US3351340A

US3351340A - Document transport for photocopy machine

Info

Publication number: US3351340A
Application number: US379205A
Authority: US
Inventors: Franklin R Levine
Original assignee: American Photocopy Equipment Co
Current assignee: American Photocopy Equipment Co
Priority date: 1964-06-30
Filing date: 1964-06-30
Publication date: 1967-11-07
Anticipated expiration: 1984-11-07

Description

Nov. 7, 1967 F. R. LEVINE 3,351,340

DOCUMENT TRANSPORT FOR PHOTOCOPY MACHINE. Fil ed June so. 1964 3 Sheets-Sheet 1 INVENTORI FRANKLIN R. Levms a 144%, 7%, VJwwM I Ar'rvs.

1967 F. R. LEVINE DOCUMENT TRANSPORT FOR PHOTOCOPY MACHINE 5 Sheets-Sheet Z Filed June 30. 1964 INVENTOR I FRANKLIN R. LEVINE W4, Mad, vJwM Nov. 7, 1967 F. R. LEVINE 3,351,340

DOCUMENT TRANSPORT FOR PHOTOCOPY MACHINE Filed June so. 1964 3Sheets-Sheet 5 LL FRANKLIN E. Lev/us 6 n &%MM, 4/J zaw m A'rrvs.

United States Patent C 3,351,340 DOCUMENT TRANSPORT FOR PHOTOCOPY MACHINE Franklin R. Levine, Elk Grove Village, 11]., assignor to American Photocopy Equipment Company, Evanston,

11]., a corporation of Illinois Filed June 30, 1964, Ser. No. 379,205 9 Claims. (Cl. 271-51) The present invention relates to an office photocopy machine and more particularly to means for transporting the original document in a machine of this type.

In the copending Kent and Levine application Ser. No. 364,698, filed May 4, 1964, entitled Electrostatic Photocopy Machine, and assigned to the assignee of the present application now Patent No. 3,303,763, means are provided for applying an electrostatic charge to an original document as it is brought into engagement with a transport drum to produce adherence of the original to the drum surface by electrostatic attraction. Several charging devices are positioned about the drum periphery for replenishing the charge on the original thereby to compensate for leakage of charge into the drum; alternatively, the drum may be covered with an insulating blanket of plastic or the like to minimize leakage. Where an insulating blanket is used there is a tendency for a charge of the applied polarity to be built up on the surface of the insulating blanket as a result of repeated exposure and, since such charge is of the same polarity as that applied to the face of the original, the efiect is to lessen the electrostatic attraction between the original and the drum. Where the original is of heavy gauge, stifi? material as, for example, Bristol board, there is risk that the leading edge of the original may spring free of the drum under certain conditions, for example, high humidity.

It is, accordingly, an object of the present invention to provide a photocopy machine having improved electrostatic means for securely holding and transporting the original through the machine. It is another object to provide a photocopy machine in which electrostatic forces are employed to hold an original document on an insulated transporting surface but which prevents the building up of any charges which might tend to neutralize the attractive forces as a result of repeated exposure to a corona unit or similar charging device. It is, on the contrary, an object of the invention to :provide a transporting arrangement for an original document in which there is applied to the face of the document, and in lesser degree to the supporting surface, an electric charge of a first polarity followed a short time later by a second charge of opposite polarity thereby to preclude any cumulative buildup of charge as a result of repeated cycling.

It is a further object to provide a photocopy machine having a drum to which an original document adheres by electrostatic attraction and which includes means for pre-curling the original document to the shape of the drum just prior to contact with the drum to reduce the possibility of the leading or trailing edges of the original springing free of the drum because of the usual tendency of an original to restore itself to a flat condition. More specifically, it is an object, in a machine of this type, to provide a set of curling members for curling an original, particularly one of a stiff or spingy nature, beyond its elastic limit just prior to depositing the original on the drum so that the original tends to cling to the drum with only minor reliance on electrostatic force and so that the original tends to maintain the contour of the drum even in the temporary absence of electrostatic force, as, for example, when the machine is inadvertently turned off before the original has been discharged. Thus, it is an object of the invention to provide a photocopy ma- 3,351,340 Patented Nov. 7, 1967 chine in which electrostatic forces are efiiciently utilized to prevent creeping or skewing of the original and which is reliable and substantially jam-proof under all conditions including wide variations in humidity, wide variations in the nature of the original, and wide variations in the voltage of the electrostatc charge.

