US3276425A

US3276425A - Copying machine

Info

Publication number: US3276425A
Application number: US306871A
Authority: US
Inventors: Lester R Rabb
Original assignee: Multigraphics Inc
Current assignee: AB Dick Co
Priority date: 1963-09-05
Filing date: 1963-09-05
Publication date: 1966-10-04
Anticipated expiration: 1983-10-04
Also published as: GB1067653A

Description

Oct. 4, 1966 L, R RABB 3,276,425

COPYING MACHINE Filed Sept. 5, 1963 INVENTOR.

W/Mm yak/47114451641, flaw mm @{/g,

United States Patent ware Filed Sept. 5, 1963, Ser. No. 306,871 Claims. (Cl. 118-637) This invention relates to a copying machine and, more particularly, to such an apparatus for transporting sheets or webs bearing loosely deposited powder or developer images.

Electrostatic printing or copying machines of the type using copy sheets or webs coated with photoconductive material generally include a charging station to which the copy sheet is fed to acquire a uniform electrostatic charge on its coated surface and a subsequent exposing station in which the coated surface is selectively discharged in accordance with the original to be copied to provide a sheet bearing an electorstatic image. This image is developed in a developer station by the application of an electroscopic powder that is loosely adhered to the copy sheet by the electrostatic image, and this powder or developer image is then fixed in permanent form by the use of a fixing unit or fuser oven in those applications in which the electroscopic powder is a synthetic thermoplastic res1n.

The transportation of the sheet or web from the developer station to the fixing unit, such as the fuser oven, in which the powder image is converted to a permanent form presents a number of problems. In the first place the powder or developer image comprises discrete particles selectively held in the image or nonimage areas in the case of a reverse print by the attraction between the charge on the coated surface of the copy paper and the oppositely .charged developer particles. The magnitude of this force is not so great as to prevent the loss of powder to the background areas of the image surface if the image surface slides over guide structures or is engaged by conventional drive or guide rollers in being transported from the developer station to the fuser unit. This problem of smearing the powder image or deposited powder to the background area can be substantially reduced or avoided by the use of feed rollers of the construction shown in United States Patent No. 2,894,744.

The most advantageous arrangement of the various components or subassemblies of an electrostatic copying machine presents a second difficulty in transporting the .copy sheet from the developer to the fuser unit. In office copying machines, for instance, it is desirable to reduce the physical size of the machine as much as possible, particularly the desk or floor area occupied by the machine. This area can be substantially reduced by placing the fuser station above the developer unit in a vertically spaced relation. However, the electrostatic image on the coated surface of the copy sheet should be faced downwardly in the developer unit to prevent it fro-m carrying off surplus powder, and it is desirable to have the surface of the sheet carrying the fused image facing upwardly for visual inspection by the machine operator when the copy sheet is discharged from the machine. This requires the copy sheet to be reversed in direction by turning it through 180 in movement between the outlet of the developer unit and the inlet to the fuser unit in a relatively short disstance of travel. This can be done with a large number of sets of guide rollers, but even with rollers of the improved construction s-hown in the above-identified patent considerable smearing and distortion of the powder image can occur.

Accordingly, one object of the present invention is to provide new and improved means for transporting sheet or web material.

Another object is to provide an electrostatic copying machine including new and improved means for transporting a sheet carrying a loosely held developer or powder image from a developer station to a fixing or fusing unit.

Another object is to provide a web or sheet handling apparatus in which the direction of movement of the web or sheet is reversed by the controlled application of one or more streams of air.

A further object is to provide an electrostatic copying machine having vertically spaced developer and fuser units and new and improved means for feeding copy sheets bearing an unfixed powder image from the developer unit to the fuser unit without smearing o-r distorting the powder image.

A further object is to provide an electrostatic copying machine having vertically spaced developer and fuser units in which pneumatic means are used to feed the powder image bear-ing sheets from the developer unit to the fuser unit to avoid smearing or distorting the powder image.

