The present invention relates to turnbars and reversers for the non-contact movement of a web of material around a turnbar or reverser on a cushion of fluid supplied through a plenum and then through tilted holes to support the web above the turnbar or reverser as it changes direction. Description of the Prior Art

Non-contact web turning guides are employed to guide a web or a belt of material, such as a photographic film, print paper or magnetic recording material, to effect a change of direction around a curved surface without permitting the web of material to make contact with the surface. Such turning guides are known as reversers and turnbars. A reverser is used to direct the web of material from a first direction to a second direction without imparting a spiral or helix, and a turnbar changes the direction and/or orientation of the web of material while imparting a spiral or helix. ϋ. S. Patent No. 3,097,971 (issued to S. S. Carlisle et al. on July 16, 1963) discloses an exemplary form of a reverser for supporting or guiding a strip or sheet of material on an air cushion in a non-contacting relationship with a support surface across which the strip material travels. To provide such non-contacting support, a pressurized fluid is introduced through a pattern of radially-aligned perforations in the support surface. The support surface can further include one or more slots around the periphery of the pattern of perforations, which slots are angled to direct the pressurized air towards the center of the pattern of perforations to allegedly enhance the air cushion effect.

U. S. Patent No. 4,824,002 (issued to J. W. Ford et al. on April 25, 1989) describes a non—contact web support guide which includes a pattern of radial pockets with apertures therethrough for providing pressurized air to support the web above the support face. Additionally, a line of smaller closely spaced pockets are provided near the entrance and exit areas of the web and transverse to the web movement. These closely spaced pockets are angled towards the center of the support face to maintain pressure at the entrance and exit areas of the web.

U. S. Patent No. 4,288,015 (issued to L. E. Curtin on September 8, 1981) describes a non-contact web turning guide, or reverser, comprising a surface which is convexly curved in the direction that the web turns. The curved surface has a pattern of radially-aligned nozzle outlets which are each elongated in width transverse to the direction of web movement, and are spaced from one another in that direction to emit pressurized air and support the web. Paired edge-jets are provided to straddle each of the opposing edges of the web in the direction of movement of the web, and are angled towards the opposing edge jets. Such edge jets are allegedly arranged to confine the web against flapping, crinkling and edgewise displacement with less pressurized air than used by other arrangements as the web moves through the zone of the turning guide. TJ. S. Patent No. 3,599,851 (issued to H. R.

Hedlund et al. on August 17, 1971) describes an exemplary turnbar for hydrodynamically supporting and changing the orientation of a continuously moving flexible sheet of material. The sheet of material floats on a cushion of air which is formed by forcing the air out of slots in the turnbar. The turnbar is

covered with a plastic coated diffusing screen. A movable sleeve inside the turnbar controls the number of slots that are open to the passage of air.

A problem encountered with reversers and turnbars is the fluttering of the web material along its edges as it passes over the support surface. Flutter has been found to cause, for example, static discharge on x-ray films, and dirt generation on paper, which are highly undesirable. Known methods to overcome flutter have added additional radially-aligned jets along the moving edges of the web to substantially stop flutter. Such additional jets increase the overall amount of air required to support the web above the reverser or turnbar, which, in turn, necessitates that a larger or additional air supply be used. This increases the processing costs. Summary of the Invention The present invention is directed to a device (e.g., a reverser or turnbar) for the non-contact movement of a web of material around a curved surface on a cushion of a fluid such as air. The device comprises a stationary body comprising a curved surface and fluid supplying means. The curved surface receives the web at a first predetermined line of tangency above the curved surface from a first predetermined path, and delivers the web to a second predetermined line of tangency above the curved surface for movement along a second predetermined path. The curved surface comprises a pattern of holes formed through the curved surface and distributed throughout areas on the curved surface comprising areas adjacent and between the first and second predetermined lines of tangency. The holes of the areas extend beyond and underneath opposing edges of a web to be moved around the curved

surf ce. Each of the holes of the pattern is tilted through the curved surface in a predetermined alignment. The fluid supplying means supplies a fluid to each of the plurality of tilted holes to form a cushion of fluid under the web, whereby, in use, the momentum of a fluid mass being injected from each hole into a cushion of fluid formed under the web supports the moving web above the curved surface, and acts locally to retard a fluid mass from escaping from under the opposing edges and the first and second predetermined lines of tangency of the web.