It is an object of the present invention in one of its aspects to provide a photocopy machine having a cylindrical path of transport with means for pre-curling the original so that it conforms snugly to the transport surface during the transporting and exposing cycle in combination with means for uncurling the original as a final step so that the original leaves the machine in substantially flat condition.

It is in general an object of the invention to provide a photocopy machine having means for securely holding and transporting the original by electrostatic forces but which is nevertheless simple and efficient producing improved adhesion and improved reliability without necessity for resorting to higher charging voltages, and which may, indeed, permit a reduction in voltage. Finally, it is an object of the invention to provide a photocopy machine of the electrostatic type which in spite of its improved -features may be constructed more compactly and at less cost than competitive photocopy machines.

Other objects and advantages will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

FIGURE 1 is a perspective view, on a reduced scale, of a photocopy machine employing the features of the present invention;

FIG. 2 is a vertical section taken through the machine of FIG. 1;

FIG. 2a is a fragmentary section taken through the periphery of the transport drum;

FIG. 3 is a schematic diagram showing the driving means for driving the transport members in FIG. 2;

FIG. 4 is a simplified diagram of the control circuit;

FIG. 5 is a diagram showing the charging circuits;

FIG. 6 is a fragmentary stop motion view showing the electrostatic charging at the leading edge portion of the original as the original is passed into the first charging unit;

FIG. 7 is a stop motion view similar to FIG. 6 but showing the reversal of electrostatic charge as the original s passed into the second charging unit;

FIG. 8 is a diagram showing the precurling rollers and the set imposed upon an original of stiff springy material, such as Bristol board, for transport through the machine;

FIG. 9 is a fragmentary view of the original-discharging portion of the machine of FIG. 2 showing an alternate roller arrangement for restoring a curved original back into substantially flat condition and showing use of an auxiliary grounded electrode for removing any residual charge from the transport surface; and

FIG. 10 is a schematic diagram of an alternate charging arrangement in which switching means are provided for applying the voltage of first and second polarity to the face of the original While the invention has been described in connection with certain preferred embodiments, it will be understood that I do not intend to be limited to the particular embodiments illustrated but intend to cover the various alternative and equivalent arrangements included within the spirit and scope of the appended claims.

Turning now to the drawings there is shown in FIG. 1 a machine 10 constructed in accordance with the invention and suitable for ofiice use. The machine includes a Work table 11 having an entry slot 12 for feeding original documents into the machine together with lateral guides 13 which are adjustable in width and which serve to aline and center the original. Upon completion of the photocopy process, the original is discharged into a tray 15 which is included within the confines of the housing and which is readily accessible from the front of the machine. The completed copies collect in a lower tray 16. The machine is put into operation by an on-off switch 17 having an associated pilot light 18 and with a control button 19 which may be actuated where a number of copies of the original are desired.

For the purpose of gripping the leading edge of an original 20 which is placed upon the table 11 face up, a pair of resilient nipping rollers 21, 22 (FIG. 2) are provided communicating with a pair of guides 23. The latter feed the original to a feed roller assembly 25 consisting of a driven roller 26 and

idler rollers

27, 28 which deposit the original on a transport drum 30 having an outer surface 31 and which is journaled in the frame in bearings 32. For the purpose of causing the original to adhere to the drum, a first corona unit 33 is provided having charged wires 34 and, spaced therefrom, about the periphery of the drum, a second corona unit 35 is provided having charged wires 36 connected to a soure of high voltage.

The original, adhering to the drum, passes into an illuminating station 40 having light sources 41 with light shields 42, respectively, which form the lower and upper edges of a slot 43 which defines the reading area on the drum. The lamps 41 are preferably of the fluorescent type extending the length of the drum and are, as shown, located closely adjacent the drum surface to provide a high level of illumination at relatively low wattage. For the purpose of stripping off the original from the drum a stripper is used which may extend the width of the drum and which has a shaft 44 from which project a series of alined fingers 45. A linkage 46 couples the shaft to the control knob 19. A spring 47 may be provided to bias the stripper in the direction of the drum normally producing a single copy. The drum is formed with a series of grooves 30a (FIG. 2a) defining fiat-topped ridges with the fingers registering in the grooves. After passing the illuminating station the original is directed upwardly into the nip of a pair of expeller rollers. This function is performed in the present instance by the roller 22 previously referred to and an adjacent roller 48 which directs the original between a pair of guides 49 and thence onto the original receiving tray.

