Sheet supply apparatus

Abstract: The present invention provides a sheet supply apparatus comprises sheet support means for stacking and supporting a plurality of sheets, first sheet absorb means (4) arranged confronting to a sheet surface of the sheet stack supported by the sheet support means for absorbing the sheet by air suction, second sheet absorb (8) means arranged confronting to a tip end of the sheet stack in a sheet supply direction (A) for absorbing the sheet by air suction and convey means for conveying the sheet absorbed to the first and second sheet absorb means. The first sheet absorb means and the second sheet absorb means are respectively disposed at positions where a distance between the first sheet absorb means and the sheet surface is different from a distance between the second sheet absorb means and the sheet surface. Thus, the sheets are separated one by one by averting a tip end of the sheet absorbed to the sheet absorb means.

Description: The present invention relates to a sheet supply apparatus and an image forming apparatus such as a copying machine, a printer, a facsimile machine and the like. In the state of the art a sheet feeding apparatus of this kind is known which is shown in the document EP 0 078 712. This known sheet feeding apparatus comprises a suction means for absorbing and conveying a deposited sheet, wherein the suction means has a plane parallel to the sheet to be conveyed in a rear portion, as well as a plane bent about a predetermined angle with respect to the sheet in its front portion. Both planes are provided with suction ports and coated with a conveyor belt. The purpose of this special embodiment consists in separating two sheets which were absorbed by the suction means by means of an air cut, wherein a gap is formed between the two absorbed sheets due to the angular position of the two a.m. planes. However, if the tip end of a first sheet is closely contacted with the tip end of a second sheet due to the sticking between fibers of first and second sheets and/or the flash of the cut edges of the sheets generated by the poor cutting, the cutting air from a nozzle will not enter between the first sheet and the second sheet, with the result that the positive pressure is generated below the second sheet. Accordingly, in this case, the air acts on the undersurface of the second sheet to promote the close contact between the first sheet and the second sheet. In particular, in thin sheets, it is feared that the second sheet is absorbed to a convey belt together with the first sheet by the absorbing force of the suction means. In this way, when the tip end of the first sheet is closely contacted with the tip end of the second sheet, it is impossible to separate the second sheet from the first sheet. As a result, there arise a problem that the double-feed of the sheets could not be prevented. Further, in order to prevent the double-feed, if the force of the air injected from the nozzle becomes stronger, the first sheet to be conveyed will also be blown out. Furthermore, the document US 3,405,935 relates to a card picker mechanism having a belt pusher mechanism, which is pushed into engagement with the belts, wherein the belts are forced against the lowermost card resting on a support plate. Since a vacuum apparatus is aligned with the holes in that belt pusher mechanism, the lowermost card is pulled into tight frictional engagement with the driven belt, which acts thereby to remove the lowermost card from the stack. This means that only by the movement of the belt pusher mechanism a suction force is exerted onto the lowermost card to draw the latter from the stack. SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a sheet supply apparatus and an image forming apparatus in which, even if a tip end of a first sheet is closely contacted with a tip end of a second sheet due to the sticking between fibers of these sheets, the first sheet can surely be separated from the second sheet, thereby preventing the double-feed of the sheets. To achieve the above object, according to the present invention, there is provided a sheet supply apparatus comprising sheet support means for supporting a plurality of sheets thereon; first sheet absorb means arranged confronting to a sheet surface of the sheet supported by said sheet support means for absorbing the sheet by an air suction; second sheet absorb means having an absorb surface and arranged confronting to a tip end of the sheet in a sheet supply direction for absorbing the sheet by the air suction; and convey means for conveying the sheet absorbed to said first and second sheet absorb means wherein the absorb surface of said second sheet absorb means is inclined at an angle relative to the sheet surface so that the absorb surface is further from the sheet surface as it extends downstream in a sheet convey direction by said convey means, wherein angle adjust means adjust the inclined angle of said second absorb means depending upon a resilience of the sheet to be absorbed thereto. According to claim 2 an image forming apparatus comprises sheet support means for stacking and supporting a plurality of sheets; first sheet absorb means arranged confronting to a sheet surface of the sheet stack supported by said sheet support means for absorbing the sheet by air suction; second sheet absorb means arranged confronting to a tip end of the sheet stack in a sheet supply direction for absorbing the sheet by air suction; convey means for conveying the sheet absorbed to said first and second sheet absorb means and image forming means for forming an image on the sheet conveyed by said convey means; wherein the absorb surface of said second sheet absorb means is inclined at an angle  relative to the sheet surface so that the absorb surface is further from the sheet surface as it extends downstream in a sheet convey direction by said convey means, wherein angle adjust means adjust the inclined angle of said second sheet absorb means depending upon a resilience of the sheet to be absorbed thereto. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an elevational sectional view of a sheet supply apparatus for illustrating a sheet supply apparatus; Fig. 2 is an elevational sectional view showing an example of an image forming apparatus having the sheet supply apparatus of the present invention; Fig. 3 is an elevational sectional view of a sheet supply apparatus according to a first embodiment of the present invention; Fig. 4 is an elevational sectional view of the apparatus of Fig. 3 in its operative condition; Fig. 5 is an elevational sectional view of a sheet supply apparatus according to a second embodiment of the present invention; Fig. 6 is a control block diagram of the apparatus of Fig. 5; Fig. 7 is a control block diagram of a sheet supply apparatus according to a third embodiment of the present invention; Fig. 8 is an elevational sectional view of a sheet supply apparatus according to a fourth embodiment of the present invention; Fig. 9 is a plan view of nozzles and therearound of the apparatus of Fig. 8; Fig. 10 is a view looked at along the arrow of Fig. 9; Fig. 11 is an elevational sectional view of the apparatus of Fig. 8 in its operative condition; Figs. 12A and 12B are sectional views of a sheet supply apparatus according to a fith embodiment of the present invention, looked at from a downstream side of a sheet convey direction; Figs. 13A and 13B are bottom views of the apparatus of Figs. 12A and 12B; Fig. 14 is a plan view of a shutter member of the apparatus of Figs. 12A and 12B; Figs. 15A and 15B are bottom views of a sheet supply apparatus according to a sixth embodiment