with the result that the thick sheets can be set without engaging by the separation claw  17 . 
     (3) In the normal sheet set position, since the releasing cam  35  depresses both the depressed portion  21   c  of the pressure plate  21  and the depressed portion  17   c  of the separation claw  17 , the separation claw  17  is lifted with respect to the pressure plate  21 , with the result that the normal sheets can be set with engaging by the separation claw  17 . 
     Incidentally, the above-mentioned group of gears (except for the sheet feeding roller shaft  79 ), separation claw  17 , releasing lever  33  and releasing cam  35  are provided on shafts provided on the right side plate of the base  20  and are rotated around the shafts. Next, function and control of the sheet feeding portion  11  in the sheet feeding will be fully explained. FIG. 6 is a flow chart showing entire control. Although such control can be divided into control effected when the sheet feeding roller  5  is in the predetermined initial position and control effected if the sheet feeding roller is not in the predetermined initial position (trouble condition), in the illustrated embodiment, only the control effected when the sheet feeding roller  5  is in the predetermined initial position will be described. 
     In FIG. 6, in response to a sheet feeding start signal, first of all, in S 200 , while referring the image data from the host (for example, a computer to which the recording apparatus is connected), a blank amount at the leading edge of the image data is read out. In S 202 , the carriage  50  is shifted to shift the drive switching lever  66  so that the driving force of the convey roller  36  can be transmitted to the sheet feeding portion  11  (ASF position). 
     Then, in S 203 , the condition of the sheet feeding roller is judged (by the roller sensor). If the sheet feeding roller  5  is in the initial position, the program goes to S 204 ; whereas, if the sheet feeding roller  5  is not in the initial position, initialization of the sheet feeding roller  5  is effected (S 207 ). When the sheet feeding roller  5  is in the initial position, in S 204 , the sheet feeding roller  5  is rotated and, in S 205 , the edge of the sensor plate  69  (change from dark to bright of the sensor) is detected. In S 206 , by counting the number (N1) of drive pulses of the LF motor  47  after the detection, the angular position of the sheet feeding roller  5  can be controlled correctly, thereby effecting high accurate control. 
     When the sheet feeding roller  5  is rotated by about 60 degrees to bring cylindrical portions of the sheet feeding rubbers  67  to a position opposed to the sheet P, the release cam  31  rotated in synchronous with the sheet feeding roller  5  releases the pressure plate  21 . As a result, since the sheet P is urged against the sheet feeding rubbers  67  by the biasing forces of the pressure plate springs  72 , the conveying force for the sheet P is generated. After the pressure plate  21  is released, the carriage  50  can be retarded, so that the initializing operation (ink pre-discharge, wiping and the like) of the recording head  49  can freely be performed during the sheet feeding. 
     In S 208 , the leading edge of the sheet P being conveyed is detected by the PE sensor  42 . If the PE sensor  42  is turned ON till the sheet feeding roller  5  is rotated by the predetermined amount, in S 209 , data (N2) of the position of the leading edge of the sheet is sought on the basis of the angular position of the sheet feeding roller  5  when the PE sensor  42  is turned ON and such data is stored. Then, in S 210 , by continuing the rotation of the sheet feeding roller  5  until the roller sensor is turned ON, the sheet P is conveyed ahead of the pair of rollers comprised of the convey roller  36  and the pinch roller  37 . In S 211 , when the roller sensor is turned ON, the rotation of the convey roller  36  is stopped, and the position data (N3) thereof is stored. 
     In the feeding operation (heading) of the leading edge to the initial position for setting the leading edge blank (S 212 ), the convey roller  36  is rotated reversely by the predetermined amount to disengage the switching output gear  83  from the input gear  25 , thereby shifting the gear  83  up to the position shown in FIG.  2 A. Thereafter, the convey roller  36  is rotated normally by the predetermined amount. When this feeding operation (heading) of the sheet is finished, the sheet feeding operation is completed. 
     Next, calculation of the normal and reverse rotation amounts of the convey roller in the feeding operation of the leading edge to the initial position for setting the leading edge blank will be explained with reference to FIGS. 7A to  7 C and FIGS. 8A to  8 C. 
     In FIGS. 7A to  7 C and FIGS. 8A to  8 C, “β” indicates a distance between the PE sensor  42  and the leading edge of the sheet when the sheet feeding roller  5  is stopped (completion of one rotation thereof), calculated on the basis of the data N2, N3; “γ” indicates a pre-set minimum reverse rotation amount required for switching the switching output gear  83  from the position shown in FIG. 2B to the position shown in FIG. 2A; “σ” indicates a pre-set normal rotation amount required for removing backlash; “δ” indicates a blank amount at the leading edge of the sheet obtained by adding the blank δ2 for the image leading portion based upon the image data referred before initiation of the feeding operation (heading) to the pre-set blank δ1 between the leading edge of the sheet and the leading portion of the record permitting area (δ1+δ2); and “ε” indicates a pre-set distance from the PE sensor  42  to the recording position (write starting position) of the recording head  49 . 
