GB2249082A

GB2249082A - Preventing double sheet feed in copying machines

Info

Publication number: GB2249082A
Application number: GB9112594A
Authority: GB
Inventors: Hiroshi Tabuchi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1990-10-25
Filing date: 1991-06-12
Publication date: 1992-04-29
Anticipated expiration: 2011-06-12
Also published as: GB9112594D0; GB9121895D0; CA2043665C; GB2249082B; JPH04164752A; CA2043665A1; GB2250715A; DE4121296A1; DE4135315A1; CA2053555C; CA2053555A1

Abstract

In a copying machine, sheets 2 are piled in a sheet cassette 3 and conveyed one by one to a sheet copying portion 1 to take copies. Between a sheet supply portion and the copying portion there is disposed a sheet separating mechanism 21 comprising a sheet forwarding roller 18, a friction retaining piece 19 partially covered by a low friction sheet 27, and a spring 20, for separating plural sheets 2 taken out from the sheet supply portion. Further, between the said sheet separating mechanism 21 and the sheet copying portion there is disposed a sheet position detector 24. Plural sheets 2 delivered from the sheet supply portion are separated one by one by the sheet separating mechanism 21, then after being synchronized with the copying portion through the action of the sheet position detector 24, each sheet 2 is conveyed, so copying can be done accurately. <IMAGE>

Description

2249032 COPYING MACHINE The present invention relates to a copying machine

wherein sheets stacked in a sheet cassette are conveyed one by one to a sheet copying portion and copied therein.

Fig. 1 is a sectional view showing a conventional paper feeder disclosed, for example, in Japanese Patent Publication No. 52378/88. In the same figure, the reference numeral 1 denotes a photosensitive drum for copying; the numeral 2 denotes a sheet; numeral 3 denotes a sheet cassette; numeral 4 denotes an inner plate on which are stacked sheets 2 in the sheet cassette 3; numeral 5 denotes a spring for pushing the inner plate 4 upwards; numeral 6 denotes a sheet separating pawl for separating the sheets 2; numeral 7 denotes-a pickup roller for conveying the sheets 2; numerals 8a and 8b denote register rollers; numerals 9a and 9b denote fixed guide plates for guiding each sheet 2 to the register rollers Sa and 8b; numeral 10 denotes a movable guide plate for guiding each sheet 2 to the register rollers 8a and 8b; numerals lla and llb denote guide plates for guiding each sheet 2 to the photosensitive drum lt numeral 12 denotes a corona discharger; numeral 13 denotes a separating belt provided at an end portion of the photosensitive drum 1; numeral 14 denotes a separating roller; numeral 15 denotes a separating roller which is in pressure contact with the separating roller 14; numeral 16 denotes a fixing device; and numeral 17 denotes a conveyor belt for conveying each sheet 2 to the fixing device 16.

The operation will now be described. The sheets 2 which are each conveyed in synchronism with an image on the photosensitive drum 1 are stacked on the inner plate 4 in the sheet cassette 3. The inner plate 4 is pushed upwards by the spring 5 and the height of the stacked sheets 2 is kept. constant by the sheet separating pawl 6. In this position the sheets 2 are delivered one by one from the sheet cassette 3 and conveyed by a predetermined length with rotation of the pickup roller 7 having a sectional shape corresponding to a partially cut-out circumference. Each sheet 2 thus delivered is guided by the fixed guide plates 9a, 9b, and the movable guide plate 10 and reaches the register rollers 8a, 8b, then is further guided by the guide plates lla, llb and reaches the photosensitive drum 1.

At an end portion of the photosensitive drum 1 there is provided the separating belt 13, and one end of the sheet 2, in a separated state from the photosensitive drum 1, is supplied with a potential by the discharge from the corona discharger 12. A toner image on the drum 1 is here transferred onto the sheet 2. After completion of the transfer, the front end of the sheet 2 is separated from the drum 1 by the separating belt 13 and is held between the separating roller 14 and the separating roller 15 which is in pressure contact with the roller 14. In this way the front end of the sheet 2 is completely separated from the photosensitive drum 1. Subsequently, the sheet is conveyed to the fixing device 16 by the conveyor belt 17.

The conventional copying machine is constructed as above, so in the event of feed of plural sheets at a time, the plural sheets are conveyed in a stacked state. Consequently, the conveyance of sheet and the copying operation may not be synchronized with each other, or there may arise deterioration of the image quality due to paper jam or defective transfer.