of the present invention; Fig. 16 is a plan view of a shutter member of the apparatus of Figs. 15A and 15B; Fig. 17 is a control timing chart of a sheet supply apparatus according to a seventh embodiment of the present invention; Figs. 18A to 18C are sectional views showing the operation of a sheet supply apparatus according to a eighth embodiment of the present invention; Fig. 19 is a sectional view showing the operation of a sheet supply apparatus according to a ninth embodiment of the present invention; Fig. 20 is an elevational sectional view of a sheet supply apparatus according to a tenth embodiment of the present invention; Fig. 21 is a bottom view of a sheet supply apparatus according to a eleventh embodiment of the present invention; Fig. 22 is a bottom view of a sheet supply apparatus according to a twelfth embodiment of the present invention; Fig. 23 is a bottom view of a sheet supply apparatus according to a thirteenth embodiment of the present invention; Fig. 24 is a bottom view of a sheet supply apparatus according to a fourteenth embodiment of the present invention; Fig. 25 is a bottom view of a sheet supply apparatus according to a fifteenth embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First of all, a sheet supply apparatus will be explained with reference to Fig. 1 for general illustration. In Fig. 1, a plurality of sheets S are stacked on a sheet stacking tray 1, and tip ends of the sheets S are abutted against an alignment guide plate 2. A sheet convey portion 3 is provided with a first sheet absorb means 4 which comprises a flat bottom plate 5 opposed to a sheet stack rested on the sheet stacking tray 1, an air absorb opening 6 formed in the bottom plate 5, and a suction chamber 7. A second sheet absorb means 8 comprises a flat bottom plate 9 disposed at a downstream side of the flat bottom plate 5 in a sheet convey direction and inclined upwardly from the bottom plate 5 by a predetermined angle , an air absorb opening 10 formed in the bottom plate 9, and a suction chamber 11. The suction chambers 7, 11 is communicated with an air absorb blower 12. The absorbing action of the blower 12 is ON/OFF controlled by a valve 13. An endless convey belt 14 is mounted on and around rollers 15, 16, 17 and 18 in such a manner that the whole bottom surfaces of the sheet absorb means 4, 8 are covered by the convey belt. The convey belt 14 has a plurality of air openings 14A formed therein. The convey belt 14 is supported by the rollers 15, 16, 17 and 18 with a predetermined tension and is intermittently driven in a direction shown by the arrow A by a drive means (not shown), thereby conveying the sheet. The roller 15 is disposed at the intersection between the horizontal flat bottom plate 5 and the inclined flat bottom plate 9 and acts as a displacement fulcrum portion 15A for displacing or bending the sheet in such a manner that the sheet becomes convex downwardly. As a result, the tip end of the sheet S sucked by the second sheet absorb means 8 is absorbed to a tip end portion 14B of the convey belt 14 inclined by a predetermined angle. A nozzle 19 serves to inject air in order to float the sheets S stacked on the sheet stacking tray 1, and a nozzle 20 serves to inject air in order to separate a single sheet from the other sheets. The nozzles 19, 20 are connected to an air injection blower 21. The injection of the air from the nozzles 19, 20 can selectively be switched by a valve 22. A pair of convey rollers 23 serve to convey the sheet S conveyed by the convey belt 14 in a downstream direction. Next, the operation of such an air sheet supply apparatus will be explained. First of all, the valve 22 is switched to a position a by a switch means (not shown) such as a solenoid so that the blower 21 is operated to inject the air from the nozzle 19 toward the tip end of the sheet stack rested on the sheet stacking tray 1. As a result, several sheets S are blown up to float. Then, the valve 13 is switched to a position c by a switch means such as a solenoid so that the blower 12 is operated to suck or absorb the air below the convey belt 14 through the absorb openings 6, 10 and the air openings 14A. As a result, a first (uppermost) sheet S1 is absorbed to the sheet absorb means 4, 8 so that the sheet is adhered to the convey belt 14. More specifically, as shown in Fig. 1, a central portion of the sheet S1 is absorbed to the sheet absorb means 4 and the tip end portion of the sheet S1 is absorbed to the sheet absorb means 8. In this case, since the absorbing forces of the sheet absorb means 4, 8 are set to be sufficiently strong, the sheet S1 is bent around the displacement fulcrum portion 15A in opposition to the resilience of the sheet itself, so that the tip end portion and the central portion of the sheet is adhered to the convey belt 14. That is to say, the sheet S1 follows the flat bottom plates 5, 9 to bend around the displacement fulcrum portion 15A so that the sheet becomes convex downwardly. Now, it is assumed that a second sheet S2 is closely contacted with the first sheet S1. In this case, a central portion of the second sheet S2 substantially follows the first sheet S1. However, since the surface of the sheet absorb means 8 is covered by the sheet S1, the absorbing force does not act on the tip end portion of the sheet S2. Accordingly, the second sheet S2 is not bent around the displacement fulcrum portion 15A in opposition to the resilience of the sheet to maintain the flat condition, so that the tip end of the sheet S2 is separated from the tip end of the sheet S1 to create a gap e between the sheets S1 and S2. Then, the convey belt 14 is driven by the drive means (not shown) to convey the sheet S1 in the direction shown by the arrow A. At the same time, the valve 22 is switched to a position b to inject the air from the nozzle 20 into the gap e between the sheets S1 and S2, so that, as shown in Fig. 1, the sheet S2 is surely separated from the sheet S1. Accordingly, only the sheet S1 is conveyed toward the downstream direction to be brought to the paired convey rollers 23. Incidentally, the operations of the blowers 12, 21 and the operation of the drive means for the convey belt 14 are controlled by a control means. Now, Fig. 2 shows an example of an image forming apparatus (copying machine) having the sheet supply apparatus of the present invention. The image forming apparatus 200 is provided with an original support 206, a light source 207, a lens system 208, a sheet supply portion 209 and an image forming portion 202. The sheet supply portion 209 has cassettes 210, 211 adpated to contain sheets S and removably mounted to the image forming apparatus 200, and a deck 213 arranged on a pedestal 212. The sheet supply apparatus of the present invention is mounted on the deck 213. The image forming portion 202 includes a cylindrical photosensitive member 214, a developing device 215 containing toner, a transfer charger 216, a separation charger 217, a cleaner 218 and a first or primary charger 219. A convey device 220, a fixing device 204 and discharge rollers 295 are arranged at a downstream side of the image forming portion 202. Next, the operation of the image forming apparatus will be explained. When a sheet supply signal is outputted from a control device (not shown) of the image forming apparatus 200, the sheet S is supplied from the cassette 210 or 211 of the deck 213. On the other hand, light omitted from the light source 207 and relfected from an original D rested on the original support 206 is incident to the photosensitive member 214 through the lens system 208. The photosensitive member 214 is previously charged