In accordance with these and many other objects, an embodiment of the present invention comprises an electrostatic copying machine including charging and exposing stations in which an electrostatic image corresponding to the original to be reproduced is formed on the coated surface of a copy sheet. This electrostatic image is fed into a developer station facing downwardly toward suitable developer powder applying means, such as a magnetic brush, which deposit developer powder on the downwardly facing surface of sheet for selective retention by those areas of the sheet carrying the electrostatic image. This powder image comprising discrete particles loosely held in engagement with the lower or coated surface of the sheet is placed in a permanent form by a fixing unit such as a fuser oven that is disposed in a position spaced vertically above the developer unit. This fuser oven includes a conveying means having an inlet generally disposed above the developer unit and an outlet through which the copy sheet is discharged from the machine preferably with the fused powder image facing upwardly to permit visual inspection by the machine operator.

To provide means for feeding the sheet bearing the downwardly facing powder image discharged from the outlet of the developer unit into the inlet of the fuser unit, pairs of feed rollers having their sheet engaging peripheries formed of a nap material are disposed adjacent the outlet of the developer section and the inlet of the fuser oven with an additional pair of these rollers disposed therebetween. These rollers, as set forth in the above-identified patent, are of a construction that does not distort or smear the powder image. The leading edge of the copy sheet discharged by the rollers adjacent the outlet of the developer unit is advanced along a generally horizontal plane until it is disposed somewhat below the intermediate pair of rollers and above and in alignment with a tapered air delivering means comprising one or a plurality of orifices through which a suitable fluid such as air is discharged. This air acts on the lower image bearing surface of the copy sheet and tends to deflect the leading edge of the sheet upwardly between the nip of the intermediate pair of rollers. The velocity of the air is such that the loosely held powder forming the image is not separated from the sheet but is of sufiicient velocity and quantity to exert the necessary force to deflect the sheet upwardly to the point at which it is received between the nip of intermediate pair of rollers.

This center pair of rollers feeds the sheet to the pair of rollers adjacent the fuser section which further advance the sheet into the inlet of the oven or fuser with the powder bearing image facing upwardly. During passage through the oven, the powder image is fused or placed in a permanent form to provide the finished copy which is discharged from the copying machine with the image facing upwardly to permit inspection by the operator. Thus, the construction and arrangement of the pneumatic means relative to the inlet of the oven and the outlet to the developer is such that the direction of movement of the copy sheet bearing the powder image is reversed in a very short distance of travel without requiring excessive engagement of the powder image and the resultant smearing or distortion thereof.

Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. 1 is a schematic sectional view of an electrostatic copying machine embodying the present invention;

FIG. 2 is a schematic perspective view of the construction shown in FIG. 1;

FIG. 3 is an end elevational view of another embodiment of the invention; and

FIG. 4 is a schematic perspective view of a third embodiment of the invention.

Referring now more specifically to FIGS. 1 and 2 of the drawings, therein is illustrated an electrostatic copying machine which is indicated generally as and which embodies the present invention. The machine 10 can be of any of the types well known in the art in which a copy web or sheet 12 is coated on at least one surface with a photoconductive material, such as zinc oxide, in a resin binder to provide a medium for receiving a graphic or printed original to be reproduced. In general, the machine 10 includes a charging unit (not shown) for applying a uniform electrostatic charge to the coated surface of the copy sheet 12 and an exposing unit (not shown) in which the uniformly charged surface of the sheet 12 is selectively illuminated in accordance with the material to be reproduced so that the charge on the illuminated areas of the sheet 12 becomes dissipated to provide a resultant electrostatic image corresponding to the material to be copied or reproduced. The copy sheet 12 bearing the electrostatic image is advanced into a developer unit indicated generally as 14 with the electrostatic image facing downwardly.

In the developer unit or station 14, a developer powder, such as a synthetic thermoplastic resin, is uniformly applied to the adjacent surface of the sheet 12 to permit the powder to be electrostatically held in engagement with this sheet in accordance with the electrostatic image thereon. The sheet 12 with the loosely held discrete particles thereon forming the powder image is then transported to a fixing unit or fuser oven indicated generally as 16 in which the developer powder is fused to the coated surface of the paper 12 to provide a permanently fixed image. To permit the machine 10 to be formed as compact as possible, the fuser station or oven 16 is disposed above the developer unit 14 with a little space as possible therebetween, and a new and improved sheet feeding or transporting assembly indicated generally as 18 including pneumatic deflecting means is disposed between the outlet of the developer unit 14 and the inlet to the fuser oven 16 to reverse the direction of movement of the sheet 12 through the machine 10 and to move the powder image from its downwardly facing position in the developer unit 14 to an upwardly facing position in the fuser oven 16 from which it is discharged with the image surface facing upwardly to permit visual inspection by the machine operator. The sheet feeding or transporting assembly 18 accomplishes this inversion in the direction of movement of the sheet 12 in a minimum distance and without smearing or otherwise obscuring the loosely held powder image on the sheet 12 discharged from the outlet of the developer station 14.