When multiple copies are desired, the knob 19 may be pulled thereby lifting the stripper from the drum and permitting the original to recirculate as often as may be desired. The control panel at the front of the machine may be equipped with a tally device to serve as a visual indication to the operator of the number of times that the drum is rotated with the same original.

Turning attention next to the lower portion of the machine, means are provided for storing a stack of photocopy sheets and for feeding the sheets one by one by a separate feed motor which is controlled by circuitry to be discussed at a later point. For the details of construction of the feed motor and the associated feed elements, reference is made to Sacre US. Patent 3,126,122 which issued on Mar. 24, 1964. Briefly stated, a stack of copy sheets 50 is provided, with a top sheet 51. In engagement with the top sheet is a rubber drive roller 52 which presses, by gravity or spring pressure, against the sheets and which is journaled in a pair of arms 53. The feed roller 52 is driven by a motor 55 with gears 56 completing the drive connection.

When the feed motor 55 is turned on, the top sheet 51 is driven through a pair of spaced guides 57 into a ready. position 58. From this position the sheet is transported, by further energization of the motor 55, into engagement with copy sheet transport means including a pair of nip rollers 61, 62 and a pair of

transport rollers

63, 64 joined by a pair of arcuate guides 65. As will be discussed,

drive means are provided for rotating the nip and transport rollers at a speed which corresponds to the peripheral speed of the original drum 39.

For the purpose of imparting an electrical charge to the front and back surfaces of the copy sheet, the sheet passes through a charging station 70 formed of

opposed corona units

71, 72, having wires 73, 74 which are charged with voltage of opposite polarity by a high voltage supply 75. The copy sheet is guided between the corona units by insulating cords of nylon or the like which are strung across the open faces of the units.-

From the charging station 70 the copy sheet is immedi- In the present instance, the development takes place in a developing tank 90 having guiding edges 91 which engage the back of the sheet and which serve to direct the sheet through a body of developer fluid 92. The developer fluid is preferably a dielectric liquid having distributed therein a colloidal suspension of pigmented particles or toner which tend to adhere to the charged areas of the copy sheet thereby to develop the latent image acquired at the exposing station. From the developing tank 90 the sheet passes between a pair of expeller or

squeegee rollers

95, 96, which are resiliently surfaced and biased together so that excess liquid runs back to the tank 90. From the

rollers

95, 96 the sheet passes into a pair of guides 97 from which the sheet is discharged into the copy tray 16 previously referred to.

For the purpose of rotating the drum 30 and the transport rollers at the same peripheral speed, they are interconnected by rubber timing belts commonly referred to as cog belts or the like. Thus, the drive motor 100, which is preferably geared down to an output speed on the order of 20 r.p.m., has a first belt 101 (FIG. 3) which is trained about

transport rollers

22, 26, 61 and 95, and a second belt 102 which is trained about the drum 30, transport roller 63, idler pulley 103 and roller 89. The rollers not directly engaged by the belts are driven by rolling friction.

It will be understood, of course, that the driving arrangement indicated at FIG. 3 is simply exemplary and that other specific belt configurations may be used without departing from the present invention.

For the purpose of casting the image of the original upon the copy sheet with both original and copy sheet moving in unison, an optical reflecting element 110 is used having a lens 111 and a mirror 112. The optical system is shielded against ambient light by a suitable optical housing 113, the optical path between the illuminating station and exposing station being indicated at 114. The light housing is preferably pyramidal or trapezoidal in cross section to conform approximately to the optical path and to define upper and

lower spaces

115, 116 for the

trays

15, 16, previouslyreferred to.

For the purpose of understanding the control circuit which controls the transport and phasing of the copy sheet with respect to the original, a control arrangement is used which is set forth in simplified form in FIG. 4. The current is taken from a pair of supply lines 121, 122, so that, when the on-ofl switch 17 is closed, the lamps 41, the high voltage supply 75, and main drive motor are energized as confirmed by the lighting of the pilot light 18.

To advance a copy sheet to the ready position 58, a normally closed switch is used (FIGS. 2 and 4) having a feeler finger 131 located at the ready position and connected in series with the copy sheet drive motor 55.

spaced the stack and which upon arrival at the ready position turns off the motor. For the purpose of additionally energizing the motor 55 for feeding of the copy sheet into the transport means in synchronism with the feeding of the original, a normally open switch 133 (FIG. 2) having a feeler finger 134 is provided in the path of movement of the original. The feeler finger 134 extends into one of the grooves 30a. Thus upon arrival of the leading edge of the original the switch 133 is closed, energizing the drive motor 55 so that the copy sheet is advanced into engagement with the nip rollers 61, 62 which then take over to advance the sheet through the guides 65 and

transport rollers

63, 64. In order to turn off the drive motor 55 after the copy sheet has been set in motion, an adjacent normally closed switch 135 having a feeler finger 136 is provided to break the circuit of the switch 133. This turns oif the drive motor until the tail of the copy sheet clears the switch 130 at the ready position which then closes to advance a subsequent sheet into the ready position.

