Web Turning And Guiding Apparatus

Abstract

An air bar is provided in the path of web travel to change the direction of travel and the air bar position is automatically adjusted to compensate for minor lateral changes in the path of web travel. The web is laterally constrained a short distance downstream of the air bar and the constraining means is adapted to move simultaneously with the air bar in order that when the air turning bar moves to make a correction in web position, the web will move simultaneously by the same amount.

Description

FIELD OF THE INVENTION

This invention relates generally to a web turning apparatus and more particularly to an air cushion, web turning and guiding device useful for inverting, changing the direction of the path of travel, or correcting the lateral position of a web, particularly a web having a surface which might be damaged by physical contact.

BACKGROUND OF THE INVENTION

In the manufacture or processing of webs, particularly webs which are coated with materials subject to scratching, it has been the practice during manufacture to change the direction of web travel by passing the web around an air turning bar. In the customary operation, the web, during passage from one coating or drying alley or machine to a parallel coating or drying alley, has its direction changed twice by passing around a pair of angularly arranged turning bars. The web, as it passes partially around the first turning bar, changes its direction by some angle, usually 90.degree.. Thus, by passing around a second appropriately arranged turning bar, the direction of travel of the outgoing web is laterally displaced and is parallel to the incoming web. Likewise, suitable configurations, of air bars are often used to invert moving webs.

Highly polished bars are commonly used as turning bars to change the direction of travel of a web. These turning bars are unsatisfactory for photographic film because the film is scratched as it slides on the turning bar. For photographic film, the web turning bars are air-cushion bars to prevent scratches or other damage to the film during changes in direction. These web turning bars are in the form of porous, slotted, perforated, or otherwise permeable tubes through which air is passed to maintain a thin cushion of air between the web and the bar. In some cases, the air cushion turning bars are movably supported for controlled movement to compensate for minor changes in the lateral position or path of the web in order that the position of the web leaving the turning bar is controlled at the desired location. Such a turning bar is termed a steerable air turning bar.

In order for the web to change its direction and to maintain even tension across the web, the angle of the incoming web path to the axis of the turning bar must be equal to the angle of the outgoing path to the axis of the turning bar.

In order to make the minor adjustments in the position of the steerable air turning bar, the bar is connected to an electric, hydraulic or pneumatic actuator. The controller for such actuators responds to signals from one or more edge sensors located a short distance downstream of the turning bar. The edge sensor detects changes in the lateral position or path of the moving web. When the incoming web changes its position on the turning bar as the result of some upstream occurrence, the position of the outgoing web is also changed. This change is detected by the edge sensor, which causes the controller output to change, which in turn causes the actuator to reposition the steerable turning bar in order that the outgoing web position is brought back to its desired location.

Many of these devices have functioned satisfactorily, however, the performance of many and perhaps all could be improved. Problems have arisen particularly in those types of situations where the web is passed partially around a roller or otherwise laterally constrained a short distance downstream of the turning bar. Also in the opposite type of situation where there is a long span of web downstream of the turning bar with little or no lateral constraint on the web in this span. In the first type of situation, the downstream constraint prevents the span of web at the turning bar from moving simultaneously with and by the same amount as the air bar, when the air bar moves in an attempt to properly position the web. Since the web position does not instantly follow the position of the air bar as it is moved, the stability of the control system and the performance of the web guiding system are reduced. Also, since the web position does not instantly and completely follow the position of the air bar, the web, at times, will follow a skewed path as it passes around the air bar. The skewed path distorts the tension profile of the web with the result that one edge may be dragged into contact with the turning bar, thereby damaging the web. The distorted tension profile may produce slack along the opposite edge of the web, which can cause errors in the sensing of web position. Since the web guiding system is a feed-back system, errors in the sensing of web position cause extraneous movement of the guider.

In the type of situation where there is a long span of web downstream of the turning bar with little or no lateral constraint on the web in this span, another problem may occur with the conventional steerable turning bar. In this situation, there is little attenuation of disturbances in web position in this span of web. Such disturbances will always be present when web is being conveyed, and because of the small amount of attenuation present, these disturbances may become large and may alter the position of the web on the steerable turning bar, reducing its effectiveness. They may also affect the position of the web at the sensor, causing the turning bar web guiding system to make extraneous steering corrections. These extraneous changes in turning bar position may in turn produce additional disturbances in the position of the downstream span of web, which may cause additional extraneous steering corrections to occur. In some situation, this effect may cause the system to cycle continuously, making the system useless for web guiding.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an air turning bar for moving webs that is adjustable in its position with respect to the web path and which avoids the difficulties of the prior art steerable turning bars. Another object of this invention is to provide an air cushion web turning bar that moves the web simultaneously with movement of the bar. A further object of this invention is to provide an air cushion, automatically adjustable, web turning bar that moves the web simultaneously with the turning bar when it moves to make a correction in web position. Another object of this invention is to provide a means of isolating the effects of downstream web position so that motion of the web does not hinder the operation of the steerable turning bar system.