The charging and exposing units (not shown) preferably are disposed toward the front of the machine 10 (to the right in FIG. 1) and include means for receiving the copy sheet 12 with the coated or photoconductive surface facing downwardly. These units apply a uniform electrostatic charge to the coated surface and selectively dissipate this charge in accordance with the graphic or printed material to be copied to provide a latent or electrostatic image on the lower or downwardly facing surface of the sheet 12. These constructions can be of any of the Well known types. Following exposure, the sheet 12 with the downwardly facing electrostatic image is fed into the developer unit 14.

This unit which can comprise one of the constructions shown, for instance, in United States Patent Nos. 2,786,440; 3,003,363; or 3,015,305 includes a storage receptacle containing a mass of magnetic or iron particles mixed with the toner or developer powder which preferably comprises a synthetic thermoplastic resin. A rotating drum or cylinder 20 contains magnetic means so that as the drum 20 is rotated the influence of the magnetic field forms the magnetic particles or iron filings into bristles or whiskers carrying the developer powder which rotate with the drum 20 through at least a portion of a cycle of rotation. The developer unit 14 also includes means for feeding the copy sheet 12 along the path illustrated in FIG. 1 to lie above the rotating drum 20. Thus, during movement of the copy sheet 12 through the developer unit 14, the magnetic bristles apply the developer powder uniformly across the width of the copy sheet 12.

Since the developer powder carries an electrostatic charge opposite to that forming the electrostatic image on the downwardly facing surface of the sheet 12, the discrete particles of developer powder are retained on the lower coated surface of the sheet 12 to form a powder image of loosely held particles. The particles of the powder which are not retained by electrostatic attraction are either retained on the bristles of the magnetic brush Or fall back into the container in the developer unit 12 and are not retained on the nonimage or background areas of the copy sheet 12. As the leading edge of the copy sheet 12 passes to the outlet of the developer unit station 14, it is fed into the nip of a pair of

feed rollers

22 and 24 which are made in the manner described in United States Patent No. 2,894,744 to avoid any distortion or smearing of the powder image. The

feed rollers

22 and 24 advance the copy sheet 12 containing the downwardly facing powder image into the sheet feeding assembly 18 in which the direction of movement is reversed and the sheet is discharged into the fixing unit or fuser oven 16 with the powder image on the upwardly facing surface of the sheet 12.

The fuser oven 16 can be of any conventional construction and includes a conveying means formed by a plurality of

flexible belts

26 and 28 passing around drive or

idler rollers

30 and 32 to transport a copy sheet 12 through the oven and to discharge the sheet with the fused powder image thereon at the front of the machine with the fused surface facing upwardly to permit its visual inspection. The fuser section 16 can include radiant or convection type heating means for fusing the thermoplastic resin forming the developer powder to the coated surf-ace of the copy sheet 12. A pair of

feed rollers

34 and 36 are disposed at the inlet to the fuser station 16 to feed the copy sheet 12 between the flights of the

conveying belts

26 and 28 forming the conveying means in the oven 16. The

feed rollers

34 and 36 preferably are of the construction disclosed in United States Patent No. 2,894,744.

The sheet transporting or feeding assembly 18 is interposed between the outlet of the developer unit 14 and the inlet to the fuser oven 16 and reverses the direction of movement of the copy sheet 12 and places the powder image which is facing downwardly as the copy sheet 12 is fed through the

rollers

24 and 22 in an upwardly facing position when the sheet 12 passes between the

feed rollers

34 and 36 at the inlet to the fuser oven 16. The assembly 18 accomplishes this while feeding the sheet 12 through as short a distance as possible and without distorting or smearing the loosely held panticles forming the powder image. The assembly 18 includes a pair of

opposed feed rollers

38 and 40 of the same construction as the

rollers

22, 24, 34, and 36 which are disposed above and beyond the

rollers

22 and 24 in the direction of movement of the copy sheet 12 out of the developer unit 14. The nip between these rollers is disposed above an opening 42 in a supporting or dividing wall structure 44 in the machine 10. An additional wall section 46 extends downwardly adjacent one edge of the opening 42 toward the

rollers

22 and 24, and a paper guide structure 48 including a pair of spaced wall sections 48a and 4812 joined by paper edge guide portions 480 is disposed between the rollers 38, 4t) and the

rollers

34, 36 at the inlet to the fuser oven 16.

