Sheet convey apparatus

Abstract: The present invention provides a recording apparatus comprising convey means for conveying a sheet in a predetermined convey direction, a pair of rollers arranged downstream of the convey means in the convey direction for conveying the sheet in the convey direction or in an opposite direction by their rotations in a normal direction or in a reverse direction, and control means for controlling the convey means and the pair of rollers, Control means control them in such a manner that, after the sheet conveyed by the convey means is conveyed in the convey direction by a predetermined amount by the pair of rollers, the pair of rollers are rotated in the reverse direction while applying a conveying force in the convey direction to the sheet by the convey means, thereby conveying the sheet in the opposite direction until the sheet passes through a nip between the pair of rollers.

Description: The present invention relates to a sheet convey apparatus according to the preamble of claim 1. Such an apparatus is used for conveying a sheet to a recording portion or a reading portion in a printer, a typewriter, a copying machine, a facsimile machine and the like, and more particularly, it relates to a sheet convey apparatus wherein a sheet can be fed in a direction perpendicular to a generatrix of a convey roller without the skew-feed of the sheet and with high accuracy. From the document EP 0 487 923 A1 a generic sheet conveying apparatus is known whose convey means comprises a plurality of rollers being supported on a shaft. The shaft is provided with a means which accumulates a force acting in the convey direction when a part of the sheet is passed through a nip of the convey means in a direction opposite to the convey direction. The rollers are fixedly mounted on the shaft so that they cannot rotate independently from each other. According to the further document WO-A-92/02441, there is disclosed a sheet conveying method in which a curved portion is formed in the sheet for generating an urge force by means of which the sheet is urged against the nip of the pair of rollers of the rotary means. As shown in Fig. 4, in a conventional recording apparatus 250, when a sheet P is set, the sheet P is rested on an inclined sheet supply tray 251, and then a knob 252 is rotated to wind the sheet P around a platen 253 once, and then the knob 252 is rotated reversely to disengage the sheet P from a nip between the platen 253 and a pinch roller 255. As a result, a leading or tip end of the sheet P is abutted against the nip between the platen 253 and the pinch roller 255 by the weight of the sheet, thereby positioning the sheet along the nip. Then, when the platen 253 is rotated normally, the sheet P is surely conveyed in a direction perpendicular to the generatrix of the platen 253. The above method has been usually used in the conventional techniques. However, in the conventional case shown in Fig. 4, after the sheet P is positioned along the nip between the platen 253 and the pinch roller 255, when the sheet is re-entered into the nip by rotating the knob 252 normally, since the urging force for abutting the tip end of the sheet P against the nip depends upon the weight of the sheet P itself, if a sheet supply direction becomes a direction near a horizontal direction, the urging force for abutting the sheet P against the nip is extremely weakened or disappeared, with the result that the sheet P cannot be re-entered into the nip. Next, in the JP-P-62-3826, as shown in Fig. 5, a sheet P supplied from a pick-up roller 261 of a sheet supply device to a drive roller 262 is fed reversely until a tip end of the sheet passes through a nip of the drive roller 262, thereby forming a loop in the sheet P between the pick-up roller 261 and the drive roller 262, so that the tip end of the sheet P is abutted against the nip of the drive roller 262. Thereafter, the sheet P is fed out by rotating the drive roller normally. In the conventional case shown in Fig. 5, the urging force for abutting the tip end of the sheet against the nip of the drive roller 262 is not influenced by the sheet supply direction since such urging force depends upon the repelling force of the sheet P for restoring the looped sheet to its original flat form. However, since the loop should be formed in the sheet P, a thick sheet which is hard to be flexed cannot be used, and since a space and a convey path length sufficient to permit the formation of the loop must be prepared, it is difficult to make the apparatus small-sized. An object of the present invention is to provide a sheet convey apparatus wherein a sheet can be conveyed correctly in a sheet supply direction even if an insertion direction for the sheet is skew and even when a thick sheet is supplied. Furthermore, there is to be provided a sheet convey apparatus wherein a plurality of sheets (which are one of various kinds of sheets such as a thin sheet, thick sheet, post card, envelope, resin film or the like) can be separated one by one, and the separated sheet is passed through a main roller in a condition that a tip end of the separated sheet is being positioned along the generatrix of the main roller, and the sheet is conveyed to a predetermined position with high accuracy (Incidentally, in the conventional techniques, since the usable sheets are limited to flexible ones, the kinds of the sheets are limited). Moreover, there is to be provided a sheet convey apparatus which can be made small-sized by reducing the large space and convey path