by the primary charger 219. Accordingly, when the photosensitive member is illuminated by the reflected light, an electrostatic latent image is formed on the photosensitive member, which latent image is then developed by the developing device 215 as a toner image. The sheet S supplied from the sheet supply portion 209 is sent to regist rollers 201, where the skew-feed of the sheet is corrected. Then, the sheet is sent to the image forming portion 202 with a predetermined timing. In the image forming portion 202, the toner image formed on the photosensitive member 214 is transferred onto the sheet S by the transfer charger 216, and then the sheet to which the toner image was transferred is separated from the photosensitive member 214 by applying to the sheet the charge opposite to that of the transfer charger 216 by the separation charger 217. The separated sheet S is sent, by the convey device 220, to the fixing device 204, where the transferred non-fixed image is permanently fixed to the sheet. The sheet S to which the image was fixed is discharged out of the image forming apparatus 200 by the discharge rollers 205. In this way, the sheet S which was supplied from the sheet supply portion 209 and on which the image was formed is discharged. Next, a first embodiment of the present invention will be explained with reference to Fig. 3. This embodiment differs from the illustrative apparatus of Fig. 1 in the point that according to the invention an angle  of the displacement fulcrum portion 15A is variable. The same constructural elements as those of the illustrative apparatus are designated by the same reference numerals and the detailed explanation thereof will be omitted, and only the above difference will be fully explained. In Fig. 3, an angle adjustment shaft support plate 25 for rotatably supporting the rollers 15, 16 is rotatably mounted on a roller shaft of the roller 15, and an angle adjustment arm 26 is rotatably attached to the angle adjustment support plate 25. A stopper shaft 27 is provided on the other end of the angle adjustment arm 26 so that the stopper shaft 27 can be locked in a recess 28A or 28B of a stopper 28. These recesses serve to previously set an angle  (referred to as "separation angle" hereinafter) to an angle satisfying the following two conditions in response to the resilience of the sheet S to be conveyed. The first condition is that only the uppermost sheet S1 is completely absorbed to the second sheet absorb means 8, and the second condition is that a force for maintaining the lower sheet S2 to a flat attitude by the resilience of the sheet is greater than a force bending the lower sheet S2 absorbed together with the uppermost sheet S1 around the displacement fulcrum portion 15A to become convex downwardly. Next, the operation of this air sheet supply apparatus in a case where the resilience of the sheet is great will be explained with reference to Fig. 3. When the resilience of the sheet is great, if the separation angle  is great, since the uppermost sheet S1 is stabilized and is not absorbed to the second sheet absorb means 8, the separation angle  is set to be small. In this case, the stopper shaft 27 is introduced into the recess 28A of the stopper 28. Thereafter, the valve 22 is switched to the position b by the switch means (not shown) such as a solenoid so that the blower 21 is operated to inject the air from the first nozzle 19 toward the tip end of the sheet stack S. As a result, several sheets S are blown up to float. Then, the valve 13 is switched to the position c by the switch means (not shown) such as a solenoid so that the blower 12 is operated to absorb the air through the air absorb openings 6, 10 and the air openings 14A. Consequently, the uppermost sheet S1 is absorbed to the first and second sheet absorb means 4, 8 and is adhered to the convey belt 14. More specifically, as shown in Fig. 3, the central portion of the sheet S1 is absorbed to the first sheet absorb means 4 and the tip end portion of the sheet S1 is absorbed to the second sheet absorb means 8. In this case, since the separation angle  was previously set to be small, the sheet S1 is bent around the displacement fulcrum portion 15A in opposition to the resilience of the sheet S1, so that the tip end portion and the central portion of the sheet S1 are closely adhered to the convey belt 14. That is to say, the sheet S1 substantially follows the flat bottom plate 5 and is bent around the displacement fulcrum portion 15A to become convex downwardly. In this case, since the separation angle  was previously set to be small as mentioned above, the lower sheet S2 is not bent around the displacement fulcrum portion 15A to maintain the flat attitude, with the result that the tip end of the sheet S2 is separated from the tip end of the sheet S1 to create the gap e therebetween. Thereafter, the convey belt 14 is driven by the drive means to convey the uppermost sheet S1 in the direction shown by the arrow A. At the same time, the valve 22 is switched to the position b, with the result that the air from the second nozzle 20 is blown into the gap e between the sheets S1 and S2, thereby separating the sheet S2 stably. Accordingly, only the sheet S1 is conveyed in the downstream direction to be sent to the paired convey rollers 23. Next, a case where the resilience of the sheet is weak will be explained with reference to Fig. 4. In the case where the resilience of the sheet S is weak, if the separation angle  is small, when the uppermost sheet S1 is absorbed, since the lower sheet S2 is apt to be absorbed together with the uppermost sheet, the separation angle  is set to be great. In this case, the stopper shaft 27 is introduced into the recess 28B of the stopper. By increasing the separation angle  in this way, the sheet having the weak resilience can also be surely separated. In this first embodiment, while an example that the separation angle  can be varied with two stages was explained, the present invention is not limited to this example, but the separation angle may be varied with any plural stages or in a stageless manner. Further, it should be noted that a range of the separation angle  (including 0°) may be appropriately set. Next, a second embodiment of the present invention will be explained with reference to Fig. 5. Incidentally, in an air sheet supply apparatus according to the second embodiment, the same constructural elements as those of the first embodiment according to Fig. 3 are designated by the same reference numerals and the detailed explanation thereof will be omitted. In the aforementioned first embodiment, the time period from when the first and second sheet absorb means 4, 8 start to the suction to when the convey belt 14 starts to drive was normally constant. However, since the second absorb means 8 is spaced apart from the uppermost surface of the sheet stack S rested on the sheet stacking tray 1, depending upon the kinds of the sheet (thick sheet, thin sheet or the like) and the change in the sheet supply environment, the time period from when the second sheet absorb means 8 starts to the suction to when the sheet S is absorbed to the second sheet absorb means 8 was varied. Accordingly, if the convey belt 14 starts to drive before the sheet S is absorbed to the second sheet absorb means 8, it was feared that the poor sheet supply occurs. To avoid this, if the time period from when the second sheet absorb means 8 starts to the suction to when the convey belt 14 starts to drive becomes long sufficient to surely absorb the sheet S to the second sheet absorb means 8, the sheet supply cycle will be longer, thereby reducing the