EP0579264A1

EP0579264A1 - A sheet feeding apparatus

Info

Publication number: EP0579264A1
Application number: EP93113438A
Authority: EP
Inventors: Ichiro Ohsawa; Yutaka Kikuchi; Masanobu Kanoto; Hideki Sato; Yoshifumi Endo; Hideshi Canon-Ryo Kawaguchi
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1987-02-17
Filing date: 1988-02-15
Publication date: 1994-01-19
Anticipated expiration: 2008-02-15
Also published as: DE3856271D1; EP0579264B1; DE3856271T2; DE3851963D1; EP0279402B1; EP0279402A2; DE3851963T2; EP0279402A3

Abstract

A sheet feeding apparatus for feeding sheets (201) to an image forming means of an image forming apparatus comprises a sheet accommodating means (202) from which the sheets are fed out by a feeding means (214, 214', 215, 215'), a separation means (227, 227') which separates the fed sheets one by one, and a transporting means (216, 216') which cooperates with the feeding means to transport the sheets to the image forming means. Further, there is provided a first passage through which the sheets separated by the separation means are fed to a position between the feeding means and the transporting means, and a second passage (229) through which sheets are fed to the above position whilst the separation means is bypassed, wherein the feeding means and the transporting means are adapted to transport the sheets fed through either the first or the second passage.

Description

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a sheet feeding apparatus usable with an image forming apparatus such as a copying machine and a printer.
Referring to Figure 1, a conventional sheet feeding apparatus includes a sheet tray 2, a sheet feeding spring 3 and a feeding roller 4, wherein a transfer material 1 on the sheet tray 2 is urged to the feeding roller 4 by the feeding spring 3. When the feeding roller 4 rotates, the leading edge of the transfer material (sheet) 1 is advanced into the space formed between a sheet guide 2' and the feeding roller 4 by friction. The coefficients of friction are so set that when plural transfer materials are advanced, the coefficient of friction µ₁ between the transfer materials 1, the coefficient µ₃ between the feeding roller 4 and the transfer material 1 and the coefficient µ₂ between the transfer material 1 and a separation pad 6 which is urged to the feeding roller 4 by a separation spring 5, satisfy µ₁ < µ₂ < µ₃. Because µ₁ < µ₂, the plural sheets are stopped from the one closest to the separation pad 6, and finally, because µ₂ < µ₃, only one transfer material 1a is conveyed between the feeding roller 4 and the separation pad 6, as shown in Figures 2 and 3. Immediately after the transfer material 1a passes between the feeding roller 4 and the separation pad 6, the speed Va of the transfer material (Figure 1) may varies depending on the relationships among the frictional coefficients µ₁, µ₂ and µ₃, and therefore, the speed is unstable. After the leading edge of the transfer material 1a is caught by the couple of the registration rollers 13 and 14, the driving of the feeding roller 4 is stopped.
The feeding roller 4 is provided with an unshown one-way clutch, so that the feeding roller 4 follows to rotate by the friction between the transfer material 1a and itself. When the trailing edge of the transfer material 1a departs from the feeding roller 4, the rotation of the feeding roller 4 stops, and therefore, the next transfer material 1b is not fed. Since the pressure between the registration rollers 13 and 14 is large enough as compared with the frictional load between the transfer material 1a and the separation pad 6, the conveying speed Vb of the transfer material 1a is stabilized.
On the other hand, a light beam 9 produced in the optical scanning means 8 is imaged on the photosensitive member 10 to form a latent image thereon, which is in turn developed with toner by a developing device. The toner image on the photosensitive member 10 is transferred onto the transfer material 1a at point P. The toner image transferred onto the transfer material 1a is fixed by a fixing device 12.
The conventional example employs a couple of registration rollers 13 and 14 in order to stabilize the speed of the transfer material at the point P where the image transfer is effected and to provide an accurate image. However, the employment of the registration roller couple makes the apparatus bulky and expensive.