length requiring for forming a loop in a sheet in the conventional techniques. The above-stated object is achieved by means of the combination of features defined in claim 1. Preferred embodiments of the subject-matter of claim 1 are set forth in the dependent claims. In the following, an embodiment of the invention is described in detail with respect to the figures. Fig. 1 is a longitudinal side sectional view of a recording apparatus to which an embodiment (sheet convey apparatus) of the present invention is applied; Fig. 2 is a perspective view of the sheet convey apparatus; Fig. 3 is a plan view of a sheet and a sheet supply portion according to the present invention; Fig. 4 is a perspective view of a recording apparatus using a conventional sheet convey apparatus; and Fig. 5 is a side view showing a main portion of another conventional sheet convey apparatus. Figs. 1 and 2 show an embodiment of the present invention, where Fig. 1 is a sectional view of recording apparatus including a sheet convey apparatus according to the embodiment, and Fig. 2 is a perspective view of a sheet convey mechanism of the recording apparatus. In Fig. 1, a recording apparatus 1 comprises an outer cover 2 and a sheet supply deck 3, and the cover 2 is provided with a sheet supply opening 2a and a sheet discharge opening 2b, and the sheet supply deck 3 is provided with a paper guide 3a. A sheet P is inserted from the sheet supply opening 2a and is discharged from the discharge opening 2b. Inside a plurality of side plates 4 of the recording apparatus 1, there are arranged a main roller 5 for conveying the sheet, a support shaft 6 on which the main roller 5 is secured, a guide plate 7 for guiding the sheet, a sensor S1 disposed in an opening formed in the guide plate, a platen 8 for establishing a print position for the sheet, a hold-down plate 9 pivotally mounted around a fulcrum 9a and biased by a spring 10 toward the main roller 5, hold-down rollers 11 rotatably mounted on a free end portion of the hold-down plate 9 and adapted to urge the sheet against the main roller 5, a carriage 13 shiftable along a plurality of guide shafts 12 in a widthwise direction of the sheet, and a recording head 14 mounted on the carriage 13 and adapted to perform the printing in response to image information. In place of the hold-down rollers 11 mounted on the free end of the hold-down plate 9, the free end itself of the hold-down plate 9 may be used as a means for urging the sheet against the main roller 5. Further, in this case (having no hold-down roller), the hold-down plate may be formed from a thin plate having the spring feature such as stainless steel. Further, within the recording apparatus 1, there are arranged a support shaft 15, a ring 16 secured to the support shaft 15, pins 16a, 16b protruded from a peripheral surface of the ring 16, auxiliary rollers 17 rotatably supported by the support shaft 15 and having a pin 17a at its side surface, a spring 18 extending between the pins 16a and 17a, a pinch roller 20 rotatably supported by a spring plate 19 and urged against the auxiliary rollers 17, and a sensor S2 disposed in the proximity of the sheet supply opening 2a. A peripheral surface of the auxiliary roller 17 is constituted by high friction material such as rubber. In Fig. 2, a motor M1 serves to rotate the main roller 5 via a motor gear 21, a two-stage gear 22 and a main roller gear 23 secured to the shaft 6 in response to a control signal from a controller (control device) 24. A rotational force of the motor M1 is transmitted to the shaft 15 via a gear 25 meshed with the main roller gear 23, a gear 26 and a one-way clutch 28. The one-way clutch 28 can transmit the rotation (in a direction shown by the arrow 30) of a gear 27 in response to the rotation of the main roller 5 in a direction shown by the arrow 29 (normal convey direction for the sheet P) to the shaft 15, but does not transmit the rotation (in a direction shown by the arrow 32) of the gear 27 in response to the rotation of the main roller 5 in a direction shown by the arrow 31 (reverse convey direction for the sheet P) to the shaft 15. A tip end of a ratchet lever 34 mounted around a shaft 34a and biased by a biasing force of a spring 35 in an anti-clockwise direction is abutted against a peripheral surface of a ratchet wheel 33 secured to the support shaft 15 and having saw-shaped teeth on its peripheral surface. The ratchet lever 34 permits the rotation of the ratchet wheel 33 in a direction shown by the arrow 30, but prevents the rotation of the ratchet wheel in a direction shown by the arrow 32. When a movable bar 37 is shifted upwardly by a plunger 36 in response to a control signal from the controller 24, since the ratchet lever 34 contacted with a lower bent portion of the movable bar 37 is rotated in a clockwise direction in opposition to the force of the spring 35, the ratchet lever is disengaged from the tooth of the ratchet wheel 33, thereby permitting the clockwise rotation of the ratchet wheel 33. Next, a sheet convey operation of the sheet convey apparatus according to the first embodiment will be explained with reference to Figs. 1 and 2. When the sheet P is inserted from the sheet supply opening 2a along the sheet supply deck 3 and paper guide 3a, a tip end of the sheet is detected by the sensor S2. On the basis of the detection of the sensor, the controller 24 energizes the motor M1 to rotate the main roller 5 in the normal sheet convey direction shown by the arrow 29. The rotation of the main roller 5 is transmitted