It is an aspect of the present invention to provide reversers or turnbars for the non—contact movement of a web of material around a curved surface on a cushion of fluid such as air supplied by a pattern of holes. The holes in the pattern are oriented to permit smaller air supplies to be used with the reverser or turnbar to maintain the fluidic cushion than found with similar sized conventional radially-aligned hole patterns. Additionally, the pattern and orientation of the holes in accordance with the present invention also permits smaller diameter reversers or turnbars to be used for a given fluid supply pressure than found with conventional radially-aligned hole patterns.

The invention will be better understood from the following more detailed description taken with the accompanying drawings and claims . Brief Description of the Drawings FIG. 1 is a flattened-out top view of a curved surface of a typical cylindrical reverser showing an exemplary hole pattern therein in accordance with the present invention;

FIG. 2 is a cross-sectional view along dashed line 2-2 of the reverser of FIG. 1 and includes a guide roller and web;

FIG. 3 is a cross-sectional side view of an exemplary orientation of each entrance holes in the first three rows of holes below the entrance area of. a web with each of the reversers of FIGS. 1 and 7, and the exemplary turnbar of FIGS. 9-10;

FIG. 4 is a cross-sectional view of an exemplary orientation of each support hole disposed between the three rows of entrance holes and the three rows of exit holes on the left-hand side of each of the reversers of FIGS. 1 and 7, and the exemplary turnbar of FIGS. 9-10;

FIG. 5 is a cross-sectional view of an exemplary orientation of each support hole disposed between the three rows of entrance holes and three rows of exit holes on the right-hand side of each of the reversers of FIGS. 1 and 7, and the exemplary turnbar of FIGS. 9-10;

FIG. 6 is a cross-sectional side view of the exemplary orientation of each exit hole in the last three rows of holes below the exit area of the web with each of the reversers of FIGS. 1 and 7, and the exemplary turnbar of FIGS. 9-10;

FIG. 7 is a flattened-out top view of a surface portion of an exemplary cylindrical reverser showing an alternative hole pattern therein from that shown in FIG. 1 in accordance with the present invention;

FIG. 8 is a cross-sectional view along dashed line 8-8 of the reverser of FIG. 7 and includes a web and guide roller;

FIGS. 9 and 10 are flattened-out top views of a curved surface of a typical cylindrical turnbar showing an exemplary hole pattern therein in accordance with the present invention; FIG. 11 shows the orientation of the combined FIGS. 9 and 10;

FIG. 12 shows a cross-sectional view along dashed line 120-120 of the typical turnbar of FIGS. 9 and 10; and

FIG. 13 shows the turnbar of FIGS. 9 and 10 at a 45 ^β orientation to spiral wrap the web around the turnbar for changing the direction and orientation of the web.

The drawings are not necessarily to scale. Detailed Description The present invention is directed to reversers and turnbars which change the direction, and possibly the orientation via a spiral wrap, of a moving web through any one of a wide range of degrees while the web rides on a fluidic cushion. The design of the hole pattern in the present reversers or turnbars tends to eliminate edge flutter or pulsations in the moving web. In addition the design reduces the amount of fluid, (e.g., air) escaping from the cushion of fluid formed beneath the moving web compared to prior art devices. For purposes of explanation, the fluid hereinafter will be considered to be air.

Edge flutter is believed to occur because the bulk of the air (fluid) flow from the holes or perforations in a turnbar flows under the web in a spiralling manner from the center towards the web edges, escaping with the flow vector oriented perpendicular to the web edges. Additionally, with either the turnbar or the reverser, at the entrance and exit tangent areas (nips) of the web with the top of the cushion of fluid, the flow of air is less ordered (i.e., turbulent) and is generally perpendicular to the axis of the turnbar. It is believed that the static pressure under the web is negative near the edges. In the flutter zones, the

typical radial hole or perforation pattern in the prior art turnbars or reversers permits localized negative pressure areas which at times extend several inches inboard of the web edges. The resulting escaping air causes a vacuum zone to collapse the web in this area, followed by the snapping back of the web into a shell form when the static pressure increases by virtue of the restriction to air flow caused by the collapsed area of the web. Such action repeats and the web edges flutter or "buzz".