More particularly, the conventional example relies on the relationship between the frictional forces wherein the frictional coefficient (and therefore force) µ₃ between the feeding roller 4 and the transfer material 1 is larger than the frictional coefficient (and therefore force) µ₂ between the separation pad and the transfer material when the transfer material or materials are between the feeding roller 4 and the separation pad 6 functioning as a separating means. For this reason, there always exists a slipping between the separation pad 6 and the transfer material 1 to be conveyed. This results in a braking force always applied to the feeding action of the feeding roller 4, and the braking force varies in accordance with materials, thickness and surface property of the transfer sheets and also with the number of sheets involved. Those are the reasons why the feeding speed Va of the feeding roller 4 is not stabilized. In order to obviate those problems, the conventional example uses a couple of registration rollers 13 and 14 between the feeding roller 4 and the transfer drum 10 so as to stabilize the feeding speed Vb at a position where the stabilized speed is required, for example, the transfer station P where an image is transferred from the photosensitive drum 10 to the transfer material. However, this makes the apparatus bulky and requires additional means, that is, a driving means for the registration roller couple, with the result that the cost of the apparatus is increased.
Additionally, even in the case that the couple of the registration rollers 13 and 14 is used, the feeding speed Va between the feeding roller 4 and the registration roller couple varies depending on the frictional coefficient of the transfer sheets or on the ambient conditions, even to such an extent that the sheet does not reach the registration roller couple in time.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention to provide a sheet feeding apparatus by which the feeding of the sheet material is stably and reliably performed, despite the simplified structure of the apparatus.
Accoriding to an embodiment of the present invention, there is provided a sheet feeding apparatus, comprising: a feeding rotatable member for feeding a sheet material from a stack of sheet materials; separation means for cooperating with said feeding rotatable member to allow only one sheet material to be fed; and a transporting rotatable member for cooperating with said feeding rotatable member to transport the sheet material separated by said separating means.
Immediately after one transfer sheet is separated out, the speed of the sheet reaches a regular level by the cooperation between the feeding roller and the transporting roller. An additional advantage is that the structure is simplified, since the feeding roller is used for two functions.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a sectional view of a conventional sheet feeding apparatus.
Figure 2 is an enlarged sectional view around a feeding roller.
Figure 3 is an enlarged sectional view around the feeding roller wherein a sheet is being fed.
Figure 4 is a sectional view of a sheet feeding apparatus according to an embodiment of the present invention.
Figure 5 is an enlarged sectional view around the feeding roller of the apparatus shown in Figure 4.
Figure 6 is an enlarged sectional view around the feeding roller of the apparatus shown in Figure 4.
Figure 7A is a longitudinal sectional view of the feeding roller shown in Figure 4.
Figures 7B and 7C are sectional views of the feeding roller of the feeding apparatus shown in Figure 4 illustrating contact between the feeding roller and a roller.
Figure 8 is a sectional view of a sheet feeding apparatus according to another embodiment of the present invention.
Figure 9 is a longitudinal sectional view of a feeding roller of the apparatus of Figure 8.
Figure 10 is a sectional view of the feeding roller of the apparatus shown in Figure 8, wherein the feeding roller is in contact with a roller.
Figure 11 is a sectional view of the feeding roller of the apparatus of Figure 8 wherein the feeding roller is out of contact with the roller.
Figure 12 is a longitudinal sectional view of a feeding roller used in a sheet feeding apparatus according to a further embodiment.
Figure 13 is a longitudinal sectional view of a feeding roller of a sheet feeding apparatus according to a further embodiment of the present invention.
Figure 14 is a sectional view of an image forming apparatus incorporating a sheet feeding apparatus according to a yet further embodiment of the present invention.
Figure 15A illustrates a driving system for the sheet feeding apparatus of Figure 14.
Figure 15B is a sectional view taken along B-B of Figure 15A.
Figure 15C is a sectional view taken along C-C of Figure 15A.
Figure 16 is a sectional view taken along D-D of Figure 15A.