number of sheets supplied per unit time. Thus, as shown in Fig. 5, a sheet detection portion (detection means) 35 comprising a flag 31 pivotally mounted on a shaft 30, a photo-sensor 32 and a stopper 33 is provided on the second sheet absorb means 8 so that it can be judged whether the sheet S is absorbed to the second sheet absorb means 8 or not. Fig. 6 shows a control block diagram of the air sheet supply apparatus according to the second embodiment. A detection signal from the sheet detection portion 35 is inputted to a control means 36, and the control means 36 controls a convey belt drive means 37 and a valve switch means 38. The flag 31 is rocked by the sheet S absorbed to the second sheet absorb means 8 to be shifted to a condition f, thereby detecting the suction of the sheet S by the photo-sensor 32. When the detection signal outputted from the photo-sensor 32 is inputted to the control means 36, the convey belt 14 is driven by the convey belt drive means 37, thereby conveying the sheet S1 in the direction shown by the arrow A. At the same time, the valve 22 is switched to the position b by the valve switch means 38 to inject air from the second nozzle 20 into the gap e between the sheets S1 and S2, thereby separating the sheet S2 stably. Accordingly, only the sheet S1 is conveyed toward the downstream direction to be sent to the paired convey rollers 23. In the above-mentioned second embodiment, while an example that the timing for starting the drive of the convey belt 14 is the timing for detecting the sheet S by the sheet detection portion 35 was explained, the present invention is not limited to this example. For example, it is assumed that the time when the valve 13 is switched to the position c is t = 0, the time period until the sheet S is detected by the sheet detection portion 35 is t = T 2 , and any time period from when the valve 13 is switched to the position c is t = T 1 , when T 2 < T 1 the drive of the convey belt 14 may be started at t = T 1 and when T 2 > T 1 the drive of the convey belt 14 may be started at t = T 2 . Thus when the time period T 2 is set to a certain large extent, since the drive of the convey belt 14 is started at t = T 1 in the normal sheet supply operation, and the drive of the convey belt is started at t = T 2 only when the suction of the sheet S to the second sheet absorb means 8 is delayed suddenly, it is possible to achieve the stable sheet supply operation. Next, a third embodiment of the present invention will be explained with reference to Fig. 7. Incidentally, in an air sheet supply apparatus according to the third embodiment, the same constructural elements as those of the second embodiment are designated by the same reference numerals and the detailed explanation thereof will be omitted. In this third embodiment, as shown in Fig. 7, the control means 36 also controls a blower output adjust means 39 for adjusting the output of the blower 12, as well as the aforementioned valve switch means 38 and convey belt drive means 37. It is assumed that the time when the valve 13 is switched to the position c is t = 0, the time period until the sheet S is detected by the sheet detection portion 35 is t = T 2 , and any time period from when the valve 13 is switched to the position c is t = T 1 , when T 2 > T 1 , the output of the blower 12 is increased by the control means 36 to increase the absorbing force of the second sheet absorb means 8. In this way, even a sheet S which is hard to be absorbed to the second sheet absorb means 8 can be absorbed surely and quickly. Thereafter, as in the aforementioned second embodiment, the convey belt 14 is driven by the convey belt drive means 47 to start the sheet supply operation. Incidentally, the output adjust means may be provided on the blower 21 in place of the blower 12 so that the blowing force of the first nozzle 19 is increased to absorb the sheet S to the second sheet absorb means 8. Of course, in place of the blower output adjust means, a switching valve and the like may be provided to adjust the absorbing force and/or the blowing force. Next, a fourth embodiment of the present invention will be explained with reference to Figs. 8 to 11. Incidentally, in an air sheet supply apparatus according to the fourth embodiment, the same constructural elements as those of the first embodiment are designated by the same reference numerals and the detailed explanation thereof will be omitted. In the aforementioned first embodiment, since the air from the second nozzle 20 is blown in the proximity of the tip end portion B (Fig. 8) of the sheet S absorbed to the second sheet absorb means 8 to separate the lower sheet S2, it is required to adjust the blowing position of the second nozzle 20 against the second sheet absorb means 8 with high accuracy. In particular, when the second sheet absorb means 8 is movable, since the second nozzle 20 is integrally formed with the first nozzle 19 and the blower 21, in response to the change in the separation angle  between the first sheet absorb means 4 and the second sheet absorb means 8, it was feared that the position of the second nozzle 20 is deviated with respect to the tip end portion B of the sheet S. To avoid this, as shown in Fig. 8, the second nozzle 20 is secured to the angle adjustment support plate 25 by a nozzle attachment plate 40 and the second nozzle is connected to the blower 21 via a flexible duct 41. With this arrangement, the air injected from the second nozzle 20 can always impinge against the tip end portion B of the sheet S, thereby eliminating the above-mentioned disadvantage. Fig. 9 is a schematic top view of the second nozzles 20 and therearound of Fig. 8, and Fig. 9 is a view looked at along the arrow C in Fig. 9. The second nozzles 20 are pinched by nozzle stays 45, 46 and are fixed to the nozzle stays by screws 47. Further, the nozzle stays 45, 46 are secured to the nozzle attachment plate 40 by screws 48, which nozzle attachment plate 40 is secured to the angle adjustment support plate 25 by screws 49. Fig. 11 shows a condition that the separation angle  is increased. In this condition, when the angle adjustment support plate 25 is shifted, the second nozzles 20 are also shifted, and, thus, since the angle between the second nozzles and the flat bottom plate 9 of the second sheet absorb means 8 is not varied, the sheet can be separated regardless of the separation angle . Next, a fith embodiment in which an area of the absorb opening of the sheet absorb means is controlled regarding the first embodiment will be explained. In this fith embodiment, the area of the absorb opening of the first sheet absorb means 4 of the first embodiment is controlled. Thus, this control will be fully explained. Figs. 12A and 12B are views of the sheet convey portion 3 looked at from the downstream side of the sheet convey direction, and Figs. 13A and 13B are views of the sheet convey portion 3 looked at from the bottom. As shown in Fig. 14, a shutter sheet (shutter member) 435a has a small opening portion 436a (having a width substantially the same as that of a small size sheet SS) corresponding to the small size sheet SS, and a large opening portion 436b (having a width substantially the same as that of a large size sheet SL) corresponding to the large size sheet SL. The shutter 435a constitutes an air absorb opening portion and is secured to rotatably supported shafts 437, 438 at its both ends and is wound around the shafts. Motors (drive means) M1, M2 serve to rotatingly drive the shafts 437, 438 to wind up the shutter 435a. With this arrangement, when the small size sheet SS is supplied, the motor M1 is driven to wind up