Referring now to FIG. 1, there is shown an exemplary hole pattern in a curved surface 12 of a stationary cylindrical reverser 10 in accordance with the present invention. FIG. 2 shows a cross-sectional view along dashed line 2-2 of the reverser 10 of FIG. 1. FIGS. 3, 4, 5 and 6 show cross-sectional views taken through dashed line 3-3, 4/4, 5-5 and 6-6, respectively, of the reverser 10 of FIG. 1. It is to be understood that FIG. 1 is merely a laid-out flattened top view of the curved surface 12 of the reverser 10 shown in FIG. 2. The cylindrical reverser 10 of FIGS. 1 and 2 is shown in FIG. 2 as having a cross-section along line 2-2 of FIG. 1 with a predetermined outside diameter D and a hole pattern for a web width W. In operation, as can be seen from FIG. 2, a web 14 arrives along a first path and is directed to the top of the cushion of fluid at a line of tangency above the curved surface 12 of reverser 10 via a free-turning guide roller 16, where the line of tangency is located above a reference entrance point of 0" on the circumference of surface 12. The roller 16 is spaced a predetermined distance from curved surface 12. The web 14 then travels around the curved surface 12 of reverser 10 on a cushion of air supplied through a

plenum 18 and the holes 20, 22 and 24 formed in curved surface 12, and leaves reverser 10 along its new second path above a reference exit point of approximately 180° on the surface 12 of reverser 10. To provide the necessary cushion of air beneath the web 14 as the web travels above and around curved surface 14, pressurized air is fed into a plenum 18 in the center of the reverser 10 from an air supply (not shown) with a sufficient pressure above a "touching pressure", as described hereinafter, for release through the holes 20, 22 and 24 in curved surface 12 to maintain the moving web 14 at a predetermined distance (as determined from the "overpressure" described hereinafter) above stationary surface 12 as the web 14 travels around reverser 10.

The hole pattern in reverser 10 shown in FIG. 1 comprises three rows of staggered entrance "nip" holes 20 located at the 0 ^β , 5 ^β and 10" radial reference points on the surface 12 shown in FIG. 2; three rows of staggered exit "nip" holes 22 located at the 175*, 180" and 185* radial reference points; and 16 rows of more widely spaced and staggered support holes 24 located at 10* radial reference point intervals between the entrance and exit "nip" hole rows. As stated hereinbefore, the term "nip" relates to the lines of entrance and exit tangency as the web approaches and leaves the reverser 10. The spaced-apart entrance and exit "nip" holes 20 and 22 of each of the "nip" hole rows extend outwards to just beyond the opposing edges of a widest web 14 to be moved around reverser 10.

The spaced-apart support holes 24 of each of the rows of support holes, however, may fall within an area extending only from just beyond the

edge of a widest web 14 to well underneath the edge of a smallest web to be moved about reverser 10. Such rows may selectively be devoid of support holes in the central area of reverser 10 in the manner shown in FIG. 1. The rows of support holes 24 in reverser 10 are arranged transverse to the curvatufe of the curved surface 12 and to the movement of the web 14. Holes 24 form a pattern of holes within a parallelogram (a rectangle for the reverser 10) with the entrance and exit "nip" hole rows. It is to be understood that the specific number of three rows of entrance and exit "nip" holes, and sixteen rows of support holes 24 therebetween, shown in FIG. 1, are specified merely for purposes of exposition of the preferred embodiment, and not for purposes of limitation. It is to be further understood that the number of entrance and exit "nip" rows can be one or more rows, but two or more rows have been found to provide improved results over the use of just one "nip" hole row. Additionally, the 5' radial reference point spacings of the entrance and exit "nip" hole rows can be any suitable spacings as, for example, more or less than 5', and the rows of support holes 24 therebetween can be spaced at any suitable spacings other than the 10* radial reference intervals shown in FIGS. 1 and 2.

Where a free-turning guide roller 16 is used, it is placed at an entrance and/or exit line of tangency of the web 14 with reverser 10, and the first row of entrance and/or exit "nip" holes 20 or 22 is centered under the guide roller 16 essentially at that line of tangency of reverser 10. For example, in FIG. 2, the guide roller 16 is centered over the first row of entrance "nip" holes 20 at the o ^β radial reference point so that the line of

tangency of web 14 with the cushion of fluid of reverser 10 is positioned over this first row. It is to be understood that an entrance guide roller 16 is desirable for use with a reverser 10, and is germane 5 to providing a stabilizing device and also serving as an air baffle in cooperation with the hole pattern "in surface 10. However, to use a roller 16, it is important that a sufficient wrap of the web 14 on the roller be maintained, which would be, for example, at 0 least 30* of wrap around the roller. The exemplary at least 30" or greater wrap is used to obtain an adequate traction to prevent slippage from occurring between the roller 16 and the web 14.

