US3450402A - Sheet stripper apparatus - Google Patents

Description

June 17, 1969 I E. A H. WEILER 7 3, I SHEET STRIPPER APPARATUS Filed July 12, 1967- Sheet 1 of 2 INVENTOR. H. WEILER A T TORNEY I United States Patent York Filed July 12, 1967, Ser. No. 652,857 Int. Cl. B65h 29/56 US. 'Cl. 271-80 5 Claims ABSTRACT OF THE DISCLOSURE An apparatus for stripping sheets from a conveyor surface having a group of wedge-shaped fingers which are forced between the leading edge of the sheet and the conveyor surface, thereby separating the sheet from the conveyor surface and redirecting the path of the sheet.

Background of the invention In many sheet handling and processing mechanisms a single sheet is conveyed by a flat or curved surface while being worked on and then stripped from the conveyor surface. For instance, in conventional automatic xerographic copiers, a single sheet is fed onto a xerographic drum where the developed image is transferred from the drum to the sheet. After the transfer step is completed, the sheet is stripped from the drum so that the transferred image can be heat fused or otherwise made permanent.

There are several known methods by which a sheet is separated from the drum; for example, that shown in US. 3,062,536 to Rutkus. This mechanism employs a manifold having multiple outlet conduits or nozzles directed against the surface of the Xerographic drum so that jets of compressed aeriform fluid from the nozzles are directed against the leading edge of the sheet being transferred to blow the edge of the material off of the drum. In this system the remainder of the sheet being transferred is then peeled from the drum due to its own weight. The manifold is supplied with compressed aeriform fluid by means of a pulsator or similar source of compresser aeriform fluid. This type of stripper mechanism does not injure the Xerographic drum during the stripping process since no mechanical part comes in contact with the drum. However, since the stripping process relies entirely upon the force of the aeriform fluid against the leading edge of the sheet, the mechanism is not entirely reliable. If the pulses of compressed fluid are not precisely synchronized with the rotation of the drum carrying the sheet, the sheet may fail to separate from the drum. In addition, if the compressed fluid is pulsed for too long a time after the leading edge of the sheet has been peeled from the drum, the unfused toner particles defining the image on the sheet may be blown about by the blast of fluid thereby destroying the image.

A second method of stripping sheets from a drum is by using mechanical arms which are physically inserted between the sheet and the conveyor surface. This type of apparatus is normally programmed so that the arm is placed against the drum surface as the sheet approaches the vicinity of the stripping area. When the sheet meets the arm, it is physically separated from the conveyor surface by the arm being inserted between the two. To as sure that the sheet is always separated and diverted from the drum the tip of the arm usually travels in recesses on the drum surface so that there is no possible way physically in which the sheet can move past the arm. In other mechanical systems of the type described above, the arms travel on the drum periphery as the sheet approaches in stead of traveling in recesses on the drum. However, in the cases where the conveyor surface cannot be scratched or marred or tolerate grooves, such as the photosensitive surface of a xerographic drum, the known strippers of this type are entirely undesirable. In addition to excessive wear to the drum surface, these mechanical stripper arms would smear the unfused image on the sheet as the sheet is being diverted from the drum.

Accordingly, it is an object of this invention to improve the apparatus for stripping sheets which overcomes the deficiencies of the prior art devices as described above.

It is a further object to improve the sheet stripping ap paratus which separates the leading edge of a sheet from a conveyor surface.

A still further object is to improve the sheet stripping apparatus used in Xerographic machine to assure that an unfused image carried by the sheet is not destroyed as the sheet is being stripped and diverted from the conveyor surface.

A still further object is to improve the sheet stripping apparatus used in a Xerographic machine so that the photosensitive drum is not worn, marred or otherwise deteriorated during stripping.

A still further object is to improve the apparatus for stripping sheets from a conveyor surface so that any size sheet may be readily stripped.

A still further object is to improve the apparatus for stripping sheets from a conveyor surface so that a sheet of any thickness may be readily stripped.

A still further object is to improve the apparatus for stripping sheets from a conveyor surface so that a sheet may be stripped regardless of the speed at which it is traveling.