In accordance with the present invention, means are provided for applying electrostatic charges of unlike polarity to successive areas of the original as it is transported on the drum 30. More specifically in accordance with the invention, the transport drum 30 is provided with an insulating blanket of plastic or the like and charging devices are spaced at successive points about the periphery of the drum for applying charges of unlike polarity to renew and reverse the charge and thus to prevent the cumulative buildup of a charge of one polarity on the surface of the blanket in successive cycles of rotation. As shown in FIGS. 5, 6 and 7, the first charging device, in the form of corona unit 33, is connected to the positive terminal of the high voltage supply, while the second unit 35 is connected to the negative terminal. By way of example, the positive voltage may be on the order of 5,000 volts positive with respect to ground while the second charging device is 5,000 volts negative. The insulating blanket 140 may, for example, consist of a Mylar, polypropylene, Teflon, nylon or the like, having good dielectric properties even under conditions of high humidity. The blanket extends beyond the corners of the ridges (FIG. 2a) to avoid any leakage of charge as a result of electrical stress.

In operation, when an original document is fed into the machine onto the insulating blanket 140, and under the corona unit 33, positive charges or ions created by the high positive charge on the wires 34 collect on the surface of the sheet as shown in FIG. 6 and, since the original under normal atmospheric conditions is slightly conductive, some of the charge will tend to migrate into the sheet to the interface between the original and the surface of the blanket 140. Since the drum is preferably grounded, either directly to the frame of the machine or through a resistor, corresponding negative charges will be induced at the surface of the metal drum as shown. The mutual attraction between the positive charges on, and in, the original, and the negative charges in the drum itself, causes the original to tightly adhere to the insulating blanket. The portions of the original which are subsequently exposed to the charging unit are similarly charged.

Subsequently when the leading edge of the original is advanced, by movement of the drum, into the field of infiuence of 'the second charging device 35, the positive charges are neutralized and replaced by negative charges from the negatively charged wires 36. The negative charges on, and in, the original induce positive charges in the drum surface on the opposite side of the insulating blanket. Any tendency for the leading edge of the sheet to lift clear during the instant of charge reversal may be taken care of by providing a guiding edge 35a or the like at 'the point of entry to the second charging unit 35 to maintain the sheet close to the drum so that when the charge is reapplied the leading edge will snap back into seated position. A similar function is performed by the guide surface 33a in unit 33 for recirculated originals. Any momentary loss of attractive force in the successive areas of the original being acted upon is of no consequence since the predominant area of the sheet is still adherent. Moreover, the resistance of the average original is sufiiciently high so that While the leading portion of the sheet may be negatively charged and the portion immediately following positively charged (see FIG. 7), there is no appreciable charge migration along the surface of the sheet.

Where the original is allowed to recirculate back to the first charging device, as it is during the making of multiple copies, charge reversal again takes place and a positive charge is reestablished as shown in FIG. 6. The charging and recharging with reversed polarity is repeated as long as the original is allowed to recirculate.

I have observed that use of opposite polarity at the two charging stations acting upon the same sheet provides 'a surprising improvement in the reliabilty of the electrostatic holding force, particularly where the drum is continuously cycled. The reason for this improvement may be explained as follows: When there is no original on the blanket, which occurs when the machine is first turned on or when the drum is rotating idly between usages, an electrostatic charge is applied directly to the surface of the blanket. Moreover, while most of the drum area is covered by the original during normal operation, the charge which is applied to the original tends to migrate to the interface, i.e., to the outer surface of the insulating blanket and is augmented at each rotation of the drum. Thus where a single polarity is employed the insulating blanket soon develops a steady high :level of charge which is of the same polarity as the charge which is applied to the surface of the original. Since the like charges repel, the net holding force then becomes a function of the difference in the charge applied to the original and the charge which has accumulated on the surface of the blanket, which differential may be quite small, particularly under conditions of high humidity.