Figure 17A shows a driving system for a sheet feeding apparatus according to a further embodiment of the present invention.
Figure 17B shows a driving system for a sheet feeding apparatus according to a further object of the present invention.
Figure 18A is a cross-sectional view of a feeding roller of a sheet feeding apparatus according to a further embodiment of the present invention.
Figure 18B is a cross-sectional view of a feeding roller of a sheet feeding apparatus according to a further embodiment of the present invention.
Figure 18C is a cross-sectional view of a feeding roller of a sheet feeding apparatus according to a further embodiment of the present invention.
Figure 19 is a sectional view of a sheet feeding apparatus according to a further embodiment of the present invention.
Figure 20 is a sectional view of a sheet feeding apparatus according to a further embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figure 4, there is shown a sheet feeding apparatus according to an embodiment of the present invention, wherein a reference numeral 1 designates transfer materials (sheets) which are stacked on a feeding tray 2 and which are to be fed from the tray 2. The transfer materials 1 on the feeding tray 2 is urged to a feeding roller 4 by a feeding spring 3. When the feeding roller 4 rotates, the leading edge of the transfer material 1 advances to the sheet guide 2' by friction. The friction coefficients are such that the friction coefficient µ₁ between plural transfer materials fed out of the tray 2, the friction coefficient µ₃ between the feeding roller 4 and the transfer material 1 and the friction coefficient µ₂ between the transfer material 1 and the separation pad 6 urged to the feeding roller 4 by a separation spring 5 satisfy µ₁ < µ₂ < µ₃. Because of the relation, µ₁ < µ₂, the feeding stops from the closest one to the separation pad 6, when plural transfer materials 1 are fed out; and finally, due to the relation µ₂ < µ₃, only one transfer material 1a is passed through between the feeding roller 4 and the separation pad 6, and it reaches a roller 7 which is urged to the feeding roller 4 and which follows the rotation of the feeding roller 4, where the transfer sheet 1a is conveyed by the cooperation between the feeding roller 4 and the transporting or conveying roller 7 (Figures 5 and 6). Since the pressure between the roller 7 and the feeding roller 4 is sufficiently larger than the frictional load between the transfer material 1a and the separation pad 6 to stabilize the conveying speed Vp of the transfer material 1a after the transfer material 1a is gripped by the nip formed between the feeding roller 4 and the roller 7.
On the other hand, a light beam 9 produced in the optical scanning means 8 is projected onto a photosensitive member 10 surface to form a latent image thereon, which is in turn developed with toner by a developing device 11. The toner image on the photosensitive member 10 is transferred onto the transfer material 1a at point P shown in the Figure. When the transfer material 1a is caught by the nip formed between the photosensitive member 10 and the transfer roller 21, the driving force applied to the feeding roller 4 is stopped. The feeding roller 4 is equipped with a one-way clutch bearing 4d so that after the driving force to the feeding roller 4 is stopped, the feeding roller 4 follows the transfer material 1a to rotate by friction therebetween. When the trailing edge of the transfer material 1a passes through a point Q where the feeding roller 4 and the roller 7 are in contact, the feeding roller 4 stops, and the next transfer material 1b stops at a position slightly advanced. The toner image on the transfer material 1a is fixed by a fixing device 12.
When a predetermined period of time passes after completion of the feeding operation of the transfer material 1a by the feeding roller 4, a solenoid 22 (Figure 7B) is energized to disengage a pawl 22b from a projection 4e of a cam plate (a clutch Cl is actuated), and simultaneously, the driving of the feeding roller 4 is resumed, so as to feed the next transfer material 1b out, and the position shown in Figure 7C is assumed, again.
By repeating those operations, the third and subsequent sheets are fed out.
Referring to Figure 7A, there is shown a longitudinal sectional view of a feeding roller of the apparatus shown in Figure 4. The rotational force of the feeding roller 4 is transmitted to the roller 7 by pressing the roller 7 to the feeding roller 4 by a station spring 15. The roller 7 is supported on a shaft which is in turn supported by bearings 16 which are supported in side plates 40.