     In the illustrated embodiment, after the sheet feeding roller  5  is rotated by one rotation, when the feeding operation of the leading edge of the sheet to the initial position is effected by the reverse and normal rotations of the convey roller  36 , before the initiation of such feeding operation, by referring the blank at the leading edge of the image data, in accordance with the blank amount at the leading edge of the sheet obtained by adding the blank at the leading edge of the image data to the blank between the leading edge of the sheet and the leading portion of the record permitting area, and in accordance with the normal rotation amount of the sheet P until one rotation of the sheet feeding roller  5  is completed after the leading edge of the sheet was detected, the conveying amount of the sheet P achieved by the reverse and normal rotations of the convey roller  36  is controlled. 
     Concretely, as shown in FIG. 7A, after the sheet feeding roller  5  is rotated by one rotation, if the relationship between the distances is (ε−σ+γ&lt;β−δ) (i.e., if the blank amount is small), as shown in FIG. 7B, the convey roller  36  is rotated reversely in a direction shown by the thick arrow to convey the sheet P in the reverse direction by a distance {(β−δ)−(ε−σ)}, so that the position of the switching output gear  83  is fixed by the drive switching lever  66 . Thereafter, as shown in FIG. 7C, the convey roller  38  is rotated again normally in a direction shown by the thick arrow to convey the sheet P in the normal direction by the distance σ. 
     More specifically, for example, similar to the conventional case, when β=20 mm, ε=8 mm, γ=5 mm, σ=1 mm, δ1=2 mm and δ2=4 mm, the shifting amount of the sheet required for the feeding operation of the leading edge to the initial position becomes {(β−δ)−(ε−σ)+σ}=8 mm, which is greatly reduced in comparison with  16  mm in the conventional case. 
     On the other hand, as shown in FIG. 8A, after the sheet feeding roller  5  is rotated by one rotation, if the relationship between the distances is (ε−σ+γ&gt;β−δ) (i.e., if the blank amount is great), as shown in FIG. 8B, the convey roller  36  is rotated reversely in a direction shown by the arrow to convey the sheet P in the reverse direction by the distance γ, so that the position of the switching output gear  83  is fixed by the drive switching lever  66 . Thereafter, as shown in FIG. 8C, the convey roller  38  is rotated again normally in a direction shown by the arrow to convey the sheet P in the normal direction by a distance {ε−(β−γ−δ)}. 
     As is in the above case, for example, similar to the conventional case, when β=20 mm, ε=8 mm, γ=5 mm, σ=1 mm and δ1=2 mm and further when δ2=8 mm (more disadvantageous in the conventional case), the shifting amount of the sheet required for the feeding operation of the leading edge to the initial position becomes {γ+ε−(β−γ−δ)}=6 mm, which is further greatly reduced in comparison with 16 mm in the conventional case. 
     When the feeding operation (heading) of the leading edge to the initial position to set the leading edge blank is completed in this way, the proper heading amount is set, and the recording can be started. 
     With the arrangement as mentioned above, according to the illustrated embodiment, the conveying amount regarding feeding operation of the leading edge of the sheet to the initial position can be minimized, thereby improving the processing speed of the apparatus. 
     Incidentally, if the record starting position of the recording head along the sheet conveying direction is varied with recording modes, the blank amount at the leading edge of the image data and the recording mode prior to the initiation of the feeding operation of the leading edge of the sheet to the initial position are referred to, and, on the basis of such information, a distance ε2 from the PE sensor  42  to a record starting position of the recording head (recording head element) corresponding to said recording mode is used, in place of the above-mentioned distance ε. In this way, the conveying amount regarding feeding operation of the leading edge of the sheet to the initial position can be further reduced. 
     In the illustrated embodiment, while an example that the printer is used as the recording apparatus was explained, the present invention is not limited to such an example, but may be applied, for example, to other recording apparatuses such as a copying machine, a facsimile and the like, and, by applying the present invention to a sheet feeding apparatus used with such a recording apparatus, the same advantages can be achieved. 
     Further, in the illustrated embodiment, while an example that the sheet feeding apparatus is detachably attachable to the recording apparatus was explained, the present invention is not limited to such an example, but may be applied, for example, to a sheet feeding apparatus integrally incorporated into a recording apparatus, and, by applying the present invention to a sheet feeding apparatus, the same advantages can be achieved. 
     Finally, in the illustrated embodiment, while an example that the recording system is of an electrophotographic type was explained, the present invention is not limited to such an example, but may use, for example, other recording systems such as an ink jet recording system.