the shutter 435a in a direction shown by the arrow (right in Fig. 13A), with the result that the sheet SS is absorbed with the opening portion 436a maintained in a condition shown in Fig. 13A. Accordingly, as shown in Fig. 12A, since the opening portion 436a is generally covered by the sheet SS, the leakage of air is prevented, thus obtaining the sufficient absorbing force. On the other hand, when the large size sheet SL is supplied, the motor M2 is driven to wind up the shutter 435a in a direction shown by the arrow (left in Fig. 13B), with the result that the sheet SL is absorbed with the opening portion 436b maintained in a condition shown in Fig. 13B. Accordingly, as shown in Fig. 12B, since the sheet SL is absorbed through its whole length, both ends of the sheet SL are also adhered to the convey belt 14. Next, a sixth embodiment of the present invention will be explained with reference to Figs. 15A, 15B and 16. Incidentally, since the fundamental construction of a sheet supply apparatus of this embodiment is substantially the same as that of the fith embodiment, the same constructural elements as those of the fith embodiment are designated by the same reference numerals and the detailed explanation thereof will be omitted. As shown in Fig. 16, the sheet supply apparatus according to the sixth embodiment has a shutter sheet (shutter member) 435b. The shutter sheet 435b has a group of openings A' corresponding to a small size sheet SS and including three opening portions 436c, and a group of openings B7 corresponding to a large size sheet SL and including four opening portions 436c. As similar to the fith embodiment, the opening group A' is arranged as shown in Fig. 15A to absorb the sheet SS. On the other hand, when the large size sheet SL is supplied, the opening group B' is arranged as shown in Fig. 15B to absorb the sheet SL. In this example, while the number of opening portions corresponding to the small size sheet SS was decreased and the number of the opening portions or the distance between the opening portions corresponding to the large size sheet SL was increased, such number of openings and/or the opening-to-opening distance may be varied. Next, a seventh embodiment of the present invention in which the injection of airs from the nozzles 19, 20 regarding the first embodiment is controlled will be explained. Since the construction of a sheet supply apparatus itself of the seventh embodiment is the same as that of the first embodiment (only the air injection controls are different from each other), the apparatus itself is not shown. When the sheet S is floated, the valve 22 is switched to the position a to inject the air from the nozzles 19, and when the sheets S are separated, the valve 22 is switched to the position b to inject the air from the nozzles 20. In this way, the sheet supply operation is effected. By the way, when the sheet supply operation of the sheet supply apparatus is not performed, the valve 22 is switched to the position a so that the nozzles 19 are controlled by a control portion (adjust means) (not shown) in such a manner that an air amount injected from the nozzles 19 in the sheet supply operation is reduced. Also in this condition, several sheets S can be blown up to float, and the air can be introduced between the floated sheets. The other constructions of this sheet supply apparatus is the same as those of the first embodiment. Fig. 17 shows a detailed drive timing chart. The blower 12 is not rotated when the sheet supply operation is not effected; but, during the sheet supply operation, the blower 12 is rotated. When the sheet supply operation is finished, the blower 12 is stopped. In this case, the blower 21 is rotated with the smaller number (P1) of rotation when the sheet supply operation is not effected, and is rotated with the number P2 (> P1) of rotation during the sheet supply operation. When the sheet supply operation is finished, the number of rotation of the blower 21 is returned from P2 to P1. Further, when the sheet supply operation is not effected, the valve 13 is in the position d; but, the valve 13 is switched to the position c in the sheet supply operation, and is returned to the position d when the sheet supply operation is finished. On the other hand, the valve 22 is in the position a when the sheet supply operation is not effected; but, the valve 22 is switched to the position b in the sheet supply operation, and is returned to the position a when the sheet supply operation is finished. Further, the drive of the convey belt 14 is turned OFF when the sheet supply operation is not effected; but, when the sheet supply operation is started and the sheet S has been adhered to the convey belt 14, the drive of the convey belt 14 is turned ON to convey the sheet S, and when the sheet supply operation is finished the drive of the convey belt 14 is turned OFF again. By controlling the blower 21 and the valve 22 as mentioned above, the blow amount of the nozzle 19 becomes as shown in Fig. 17 so that, when the sheet supply operation is not effected, the air is injected with the blow amount Q2 smaller than the blow amount Q1 (during the sheet supply operation). In this way, when the sheet supply operation is not effected, by injecting the air against the sheet stack S, since it is possible to float several sheets and to pass the air along both surfaces of each sheet, thereby reducing the moisture absorption of the sheet and making the hygroscopicity of the sheets uniform, it is possible to perform the excellent image formation without any image flow and the curl in the sheet S. Further, particularly in this embodiment, since the air blowing means for reducing the moisture absorption of the sheet and for making the hygroscopicity of the sheets uniform also serves as the air blowing means (blower 21 and nozzle 19) for floating the sheets in the sheet supply apparatus, the sheet supply apparatus is prevented from making large-sized and expensive. Furthermore, in this embodiment, while the blow amount from the nozzle 19 in the non-sheet supply period was smaller than the blow amount in the sheet supply operation to reduce the noise, the blow amount in the non-sheet supply period may be equal to the blow amount in the sheet supply operation, or, when the sheet supply apparatus is used under the high humidity condition, the blow amount in the non-sheet supply period may be greater than the blow amount in the sheet supply operation to further reduce the moisture absorption of the sheet S and to make the hygroscopicity of the sheets further uniform. Next, a eighth embodiment of the present invention will be explained with reference to Figs. 18A to 18C. Incidentally, since the fundamental construction of a sheet supply apparatus according to the eighth embodiment is substantially the same as that of the seventh embodiment, the same constructural elements are designated by the same reference numerals and the explanation thereof will be omitted. Figs. 18A to 18C are sectional views showing the variable condition of the valve 22 of the air blowing means. In accordance with the kinds of the sheets S, the operator manipulates a switch means (not shown) exposed from the sheet supply apparatus. For example, when the kinds of the sheets S are grouped into three (thick sheet, thin sheet and normal sheet), the operator can shift the switch means to one of three positions corresponding to three kinds of sheets. In response to the shifting movement of the switch means, a regulating valve (adjust means) 22a is shifted along a plane including the lower openings of the nozzles 19, 20 to control the opening areas of the nozzles 