These and other objects and advantages of this invention are accomplished by providing a turning bar whose position relative to the web path is automatically adjustable in response to sensors detecting the lateral position of the outgoing web, and a device for laterally constraining the outgoing web which is located near the turning bar and constructed and arranged for simultaneous movement with the turning bar. The axis of movement of the lateral constraint device is in a direction that is about perpendicular to the outgoing web path. This arrangement provides stable, automatic web steering at high speeds and will maintain equal angular relationships between the incoming web path and the axis of the turning bar and the outgoing web path and the axis of the turning bar, so that tight and slack edges do not occur during steering movement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a web turning apparatus emboyding this invention;

FIG. 2 is a side elevational view of the apparatus of FIG. 1;

FIG. 3 is a schematic illustration of an alternative embodiment of this invention; and

FIG 4. is a schematic illustration of turning bars for reversing web direction

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2 of the drawings wherein one embodiment is illustrated, reference numeral 10 denotes a frame or support for the web turning apparatus of this invention with the moving web 12 entering the apparatus from a coating or drying alley (not shown) or other web manufacturing or processing equipment. To conserve floor space in the coating or drying of wide webs of material, such as photographic film, and to provide for the unwinding and winding at the same end, the direction of travel or path of web 12 must be reversed after passing through one half of the processing equipment.

In order to reverse the direction of travel of the web 12, it is partially wrapped around an angularly placed turning bar 14' (FIG. 4) and then around a second angularly placed turning bar 14. In one embodiment, a first turning bar 14' is placed at approximately a 45.degree. angle to the outside edge 13 of the incoming web 12' and the second turning bar 14 is placed at approximately a 45.degree. angle to the outside edge 15 of the outgoing web 12" . The axes of the two turning bars if extended to a point of intersection would be at 90.degree. to each other.

The turning bar 14 has a hollow, tubular body 16 having a substantially flat top surface 18, a substantially flat bottom surface 20, a curved web turning surface 22 joining one edge of each of the top and bottom surfaces 18 and 20 and a substantially flat and vertically disposed side surface 24 opposite the turning surface 22 and joining the other edge of each of the top and bottom surfaces. Other configurations of turning bars, such as a cylindrical bar, may be used equally well. Each of the top, bottom and turning surfaces 18, 20, and 22, are provided with a multiplicity of perforations 26 through which air flows to provide an air cushion for the web 12 in the conventional manner. The axis of the web turning bar 14 is positioned at approximately a 45.degree. angle to the center line of the incoming web 12' in order that the web direction will be changed 90.degree. by passing over the top surface 18, the turning surface 22, and the bottom surface 20, all in that order. The web direction may also be changed by passing first over the bottom surface, then the turning surface and last over the top surface.

The air to provide the air cushion is supplied to the ends 28 and 29 of the turning bar 14 through elbows 30 and 31 connected by expansion ducts 32 and 33 to a supply duct 34. This apparatus for supplying the cushion air is conventional and well known to those skilled in the art.

In order to correct or compensate for changes in the path of the incoming web, the turning bar 14 is movably positioned to reciprocate over a short distance along a path that is approximately laterally perpendicular to the outgoing path 12" of the web 12. The turning bar 14 is provided at each end 28 and 29 with a pair of bosses 36 each of which carries a bearing (not shown). A rod 38 extends between and beyond each pair of bosses 36 and reach rod extends through the bearings. The rods 38 are arranged with their axes approximately parallel to the center line of the incoming web path 12' and are supported by being rigidly secured to a pair of brackets 40 which brackets 40 are carried by a support plate 42 affixed to the frame 10.

With each end 28 and 29 of the turning bar 14 supported for sliding movement on the rods 28, the turning bar 14 may then be moved or reciprocated to compensate for changes in the path 12' of the incoming web. The turning bar 14 is moved by a piston rod 44 connected to a hydraulic actuator 46. The piston rod 44 is affixed to the flat side surface 24 of the turning bar 14. The actuator 46 responds to signals from a controller 48 of conventional design which responds to signals from one or more edge sensors 50 as will be explained hereinafter. The turning bar 14 is illustrated for movement in a direction laterally perpendicular to the outgoing web path. It should be understood that the turning bar may be supported for reciprocal movement in other directions.

The web 12 after passing around the turning bar 14 and changing its direction or path by 90.degree. passes partially around a roller 52 located a short distance downstream of the turning bar. The tension on the web and the friction between the web and the roller results in the web being laterally constrained as it passes around the roller. The roller 52 is adapted for reciprocating, axial movement in a direction approximately parallel to the center line of the incoming web 12' and the axes of the rods 38. The axis of the roller 52 is approximately normal to the edge 15 of the web 12. One end 54 of the roller is supported by a ball bushing bracket 56 having a ball bushing (not shown) engaging a rod 58 supported on the frame 10. The other end 60 of the roller 52 is rotatably supported by a bracket 62 carried by the turning bar 14 in order that the roller 52 will move simultaneously with the turning bar. The lateral constraint on the web insures that the web leaving the web turning apparatus or guider moves laterally by the same amount that the turning bar moves.