Where no guide roller is associated with a 5 row of entrance and/or exit "nip" holes, the outermost row of "nip" holes 20 or 22 is located beyond the line of tangency of the web 14 with the cushion of fluid of reverser 10. For example, in FIG. 2, no guide roller is associated with the three 0 rows of exit "nip" holes 22, and, therefore, the last row of exit "nip" holes at the 185* radial reference point is located beyond the line of tangency of the web 14 with the cushion of fluid as the web 14 departs from reverser 10. In FIG. 2, this exit line 5 of tangency is above the 180* radial reference point, and the last row of exit "nip" holes is located 5* beyond the line of tangency of web 14 with reverser 10. It is to be understood that the 5° placement of the last row beyond the line of tangency is merely ° for purposes of description and not for purposes of limitation since the last row of "nip" holes can be located at any suitable distance just beyond the line of tangency as, for example, from 1° up.

The concept to be understood is that on the ⁵ exit side without a guide roller 16, if the last row

of holes is aligned with the line of tangency of the web, adverse consequences, such as pulsing, would generally be caused by the resulting curtain of fluid. On the entrance side of web 14 with the guide roller 16, however, it is not as important to extend the rows of "nip" holes beyond the line of tangency of the web 14 with the cushion of fluid above the surface 12, since the roller 16 guides and supports the web 14 to reduce such adverse consequences. Additionally, if the first row of holes were located beyond the line of tangency produced by the roller, air would be wasted since such holes would not aid in forming the air cushion beneath the entrance "nip" area of the moving web 14. Referring now to the rows comprising entrance "nip" holes 20, these holes are preferably staggered relative to the corresponding entrance "nip" holes in adjacent rows. In the exemplary arrangement shown in FIG. 1, the middle row of entrance "nip" holes 20, at the 5* radial reference point around reverser 10, includes a hole placed at the approximate middle of the pattern of holes of the reverser 10. The remaining holes of that row are spaced outwards from the central hole at sequential predetermined (e.g., 1.00 inch) reference distances. The first and third row of entrance "nip" holes, at the 0 ^β and 10 ^β radial reference points, respectively, include holes which are staggered at first and second (e.g., at .60 and 0.40 inch) reference distances, respectively, on the right-hand side of the pattern of holes of reverser 10. The remaining holes 20 of each of the first and third rows are spaced at sequential (e.g., 1.00 inch) reference distances apart. Therefore, the corresponding holes of adjacent rows are staggered at an exemplary 0.40 inch

reference distance (but could be as small as approximately 0.20 inch reference distance) from each other, and extend outwards to slightly beyond each of the opposing edges of the widest web to be moved 5 around reverser 10. The entrance "nip" holes 20 are each also tilted at an exemplary angle of 45* through the adjacent surface 12 of reverser 10, and in a direction towards the movement of web 14 as shown in FIGS. 2 and 6, where FIG. 6 shows a cross-sectional 0 view of the hole 20 along dashed line 6-6 of FIG. 1. The tilting of holes 20 causes each of the holes 20 to form a somewhat oval-shaped orifice on both the inside surface and the outside surface 12 of the curved cylindrical wall of reverser 10, thus forming 5 a converging intake and a diverging exhaust nozzle in each hole. The wall thickness of reverser 10 is sufficiently larger than the hole diameter to form a "throat" area in the nozzle which is less than either of the oval-shaped intake and exhaust areas . 0 The exit "nip" holes 22 are staggered in their adjacent rows in a similar manner to the entrance "nip" hole. As shown in FIG. 1, the top - row, at the 185" radial reference point, is shown as having a hole 22 located at the approximate middle of 5 the hole pattern of the reverser 10, and the remaining holes of that row are spaced outward therefrom at sequential predetermined (e.g., 1.00 inch) reference distances. The first and second exit "nip" hole rows at the 175" and 180" radial reference ° points, respectively, have their holes staggered from the top row by respective first and second (e.g., 0.20 and 0.60 inch) reference distances in the right-hand direction from the corresponding holes of the top row. Each of the exit "nip" hole rows extends outwards from the approximate middle of the

hole pattern of the reverser 10 to beyond the opposing edges of the widest web 14 to be moved around reverser 10. The exit "nip" holes 22 are als-o tilted at an exemplary angle of 45* to the adjacent surface 12 of reverser 10, and in a direction opposite the movement of web 14 as shown in FIGS. 2 and 3, where FIG. 3 shows a cross-sectional view of the hole 22 along dashed line 3-3 of FIG. 1. It is to be understood that the entrance and exit "nip holes can be oriented at any suitable angle other than the 45° shown in FIGS. 3 and 6, but should not be 90° (radially aligned in reverser 10) and preferably should be less than about 85* to provide the proper air cushion effect in accordance with the present invention.