19, 20. Figs. 18A to 18C show schematic positional relation of the regulating valve 22a between the above-mentioned three kinds of sheets. Fig. 18A shows a condition that the thick sheet is handled. In this case, the regulating valve is adjusted so that the blow amount from the nozzle 19 becomes greater than the blow amount from the nozzle 20 (f > g), thereby increasing the floating force for floating the sheets S. Fig. 36B shows a condition that the thick sheet is handled. In this case, the regulating valve is adjusted so that the blow amount from the nozzle 19 becomes smaller than the blow amount from the nozzle 20 (f < g), thereby decreasing the floating force for floating the sheets S to enhance the separating ability. Fig. 36C shows a condition that the normal sheet is handled. In this case, the regulating valve 22a is adjusted so that the opening area of the nozzle 19 becomes substantially the same as that of the nozzle 20 ( f = g ). That is to say, the regulating valve 22a is shifted to control the air amounts from the nozzles 19, 20 so that the sum of the air amount from the nozzle 19 and the air amount from the nozzle 20 is always constant, thereby supplying the air amounts in accordance with the property of the sheet. When the regulating valve 22a is fixed on the basis of the above-mentioned positional relation, then, the valve 22 is switched to the position a by the switch means (not shown) such as a solenoid so that the blower 21 is operated inject the air from the nozzle 19 toward the tip end of the sheet stack S. As a result, several sheets S are blown up to float. Then, the valve 13 is switched to the position c by the switch means (not shown) such as a solenoid so that the blower 12 is operated to suck the air through the absorb openings 6, 10 and the air openings 14a. In this way, the uppermost sheet S1 is absorbed to the first and second sheet absorb means 4, 8 and is closely contacted with the convey belt 14. Next, a ninth embodiment of the present invention will be explained with reference to Fig. 19. Incidentally, since the fundamental construction of a sheet supply apparatus according to the ninth embodiment is substantially the same as that of the seventh embodiment, the same constructural elements are designated by the same reference numerals and the explanation thereof will be omitted. Fig. 19 is a sectional view showing the air blowing means. In the eighth embodiment, while the regulating valve 22a was slidingly shifted to regulate the opening areas of the nozzles 19, 20, in this ninth embodiment, the regulating valve 22a is of rotatable type in which the rotation angle of the regulating valve is changed in accordance with the kinds of the sheets to regulate the opening areas of the nozzles 19, 20. That is to say, when the thick sheet is handled, a wall 23a protruded from the regulating valve 22a is brought into a position h, where the opening areas of the nozzles are regulated so that the opening area of the nozzle 19 becomes greater than the opening area of the nozzle 20. Further, when the thin sheet is handled, the wall is brought into a position j (opposite to the position h), where the opening area of the nozzle 19 becomes smaller than the opening area of the nozzle 20. Further, when the normal sheet is handled, the wall is brought into a position i, where the opening area of the nozzle 19 becomes substantially the same as the opening area of the nozzle 20. Next, a tenth embodiment of the present invention will be explained with reference to Fig. 20. Incidentally, since the fundamental construction of a sheet supply apparatus according to the tenth embodiment is substantially the same as that of the seventh embodiment, the same constructural elements are designated by the same reference numerals and the explanation thereof will be omitted. Fig. 20 is a sectional view showing the air blowing means. In this embodiment, the valve 22 and the regulating valve 22a are not used, but air blowing blowers 21 having the same ability are attached to the nozzles 19, 20, respectively. These blowers 21 are set so that a service voltage is proportional to the number of rotation of the blower 21 (i.e., air amount injected from the blower). By an electric means (not shown) for changing the voltages V1, V2 ( V1 + V2 = V ) supplied to the blowers 21 relatively, when the thick sheet is handled, a relation V1 > V2 is established, and, when the thin sheet is handled, a relation V1 < V2 is established, and when the normal sheet is handled, a relation V1 = V2 is established. In this way, the air amounts injected from the nozzles 19, 20 are regulated relatively, thereby achieving the same technical effect as that of the ninth embodiment. Next, further embodiments of the present invention regarding the air absorb opening of the sheet absorb means 4 in the first embodiment will be explained. Incidentally, since the fundamental construction of one of the further embodiments is the same as that of the first embodiment, the detailed explanation thereof will be omitted, but only the characteristic portion will be fully explained with reference to Fig. 21 which is a bottom view of the sheet absorb means showing a eleventh embodiment. In the conventional sheet supply apparatus, while air openings 6a formed in the flat bottom plate 5 of the air suction chamber 7 provided in the sheet convey portion 3 had same diameter, such air openings 6a are so arranged that the area of each air opening disposed nearest to the air sucking blower 12 is minimum and the area of each air opening disposed farthest from the air sucking blower 12 is maximum and the areas of the air openings are gradually increased as the openings go away from the air sucking blower 12. In Fig. 21, the air suction chamber 7 is covered by a plurality of identical convey belts 14, and is communicated with the air sucking blower 12 at one end of the chamber (in a direction perpendicular to the sheet convey direction, i.e., a widthwise direction of the sheet), so that the air sucked from the air suction chamber 7 flows along a direction substantially perpendicular to the sheet convey direction. Further, a plural rows (along the sheet convey direction) of air openings 6a having different opening areas are formed in the flat bottom plate 5 defining the suction chamber 7 at positions corresponding to the positions of the rows of the air openings 14A formed in the respective convey belts 14 in such a manner that the diameters of the air openings 6a in each row are identical and the areas of the air openings 6a are gradually increased as the air openings go away from the air sucking blower l2. That is to say, the opening areas of the air openings are selected so that, when the opening area of each air opening 6a nearest to the air sucking blower l2 is S1, the opening area of each air opening adjacent to the aforementioned one is S2 and so on, a relation Sl < S2 < S3 < S4 < S5 < S6 < ··· < Sn is established, and the air sucking pressure loss of each air opening is identical to each other. The air sheet supply apparatus having the air suction chamber 7 with the above-mentioned arrangement is operated as follows, The air injection belower 2l is operated by a predetermined manipulation so that the air from the floating nozzle l9 is injected against the tip end of the sheet stack, thereby blowing up several sheets S to float, Then, the suction valve l3 is switched by the switch means (not shown) such as a solenoid from a position d shown by the broken line to a position c shown by the solid line so that the air sucking blower l2 is operated to suck the sheet S through the air openings 6a, l4A, thereby adhering