Advancing material of indeterminate length – By fluid current – Floating web
Reexamination Certificate
2002-01-30
2003-12-09
Mansen, Michael R. (Department: 3654)
Advancing material of indeterminate length
By fluid current
Floating web
C034S530000, C034S559000
Reexamination Certificate
active
06659323
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to web processing equipment and, more specifically, to methods and apparatus for steering the web as it travels through the processing equipment.
BACKGROUND OF THE INVENTION
Web coating refers to the process of depositing one or more materials onto a thin heat-sensitive substrate, supplied in the form of a continuous, large-quantity roll (i.e., a “web”). The web is unwound and passed through one or more stations in processing equipment, each of which deposits a material onto the web, generally under vacuum. After the web passes through all of the stations, it is rewound onto another roll and readied for further processing or shipment. One product typically manufactured by such a process is magnetic recording tape, where a polyester film is coated with ferromagnetic material.
Processing equipment used for web coating generally includes a series of web transport rollers. These rollers unwind, tension, steer, and wind the web as it travels through the processing equipment. Frictional forces at the interface between the web and a roller provide traction that causes the web to move through the equipment in the direction that the rollers establish.
FIG. 1
depicts a simplified schematic representation of an example of web processing equipment
100
. Processing equipment
100
includes a source
102
of web material
104
in roll form. A pumping system
116
with a pumping port
118
helps maintain the proper pressure (e.g., vacuum) in the processing equipment
100
. Also included are three material deposition stations
106
,
108
,
110
, each of which can deposit a different material onto the web
104
. As the web
104
exits the last material deposition station
110
, it is rewound onto a take-up roll
112
.
Generally included in each material deposition station
106
,
108
,
110
is a web transporting roller
114
and a steering section
200
. Material is deposited on the web
104
as the web
104
travels about the web transporting roller
114
.
FIG. 2
shows the steering section
200
in detail. In the present example, the steering section
200
includes an entering roller
202
that receives the leading edge of the web
104
. The web
104
is then received by a first guide roller
204
and a second guide roller
206
. The guide rollers
204
,
206
are parallel to each other. The web
104
then passes to an exit roller
208
en route to the web transporting roller
114
and then on to another material deposition station or the take-up roll
112
.
One common problem with the aforementioned processing equipment
100
is a misalignment
210
between the entering roller
202
relative to the guide rollers
204
,
206
. An additional misalignment
212
between the exiting roller
208
and the guide rollers
204
,
206
can also happen. When one or both of these conditions occur, the steering section
200
often cannot restore the proper alignment. A result of this condition is that wrinkles, or creases, or both, form in the web
104
as it travels through the processing equipment
100
. The wrinkles or creases tend to accelerate degradation of the coated web product. Further, the wrinkles or creases can hamper the efficient operation of the processing equipment
100
, causing downtime as an equipment operator must, for example, manually realign the web
104
.
From the foregoing, it will be apparent that there is still a need for a way to control the travel of the web
104
through the processing equipment
100
in order to minimize or eliminate wrinkles, or creases, or both, with minimal or no operator intervention.
SUMMARY OF THE INVENTION
The present invention affords control over the degree to which a web floats over (i.e., avoids contact with) or tracks (i.e., contacts) a web transporting roller in processing equipment, such as coating machinery, typically when under vacuum. Adjusting the web tension, or web transporting roller configuration, or both, facilitates this control. A result is that web wrinkling or creasing induced by, for example, steering or other rollers, is reduced or eliminated. This leads to improved performance and decreased downtime of the processing equipment, and minimizes degradation of the web product.
In one embodiment, the invention provides a method for prescribing the operational web tension pressure in relation to the web outgassing pressure. Briefly, outgassing is the evolution of gas embedded in a liquid or solid. The gas is typically released when the liquid or solid is heated, or the surrounding pressure is reduced, or both. In one embodiment discussed herein, the web is placed under vacuum in the processing equipment, which causes the release of gas embedded in the web. By adjusting the web tension pressure so it is less than the web outgassing pressure, the web is caused to float over the web transporting roller. Conversely, setting the operational web tension pressure so it exceeds the web outgassing pressure will cause the web to track the web transporting roller. The choice of causing the web to float or track depends on, for example, the type of web material used and the nature of the processing performed.
One way of setting the operational web tension pressure is to compute the molecular density of the substance (typically water vapor) outgassing from the web. From this density value one can compute a target web tension pressure and set the operational web tension pressure accordingly.
The operational web tension pressure can also be controlled dynamically. During operation, a system according to the invention monitors the web outgassing pressure. The system then adjusts the operational web tension pressure to maintain the desired relationship between it and the web outgassing pressure. The adjustment can be performed in real time, automatically, and without operator intervention, typically using a closed-loop control system.
In another embodiment, the invention provides a method for prescribing the degree to which a web floats or tracks as it passes over one or more web transporting rollers by selecting a particular configuration of rollers for use in the processing equipment. The configuration is based in part on the average surface roughness of each web transporting roller. The average surface roughness required to achieve a desired degree of floating or tracking may be based at least in part on a computed molecular density of the substance outgassing from the web and a desired operational web tension pressure. Web transporting rollers having the appropriate average surface roughness corresponding to the molecular density and the desired operational web tension pressure are then selected for use in the equipment.
One version of the invention includes apparatus for adjusting the operational web tension pressure. In this version, sensors monitor the ambient pressure due to outgassing about the web transporting roller and the tension pressure of the web. A tensioning roller responds to the ambient pressure and adjusts the web tension pressure to maintain the desired relationship between the pressure values. A variation of this version includes a controller that accepts data from the pressure sensors and operates an actuator that, in turn, adjusts the tensioning roller accordingly. A further variation includes the logic necessary to compute molecular density and target web tension pressure and adjust the tensioning roller in relation to the latter.
Another embodiment of the invention provides an article of manufacture that includes a program storage medium having computer-readable program code for prescribing the degree to which a web floats about a web transporting roller. The code includes portions for monitoring web outgassing pressure during web transporting roller operation, and adjusting operational web tension pressure in relation to the monitored pressure. Additional code causes a computer to compute a web outgassing molecular density and target web tension pressure, and set the operational web tension pressure in relation to the latter. In another embodiment, a prog
Lowd Robert Bruce
Vaidyanathan Nandakumar
Mansen Michael R.
Presstek Inc.
Testa Hurwitz & Thibeault LLP
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