The present invention has been accomplished for solving the abovementioned problems and it is an object thereof to provide a copying machine capable of separating and delivering only the sheet to be fed and copying sheets accurately one by one even in the event of feed of plural sheets at a time.

it is another object of the present invention to provide a copying machine capable of separating and delivering only the sheet to be fed and copying sheets accurately one by one even in the event of feed of plural sheets at a time, by a simple and inexpensive means without using a complicated and expensive apparatus.

It is a further object of the present invention to provide a copying machine which is far superior to the conventional copying machines in point of sheet separating accuracy and performance in feeding paper and can be realized at a relatively low cost.

In the copying machine of the present invention, in order to achieve the above-mentioned objects, a sheet separating mechanism for separating plural sheets when taken out from a sheet supply portion is provided between the sheet supply portion and a copying portion, and a sheet position detecting means is provided between the sheet separating mechanism and the sheet copying portion.

Thus, in the copying machine of the present invention, in the event of feed of plural sheets at a time in the sheet supply portion, the sheets are separated one by one in the sheet separating mechanism and the position of each sheet thus separated is detected to take synchronism with the sheet copying stage.

The above and further objects and novel features of the present invention will more fully appear from the following detailed description when read in connection with the accompanying drawings. It is to be understood, however, that the drawings are for the purpose of illustration only, not restricting the scope of the invention.

Fig. 1 is a schematic sectional view of a body of a conventional copying machine; Fig. 2 is a schematic sectional view of a copying machine according to an embodiment of the present invention; Fig. 3 is a partial enlarged view of a separating mechanism disposed in the copying machine body shown in Fig. 2; and Fig. 4 is a schematic sectional view of a body of a copying machine according to another embodiment of the present invention.

Preferred embodiments of the present invention will be described in detail hereinunder with reference to the accompanying drawings. The portions indicated by the same reference numerals as those referred to above in connection with Fig. 1 represent the same portions, so explanation will be omitted with respect to some of them.

in Fig. 2, the reference numeral 18 denotes a roller provided between a pickup roller 7 and register rollers 8a, 8b and adapted to rotate in the direction of arrow A; numeral 19 denotes a separating piece made of rubber for example, numeral 20 denotes a pressing piece made of a spring material for example to press the separating piece 19 to the roller 18; numeral 21 denotes a separating mechanism constituted by the roller 18, separating piece 19 and pressing piece 20; numerals 22a and 22b denote guide plates fo-r guiding sheets 2 to the separating mechanism 21; numerals 23 denotes guide plate for guiding each sheet 2 to the register rollers 8a and 8b; and numeral 24 denotes a sensor for detecting a front end portion of each sheet 2.

Referring to Fig. 3, which is a partial enlarged view of the separating mechanism shown in Fig. 2, the same members as in Fig. 2 are indicated by the same reference numerals. In Fig. 3, numeral 25 denotes a top sheet to be fed; numeral 26 represent the second and following sheets fed plurally; arrow B represents an urging force created by the pressi ng piece 20; Nl represents a frictional force created between the roller 18 and the sheet 25; N2 represents a frictional force created between the sheets 25 and 26; N3 represents a frictional force created between the sheets 26 and the separating piece 19.

The operation of the paper feeder constructed as above will now be described. The sheets 2 are stacked in a sheet cassette, and with rotation of the pickup roller 7, the sheets are delivered one by one from the sheet cassette 3 and conveyed a predetermined length. Each sheet 2 thus delivered is guided by the guide plates 22a and 22b and reaches the separating mechanism 21. In the event of feed of a plurality of sheets at a time, the top sheet 25 is conveyed by the roller 18 which is rotating in the direction of arrow A, under the frictional force N1, rotatively together with the roller 18, while the conveyance of the second and following sheets 26 is prevented by the frictional force N3 which is larger than the frictional force N2. Hence, the plurality of sheets which have been fed together are separated one by one and then conveyed. The front end portion of sheet 25 thus delivered is detected by the sensor 24. Detection of the front end portion of the sheet 25 allows the movement of the sheet 25 to be synchronised with the movement of an image on the photosensitive drum 1. The sheet 2 which has passed the sensor 24 is guided by the guide plate 23 and the movable guide plate 10 and reaches the register rollers 8a and 8b. The sheet 25 is then guided by guide plates 11a and 11b and reaches the photosensitive drum 1. The operations which follow are the same as in the prior art.