The edge sensors 50 are conventional pneumatic sensors which detect the position of the edge of the web 12 before it comes into contact with the surface 64 of the roller 52. The sensor or sensors may be located downstream of the roller 52. The sensors or sensor depending upon whether center guiding or edge guiding is desired, are mounted on the frame 10 and they are adjusted for the desired position of the traveling web in the conventional manner. If conditions upstream cause the web to move out of its established path, the movement will be detected by the edge sensor or sensors. A signal or signals will be sent to the controller 48 in the conventional manner which signals are translated into directions to the hydraulic actuator 46 to change the position of the turning bar 14 to compensate for the change in web path.

In the prior art devices, changes in the position of the turning bar would initially affect a change in the path of the web which is less than the guider movement and would produce a skew in the path of the web near the turning bar. In the apparatus of this invention the roller 52 moves with the turning bar and simultaneously moves the web 12 by the same amount. This movement of the roller 52 maintains the center line of the web 12" at a 90.degree. angle to the axis of the roller and insures that movement of the guider will not distort the angle between the center line of the outgoing web 12" and the turning bar 14, nor the angle between the incoming web 12' and the turning bar 14, both of which are normally about 45.degree.. This alignment will be maintained throughout movement of the turning bar 14 and the roller 52 in response to changes in the incoming path 12'.

Referring now to FIG. 3 wherein an alternative embodiment is schematically illustrated, the web 12 passes under the air cushion turning bar 14, around the curved surface 22 and over the top surface 18, thereby changing its direction by approximately 90.degree.. movement of the turning bar in the direction of the arrows 76 is accomplished by the hydraulic actuator 46 operated by the controller 48.

Changes in the web position wherein the outgoing web path 12" is not held at the desired lateral position are detected by the edge sensors 50 which signal the controller to move the turning bar to return the outgoing web to its proper position. A suction box 70 is located a short distance downstream from the turning bar and the suction box 70 is mounted for reciprocating movement in the direction of the arrows 78. It is moved by being attached to the bracket 72 carried by the turning bar 14. The suction box consists of three rollers 74 which cover a box in which a vacuum has been developed. The vacuum causes the web to partially wrap the rollers thereby developing the necessary traction to assure simultaneous lateral movement of the web with the rollers. The rollers may or may not be driven.

This web turning and guiding apparatus has been described wherein the web path to the axis of the turning bar is at a 45.degree. angle. It should be understood that the web path may be at other angles to the axis of the turning bar provided that the angle on the incoming side is equal to the angle on the outgoing side. Various arrangements may be utilized so long as the outgoing web path is perpendicular to the axis of the lateral constraint or restraint that is simultaneously movable with the steerable turning bar. It is preferred that the turning bar be of the air cushion type, however, other devices for changing the web direction such as polished bars or rollers may also be utilized.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

We claim:

1. In a steerable web turning bar assembly wherein the turning bar is movable in a direction approximately laterally perpendicular to the path of outgoing web leaving the turning bar, the improvement comprising lateral constraint means for said outgoing web, said lateral constraint means being movable laterally and approximately perpendicularly with respect to said outgoing web path and simultaneously with movement of said turning bar.

2. The invention according to claim 1 wherein said lateral constraint means includes a movable roller supported a short distance downstream of said turning bar and said web is partially wrapped about said roller.

3. The invention according to claim 1 wherein the path of the web entering the turning bar is at about a 90.degree. angle to the path of the outgoing web, and each of said paths is at about a 45.degree. angle to the axis of said turning bar.

4. The invention according to claim 2 wherein support means are provided for the movable turning bar which support means also support said roller.

5. A steerable web turning and guiding apparatus comprising an air cushion turning bar adapted to change the direction of a web having an incoming path and an outgoing path, means supporting said bar for reciprocating movement in a direction approximately laterally perpendicular to said outgoing path, lateral constraint means for said web in said outgoing path, said lateral constraint means being movable laterally and approximately perpendicular with respect to said outgoing web path and simultaneously with movement of said turning bar.

6. A steerable web turning and guiding apparatus according to claim 5, wherein said lateral constraint means includes a movable roller supported a short distance downstream of said turning bar and said web is partially wrapped about said roller.

7. A steerable turning and guiding apparatus for a moving web comprising a turning device in the path of the web, said web path having an incoming portion and an outgoing portion with said turning device separating said portions, said turning device being supported for reciprocating movement, a lateral constraint for said web in said outgoing portion, said lateral constraint being movable simultaneously with said turning device and in the same direction, and means for moving said turning device and lateral constraint to adjust the path of said web.

8. A steerable turning and guiding apparatus for a moving web according to claim 7 wherein said lateral constraint is movable by means carried by said turning device.

9. A steerable turning and guiding apparatus for a moving web according to claim 7 wherein said lateral constraint means includes a movable roller supported a short distance downstream of said turning device and said web is partially wrapped about said roller.

10. A steerable turning and guiding apparatus for a moving web according to claim 7 wherein said lateral constraint means includes a suction box having a plurality of rollers partially in contact with said web.

11. A steerable turning and guiding apparatus for a moving web according to claim 7 wherein said turning device and said lateral constraint are movable in different directions.