Where opposite polarities are used at the two charging stations, accumulation of charge during successive drum rotations is not only completely overcome but a condition is produced at the original-blanket interface which may actually augment the holding power of the charge applied to the face of the original. Taking first the case of anew original, for example, when the machine is first put into operation, when a given area of the insulating blanket leaves the vicinity of the charging unit 35, the residual charge on the surface of the blanket is negative. Thus, when the surface is covered by an original 20 and fed into the first charging unit 33, a positive charge deposited on, and in, the original is attracted not only by the induced negative charge in the drum but also by the residual negative charge which may exist on the surface of the blanket. During the time that it takes the original to rotate from the first charging unit to the second, migration of charge will normally occur in the sheet so that by the time the original reaches the second unit the residual charge at the interface may be slightly positive. Such charge coacts with the negative charge applied to the original at the second station to provide additional holding force. Where the original is not removed but is allowed to recirculate for multiple copies, any residual charge on the blanket when the same leaves the second charging station is negative. The charge on the original is immediately neutralized and replaced by a positive charge when the surface of the original again enters the region of the first charging unit 33, with the residual tending, again, to augment the holding force. Thus, regardless of whether the original is new or recirculated, the same conditions of charge and hold ing force exist during successive revolutions of the drum and there is uniformity of function and result regardless of whether the original circulates only once or a hundred times. On the contrary, securing the sheet tightly to the drum not only insures uniformity of optical conditions in successive revolutions but there is no possibility of the sheet skewing or shifting which sometimes occurs during recirculation where other types of sheet holding means are employed.

While the invention has been discussed in connection with two charging units of opposite polarity, it will be apparent to one skilled in the art that the invention is not limited to use of two units and additional units may be employed such as that indicated in dot-dash outline at 33a (FIGS. 2 and 5). The unit 33a'may be positively charged in order to augment the charge applied at the unit 33 or may be negatively charged to augment the negative charge applied at unit 35. Still additional charging units may be used, provided only that there is at least one reversal of polarity per cycle of rotation of the drum.

Further, in accordance with the present invention means are provided for pre-curling the original prior to engagement with the drum 30 by stressing it beyond its elastic limit so that it acquires a set and tends more nearly to conform to the curvature of the drum surface. In the present instance such pre-curling is brought about by forcing the original about a substantial portion of the periphery of a roller having a curvature which greatly exceeds the curvature of the drum. Thus, referring to the roller assembly 25 shown in FIG. 8, the driven roller 26 is in rolling engagement with

idler rollers

27, 28 which are spaced, by angle a, about the periphery of the roller 26. The roller 26 is resiliently surfaced and has a nominal diameter which may be on the order of of the diameter of the drum 30 with which it is used. Preferably the two

rollers

27, 28 are resiliently surfaced and spaced to define an are a of forced contact which is on the order of 75, i.e., an appreciable fraction of the total periphery. In any event, the radius r of the pre-curl roller 26 and the arc of forced contact are preferably chosen so that the resulting radius of curvature or set of the original, indicated at r in FIG. 8, is on the order of the radius of the curvature of the drum itself. Thus the original tends, naturally, to conform to the surface of the drum and the electrostatic forces need not be relied upon to overcome any self-straightening effect in the original.

While it is true that the radius of curvature of the precurled original, indicated at r will apply to originals having average characteristics, for example, good quality letterhead, nevertheless it is found that variations on each side of the average tend to be self-compensating. Thus, in the case of originals of greater than average thickness the curvature of the pre-curl will exceed the elastic limit to the extent that the set radius may actually be less than the radius of curvature of the drum causing the original to cling intimately to the drum event without electrostatic holding force. Conversely, where the original is a thin tissue, the pre-curl roller may not be as effective to impart a well defined setto the original but, by the same token, a tissue conforms to the surface of the drum readily and with only a small electrostatic holding force even where it has no set whatever. Moreover, the precurl eifect brought about by a given set of pre-curling rollers tends to be self-compensating as regards wide variation in humidity. Thus, under dry conditions where a given original tends to be a little stiffer or more elastic than usual resulting in a set of greater radius, i.e., less conforming, leakage of charge is reduced, resulting in augmented electrostatic forces easily capable of maintaining the original in secure contact with the drum. Conversely, where the humidity is high, accompanied by greater leakage of charge and slightly lower electrostatic forces, the original is more conformable and amenable to set and thus more easily held in place by the reduced electrostatic charge.

It may be seen, therefore, that a given pre-curling setup, such as that illustrated in the drawings, sufiices for a wide range of originals from thinnest tissue to paperboard and over a broad range of humidity, from arid to approaching saturation, permitting full utilization of the electrostatic holding force in preventing creep or skew.