As for a registration means for alignment between the leading edge of the transfer material 1 and the image on the photosensitive member 10, a switch SW1 (Figure 4) is preferable. More particularly, in response to or with a predetermined delay after the leading edge of the sheet actuating the switch SW1, the writing onto the photosensitive member 10 starts. The timing therebetween is determined by one skilled in the art depending on the distance between the switch SW1 or the point Q and the point P and the distance between a point S of the photosensitive member 10 and the point P.
As an alternative, the timing may be determined using a timer, rather than the switch SW1, which timer starts the timer period at the start of the sheet feeding.
Referring to Figures 8 and 9, another embodiment of the present invention will be described. In this embodiment, the leading edge of the transfer material 1a reaches the point P in the same process as with the above described embodiment. Together with the movement of the transfer material 1a to the point P, a cam plate 104c mounted to the shaft 4b of the feeding roller 4 is rotating, and until the leading edge of the transfer material 1a reaches the point P, the feeding roller 104 and the roller 107 are kept in contact (Figure 10). Immediately after the leading edge of the transfer material 1a reaches the point P, a control ring 4e is limited by a pawl 22b of a solenoid 22, as shown in Figure 11 so that the cam plate 104c stops at a position where it is contacted to a spacer 107c. At this time, the input gear 23 is rotating, but the shaft 4b is not rotating. When the cam plate 104c is contacted to the roller 107, the feeding roller 104 and the roller 107 are disengaged. This state, referring back to Figure 8, corresponds to the state wherein the roller 107 takes the position indicated by a reference 107'. With this state, the feeding roller 104 is mainly driven by a friction with the transfer material 1a at a point R. When the trailing edge of the transfer material 1a passes by the point R, the feeding roller 104 stops, whereby the next transfer material 1b is not fed out. This embodiment is particularly preferable when the intervals between a transfer material and the next transfer material are desired to be controlled accurately after the transfer materials are fed out.
Referring to Figure 12, a third embodiment of the present invention will be described. Figure 12 is a longitudinal sectional view around a feeding roller of the feeding apparatus according to this embodiment. This embodiment is similar to the embodiment of Figure 7A, but is additionally provided with gears 17 and 18. The rotation of the feeding roller 4 is transmitted to the roller 7 through the gears 17 and 18. The gear ratio is so determined that the peripheral speed of the feeding roller 4 and the roller 7 are substantially equal.
Referring to Figure 13, there is shown a further embodiment. This Figure shows a longitudinal sectional view around a feeding roller of the sheet feeding apparatus according to this embodiment. This embodiment is similar to the embodiment described with Figure 7A but is provided with gears 17, 19, 18 and 20. The rotation of the feeding roller 4 is transmitted from the gear 19 through the gear 17. On the other hand, the rotation of the roller 7 is transmitted from the gear 20 through the gear 18. In this embodiment, it is possible to change the peripheral speed of the feeding roller 4 and that of the roller 7 independently from each other.
Referring to Figures 14 - 16B a yet further embodiment of the present invention will be described. A number of transfer materials (cut sheets) 201 are stacked on a feeding tray 202, and the leading edge portions of the cut sheets 201 are urged to feeding rollers 214, 214' and idler rollers 215 and 215' by a supporting plate 213 rotatably supported and spring biased by a compression spring 203. The feeding rollers 214 and 214' are provided with portions having smaller diameters, respectively, so that at least one portion of a circumference of each of the feeding rollers 214 and 214' has a shape to provide an initializing position wherein it does not in contact with the cut sheet or the feeding roller 216 or 216'. The feeding rollers 214 and 214' may have a length smaller than the minimum width of the sheet usable with this apparatus, and they are spaced apart longitudinally as shown in Figure 15B. The feeding rollers 214 and 214' are fixed on a driving shaft 217 which is controlled by a spring clutch 218 and a solenoid 219 adjacent a longitudinal end thereof which is effective to provide a one turn rotation control.