To provide means for sharply changing the direction of movement of the copy sheet 12 discharged from the developer unit 14 by the

rollers

22 and 24, a pneumatic deflecting means is provided including an air conveying means 50 connected at its lower end to a blower construotion 52 driven by an electric motor 54. The upper end of the conveying means 50 terminates in an air discharging area or orifice 56 which inclines upwardly and outwardly relative to the

feed rollers

22 and 24 from a position disposed somewhat below the nip of these rollers to a position below the nip of the

rollers

38 and 40. If desired, the use of the separate blower 52 and drive motor 54 can be avoided by supplying the conveying means 50 with a moving body of air derived, for example, from the discharge of the blower for the lamp cooling means in the machine 10.

During operation of the machine and when the leading edge of a copy sheet 12 bearing the loosely held powder image on its lower surface is advanced beyond the

feed rollers

22 and 24 by rotation of these rollers, this leading portion of the copy sheet 12 is supported in the manner of a cantilever beam and is advanced to the left or toward the rear of the machine 10 (FIG. 1) until this leading port-ion is advanced to a position overlying the discharge orifice 56 of the air conveying means 50. At this time, the upwardly directed stream of air acts on the unsupported leading portion of the copy sheet 12 to deflect this sheet upwardly and to support this leading portion of the sheet during its continuing movement. The column of air continues to support and deflect the free end of the sheet 12 in the portion disposed to the left of the

feed rollers

22 and 24 until the leading edge enters the nip between the

feed rollers

38 and 40, the column of air being discharged through the opening 42 in the supporting frame 44 in immediate proximity to and in a position spaced slightly below the

rollers

38 and 40.

The

rollers

22, 24 and 38, 40 together with the

rollers

34, 36 are driven in synchronism so that the somewhat arcuate or reverse bend configuration of the path of movement of the sheet 12 illustrated in FIG. 1 is preserved as the sheet 12, now supported between the

rollers

38, 40 and 22, 24, is further advanced. The leading edge of the sheet 12 is now advanced through the paper guide 48 into the nip between the

rollers

34 and 36 from which sheet is then advanced between the flights of the flexible conveying

means

26 and 28 in the oven 16. Because of the reversal in the direction of movement of the copy sheet 12, the powder image is now disposed facing upwardly within the fuser oven 16. When the trailing edge of the copy sheet 12 passes beyond the nip of the

rollers

22, 24, this trailing edge does not fall into engagement with any surfaces that might cause dislodgment of the loosely held developer particles because the column of air discharged through the orifice 56 continues to support the trailing portion of the copy sheet 12 until such time as it depends from the portion engaged in the nip of the

rollers

38 and 40 in a position spaced from contact with any surfaces. In this manner, the web or sheet transporting or conveying assembly 18 reverses the direction of movement of the copy sheet 12 in a minimum distance and with only the pile or nap material on the periphery of the

rollers

22, 24, 38, 40, 34, and 36 engaging the sheet during its travel so as to avoid any dist-ortion or smearing of-the loosely held powder image.

