Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-07-03
2001-11-06
Sheikh, Ayaz (Department: 2155)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C226S044000, C318S006000, C318S007000
Reexamination Certificate
active
06314333
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
FIELD OF THE INVENTION
This invention relates to the processing of continuous webs such as paper, film, composites, or the like, in dynamic continuous processing operations. More particularly, the invention relates to controlling tension in such continuous webs during the processing operation.
BACKGROUND OF THE INVENTION
In the paper and plastic film industries, a dancer roll is widely used as a buffer between first and second sets of driving rolls, or first and second nips, which drive a continuous web. The dancer roll, which is positioned between the two sets of driving rolls, is also used to detect the difference in speed between the first and second sets of driving rolls.
Typically, the basic purpose of a dancer roll is to maintain constant the tension on the continuous web which traverses the span between the first and second sets of driving rolls, including traversing the dancer roll.
As the web traverses the span, passing over the dancer roll, the dancer roll moves up and down in a track, serving two functions related to stabilizing the tension in the web. First, the dancer roll provides a tensioning force to the web. Second, the dancer roll temporarily absorbs the difference in drive speeds between the first and second sets of driving rolls, until such time as the drive speeds can be appropriately coordinated.
A web extending between two drive rolls constitutes a web span. The first driving roll moves web mass into the span, and the second driving roll moves web mass out of the span. The quantity of web mass entering a span, per unit time, equals the web's cross-sectional area before it entered the span, times its velocity at the first driving roll. The quantity of web mass exiting a span, per unit time, equals the web's cross-sectional area in the span, times its velocity at the second driving roll. Mass conservation requires that over time, the web mass exiting the span must equal the mass entering the span. Web strain, which is proportional to tension, alters a web's cross-sectional area. Typically, the dancer roll is suspended on a support system, wherein a generally static force supplied by the support system supports the dancer roll against an opposing force applied by the tension in the web and the weight of the dancer roll. The web tensioning force, created by the dancer system, causes a particular level of strain which produces a particular cross-sectional area in the web. Therefore, the web mass flowing out of the span is established by the second driving roll's velocity and the web tensioning force because the web tensioning force establishes web strain which in turn establishes the web's cross-sectional area. If the mass of web exiting the span is different from the mass of web entering the span, the dancer roll moves to compensate the mass flow imbalance.
A dancer roll generally operates in the center of its range of travel. A position detector connected to the dancer roll recognizes any changes in dancer roll position, which signals a control system to either speed up or slow down the first driving roll to bring the dancer back to the center of its travel range and reestablish the mass flow balance.
When the dancer roll is stationary, the dancer support system force, the weight of the dancer roll, and the web tension forces are in static equilibrium, and the web tension forces are at their steady state values. Whenever the dancer moves, the web tension forces change from their steady state values. This change in web tension force supplies the effort that overcomes friction, viscous drag, and inertia, and causes the dancer motion. When the dancer moves very slowly, viscous drag and inertia forces are low and therefore the change in web tension is slight. However, during abrupt changes in mass flow, as during a machine speed ramp-up or ramp-down, the viscous drag, and inertia forces may be several times the web's steady state tension values.
The dancer roll's advantages are that it provides a web storage buffer that allows time to coordinate the speed of machine drives, and the dancer provides a relatively constant web tension force during steady state operation, or periods of gradual change. A limitation of dancer rolls, as conventionally used, is that under more dynamic circumstances, the dancer's ability to maintain constant web tension depends upon the dancer system's mass, drag, and friction.
It is known to provide an active drive to the dancer roll in order to improve performance over that of a static system, wherein the web is held under tension, but is not moving along the length of the web, whereby the dynamic,disturbances, and the natural resonance frequencies of the dancer roll and the web are not accounted for, and whereby the resulting oscillations of the dancer roll can become unstable. Kuribayashi et al, “An Active Dancer Roller System for Tension Control of Wire and Sheet.” University of Osaka Prefecture, Osaka, Japan, 1984.
More information about tension disturbances and response times is set forth in U.S. Pat. No. 5,659,229 issued Aug. 19, 1997, which is hereby incorporated by reference in its entirety. U.S. Pat. No. 5,659,229, however, controls the velocity of the dancer roll and does not directly control the acceleration of the dancer roll.
Thus, it is not known to provide an active dancer roll in a dynamic system wherein dynamic variations in operating parameters are used to calculate variable active response force components for applying active and variable acceleration to the dancer roll, and wherein appropriate gain constants are used to affect response time without allowing the system to become unstable.
SUMMARY OF THE DISCLOSURE
This invention describes apparatus and methods for controlling tension and tension disturbances in a continuous web during processing of the web. In a first aspect, the invention can be used to attenuate undesired tension disturbances in the web. In a second aspect, the invention can be used to create desired tension disturbances in the web.
In a typical converting process, a parent roll of paper, composite, or like web of raw material is unwound at one end of a processing line, and is processed through the processing line to thereby convert the raw material, such as to shorter or narrower rolls of product; or to shape products from the raw material, to separate products from the raw material, and/or to combine the raw material with other input elements to thereby create a product or product pre-cursor. Such processing operations are generally considered “continuous” processes because the roll of raw material generally runs “continuously” for an extended period of time, feeding raw material to the processing system.
A first family of embodiments of the invention is illustrated in a processing apparatus for advancing a continuous web of material through a processing step wherein the web experiences an average dynamic tension along a given section of the web, the processing apparatus comprising a dancer roll operative for controlling tension on the respective section of web; an actuator apparatus (i) for applying a first static force component, to the dancer roll, having a first value and direction, and balancing the dancer roll against static forces and the average dynamic tension in the respective section of the web, and a controller connected to the actuator apparatus, the controller outputting a second variable force component, through the actuator apparatus, effective to control the net actuating force imparted to the dancer roll by the actuator apparatus, and to periodically adjust the value and direction of the second variable force component, each such value and direction of the second variable force component replacing the previous such value and direction of the second variable force component, and acting in combination with the first static force component to impart a target net translational acceleration to the dancer ro
Lorenz Robert Donald
Rajala Gregory John
Backer Firmin
Kimberly--Clark Worldwide, Inc.
Sheikh Ayaz
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