It is preferred to make the roller 27 of relatively small diameter and the roller 28 of resilient material and of relatively large diameter. The latter thus tends to wipe the leading edge of the original reliably into the nip between the

rollers

26, 28 even where the original fed into the machine has an initial curvature which might cause it to miss the nip. Any one of the rollers may be driven but I prefer to drive the roller 26.

In general, it is found that the ironing effect of the

expeller rollers

22, 48 and the reverse curvature on the guides 49 is adequate to straighten out a pre-curled origi nal after it is stripped from the surface of the drum 30. L

However, where more complete straightening of the precurl is desired, and in accordance with one of the more detailed aspects of my invention, an uncurling roller assembly 25a (FIG. 9) may be used at the point of exit from the drum 30 consisting of an uncurling roller 26a and cooperating rollers 22a, 28a. As in the case of the precurl roller 26, the arc of forced contact is indicated at a; however, the radius r is preferably greater than that of roller 26 to avoid producing a set in the opposite direc tion. Setting the radius to produce a fiat letterhead original is a matter within the skill of the art. Either

roller

26a or 22a may be driven, whichever. is more convenient.

I have found that use of pre-curl combined with electrostatic adherence to a transport drum results in a number of significant advantages. In the first place, it is found that a wide range of thickness of original may be accommodated with complete reliability, even up to paper board, with no tendency for the leading edge of the original to spring free even under conditions of extreme humidity or high leakage. Lower charging voltages become possible. Then, too, the original tends to remain in contact with the transport drum even in the event that the supply circuit is accidentally interrupted or inadvertently turned off while the original is in the machine. In the present machine turning on the charging units after an interruption causes the holding force between the original and the ground to be reestablished in the regions of the charging units which is adequate to initiate movement, and the leading edge is kept sufficiently close to the drum so that it does not become hung up within the machine. Possible damage to the original or the necessity for a service call is thus averted.

While the invention has been described above in connection with charging units of unlike polarity and at spaced positions around the periphery of the drum, and while this constitutes the preferred form of the invention, attention is nevertheless directed to the alternative embodiment shown in FIG. 10, in which unlike polarities are applied to the successive areas of the original by switching between the terminals of the power supply 75 as the drum is rotated and with the period of switching being so related to the period of rotation of the drum so that the same areas of the drum are not subjected repeatedly to the same polarity of electrical charge. The switch 150, having contacts 151, 152 is coupled to the drive motor by any means 153 capable of making alternate contact. The switching produces alternating bands across the Width of the original as shown.

In one of the aspects of the invention accumulation of charge on the insulating blanket when using a single polarity may be avoided by contacting the surface of the blanket with a grounded metal roller 155 (FIG. 9). Such a roller extends the width of the drum and is biased in the drums direction by any suitable means. Preferably the roller is positioned between the stripping assembly and the first charging unit, permitting direct contact with the blanket between successive originals. If desired, the roller 155 may be replaced by a corona wire excited by high voltage A-C.

It has been convenient in the above discussion to speak in terms of an original document fed into an ofiice photocopy machine. It will be apparent, however, to one skilled in the art that the invention is not limited to transport of an original in the strict sense and that the term original used in the following claims refers to any sheet of paper or the like requiring transport in fixed position with respect to the surface of a rotating drum. Moreover, while a rigid, conducting drum of circular'section has been disclosed in the drawings, the term is not necessarily limited to a circular drum but may include any equivalent transport member, such as a belt, presenting an extensive gen erally cylindrical outer surface capable of electrostatically adhering the transported sheet. Furthermore, it will be appreciated by one skilled in the art that the present device is not limited to charging of the sheet by means of wires in the air, but would include equivalent charging means, and hence the term corona unit shall be understood to be directed to sheet charging means generally. Finally, the term roller, applying in the present instance to journaled cylindrical members, is not necessarily limited to rotating elements and if desired, the undriven one of a pair of rollers may consist of a polished rod.

I claim as my invention:

1. In an electrostatic photocopy machine or the like requiring transport of an original sheet alonga curved path of transport, the combination comprising a frame, a cylindrical drum grounded to and journalled in the frame and having means for driving the same, an insulating blanket on the drum, means for feeding an original sheet to the drum for seated transport on the blanket, a first source of high charging voltage which is of first polarity with respect to ground, a second source of high charging voltage which is of second and opposite polarity with respect to ground, means for applying the voltages to the face of the original sheet for causing the latter to seatingly adhere to the drum, said voltages being applied in such sequence that a given area on the surface of the blanket is alternately subjected to charges of first and second polarity thereby to avoid any tendency toward accumulation on the surface of the blanket of a charge of one polarity incident to successive cycles of rotation of the drum.