If the copying machine 10 is of the type including means for automatically feeding copy sheets 12 from a supply stack thereof, there is a possibility that a malfunction in the automatic feeding apparatus may result in the concurrent feeding of a plurality of sheets to the machine. The volume of air provided by the blower 52 is adjusted to provide sufficient support for a single sheet of the weights and types of paper normally used with the machine 10 and is capable of handling a rather wide range of paper weights Without requiring readjustment. However, if several sheets are concurrently discharged from the developer unit 14 by the

feed rollers

22 and 24, the weight of the plurality of sheets may be too great to be supported and deflected during their movement by the air discharged from the orifice 56. To prevent a paper jam in these situations, a paper guide 58 is secured at its lower end to a suitable support, such as the upper end of the conveying means 50, by fastening means 60. The paper guide 58 extends upwardly through the opening 42 in the wall 44 and includes an offset upper end portion 58a which bears against or is disposed immediately adjacent the soft pile outer periphery of the feed roller 38. When the plurality of sheets fed by the

rollers

22 and 24 have a weight sufficient to prevent their deflection and support by the column of air discharged from the conveying means 50, the leading edges of these sheets impinge on the upwardly tapered edge of the conveying means 50 defining the orifice 56 and slide in engagement with this tapered surface and the inner surface of the guide 58 to impinge on the periphery of the feed roller 38. Rotation of the feed roller 38 will then deflect the sheets into the nip between the

rollers

38 and 40 and permit continued feeding of the sheets through the machine 10. Thus, the possibility of a paper jam is avoided in even those instances in which an excessive number of sheets is supplied to the machine.

As illustrated in FIG. 2 of the drawings, the sheet or web conveying or transporting assembly 18 requires only the single air stream discharged through the orifice 56 substantially midway along the transverse dimension of copy sheet 12. If desired, the assembly 18 can include a plurality of conduits or fluid conveying means 50 (FIG. 3) with discharge orifices 56 which are connected to the output of the blower 52 by a header 70. The air conveying capacities of the conveying means 50 and the discharging areas of the orifices 56 together with the positions of the conveying means 50 are so chosen as to equally distribute the supporting and deflecting force across the transverse dimension of the sheet fed by the

rollers

22 and 24 so that the sheet is evenly supported and deflected into the nip between the

feed rollers

38 and 40 following its discharge from the

rollers

22 and 24.

FIG. 4 of the drawings illustrates an additional modification in the construction of the web or sheet transporting assembly 18 in which a plurality of fluid con-r veying means 72, 74, and 76 are provided connected by a header 78 to the output of the blower 52. The upper ends of the

fluid conveying means

72, 74, and 76 are provided with air discharging orifices, such as an opening 72a in the conveying means 72, which are staggered in position corresponding to the varying lengths of these conveying means to provide an effective air delivering opening approximately that afforded by the single orifice 56. The assembly 18 can include a single set of the conveying

means

72, 74, and 76 disposed substantially midway across the transverse direction of the copy sheet 12 in the manner of the single conveying means 50' shown in FIG. 2 or can be arranged in a plurality of sets spaced across the transverse dimension of the sheet 12 in the manner illustrated in FIG. 3 to afford a distributed defleeting and supporting force for the copy sheets 12.

The preferred embodiments of the assembly 18 illustrated in the drawings are shown as including the conveying

means

50, 72, 74, and 76 for confining and directing the body of air to a position adjacent the path of movement of the copy sheet 12. In operating the machine 10, it has been found that it is possible to produce columns or bodies of air that support and direct movement of certain types of the sheets 12 by dispensing with the conveying

means

50, 72, 74, and 76 and forming the air flow at one or more points remote from and disposed below the path of movement of the portion of the sheet 12 discharged from the

rollers

22 and 24.

Although the present invention has been illustrated with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An apparatus for making a copy on a sheet or web of material having an electrostatic image comprising developer means for applying a developer in a discrete form for attraction to the electrostatic image on the paper, first web or sheet feeding means for feeding the image bearing sheet through the developer means with the image hearing surface facing downwardly toward the developer means to receive a downwardly facing developer image corresponding to the electrostatic image, fixing means disposed above the developer means for converting the developer image into a permanent form and including both means acting on an upwardly facing surface of the web or sheet and second feeding means for feeding a sheet or web through the fixing means in a direction generally opposite to the direction of movement of the sheet or web through the developer means, and means for reversing the direction of movement of the sheet or web discharged from the first feeding means including means applying a stream of fluid against the surface of the sheet or web bearing the developer image.

2. In an apparatus in which an image formed of discrete particles loosely adhered to one surface of a sheet or web in a developer unit is converted to a permanent form in a fixer unit, a first set of rollers having a sheet or web engaging periphery for discharging a sheet or web from the developer unit with the surface bearing the image of loosely adhered particles facing downwardly, means including a second set of rollers having a sheet or web engaging periphery for feeding a sheet or web into the fixer unit with the image bearing surface facing upwardly, and means consisting solely of means for applying a controlled stream of air to the image bearing surface of the sheet or web for reversing the direction of movement of the sheet or web to feed the sheet or web between the second set of rollers with the image bearing surface facing upwardly.