Outside the maximum width of the cut sheet usable with this apparatus, cam plates 220 and 220' are mounted to the driving shaft 217 to swing the supporting plate 213. The supporting plate 213 is provided with cam followers 221 and 221' corresponding to the cam plates 220 and 220'. Therefore, by the control of the rotation of the driving shaft 217, the supporting plate 213 moves substantially vertically so as to selectively urge the stacked cut sheets to the feeding rollers 214 and 214' and the idler rollers 215 and 215'. Because of this structure, when the operator loads the cut sheet into this apparatus, the supporting plate 213 takes a lower position as shown in Figure 14 and Figure 16A, thus allowing smooth loading of the cut sheets. Additionally, the operator is not required to perform an action of lowering the supporting plate 213. Adjacent outside longitudinal end of the feeding rollers 214 and 214', idler rollers 215 and 215' are mounted to the driving shaft 217 for smooth rotation relative to the driving shaft 217. The idler rollers 215 and 215' have a diameter which is slightly smaller than that of the feeding rollers 214 and 214', for example, by 0.5 - 1 mm.
The conveying rollers 216 and 216' are swingable about a drive input shaft 224 by a swinging arm 222, and is press-contacted to the idler rollers 215 and 215' by a spring 223 stretched between a frame of the apparatus and the conveying roller assembly. The driving force is applied to the conveying rollers 216 and 216' through a driving gear 225 fixedly mounted to the drive input shaft 224 and conveying gear fixedly mounted to the conveying rollers 216 and 216'. The driving and conveying gears are preferably disposed between conveying rollers 216 and 216' as in this embodiment, since then the application of the driving force does not result in an unbaranced pressing force of the conveying rollers, and therefore, the pressing force is stabilized.
To the feeding rollers 214 and 214' and idler rollers 215 and 215', a friction member is press-contacted to separate the cut sheet 201. The friction member is supported at its longitudinal center with a spring 226 for equalizing and pressing it to them. The separation member is in this embodiment separation pads 227 and 227' which is rubber material containing cork. The separation pads may be separated into two pads 227 and 227', as shown in Figure 15B, if they exist corresponding to the feeding rollers 214 and 214' and idler rollers 215 and 215'. In this case, the portion not provided with the separation pad functions as a sheet guide 228 to guide the cut sheet to the conveying rollers 216 and 216'.
The sheet feeding apparatus according to this embodiment is provided with an additional or second cut sheet inlet 229 which is effective to introduce a cut sheet into the nips formed between the conveying rollers 216 and 216' and the idler rollers 215 and 215' from other than the feeding tray 202. Therefore, it is possible that an optional feeding means such as a sheet deck capable of accommodating a great number of cut sheets is disposed below the apparatus so as to feed the sheet from the feeding means to the second cut sheet inlet, and therefore, the apparatus is ready for expansion. The feeding roller 214 and the roller 215 are not necessarily coaxial, but may be parallel. The roller 214 and the roller 215 may have the same diameter.
Downstream of the nips formed between the conveying rollers 216 and 216' and the idler rollers 215 and 215', a sensor lever 230 is disposed, which is supported on a swingable arm 222 to detect the leading edge of the cut sheet with the aid of a photointerruptor 231. The sensor may otherwise be constructed by a transparent type or reflection type sensor other than the combination of the sensor lever 231 and the photointerruptor 239. After the cut sheet 201 actuates the sensor lever 203 by its leading edge, it is guided by a guiding portion 232 having a radius of curvature which is slightly larger than that of the feeding rollers 214 and 214', and is introduced into a nip formed between the photosensitive drum 301 and a transfer roller 233. The transfer roller 233 is of a semiconductor rubber to which a bias voltage of about 1 KV DC is applied, and is in contact with the photosensitive drum 301 to rotate therewith. The guiding portion 232 may preferably be constructed using a casing for the developing device 302 disposed below the photosensitive drum 301, since then the accuracy relative to the photosensitive drum 301 can be easily achieved, also since the number of parts is decreased with easiness of construction and with lower cost.