The support holes 24 in the rows between the 25° and 165 ^β radial reference points on reverser 10 may be more widely spaced than found between the holes 20 and 22 in the entrance and exit "nip" rows. The support holes 24 of each row extend inwards from just outside the opposing edges of the widest web 14 to be moved around reverser 10 to well underneath the opposing edges of the narrowest web 14 to be moved around reverser 10. Therefore, some of the support holes 24 of each of these middle rows will straddle the edge of any web 14 moving around reverser 10. The support holes 24 of adjacent rows are staggered relative to each other by at least a reference distance (e.g., 0.40 inch) as shown in FIG. 1 for the left-hand and right-hand support holes 24. The left-hand support holes 24 are tilted at a predetermined angle, e.g., 60°, towards the approximate middle of the hole pattern of the reverser 10 as shown in FIG. 4, where FIG. 4 shows a cross-sectional view of the hole 24 along dashed line 4-4 of FIG. 1. The right-hand support holes 24 are

tilted at the same predetermined angle, e.g., 60°, as the left—hand support holes 24, but directed in the opposite direction to the left-hand support holes 24 and towards the approximate middle of the hole pattern of the reverser 10 as shown in FIG. 5, where FIG. 5 shows a cross—sectional view of the support hole 24 along dashed line 5-5 of FIG. 1. It is to be understood that the 60* tilt of the support holes 24 shown in FIGS. 4 and 5 is merely for the purpose of description and can have any other suitable angle orientation other than 90 ^β (radial alignment with reverser 10) and should preferably be less than 85 ^β to achieve the proper air cushion effect. The principles imparted by the hole pattern and orientations described hereinbefore (and hereinafter for FIGS. 7, 9 and 10) will be described after the following discussions of the arrangements of FIGS. 7-13.

Referring now to FIG. 7, there is shown an exemplary cylindrically-shaped reverser 30 in accordance with the present invention with an outside diameter D for a web 14 with a width W, and a rectangular hole pattern alternative to that of the reverser 10 of FIGS. 1 and 2. FIG. 8 shows a cross-sectional view taken along dashed line 8-8 of the reverser 30 of FIG. 7, a web 14 and a free-turning guide roller 36. The web 14 is directed around the free-turning guide roller 36 to a line of tangency above the 220" radial reference point on the surface 32 of reverser 30. Web 14 then travels around reverser 30 on a cushion of air produced by entrance "nip" holes 40, support holes 44, and exit "nip" holes 42, and departs reverser 30 at a line of tangency above the 0" radial reference point on the surface 32. FIG. 7 illustrates only a major portion

of the hole pattern on the left-hand side of reverser 30, with the entrance "nip" holes 40, exit "nip" holes 42, and support holes 44 being staggered in a manner similar to that shown for the reverser 10 in FIG. 1. Each of the rows of support holes 44 and entrance and exit "nip" holes 40 and 42 similarly extend outwards to just beyond the opposing edges of the widest web 14a (with a width W ) to be moved about reverser 30. In the hole pattern of FIG. 7, the entrance

"nip" holes 40, at the 210 ^β , 215 ^β and 220* radial reference points, have both a staggered configuration between rows, and also an angled orientation of each hole as shown in FIG. 3. This is similar to the entrance "nip" holes 20 of FIG. 1. However, in the area well underneath the opposing edges of the narrowest web 14b (with a width W, ) to be moved around reverser 30, the entrance "nip" holes 40 are shown as including wider spacings which are equivalent, for example, to the spacings found for the support holes 44. As found with the entrance "nip" hole 20 arrangement of FIG. 1, the first row of entrance "nip" holes 40 at the 220* radial reference point is located under guide roller 36 at the line of tangency of web 14 with the cushion of air of reverser 30. Because of the stabilizing and air baffling effect of roller 36, as described hereinbefore, the entrance "nip" hole rows can include the wider spacings in the central area of these rows.