Summary The sheet stripping apparatus consists of an arm carrying a multitude of Teflon-coated, rigid fingers located adjacent to and spaced across the path of travel of a sheet being carried by a conveyor surface. The fingers are biased against the conveyor surface when the leading edge of a sheet reaches the vicinity of the fingers and is separated by them. After the leading edge of the sheet is separated, the arm rotates moving the fingers and the leading edge of the sheet away from the conveyor surface. The remainder of the sheet is stripped from the conveyor surface as the surface continues past the fingers.

Brief description of the drawings For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be used in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a conventional automatic Xerographic machine in which the stripping apparatus is used.

FIG. 2. is an isometric view of the apparatus showing the relationship between the stripping apparatus, conveyor and collateral transport apparatus.

FIG. 3a is a schematic illustration of the relative locations of the various parts of the stripping apparatus when the fingers are in contact with the drum.

.FIG. 3b is a schematic illustration of the relative locations of the various parts of the stripping apparatus as the fingers are moved away from the drum.

FIG. 30 is a schematic illustration of the relative locations of the various parts of the stripping apparatus when the fingers are at their most remote position from the drum.

Description of the preferred embodiment The present invention will separate the leading edge of a sheet from a conveyor surface and redirect its path according to the direction in which the sheet is to be diverted. Although the invention is construed to have general application, it is particularly useful in the field of xerography. Therefore for the purposes of the following disclosure, the various steps in the xerographic process are briefly described in conjunction with FIGURE 1 in order that the context in which the stripper apparatus functions is fully understood.

In the conventional automatic xerographic reproducing apparatus the principal element is member 800 bearing a photoconductive layer or light receiving surface formed in the shape of a drum which is mounted for rotation. The drum is first passed through a charging station 100 at which a uniform electrostatic charge is deposited on the photoconductive layer. The drum is then passed through exposure station 200 at which a light or radiation pattern if projected onto the drum surface to dissipate the charge in the exposed areas thereof and thereby form a latent electrostatic image of the copy to be reproduced. Next, the drum is passed through developing station 300 at which a xerographic developing material including toner particles having an electrostatic charge opposite to that of the electrostatic latent image are cascaded over the drum surface whereby the toner particles adhere to the electrosattic image to form a xerographic powdered image in the confiiguration of the copy to be reproduced. After developing the latent electrostatic image, the drum passes through transfer station 400 at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer material or sheet. Thereafter the drum surface is brushed at station 600 to remove any residual toner particles remaining on it after image transfer, and the drum surface is exposed at station 700 to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining on it in preparation for the next cycle.

After the development step and prior to the transfer step, the sheet to which the toner image is to be transferred is fed onto the drum, the periphery of the drum becoming its conveyor surface. The size of this sheet can be any size desirable in the automatic xerographic process; for instance, a continuous web fed from a roll or conventional 8 /2 x 11" letter-size sheets fed from a stack. For the purposes of the following explanation, it is assumed arbitrarily that standard letter-size sheets are fed onto the drum; however, it should be pointed out that the size of the sheet does not matter as far as the operation of the stripping apparatus is concerned. However, the sheet should be made of a semi-flexible material such as paper, plastic, film, etc.

The stripping apparatus designated as 500 is positioned adjacent the drum subsequent the image transfer station, but prior to the cleaning station. It is necessary to remove the sheet from the drum at this point in order to further process the sheet at a location remote from the drum. For instance, once the sheet is removed from the vicinity of the drum the toner image can be fused to the sheet or otherwise made permanent without any deleterious side effect to the photoconductive surface of the drum. It is believed that the foregoing description is sufiicient for purposes of this application to show the general operation of a xerographic reproducing apparatus using a sheet stripping apparatus constructed in accordance with the invention. For further details concerning the specific construction of the xerographic apparatus reference is made to U. S. 3,105,770.

Referring to FIGURE 2, sheet 12 adheres to and is transported by drum 11, the photoconductive member of a xerographic machine. Drum 11 turns in the counterclockwise direction, as shown by the arrow, carrying sheet 12 with it towards the stripper arm, generally desig nated by 13. The arm comprises rotatable shaft 14 having rigidly attached to it six fingers 33, 34, 35, 36, 37 and 38 and link 16. The shaft is mounted for rotation on standards 31 and 32.