Around the photosensitive drum 301, there are an exposure station A for exposing the photosensitive drum 301 to a laser beam 402 from a laser scanning optical system 401 disposed at a left hand side of the apparatus as viewed in Figure 14, a developing station B provided with a developing sleeve 303 for developing a latent image formed on said photosensitive drum 301 by the image exposure at the exposure station A, a transfer station C provided with a transfer roller 233, a cleaning station D provided with a cleaner 304 for cleaning the photosensitive drum 301 after a developed image has been transferred from the photosensitive drum 301 to the transfer sheet, and a primary charging station E provided with charging means such as a corona charger 306 for uniformly charging the photosensitive drum 301 before the imagewise exposure. By the cooperation of those stations, an image is formed on the transfer sheet. The cut sheet having received the toner image transferred thereonto at the transfer station C is introduced along a transportation guide which also functions as an inlet guide for an image fixing device. The image fixing device is provided with a heating roller 235 containing therein a heater and a pressing roll 236 made of a heat-resistive elastic member such as silicone rubber, which form a nip, into which the sheet is inserted. During the sheet passing through the nip, the image is fixed on the sheet. Thereafter, the sheet is discharged outside the image forming apparatus by a roller 237 disposed downstream of the fixing device and made of an elastic material such as rubber and NORSOREX (tradename, available from CDF CHIMIE, France) and having fins.
In operation, an unshown motor which is a driving source starts to rotate prior to the start of the sheet feeding operation. Then, a conveying roller driving gear 238 fixed to the drive input shaft 224 for the conveying rollers 216 and 216' starts to rotate, by which the rotation is transmitted to the conveying or transporting rollers 216 and 216' through the drive input shaft 224, the driving gear 225 and the conveying gear. Since the conveying rollers 216 and 216' are press-contacted to the idler rollers 215 and 215', respectively, the conveying rollers 216 and 216' and the idler rollers 215 and 215' are rotated together, respectively. At this time, even if the idler rollers 215 and 215' are in contact with the cut sheet 201, the cut sheet 201 is not fed since the frictional force between the cut sheet 201 and the separation pads 227 and 227' is larger than the frictional force between the idler rollers 215 and 215' and the cut sheet 201. However, in the stand-by state, as described hereinbefore, the supporting plate 213 takes a lower position by the cam plates 220 and 220' and the cam followers 221 and 221' so that the cut sheet does not contact the idler rollers 215 and 215'.
By the rotation of the conveying roller driving gear 238, a sheet feed driving gear 239 rotates which is connected through a spring clutch 218 to the driving shaft 217 for the feeding rollers 214 and 214'. When the solenoid 219 is not energized, the rotation of the feed driving gear 239 is not transmitted to the driving shaft 217. The spring clutch 218 is provided with a one turn controlling 240, so that a one turn drive transmission is performed in response to of/off pulse of the solenoid 219. When the solenoid 219 is energized in response to a feed start signal, the pawl of the control ring 240 is moved away, with the result that the driving force is transmitted from the feed driving gear 239 to the driving shaft 217 through the spring clutch 218. Then, the driving shaft 217 starts to rotate, and the cam plate 220 rotates so that the supporting plate 213 is urged upwardly by the spring 3, as shown in Figure 16B. By this, the cut sheets stacked on the tray are urged to the feeding rollers 214 and 214' and to the idler rollers 215 and 215'. Even if the sheet is contacted to the rotating idler roller, the sheet is not fed out because the frictional force between the sheets is larger than the frictional force between the idler roller and the sheet. However, simultaneously with or slightly before or after the urging, that portion of the feeding rollers 214 and 214' which have a diameter larger than that of the idler rollers 215 and 215' come to contact to the cut sheet, by which the feeding rollers 214 and 214' feed the cut sheet out. Then, the cut sheet reaches the separation pad 227, where the relationship between the friction coefficients are as in the conventional, so that only the topmost sheet is conveyed to the downstream of the separation pad 227. Sooner or later, the cut sheet reaches the rotating conveying rollers 216 and 216', and