2. In an electrostatic photocopy machine or the like requiring transport of an original sheet along a curved path of transport, the combination comprising a frame, a cylindrical drum grounded to and journalled in the frame and having means for driving the same, an insulating blanket on the drum, means for feeding an original sheet to the drum for seated transport on the blanket, a first source of high charging voltage which is of first polarity with respect to ground, a second source of high charging voltage which is of second and opposite polarity with respect to ground, means for applying the voltages of opposite polarity in sequence to the face of the original sheet so that a given area of the original sheet is first caused to acquire a charge of first polarity inducing a charge of second polarity in the adjacent region of the drum for causing the document to seatingly adhere to the blanket as it is transported and so that said given area is shortly thereafter caused to acquire a charge of second polarity inducing a charge of first polarity in the adjacent region of the drum for causing the document to continue to adhere to the blanket and thereby to avoid any tendency toward accumulation in the surface of the blanket of a charge of one polarity in successive cycles of rotation of the drum.

3. In an electrostatic photocopy machine or the like requiring transport of an original sheet along a curved path of transport, the combination comprising a frame, a cylindrical drum grounded to and journalled in the frame and having means for driving the same, an insulating blanket on the drum, means for feeding an original sheet to the drum for seated transport on the blanket, a first source of high charging voltage which is of first polarity with respect to ground, a second source of high charging volt age which is of second and opposite polarity with respect to ground, means including a corona unit for applying voltage to the face of the original sheet for causing electrostatic adherence of the sheet to the drum, a switch for 10 alternately connecting the corona unit first to one voltage source and then to the second voltage source, and means for continuously and automatically cycling the switch incident to rotation of the drum to avoid any tendency toward accumulation in the surface of the blanket of the charge of one polarity in successive cycles of rotation.

4. In an electrostatic photocopy machine or the like requiring the transport of an origin-a1 sheet along a curved path of transport, the combination comprising a frame, a cylindrical drum journalled in the frame and having means for driving the same, an insulating blanket on the drum, means for feeding an original sheet to the drum for transport thereon, means for applying an electrostatic charge to the original sheet for causing the same to adhere electrostatically to the drum, said feeding means including curling members for curlingly stressing the original beyond its elastic limit and for imparting curvature thereto on the order of the curvature of the drum to rnin1- mize restoring forces in the original tending to restore the same to flat condition and thereby insuring maintenance of contact between the leading edge of the original and the blanket over a wide range of electrostatic charge at the leading edge.

5. In an electrostatic photocopy machine or the like requiring transport of an original sheet along a curved path, the combination comprising a frame, a cylindrical drum journalled in the frame and having means for driving the same, an insulating blanket on the drum, means including a pre-curling device for feeding the original to the drum so that the original is conformingly seated on the blanket, a first charging device adjacent the pre-curling device for charging the face of the original with a charge of one polarity, a second charging device spaced from the first along the path of transport for dissipating the charge applied by the first charging device and for applying to the face of the sheet an electrostatic charge of opposite polarity, means for stripping the original from the drum following circulation thereof, and discharge means inc-luding an uncurling device for stressing the original in the opposite direction for discharge from the machine in substantially flat condition.

6. In an electrostatic photocopy machine or the like requiring transport of an original sheet along a curved path, the combination comprising a frame, a cylindrical drum journalled in the frame having means for driving the same, an insulating blanket on the drum, a feed roller for feeding a sheet to the drum for seated transport thereon, first and second rollers engaging the feed roller at spaced points about the periphery of the feed roller, at least one of the rollers being power driven at a peripheral speed corresponding to the speed of the drum, the feed roller having a diameter which is a minor fraction of the diameter of the drum and the first and second rollers being spaced about an appreciable are so that the original sheet fed between the feed roller and the first and second rollers is stressed beyond its elastic limit resulting in a set of curvature which is in the direction of the curvature of the drum for nesting of the sheet closely against the surface of the drum thereby to minimize any tendency for the sheet to spring free self-restoringly from the surface at its leading and trailing edges.