3. In an apparatus in which an image formed of discrete particles loosely adhered to one surface of a sheet or web in a developer unit is converted to a permanent form in a fixer unit, a first set of rollers having a sheet or web engaging periphery for discharging a sheet or web from the developer unit with the surface bearing the image of loosely adhered particles facing downwardly and with the sheet or web traveling in a generally horizontal direction, means spaced from the first set of rollers in the direction of movement of the sheet or web for applying a stream of air to the image bearing surface of the sheet or web in a direction transverse to the direction of movement of the sheet or web to deflect the sheet or web to a generally reverse bend formation, and means including a second pair of rollers for receiving the deflected sheet or web and for advancing the sheet or web into the fixer unit with the image bearing surface facing upwardly.

4. In a web and sheet handling apparatus means including a first set of rollers for feeding a web or sheet along a generally horizontal path in a first direction, means including a second pair of rollers disposed above the first set of rollers for feeding the web or sheet along a generally horizontal path in a second direction opposite to the first direction, and control means disposed beyond the first set of rollers in the first direction for applying a stream of air to the web or sheet to deflect the web or sheet upwardly toward the second set of rollers to reverse the direction of movement of the sheet or web without requiring the use of structure engaging the sheet or web.

5. The handling apparatus set forth in claim 4 includi g an air impelling means and outlet means for the air impelling means extending from a point below the path of movement of the sheet or web advanced by the first set of rollers to a point disposed above this path of movement.

6. In a sheet handling apparatus, first feeding means having an outlet means for discharging the leading edge of a sheet along a generally horizontal path in which the leading edge is not supported, second feeding means disposed above the first feeding means and including inlet means spaced above and beyond the outlet means for the first feeding means, and sheet deflecting means supplying a fioW of air generally transverse to the horizontal path extending upwardly from a point disposed below the inlet means for deflecting the unsupported leading edge of the discharged sheet upwardly into the inlet means for the second feeding means.

7. The sheet handling apparatus set forth in claim 6 in which the sheet deflecting means includes structure forming at least one air discharge orifice tapered upwardly and outwardly from a point adjacent the horizontal path to a point adjacent the inlet means.

8. The sheet handling apparatus set forth in claim 6 in which the sheet deflecting means includes air discharging means extending upwardly and away from the outlet means of the first feeding means.

9. The sheet handling apparatus set forth in claim 6 in which the sheet deflecting means includes a series of air discharging orifices extending upwardly and away from the outlet means.

10. The sheet handling apparatus set forth in claim 6 in which the sheet deflecting means includes at least a pair of air discharging orifices spaced from each other in a direction transverse to the direction of movement of the sheet discharged from the outlet means.

References Cited by the Examiner UNITED STATES PATENTS 1,770,659 7/1930 Oehmichen 27l-74 X 2,901,246 8/1959 Wagner 271- X 2,991,893 7/1961 Kirsch et a1. 3,173,324 3/1965 Pass 83-98 X FOREIGN PATENTS 576,010 8/1934 Germany.

CHARLES A. WILLMUTH, Primary Examiner. P. FELDMAN, Assistant Examiner.

Claims

6. IN A SHEET HANDLING APPARATUS, FIRST FEEDING MEANS HAVING AN OUTLET MEANS FOR DISCHARGING THE LEADING EDGE OF A SHEET ALONG A GENERALLY HORIZONTAL PATH IN WHICH THE LEADING EDGE IS NOT SUPPORTED, SECOND FEEDING MEANS DISPOSED ABOVE THE FIRST FEEDING MEANS INCLUDING INLET MEANS SPACED ABOVE AND BEYOND THE OUTLET MEANS FOR THE FIRST FEEDING MEANS, AND SHEET DEFLECTING MEANS SUPPLYING A FLOW OF AIR GENERALLY TRANSVERSE TO THE HORIZONTAL PATH EXTENDING UPWARDLY FROM A POINT DISPOSED BELOW