thereafter, the conveying speed of the cut sheet is stabilized by the conveying rollers 216 and 216'. Then, the cut sheet reaches the detecting station H, where the leading edge of the sheet is detected, in response to which the image light starts onto the photosensitive member. By doing so, the cut sheet is continuously conveyed by the conveying rollers 216 and 216' without interruption. Therefore, it can be avoided that a shock resulting from actuation or deactuation of the registration roller is imposed on an image. In order that the laser image writing control is performed in response to the detection of the leading edge of the cut sheet, the length L1 of the sheet passage from the leading edge detecting position H to the transfer station C is longer than the peripheral length L2 of the photosensitive drum 301 from the image exposure station A to the transfer station C (L2 < L1). When the leading edge of the sheet reaches the roller 233, it is detected by a detecting sensor or by a timer starting from the output of the sensor 230. Then, the solenoid 219 is operated to stop the roller 214. However, the roller 216 continues to rotate, whereas the roller 215 rotates idly, and therefore, the roller 215 does not put any burden to the sheet feeding by the roller 214.
If the sheet sensing position by the sensor lever 230 of the sheet leading edge sensor H is disposed adjacent an inside end of the minimum sheet width which is opposite to the reference position, a warning or prohibition can be performed when a user erroneously uses a sheet having a width smaller than the minimum usable width. As a result, it does not occur that the sheet having a width smaller than the minimum width reaches to the photosensitive drum. Also, the image writing on the photosensitive drum can be prevented, so that the damage and contamination to the drum can be minimized. Referring to Figures 17A and 17B, a further embodiment of the present invention will be described. In the foregoing embodiments, the sheet reference position is disposed at a lateral end, and on the basis of which the minimum width range and the maximum width range are determined. However, the present invention is not limited to this, and applicable to a central reference position feeding system. As shown in Figures 17A and 17B, the feeding rollers 514 and 514', idler rollers 515 and 515' and conveying rollers 516 and 516' may not be divided but may be continuous rollers.
In Figure 17A, an idler roller 515 is disposed in the middle, whereas the feeding rollers 514 and 514' are disposed adjacent opposite ends of the idler roller 515, and a separation pad 527 is integral and is opposed both to the feeding rollers 514 and 514'. Also, the conveying roller 516 is an integral one roller. The conveying roller 516 is not swingable to be pressed to the idler roller 515, but it is urged through bearings 542 and 542' which are spring-biased by compression springs 541 and 541'. The conveying roller 516 receives a driving force from a driving gear 538. The separation pad 527 may be urged through a swingable arm 543. Or, as in this embodiment, the structure is such that the conveying roller 516 is contacted only to the idler roller. With such structures, the sheet is prevented from being conveyed while being gripped between the feeding rollers 514 and 514' and a conveying roller 516 which provide a strong conveying force, and therefore, production of paper dust can be prevented, and the conveying load can be decreased. The rotation of the gear 538 is transmitted from the shaft 624 to the shaft 617, similarly to the described above.
Figure 17B is a modification of Figure 17A structure. In this modification, the feeding roller 614 is disposed in the middle, whereas the idler rollers 615 and 615' are disposed adjacent the opposite ends of the feeding roller 614. An integral separation pad 627 is contacted to both to the idler rollers 615 and 615'. The conveying rollers 616 and 616' are disposed opposed to the idler rollers 615 and 615'. In this structure, the driving force and the pressure are applied in the middle position.
Referring to Figures 18A, 18B and 18C, there are shown further embodiments. In Figure 18A, a circular rubber member 714 is eccentrically fixed on the driving shaft 717. With this structure, the manufacturing is easy, and the contact between the cut sheet and the pad or the like is continuous and smooth. In Figure 18B, a cam member 814 made of rubber material is employed which has a continuously increasing diameter. Also, with the structure, the contact between the cut sheet and the pad or the like is smooth. In Figure 18C, the control of the feeding roller 914 is not one-rotation control, but is a halfturn control.