to the gear 27 (as the rotation in the direction shown by the arrow 30) via the gears 25, 26. When the gear 27 is rotated in the direction shown by the arrow 30, since the one-way clutch 28 connects gear 27 to the support shaft 15, the support shaft 15 is also rotated in the same direction. The rotation of the support shaft 15 is transmitted to the auxiliary rollers 17 via the ring 16 secured to the support shaft 15, the pin 16a protruded from the ring 16, the pin 17a formed on the side surface of the auxiliary rollers 17 and the spring 18 connecting between the pins 16a, 17a, thereby rotating the auxiliary rollers 17 in the direction shown by the arrow 30. During the above rotation, the pin 17a is always abutted against the pin 16b with a predetermined force by the spring 18. By rotating the auxiliary rollers 17 in the direction shown by the arrow 30, the sheet P is conveyed toward that side of the apparatus; meanwhile, when the tip end of the sheet is detected by the sensor S1, the controller 24 controls the motor M1 to feed out the tip end of the sheet by a length L shown in Fig. 1. Now, a protruded amount N of the tip end of the sheet from the nip between the main roller 5 and the hold-down rollers 11 will now be explained with reference to Fig. 3 which is a plan view of the sheet convey portion of the recording apparatus of Fig. 1. In a condition that the sheet P is skew-fed as shown by P 1 , the protruded amount N at left side differs from that at the right side, and there is the following difference W between the left protruded amount T and the right protruded amount U: W = T - U When it is assumed that the difference W is a skew amount, if the amount of the difference W is great, the protruded amount N must be increased accordingly; however, the protruded amount is limited due to the size of the sheet supply opening 2a. The means 3a, 3b for regulating lateral edges of the sheet is effective to regulate the protruded amount difference W; When it is assumed that the protruded amount difference W is 3 mm and the margin of slip between the sheet P and the convey rollers is 2 mm, the protruded amount N becomes as follows: N = 3 + 2 = 5. From a condition that the tip end of the sheet is protruded by the amount N, the main roller 5 is rotated in the sheet reverse convey direction shown by the arrow 31 under the control of the controller 24. The rotational amount of the main roller 5 is greater than at least the protruded amount N, and, desirably, is (2 x N)- (3 x N). In response to the rotation of the main roller 5 in the direction shown by the arrow 31, the gear 27 is rotated in the direction shown by the arrow 32. However, this rotation is not transmitted to the support shaft 15 by the action of the one-way clutch 28. In synchronous with the reverse movement of the sheet P, the auxiliary rollers 17 are rotated in the direction shown by the arrow 32. On the other hand, although the pin 17a is also rotated, since the support shaft 15 cannot be rotated in the direction shown by the arrow 32 by the action of the ratchet wheel 33 and the ratchet lever 34, the pin 16a is not rotated, with the result that the rotation of the auxiliary rollers 17 results in only the extension of the spring 18. Since the tension force of the spring 18 acts to rotate the auxiliary rollers 17 in the direction shown by the arrow 30, during this, the auxiliary rollers 17 always give a normal direction conveying force to the sheet. Further, since the plurality of auxiliary rollers 17 are rotatably mounted on the support shaft 15 so that they can be rotated independently, the auxiliary rollers 17 can be rotated independently even if the shifting amounts of the sheet differ from each other in the widthwise direction of the sheet. In Fig. 3, if the sheet P is conveyed reversely from the condition P 1 , first of all, the right protruded amount U is conveyed to the nip (contact position) between the main roller 5 and the hold-down rollers 11, and when the right end passes through the contact position, the right end is not further shifted reversely. At the same time, although the left protruded amount T is conveyed to the nip, since U < T, the left end is conveyed to the contact position later than the right end. As a result, the right and left ends of the sheet P are stopped along the contact position to establish a condition P 2 . The biasing force of the spring 18 is selected so that the tip end of the sheet is not flexed in the condition P 2 . The condition P 2 is referred to as a sheet registration start position. From this condition, when the main roller 5 is rotated in the direction shown by the arrow 29 by a predetermined amount by the controller 24, by the normal direction conveying force of the auxiliary rollers 17, the left and right tip ends of the sheet P enter into the contact position along the contact position and then are conveyed to a record position of the recording head 14 without any skew-feed and with high accuracy. Next, in response to a record signal, the sheet P is fed normally by a predetermined amount and then the carriage 13 is shifted reciprocally in the widthwise direction, thereby effecting one line recording by the recording head 14. By repeating such operations, one page recording of the sheet is effected. During the recording, when a special record mode is performed (for example, when the recording head 14 is returned to the previously recorded line and the recording is effected again on that line), the controller 24 energizes the plunger 36 to permit the rotation of