the sheet S to the convey belts l4. In this case, even when the sheet S to be conveyed is thickest, since the absorbing force of each convey belt l4 along the sheet convey direction is substantially constant, the sheet is not skew-fed and the end of the sheet is not depended down, with the result that only the uppermost sheet is surely adhered to the convey belts 14 closely by the positive separation action of the separating nozzle 20 and the sheet is surely conveyed in the downstream direction by the rotations of the rollers 15, 16, 17, 18. Incidentally, in the above embodiment, while the air openings were circular, for example, a plural rows of air openings in the form of a trapezoid contacting with the circles S1 and S2, a trapezoid contacting with the circles S3 and S4 and a trapezoid contacting with the circles S5 and S6 respectively and having gradually increased opening areas, or integral air openings in the form of a trapezoid contacting with the circles S1 and S6 may be formed in the flat bottom plate. Next, a twelfth embodiment of the present invention will be explained. Fig. 22 shows the twelfth embodiment and is a bottom view of a sheet convey means to which the present invention is applied. In the twelfth embodiment, as shown in Fig. 22, the air sucking blower 12 is connected to a central portion of one surface (facing the sheet convey direction) of the air suction chamber 7, and air openings 6b are arranged so that the opening areas of the air openings are gradually increased from a central portion (nearest to the blower 12) of the chamber to both ends of the chamber. In this way, the same technical effect as that of the above-mentioned embodiments can be obtained. Fig. 23 shows the thirteenth embodiment and is a bottom view of a sheet convey means to which the present invention is applied. In the eleventh embodiment, while the air openings 6a having the different opening areas were formed in the flat bottom plate 5 defining the air suction chamber 7, in the thirteenth embodiment, as shown in Fig. 23, although the air openings 6a having the same opening area are formed in the same manner as the conventional case in correspondence to the width of each convey belt 14, a plurality of air openings 14B formed in the convey belts 14 are arranged so that, as in the ninth embodiment, the opening areas of the air openings 14B are gradually increased as the air openings go away from the air sucking blower 12. Next, a fourteenth embodiment of the present invention in which the arrangement of the blower 12 is changed with respect to the first embodiment will be explained. Since the fundamental construction and the general function of this embodiment are the same as those of the first embodiment, the detailed explanation thereof will be omitted, but only the characteristic portion will be fully explained with reference to Fig. 24 which is a bottom view of the sheet convey means showing the characteristic of the fourteenth embodiment clearly. In Fig. 24, air sucking blowers 12 having the identical ability are connected to both ends of the air suction chamber (in a direction perpendicular to the sheet convey direction), so that the air sucked from the air suction chamber 7 flows from a center of the air suction chamber 7 to the both ends thereof as shown by the arrows B. Further, a plurality of air openings 6a, 6b, 6c are formed in the flat bottom plate 5 defining the air suction chamber 7 at positions corresponding to the positions of the air openings 14A formed in the respective convey belts 14. Particularly, the opening areas of the air openings are so selected that the absorbing forces of the air sucking blowers 12 at the air openings 6a and 6c are equal to each other and the air suction pressure losses at the air openings 6a and 6b are equal to each other. For example, when distances between the air sucking blowers 12 positioned at both ends (in a direction perpendicular to the sheet convey direction) of the suction chamber and the air openings 6a, 6c are L1, L2, respectively, and the opening areas of the air openings 6a, 6c are S11, S12, respectively, the opening areas are adjusted independence upon the above-mentioned distances so that when L1 = L2 a relation S11 = S12 is established and when L1 > L2 a relation S11 > S12 is established and when L1 < L2 a relation S11 < S12 is established, thereby equalizing the sheet absorbing forces at both ends of the sheet (in a widthwise direction). The air sheet supply apparatus having the sheet convey means with the above-mentioned arrangement is operated as follows. As in the conventionl apparatus, the air injection blower 21 is operated by a predetermined manipulation so that the air from the floating nozzle 19 is injected against the tip end of the sheet stack, thereby blowing up several sheets S to float. Then, the suction valve 13 is switched by the switch means (not shown) such as a solenoid from a position d shown by the broken line to a position c shown by the solid line so that the air sucking blowers 12 are operated to suck the air through the air openings 6a, 6b, 6c and 14A, thereby adhering the sheet S to the convey belts 14. In this case, even when the sheet S to be conveyed is thickest, since the absorbing forces to the convey belts 14 in the widthwise direction of the sheet are substantially the same, the sheet is not skew-fed and the end of the sheet S is not depended down, with the result that only the uppermost sheet is surely adhered to the convey belts 14 closely by the positive separation action of the separating nozzle 20 and the sheet is surely conveyed in the downstream direction by the rotations of the rollers 15, 16, 17 and 18. Lastly, a fifteenth embodiment of the present invention of the present invention will be explained. The same constructural elements as those of the fourteenth embodiment are designated by the same reference numerals and the explanation thereof will be omitted. Fig. 25 shows the fifteenth embodiment and is a bottom view of the sheet convey means to which the present invention is applied. In the fourteenth embodiment, while the air sucking blowers 12 were directly connected to both ends of the chamber 7 in the direction perpendicular to the sheet convey direction, in this embodiment, as shown in Fig. 25, one or more blower 12 is arranged within the central convey belt 14 and is connected to the air suction chamber 7 via ducts 12a connected to both ends of the chamber in the direction perpendicular to the sheet convey direction, thereby achieving the same technical effect as that of the fourteenth embodiment. Incientally, in Fig. 48, while the air sucking blower 12 was arranged within the central convey belt, it may be arranged outside of such convey belt. The present invention provides a sheet supply apparatus comprises sheet support means for stacking and supporting a plurality of sheets, first sheet absorb means arranged confronting to a sheet surface of the sheet stack supported by the sheet support means for absorbing the sheet by air suction, second sheet absorb means arranged confronting to a tip end of the sheet stack in a sheet supply direction for absorbing the sheet by air suction and convey means for conveying the sheet absorbed to the first and second sheet absorb means. The first sheet absorb means and the second sheet absorb means are respectively disposed at positions where a distance between the first sheet absorb means and the sheet surface is different from a distance between the second sheet absorb means and the sheet surface. Thus, the sheets are separated one by one by averting a tip end of the sheet absorbed to the sheet absorb means.