Although merely one finger will strip the leading edge of the sheet from the drum, it is more advantageous to have a multitude of fingers; for instance, six fingers as shown in FIGURE 1.. When a multitude of fingers spaced across the entire width of the drum is used, virtually any size sheet is readily stripped regardless of its position on the drum. Further, in the case of wider sheets, the leading edge will be stripped from the drum at several places assuring that the sheet separates from the drum in a more orderly fashion thereby preventing tearing or other mutilation to the sheet material. The fingers can be made of any suitable material such as plastic, steel or other metal; however, care must be taken to make certain that the drum is not marred by the finger. In this regard, the portion of the finger which contacts the drum surface should be covered with a substantially softer material than the photoconductive layer on the drum. One such material is tetrafluoroethylene resin sold under the trademark Tefion by E. I. Dupont de Nemours & Co., Wilmington, Del.

As mentioned beforehand, the number of fingers shown in FIGURE 1 is six which are all rigidly attached to shaft 14. To further avoid mutilation of the leading edge of the sheet being stripped from the drum as it separates from the drum surface, it is best to separate certain portions of the leading edge of the sheet separated are the corners of the sheet. In other words, the leading edge of the sheet is separated from the drum in the vicinity of fingers 33 and 38 initially. As the sheet advances with the drum its leading edge is stripped by fingers 34 and 37 next, and then by fingers 35 and 36 at which time the entire leading edge is separated from the drum. This progressive manner of stripping is .accomplished by the locations of the fingers relative to each other. As can best be seen in FIGURE 3a the advancing sheet would first contact finger 33, next finger 34 and finally finger 35 as the drum rotates counterclockwise since finger 33 is lowest, finger 34 is next lowest and finger 35 is highest. In this view fingers 36, 37 and 38 are hidden behind and at the same elevation as fingers '35, 34 and 33, respectively. On the other hand, if the center portion of the leading edge of the sheet were stripped from the drum first there would be ample opportunity for the sheet to tear or distort due to the stress placed on it should its edges continue to adhere to the drum. The progressive stripping of the leading edge of the sheet from its corners toward its center avoids such stress and hence, avoids mutilation of the sheet.

Again referring to FIGURE 2, it is seen that the actuating mechanism for the arm ultimately depends on the position of cam 23. Cam 23 is rigidly mounted on drum 11 and is shaped so that microswitch 20 is activated and arm 13 pivots counterclockwise from the drum after the leading edge of the sheet is completely stripped from the drum. This cam drives cam follower 22 which, in turn, activates switch 20. When the switch is activated solenoid 21 is also electrically activated through wiring connecting it to the switch. Activation of the solenoid causes link 30 to move to the left against the force of spring 18. The spring biases the arm in the clockwise direction thereby normally keeping the fingers against the drum surface. Spring 18 is connected to link 16 at one end and support 39 at the other end. Support 39 also holds the solenoid. Link 16, joined to link 30 by link 19, moves according to the motion of link 30 and is rigidly fastened to shaft 14. Therefore, when link 16 moves, it rotates arm 13. The foregoing elements which activate the arm are not crucial to the operation of the stripping apparatus, generally speaking, but are intended to be an example of a system which can be used to activate the arm.

In FIGURE 2, the arm is shown in a position where the fingers maintain contact with drum 11. When cam 23 rotates to actuate follower 22 the fingers swing away from the drum. Subsequently, when the cam allows the follower to assume its original position, as shown in FIGURE 2,

the solenoid is inactivated causing (mechanism not shown) link 30 to move to the right and the fingers to again contact the drum. This cycle will be explained more completely below.