In the above embodiment, at certain mounting angles of the separating piece 19, the sheet 2 when entering the separating mechanism 21 buckles due to the frictional force of the separating piece and causes - 7 paper jam, so it is difficult to adjust the mounting angle of the separating piece 19. In order to solve this problem, in the embodiment illustrated in Fig. 4, the separating piece 19 is covered with a sheet 27 of a low friction material up to a position near the separating portion. Consequently, even without adjusting the mounting angle of the separating piece 19, or even when the sheet 2 is of weak stiffness, the sheet does not buckle when entering the separating mechanism 21, the assembling work efficiently is high, and there can be attained the same effects as in the previous embodiment.

Although in the above embodiments the sensor 24 is provided between the separating mechanism 21 and the register rollers 8a, 8b, even the provision thereof between the register rollers 8a, 8b and the photosensitive drum 1 can afford the same effects as in the above embodiments.

According to the present invention, as set forth above, since the sheet separating mechanism is provided between the sheet supply portion and the sheet copying portion, only the sheet to be fed can be separated and delivered even in the event of feed of plural sheets of paper at time. Besides, since the sheet position detecting means is provided between the sheet separating mechanism and the sheet copying portion, it is possible to make copying accurately.

- 8

Claims

1. A copying machine having a sheet supply portion from which stacked sheets are taken out and a sheet copying portion for copying on each of the sheets thus taken out, said copying machine including a sheet separating mechanism disposed between said sheet supply portion and said sheet copying portion for separating a plurality of sheets when taken out from the sheet supply portion, and a sheet position detecting means disposed between said sheet separating mechanism and said sheet copying portion.

2. A copying machine as claimed in Claim 1, wherein said sheet separating mechanism comprises a roller adapted to rotate so as to move each sheet in a forward direction, a separating piece having a predetermined frictional force and adapted to hold each sheet between it and said roller, and a pressing piece for pressing said separating piece toward said roller, and wherein when plural sheets are taken out at a time from said sheet supply portion, said sheet separating mechanism separates only the sheet which is in close contact with said roller from the other sheet or sheets and moves it forward.

3. A copying machine as claimed in Claim 2, wherein said sheet separating mechanism is constructed so that if a frictional force between said roller and a sheet is N1, - 9 a frictional force between sheets is N2 and a frictional force between a sheet and said separating piece is N3, said frictional forces satisfy the following relationship:

N1 > N3 > N2

4. A copying machine as claimed in Claim 2 or Claim 3, wherein said sheet separating mechanism includes a sheet guide means comprising a low friction member on an upstream side in the sheet conveyance direction with respect to a contact portion of the upper surface of said separating piece with said roller.

5. A copying machine substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

0

5. A copying machine as claimed in any one of the preceding claims, wherein said sheet position detecting means has both a detecting function of detecting a front end portion of a sheet which has been conveyed from said sheet separating mechanism and a synchronizing function of stopping said sheet for a while, taking synchronism with said copying portion and thereafter conveying the sheet.

6. A copying machine substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.

7. A copying machine substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

- 10 1 AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS.

A copying machine having a sheet supply portion from which stacked sheets are taken out and a sheet copying portion for copying onto each of the sheets thus taken out, said copying machine including a sheet separating mechanism disposed between said sheet supply portion and said sheet copying portion for separating a plurality of sheets when a plurality of sheets are taken out from the sheet supply portion together, said sheet separating mechanism comprising a roller adapted to rotate so as to move each sheet in a forward direction, a separating piece having a predetermined frictional force and adapted to hold each sheet between it and said roller, and a pressing piece for pressing said separating piece toward said roller, and wherein when plural sheets are taken out together from said sheet supply portion, said sheet separating mechanism separates only the sheet which is in close contact with said roller from the other sheet or sheets and moves it forward, and a sheet position detecting means disposed between said sheet separating mechanism and said sheet copying portion, said sheet position detecting means having both a detecting function of detecting a front end portion of a sheet which has been conveyed from said sheet separating means, and a synchronizing function of temporarily stopping said sheet. and conveying the sheet-in such a manner that movement of the sheet is synchronized with the copying portion.

2. A copying machine as claimed in Claim 1, wherein said sheet separating mechanism is constructed so that if frictional force between said roller and a sheet is N1, frictional force between sheets is N2 and a fpictional force between a sheet and said separating piece is N3, said frictional forces satisfy the following relationship:

N1 > N3 > N2 3. A copying machine as claimed in Claim 1 or Claim 2, wherein said sheet separating mechanism includes a sheet guide means comprising a low friction member on an upstream side in the sheet Conveyance direction with respect to a contact portion of the upper surface of said separating piece with said roller.

4. A copying machine substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.