Claims: A sheet supply apparatus, comprising: sheet support means (1) for supporting a plurality of sheets (S) thereon; first sheet absorb means (4) arranged confronting a sheet surface of the sheet (S) supported by said sheet support means (1) for absorbing the sheet by an air suction; second sheet absorb means (8) having an absorb surface (9) and arranged confronting a tip end of the sheet in a sheet supply direction for absorbing the sheet (S) by the air suction; and convey means (3) for conveying the sheet (S) absorbed to said first and second sheet absorb means (4, 8); wherein the absorb surface (9) of said second sheet absorb means (8) is inclined at an angle  relative to the sheet surface so that the absorb surface (9) is further from the sheet surface as it extends downstream in a sheet convey direction by said convey means (3), characterized in that angle adjust means (25 - 28) adjust the inclined angle () of said second absorb means (8) depending upon a resilience of the sheet (S) to be absorbed thereto. An image forming apparatus, comprising: sheet support means (1) for stacking and supporting a plurality of sheets (S); first sheet absorb means (4) arranged confronting a sheet surface of the sheet (S) stack supported by said sheet support means (1) for absorbing the sheet (S) by air suction; second sheet absorb means (8) arranged confronting a tip end of the sheet stack in a sheet supply direction for absorbing the sheet (S) by air suction; convey means (3) for conveying the sheet (S) absorbed to said first and second sheet absorb means (4, 8); and image forming means (200) for forming an image on the sheet (S) conveyed by said convey means (3); wherein the absorb surface (9) of said second sheet absorb means (8) is inclined at an angle  relative to the sheet surface so that the absorb surface (a) is further from the sheet surface as it extends downstream in a sheet convey direction by said convey means (3), characterized in that angle adjust means (25 - 28) adjust the inclined angle () of said second sheet absorb means (8) depending upon a resilience of the sheet (S) to be absorbed thereto. A sheet supply apparatus according to claim 1, wherein an absorb surface (5) of said first sheet absorb means (4) is disposed substantially parallel to the sheet surface of the sheet (S) supported by said sheet support means (1). A sheet supply apparatus according to claim 1, wherein said first absorb means (4) absorb an uppermost sheet (S) of the sheets supported by said sheet support means (1). A sheet supply apparatus according to claim 1, wherein said first sheet absorb means (4) absorbs a lowermost sheet (S) of the sheets supported by said sheet support means (1). A sheet supply apparatus according to claim 1, wherein said convey means (3) comprises a rotatable convey belt (14) mounted on rollers (15 - 18) to cover each surface (5, 9) of said first and second sheet absorb means (4, 8), and said convey belt (14) is provided with a plurality of air openings (14A), so that when said sheet absorb means (4, 8) absorb the air the sheet (S) is absorbed through said air openings (14A) for conveying. A sheet supply apparatus according to claim 6, wherein said convey belt (14) is rotated by rotating said rollers (15 - 18) on which said convey belt (14) is mounted, and one of said rollers (15 - 18) disposed at an upstream side of said sheet absorb means (4, 8) is a drive roller and the other rollers (15 - 18) disposed at a downstream side of said sheet absorb means (4, 8) are driven rollers. A sheet supply apparatus according to claim 7, further comprising a blower (12) connected to said sheet absorb means (4, 8) for absorbing the air, and opening areas of air openings formed in a sheet absorb side of said sheet absorb means are increased as said air openings go away from said blower. A sheet supply apparatus according to claim 1, further comprising air blowing means (11) for blowing the air against the tip end of the sheet (S) to float the sheet (S) from said sheet support means (1) and to absorb the sheet (S) to said sheet absorb means (4, 8). A sheet supply apparatus according to claim 1, further comprising air blowing means (20) for blowing the air against the tip end of the sheet (S) absorbed in order to promote the separation of the sheets (S) absorbed to said first and second sheet absorb means (4, 8). A sheet supply apparatus according to one of claims 1 and 3 to 10, characterized in that said angle adjust means (25 - 28) comprises an angle adjustment arm (26) which is rotatably attached to a support plate (25) of said second sheet absorb means (8) and which can be locked in one of several recesses (28A, 28B) of a stopper (28) in order to set the angle  to a predetermined separation angle.

Inventors: AOYAMA TAKESHI, KOMINATO RYUSEI, TAKAHARA HIROYUKI, TANAKA MAKOTO, UBAYASHI SHINSUKE, YOSHIDA YASUMI, AOYAMA, TAKESHI, KOMINATO, RYUSEI, TAKAHARA, HIROYUKI, TANAKA, MAKOTO, UBAYASHI, SHINSUKE, YOSHIDA, YASUMI, AOYAMA, TAKESHI, C/O CANON KABUSHIKI KAISHA, KOMINATO, RYUSEI, C/O CANON KABUSHIKI KAISHA, TAKAHARA, HIROYUKI, C/O CANON KABUSHIKI KAISHA, TANAKA, MAKOTO, CANON KABUSHIKI KAISHA, UBAYASHI, SHINSUKE, C/O CANON KABUSHIKI KAISHA, YOSHIDA, YASUMI, CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: B65H3
IPC codes: B65H3