The pivotal movement of arm 13 is best seen by reference to FIGURES 3a, 3b and 3c. FIGURE 3a shows the leading edge of sheet 12 being stripped from the drum as it comes into the vicinity of the fingers. The edge portion of the sheet is separated from the drum initially and as the drum continues to rotate the entire leading edge is stripped, the center portion being separated from the drum last. At this particular time in the cycle, the solenoid is inactive due to the position of the cam and hence, all the fingers maintain contact with the drum. In FIGURE 3b cam 23 has positioned the follower to activate the solenoid. The arm begins to rotate only after the leading edge of the sheet has contacted all fingers adjacent it and has been completely separated from the drum. Regardless of the thickness of the sheet on the conveyor the leading edge of the sheet is always stripped since the tips of the fingers separate the sheet and drum along a plane coincident with their interface. The portion of the fingers in the vicinity of the leading edge of the sheet is basically wedge-shaped; however, its exact contour is of a special nature. The contour of the wedge is such as to allow only the leading edge of the sheet to maintain contact with it at any time. This type of contact with the sheet is necessary in order to avoid destruction of the unfused image; that is, if portions of the sheet other than the leading edge were allowed to contact the fingers, such contact would smear the image before it was made permanent. Therefore, as the sheet contacts the fingers and travels across its wedge-shaped contour, only the leading edge of the sheet actually touches the fingers. As the fingers are rotated away from the drum, as shown in FIGURE 3b, the leading edge of the sheet slides across the contour of the fingers until the weight of that portion of the sheet separated from the drum causes the sheet to fall towards transporter 25 and away from the fingers.

Now referring to FIGURE 30, the fingers are shown in their most remote location from the drum. In this position the fingers are completely out of the vicinity of the stripped sheet and cam 23 is preparing to move follower 22. and solenoid 21 to the inactive position at which time arm 13 will rotate in the clockwise direction bringing the fingers in contact with the drum again in preparation for the next sheet to be stripped. At this time, sheet 12, which is nearly totally separated from the drum, is completely Stripped due to the force of its own weight and the force that transporter 25 imparts to it. The contour of cam 23 is such that the fingers do not proceed to contact the drum at least until after the prior sheet is completely stripped.

The sheet, after being stripped from the drum, can be allowed to fall into the area immediately below the stripping arm; however, it is usually more advantageous to have the sheet fall onto a transporter, as shown in FIG- URE 3c, to be transported to the fusing area. Transporter 25 consists of endless belt 24 supported and driven by rollers 26 and 27 which revolve about shaft 28 and 29, respectively. Transporter 25 receives the sheet after it has been speed, etc.

In addition to the apparatus and method outlined above many other modifications and/ or additions to this invention will be readily apparent to those skilled in the art upon reading this disclosure, and these are intended to be encompassed within the scope of the invention.

What is claimed is:

1. A sheet stripping apparatus for separating flexible sheets having a leading edge from a conveyor surface comprising:

(a) a rigid standard adjacent the conveyor surface;

. (b) at least one rigid finger having a wedge-shaped end and a pivot end, the pivot end being rotatably mounted on the standard and the narrow-edge of the wedgeshaped end normally biased in contact with the conveyor surface,

(0) means to pivot the finger away from the conveyor surface; and

(d) means to control the position of the finger whereby it is pivoted away from the conveyor surface only after the wedge-shaped end of the finger has separated at least a portion of the leading edge of the sheet from the conveyor surface.

5 '2. The sheet stripping apparatus in claim 1 having a pluraliyt of fingers spaced apart from one another adjacent the conveyor surface, the fingers being located so that the leading edge of the sheet contacts the fingers nearest the corners of the leading edge of the sheet first and the fingers nearest the center of the leading edge of the sheet last whereby the leading edge of the sheet is progressively separated from the surface toward its center.

3. The sheet stripping apparatus in claim 1 in which the conveyor surface is in the shape of a drum.

.v 4. The sheet stripping apparatus in claim 1 in which the conveyor is a photosensitive surface and at least the portion of said finger that contacts the surface is coated with a substantially soft material whereby the photosensitive surface is prevented from being mar-red.

,5. The sheet stripping apparatus in claim 4 wherein the soft material is tetrafiuoroethylene resin.

References Cited UNITED STATES PATENTS 1,737,616 12/1929 Saatman. 1,750,587 3/1930 Fischer 101-232 RICHARD E. AEGERTER, Primary Examiner.

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