The rows of exit "nip" holes 42, at the 5 ^β , 0 ^β and 355' radial reference points are not associated with a guide roller and, therefore, comprise a similar staggering between rows, tilt of each hole (FIG. 6) in the row, and spacing between

holes of a row as found with the exit "nip" hole rows of the reverser 10 of FIG. 1. Since no guide roller is associated with the exit "nip" hole rows of reverser 30, the exit "nip" hole row at the 0* radial reference point, rather than the row at the 355 ^** radial reference point, is aligned with the exit li ^' ne of tangency of web 14 with reverser 30 for the same reasons provided hereinbefore for the exit "nip" hole row at the 180° radial reference point of reverser 10 of FIG. 1. The support holes 44 of reverser 30 comprise a similar (a) staggering between adjacent rows of, for example, a minimum 0.20 inch stagger, (b) spacing between holes of each row, (c) tilting of each hole 44 (FIG. 4), and (d) overall width of a hole pattern in a row on the left-hand and right-hand side of the overall pattern as shown for the support holes 24 of FIG. 1. However, as shown in FIG. 7, the rows of support holes 44 between the 165* and 65' radial reference points have a 20° radial reference spacing rather than the 10" radial reference spacings of the support holes 24 of FIG. 1 and the remaining support hole rows of FIG. 7.

Referring now to FIGS. 9 and 10, there is shown a left and a right hand exemplary hole pattern in a curved surface 52 of a turnbar 50 in accordance with the present invention. FIG. 11 shows how the portions of turnbar 50 of FIGS. 9 and 10 fit together. FIG. 12 shows a cross-sectional view along dashed a line 120-120 of the turnbar 50 of FIG.9 and a web 54. Turnbar 50 comprises a surface 52 with a plenum 56 in the center thereof, and a pattern of holes within a parallelogram. The holes extend from plenum 56 through the surface 52 for providing a cushion of fluid (e.g., air) for redirecting the track of a web 54, moving in either direction around

turnbar 50, a predetermined amount to one side through an exemplary 90* angle and through a 180 ^β arc. For purposes of explanation it will be assumed that the turnbar 50 of FIGS. 9-12 has an outside diameter D and a hole pattern for a web 54 of a width W.

The hole pattern within a parallelogram extends from a 185° to a 355 ^β radial reference point around surface 52 of turnbar 50 in FIG. 12. For a web 54 direction entering at the bottom and exiting at the top of the cross-sectional view of FIG. 12, the pattern of holes comprises three rows of entrance "nip" holes 60 at the 185°, 180° and 175° radial reference points, three rows of exit "nip" holes 62 at the 5*. 0* and 355* radial reference points, and a plurality of sixteen rows of support holes 64 located at 10° radial reference spacings between the 15* to 165 ^β radial reference points. The rows of entrance and exit "nip" holes 60 and 62 and support holes 64 are disposed in a parallel spaced-apart relationship to each other and extend transverse to the curvature of turnbar 50. Additionally, each of the support holes 64 on the left-hand side of the pattern is skewed from the line of the associated row by an angle approximating the angle of helical or spiralling travel (e.g., +45*) of the web 54 around turnbar 50, while each of the support holes on the right-hand side of the pattern is skewed by an angle approximating the same but opposite angle of helical or spiralling travel (e.g., -45°).

FIGS. 9 and 10 illustrate an exemplary flattened-out top view of the two halves of the turnbar 50 which are oriented as shown in FIG. 11. The three rows of entrance or exit "nip" holes 60 and 62 are each preferably staggered relative to each

other in the direction of web travel, and have hole spacings which are closely spaced in the areas from just outside the opposing edges of the widest web 54a to be moved around turnbar 50 to well underneath the opposing edges of the smallest web 54b to be moved around turnbar 50. Between these two outside areas of the entrance "nip" holes 60, the remaining entrance "nip" holes are shown more widely spaced similar to the arrangement of the entrance "nip" hole 40 of the reverser 30 shown in FIG. 7. Each of the entrance "nip" holes 60 is also tilted through turnbar 50 along the dashed line 6-6 of FIG. 9 at the exemplary 45* angle as shown in FIG. 6.

The rows of exit "nip" holes 62 have a similar arrangement to that of the rows of entrance "nip" holes 60. However, each of the exit "nip" holes are tilted through turnbar 50 along the dashed line 3-3 of FIG 10 at the exemplary 45 ^β angle as shown in FIG. 3. Therefore, the entrance and the exit "nip" holes are angled to direct the pressurized air jetting through the holes from plenum 56 towards each other under web 54. As shown in FIG. 12, the entrance line of tangency of web 54 is above the 180 ^β radial reference point on surface 52, and the exit ϋne of tangency of web 54 is above the 0* radial reference point. Since no guide rollers are used with typical turnbars at the entrance and exit line of tangency of the web 54 above turnbar 50, the first row of entrance "nip" holes 60 is placed at the 185* radial reference point, and the last row of exit

"nip" holes 62 is placed at the 355" radial reference point in order that these rows are positioned to begin slightly outside the entrance and exit lines of tangency of web 54, respectively, for the reason expressed hereinbefore for the "nip" row areas without a guide roller.