the ratchet wheel 33 in the direction shown by the arrow 32. At the same time, when the main roller 5 is rotated in the direction shown by the arrow 31 by a predetermined amount in order to return the sheet P to the previously recorded line, since the auxiliary rollers 17 do not generate the normal direction conveying force and are freely rotated by the reverse movement of the sheet P, the sheet P is returned with the convey accuracy of the main roller 5. Thereafter, when the main roller 5 is rotated normally again, the controller 24 stops the operation of the plunger, thus restoring the original condition. As another method for controlling the plunger 36, when the sheet P reaches the record position of the recording head 14, the plunger 36 may be driven to lift the lever 34 and the plunger 36 may be stopped at the time when the recording operation is completed. When a trailing end of the sheet P is detected by the sensor S1, the main roller 5 feeds the sheet by a predetermined amount for the recording under the control of the controller 24. After the last feeding of the sheet is completed, the main roller 5 is rotated by a predetermined amount for the discharge of the sheet, thereby discharging the sheet from the discharge opening 2b. When the whole sheet feeding amount for the recording previously stored on the basis of the command from a computer is completed, the controller 24 rotates the main roller 5 to discharge the sheet, even without the detection signal of the sensor S1 representative of the fact that the trailing end of the sheet is detected. After the sheet is discharged by the main roller 5, the controller 24 sets the recording apparatus 1 to the initial condition when the signal from the sensor S1 indicates the absence of the sheet. On the other hand, if the signal from the sensor indicates the presence of the sheet, the controller judges the fact that a poor sheet convey condition occurs, and emits an alarm signal via display means or a sound means. The present invention provides a recording apparatus comprising convey means for conveying a sheet in a predetermined convey direction, a pair of rollers arranged downstream of the convey means in the convey direction for conveying the sheet in the convey direction or in an opposite direction by their rotations in a normal direction or in a reverse direction, and control means for controlling the convey means and the pair of rollers. Control means control them in such a manner that, after the sheet conveyed by the convey means is conveyed in the convey direction by a predetermined amount by the pair of rollers, the pair of rollers are rotated in the reverse direction while applying a conveying force in the convey direction to the sheet by the convey means, thereby conveying the sheet in the opposite direction until the sheet passes through a nip between the pair of rollers.

Claims: A sheet convey apparatus, comprising: a convey means (15,17) for conveying a sheet (P) in a convey direction; a rotary means (5) arranged downstream of said convey means in the convey direction for conveying a sheet in the convey direction and in an opposite direction by rotation of said rotary means; and a control means (24) for controlling said convey means and said rotary means in such a manner that, after a sheet has been conveyed by said convey means and said rotary means in the convey direction until a leading end of the sheet passes through a nip of said rotary means, said rotary means conveys the sheet in the opposite direction until said leading end of the sheet passes through said nip of said rotary means , and said convey means allows a part of the sheet to pass trough a nip of said convey means in the opposite direction while applying a biasing force in the convey direction to the sheet, characterized in that said convey means includes a shaft (15) which is rotatable in the convey direction and non-rotatable in the opposite direction, a plurality of rollers (17) which are supportet by said shaft so that said plurality of rollers are independently rotatable in the convey direction and in the opposite direction, and a plurality of springs (18) which are provided for said plurality of rollers respectively so that said plurality of springs apply the biasing force in the convey direction to said plurality of rollers. A sheet convey apparatus according to Claim 1, wherein, when said shaft is rotated in the convey direction, said plurality of rollers are roteted by a rotary force of said shaft in the convey direction, and when said shaft is rotated in the opposite direction, the sheet conveyed in the opposite direction rotates said plurality of rollers in the opposite direction with said plurality of springs being extended so that a conveying force in the convey direction is applied to the sheet by tension force of said plurality of springs. A sheet convey apparatus according to claim 1, wherein each of said plurality of springs is connected to a corresponding one of said plurality of rollers at one end, and is connected to a corresponding one of rings fixed to said shaft at the other end. A sheet convey apparatus according to claim 1, wherein the biasing force of said plurality of springs is set at a value so that the leading end of the sheet is not flexed in a state in which the leading end of the sheet is stagnated along the nip of said rotary means.

Inventors: KIYOHARA TAKEHIKO, KIYOHARA, TAKEHIKO, KIYOHARA, TAKEHIKO, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: B41J13
IPC codes: B65H3, B65H5, B41J11, B41J13, B65H9