Figures 19 and 20 show a yet further embodiments. In Figure 19, an auxiliary roller 700 is used in addition to the roller 4. In this structure, each two or three sheet materials are separated from the stack on the feeding tray 2, and subsequently one sheet is separated out by the cooperation between the roller 4 and the pad 6. An inclined guide 2'' is coated with friction resistance member.
In Figure 20, separation pawls 802' is provided in the feeding tray 802, and by the cooperation between the roller 4 and the separation pawl 802'', the sheet materials are separated one by one from the tray 802.
In place of the roller 4, a belt is usable, and the stacked sheets may be separated from the bottom.
A sheet feeding apparatus for feeding sheets 201 to an image forming means of an image forming apparatus comprises a sheet accommodating means 202 from which the sheets are fed out by a feeding means 214, 214', 215, 215', a separation means 227, 227' which separates the fed sheets one by one, and a transporting means 216, 216' which cooperates with the feeding means to transport the sheets to the image forming means. Further, there is provided a first passage through which the sheets separated by the separation means are fed to a position between the feeding means and the transporting means, and a second passage 229 through which sheets are fed to the above position whilst the separation means is bypassed, wherein the feeding means and the transporting means are adapted to transport the sheets fed through either the first or the second passage.

Claims

A sheet feeding apparatus for feeding sheets (201) to an image forming means (233, 235, 236, 301 - 304, 306, 401, 402), comprising
a sheet accommodating means (202) for accommodating the sheets (201),
a feeding means (214, 214', 215, 215') for feeding out the sheets (201) accommodated in said sheet accommodating means (202),
a separation means (227, 227') for separating one by one the sheets (201) fed by said feeding means (214, 214', 215, 215'),
a transporting means (216, 216') for cooperating with said feeding means (214, 214', 215, 215') to transport the sheets (201) to said image forming means (233, 235, 236, 301 - 304, 306, 401, 402),
a first passage for feeding the sheets (201) separated by said separation means (227, 227') to a position between said feeding means (214, 214', 215, 215') and said transporting means (216, 216'),
a second passage (229) for feeding sheets to a position between said feeding means (214, 214', 215, 215') and said transporting means (216, 216'), whilst bypassing said separation means (227, 227'),
wherein said feeding means (214, 214', 215, 215') and said transporting means (216, 216') are adapted to transport the sheets fed through either the first or the second passage (229).
An apparatus according to claim 1, wherein said sheet accommodating means (202) is adapted to accommodate the sheets (201) in a stacked manner, and said feeding means (214, 214', 215, 215') is adapted to act on the topmost sheet of the stack of sheets (201).
An apparatus according to claim 1, further comprising a driving source for driving said transporting means (216, 216'), and a clutching means (218) provided between said driving source and said feeding means (214, 214', 215, 215').
An apparatus according to claim 1, further comprising a pressing means (222, 223) for pressing said transporting means (216, 216') against said feeding means (214, 214', 215, 215').
An apparatus according to claim 1, wherein said feeding means comprises feeding rollers (214, 214') having a feeding portion for applying a feeding force to the sheets (201) accommodated in said sheet accommodating means (202), and a non-feeding portion not applying a feeding force thereto, and freely rotatable members (215, 215') coaxially disposed with said feeding rollers (214, 214').
An apparatus according to claim 1, further comprising a means (230, 231) for generating a signal in order to start the image forming operation of said image forming means (233, 235, 236, 301 - 304, 306, 401, 402) in time relation with the transport of the sheets by said transporting means (216, 216').
An image forming apparatus, comprising a sheet feeding apparatus according to one of the preceding claims, and an image forming means (233, 235, 236, 301 - 304, 306, 401, 402) for forming an image onto the sheets (201) transported by said feeding means (214, 214', 215, 215') and said transporting means (216, 216').