The support holes 64 of FIGS. 9 and 10 are staggered relative to each other in adjacent rows to achieve the appropriate air cushion support of the web 54 moving around turnbar 50. All of the support holes 64 on the left-hand side of turnbar 50 are tilted at the exemplary 60* degrees (along dashed line 4-4 of FIG. 9) in accordance with the cross-sectional view of FIG. 4, but rotated upwards (e.g., +45 ^β ) by the amount of skew in the web 54 travel around turnbar 50 and form a compound angle. Similarly, all of the right-hand support holes 64 are tilted at the exemplary 60* along dashed line 5-5 of FIG. 10 in accordance with the cross-sectional view of FIG. 5, but rotated downwards (e.g., -45') by the amount of skew in the web 54 travel around turnbar 50 to form a compound angle. Such pattern provides a proper cushion of air when web 54 is moved in a spiral around turnbar 50.

Referring now to FIG. 13, the turnbar 50 of FIGS. 9, 10 and 12 is shown in a typical production environment to invert and change the orientation of a web 54 by 90". As shown in FIG. 13, web 54 is directed towards turnbar 50 by the upstream roller 70 with a predetermined amount of tension applied to the web 54 by a tension means (not shown) before it approaches the turnbar 50. Air at a predetermined pressure is supplied to a plenum (not shown here but being essentially the same as plenum 56 of FIG. 12) through a feed 74 from an air supply (not shown), and is jetted from "nip" holes 60 and 62, and support holes 64, to form a cushion of air to support web 54 at a predetermined distance above turnbar 50 as web 54 spirals around turnbar 50. A second roller 72, located downstream of the exit line of tangency of web 54 above turnbar 50, provides a predetermined direction to the web 54 exiting turnbar 50.

Referring now to the principles of the present invention, to ensure that the web travels around a present reverser or turnbar at a predetermined distance thereabove, the required air pressure must exceed a "touching pressure" which relates to the tension in the web traveling around the reverser or turnbar. The touching pressure of a reverser can be determined from the equation:

P = T/RW (1) where P is the touching pressure, T is the total tension on the web, R is the outside radius of the reverser, and W is the width of the web. The touching pressure for a turnbar for a 45* helix, or a 90 ^β turn, can be determined from the equation: P = T/2RW. (2)

It is to be understood that this equation changes slightly for other than a 45* helix. These equations are based on the known "hoop" equation or a force balance which looks at the projected area of the air cushion supporting the web, multiplied by that pressure which develops a force vector in one direction against the force vectors of tension in the other direction(s). The tension T is uniform throughout the wrap of the web around the reverser or turnbar. A complex technique can be used to correlate the clearance expected with the amount of overpressure that is imparted, but as a general guideline, a doubling of the touching pressure can be used as the plenum pressure inside the reverser or turnbar. Normally the pressure to be used is determined experimentally to obtain the desired air cushion.

The principles of the present invention include the Bernoulli effect and can be explained as follows. With radially-aligned holes in a reverser

or turnbar, as found in the prior art, the air escapes outward from the edges and the "nip" areas to cause what is called the Bernoulli effect. The edges and "nip" holes establish orifices through which the air flows to form the cushion. More particularly, with an orifice there is a pressure drop due to the Bernoulli effect and air is suddenly expanding into a larger volume or open space at the exit of the orifice. When a pressure profile is observed, or the pressure in a cushion of air under the web is surveyed, one is interested in the static pressure that is prevalent, because the amount by which the web is floated over the surface of the reverser or turnbar is dependent on that static pressure. When a conventional reverser with a pattern of radially-aligned holes is used, air escapes from various nip and edge areas. Obviously, at the edges and "nips" of such reverser or turnbar, there is a static pressure loss due to the Bernoulli effect. There may even be negative static pressure (partial vacuum). Such negative static pressure tends to cause the adjacent web edge to be sucked downwards towards the surface of the reverser or turnbar. With such occurrence, the outward air flow is restricted and the web tends to pop outwards, which rapid sequential downward and upward edge movement of a web is commonly termed "flutter".