7. In an electrostatic photocopy machine or the like requiring transport of an original sheet along a curved path, the combination comprising a frame, a cylindrical drum journalled in the frame having means for driving the same, an insulating blanket on the drum, a feed roller for feeding a sheet to the drum for seated transport thereon, first and second rollers engaging the feed roller at spaced points about the periphery of the feed roller, at least one of the rollers being power driven at a peripheral speed corresponding to the speed of the drum, the feed roller having a diameter which is a minor fraction of the diameter of the drum and the first and second rollers being spaced at an appreciable are so that the original sheet fed between the feed roller and the first and second rollers is stressed beyond its elastic limit resulting in a set of curvature which is in the direction of the curvature of the drum for nesting of the original sheets closely against the surface of the drum, said second roller beinglarger than the first roller or feed roller and surfaced to provide-a transverse wiping action against the leading edge of the original so that the original is wiped into the nip between the second roller and thefeed roller.

8. In an electrostatic photocopy machine or the like requiring transport of an original sheet along a curved path, the combination comprising a frame, a cylindrical drum joumalled in the frame having means for driving the same, an insulating blanket on the drum, a roller for feeding a sheet to the drum for seated transport thereon and having a diameter which is a minor fraction of the diameter of the drum, means for causing the sheet to conform to the curvature of the roller so that the sheet is curlingly stressed beyond its elastic limit resulting in a set of curvature which is in the direction of the curvature of the drum for nesting of the sheet intimately against the surface of the drum thereby to minimize any tendency for the sheet to spring free self-restoringly from the surface at its leading edge, and means for applying an attractive force radially inward between the original and the drum to prevent relative creep between the original and the blanket incident to multiple rotation of the original sheet on the drum.

9. In an electrostatic photocopy machine or the like for transport of an original sheet along a curved path, the combination comprising a frame, a cylindrical drum journalled in the frame and having means for driving the same, means for feeding an original sheet to the drum for seated transport on the blanket, a charging device at the periphery of the drum for applyingelectrostatic charge to the original sheet for causing the same to adhere to 5 the drum, the drum being formed with a plurality of peripheral grooves spaced side by side defining flat topped ridges, sheet-stripping means extending into the grooves and angling outwardly therefrom for stripping the original sheet from the drum following completion of a desired number of cycles of drum rotation, an insulating blanket on the surface of the drum covering the flat topped ridges and extending beyond the corners thereof to prevent leakage of charge from the corners, and means at the surface of the drum for removing the charge applied by the charging device thereby to prevent cumulative buildup of charge on the surface of the blanket as a result of successive cycles of rotation of the drum.

References Cited 1 20 UNITED STATES PATENTS 287,957 11/1833 Osborne 226-1 3,100,112 8/1963 Davis 271-53 3,172,657 3/1965 Brandt 271+51 OTHER REFERENCES Noel, N. G., IBM Technical Disclosure Bulletin, vol. 4, No. 2, p. 27, July 1961, Capstan With Electrostatic Field Control.

Claims

1. IN AN ELECTROSTATIC PHOTOCOPY MACHINE OR THE LIKE REQUIRING TRANSPORT OF AN ORIGINAL SHEET ALONG A CURVED PATH OF TRANSPORT, THE COMBINATION COMPRISING A FRAME, A CYLINDRICAL DRUM GROUNDED TO AND JOURNALLED IN THE FRAME AND HAVING MEANS FOR DRIVING THE SAME, AN INSULATING BLANKET ON THE DRUM, MEANS FOR FEEDING AN ORIGINAL SHEET TO THE DRUM FOR SEATED TRANSPORT ON THE BLANKET, A FIRST SOURCE TO HIGH CHARGING VOLTAGE WHICH IS OF FIRST POLARITY WITH RESPECT TO GROUND, A SECOND SOURCE OF HIGH CHARGING VOLTAGE WHICH IS OF SECOND AND OPOSITE POLARITY WITH RESPECT TO GROUND, MEANS FOR APPLYING THE VOLTAGES TO THE FACE OF THE ORIGINAL SHEET FOR CAUSING THE LATTER TO SEATINGLY ADHERE TO THE DRUM, SAID VOLTAGES BEING APPLIED IN SUCH SEQUENCE THAT A GIVEN AREA ON THE SURFACE OF THE BLANKET IS ALTERNATELY SUBJECTED TO CHARGES OF FIRST AND SECOND POLARITY THEREBY TO AVOID ANY TENDENCY TOWARD ACCUMULATION ON THE SURFACE OF THE BLANKET OF A CHARGE OF ONE POLARITY INCIDENT TO SUCCESSIVE CYCLES OF ROTATION OF THE DRUM.