This problem is solved in accordance with the present invention by using a hole pattern within a parallelogram which tilts the holes of the pattern towards the direction of the escaping air normally found with the prior art radially-aligned hole patterns. The present hole pattern, therefore, uses the momentum of the air mass that is being injected

to compete with the slipstream of air that is trying to escape out from under the web to locally slow down the escaping air velocity, and thereby favorably influence changes in the static pressure at the web edges which otherwise cause the fluttering effect. The present designs also are related back to equations (1) and (2). With these equations, it can be seen that for both a given tension T and a reverser or turnbar for web width W, the larger the outside diameter, and in turn the radius R, the lower the touching pressure P that is required and in turn the actual pressure needed to float the web above the reverser or turnbar. Therefore, with larger bodied reversers or turnbars, the holes of the pattern can be more widely spread to maintain the appropriate air cushion without flutter using a given air supply pressure.

An important aspect of the present design, is that by reducing the amount of air escaping from the edges of the traveling web by the appropriate tilting of the present nip and support holes, the amount of operating air pressure and/or flow volume needed for a particularly dimensioned reverser or turnbar is substantially less than found with the comparable prior art designs using a pattern of radially-aligned holes. Such substantial savings in air supply pressure avoids the necessity of buying or using a larger air supply and thereby reduces cost and energy usage. Additionally, the present design may be used where less than the "normal" twice touching pressure is available. Under such condition, a reverser using a conventional radially—aligned hole pattern would require a substantially larger diameter to achieve the same results as the present design

will provide with a smaller diameter reverser. Such capability for the reduction in reverser size is important where space limitations in a production environment are critical and/or where a common air supply can be used to feed several sizes of air cushion devices. Another aspect of the present design is that by forming a converging intake-diverging exhaust nozzle in each hole, whistling is avoided without the need for the more costly "chamfers" or radii on each hole.

Another aspect of the present design is that "weave" (lateral oscillations) on the moving web is reduced with the present air cushion reversers and turnbars. This is believed to be achieved by a "flatter" (more level or uniform) static pressure profile observed under the web as compared with the "dome-shaped" static pressure profile observed with radially-aligned hole patterns. In addition, when a closely-spaced entrance roller is utilized as described hereinbefore, it has an additional stabilizing effect by "anchoring" the web, against air-induced lateral oscillations, as close as possible to the air cushion.

Another aspect of the present design is that a closely-spaced entrance roller partially "baffles" the escape path of the air from the air cushion. This further enhances the air efficiency of the design.

Another aspect of the present design is that longer spans, and thus fewer support devices, are feasible in multi-span web conveyance systems where predetermined web footage within a pre ^' determined space is important. This is achieved by the improved stability and air efficiency of the present angled-hole design.

Another aspect of the present design is that moderate de-centering of the web relative to the hole pattern is tolerated without "tracking" or increased "weave" propensity normally experienced with de-centered web operation over radially-aligned hole patterns. This benefit is believed to result from the "flatter" static pressure profile under the web as discussed hereinbefore.

It is to be understood that the specific embodiments described herein are intended merely to be illustrative of the spirit and scope of the invention. Modifications can readily be made by those skilled in the art consistent with the principles of this invention. For example, each of the entrance and/or exit "nip" holes can be tilted inwards towards the center of the pattern of holes. With such tilting, the outermost "nip" holes would be angled both parallel to the curvature of the reverser or turnbar and towards the center of the pattern of holes, which compound angle is less for each "nip" hole in a row as one approaches the approximate middle of the hole pattern of the reverser or turnbar. A similar alignment could also be done with the support holes. It must be understood that such enhancement or alignment of the pattern of "nip" holes, and also the support holes, increases the cost of a reverser or turnbar significantly and does not of necessity significantly improve the efficiency of air use to warrant the extra cost. Still further, a different optimum hole size, spacing and tilt angle are possible for each hole depending on its location in the pattern relative to each of the web edges, the center of the pattern, and the "nip" holes. Such optimization, if warranted by improved efficiency versus the extra cost, is considered within the

principles of the present invention. Furthermore, it is to be understood that "hybrid" designs may be used for special cases wherein portions of a hole pattern would use angled holes in combination with radially-aligned holes. For example, a pre-existing radial hole pattern can be modified to replace a portion of the radially-aligned holes with angled holes to solve a localized "flutter" problem without exploiting the other advantages of the entire present invention.

It is to be also understood that all of the embodiments described herein entail spaced-apart parallel rows of holes for convenience of defining specific patterns illustrative of the spirit and scope of the invention. Other methods of distributing the holes throughout the areas described herein are possible and are within the scope of the present invention. For example, the holes may be randomly scattered within the defined areas while keeping balanced the quantities associated with opposing edges and/or with entrance versus exit nips.