Patent Description:
Winders and rewinders are machines that roll lengths of web material, such as paper and nonwoven materials or any other material that may be spirally about a core to form a roll. A winder is typically known as an apparatus that performs the very first wind of a web, forming what is generally known as a parent roll. A rewinder, on the other hand, is typically known as an apparatus that unwinds the parent roll into smaller rolls that represent the finished product. For instance a parent roll of bath tissue may be unwound in a continuous fashion by a rewinder and fed into a process by which the tissue is wound onto cores supported on mandrels to provide individual, relatively small diameter logs of material. The rolled product log material may then be cut to designated lengths into the finalized product. In addition to toilet tissue rolls, other finalized products that may be made by this process include paper towels, paper rolls, nonwoven materials or any other material that may form a parent roll.

Typically, the parent rolls are moved to storage locations until they are consumed in a converting process during which the finalized products are made. The handling and storage of the parent rolls may subject the rolls to certain stresses that cause the rolls to become disoriented from a pure cylindrical shape. Storing a parent on a hard surface, for instance, may cause a flat spot on the roll. Such rolls can have an elliptical or eccentric shape, often referred to as an out-of-round roll (OOR), depending upon how the roll is handled.

As the rolls are unwound by a rewinder, any out-of-roundness characteristics may cause tension disturbances within the web. These tension disturbances may cause many problems. Differences in tension in the web as the web is fed into a process may cause machine malfunctions, web breaks, and can lead to the production of non-uniform finalized products.

In the past, in order to control tension fluctuations, dancer rolls were inserted into the process between first and second sets of driving rolls or between first and second nips. The basic purpose of a dancer roll is to maintain constant tension on the continuous web (or sheet) as the web is fed into a downstream process and traverses a span between first and second sets of driving rolls.

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 damping effect on intermediate term disturbances in the tension in 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.

Usually 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. So long as the tension in the web is constant, the dancer roll remains generally centered in its operating window on the track.

When the web encounters an intermediate or long term tension disturbance, temporarily increasing or decreasing the tension in the web, the imbalances of forces on the dancer roll cause translational movement in the dancer roll to temporarily restore the tension, and thereby the force balance. So when difference in the speeds of the first and second sets of drive rolls tend to accord a change in the web tension, the dancer roll temporarily maintains the tension. While the dancer roll, as conventionally used, provides valuable functions, it also has its limitations. Examples of dancer rolls are described in <CIT>, <CIT> and in <CIT>. Other related art includes <CIT> which discloses a tensioning mechanism for use when unwinding web material from roll.

Further improvements are still needed, however, for an apparatus for controlling a web tension that has fast and variable response times, especially when the web is moving at high speeds.

The current invention is generally directed to apparatuses and methods for controlling tension and tension disturbances in a web being continuously unwound from a parent roll, and more particularly, an out-of-round (OOR) roll of spirally wound web material. In accordance with the present invention, a rotary dancer mechanism is used for applying active and variable forces to a moving web in response to irregularities, such as variations in tension. The web tension control apparatuses and methods of the current invention are an improvement over conventional active and passive dancer rolls, which are generally limited in their ability to control downstream web tension while in motion. Unlike conventional active and passive dancer rolls, which generally experience large forces due to gravity and static friction that limit their ability to attenuate tension disturbances, the rotary dancer of the current invention experiences limited gravitational forces and only limited bearing friction when in use. Additionally, the apparatus of the current invention is a fairly simple design with few moving parts, which is in contrast to conventional active and passive dancer rolls that have a complex set of cable and pulley assemblies.

In a first aspect, the present invention provides a method for controlling tension in a web being unwound from an out-of-round roll of spirally wound web material, as claimed in claim <NUM>.

In a second aspect, the present invention provides a method for controlling tension in a web being fed to a process, as claimed in claim <NUM>.

In a third aspect, the present invention provides an apparatus for unwinding a web, as claimed in claim <NUM>.

Further features of the present invention are set out in the dependent claims. Many modifications and variations of the present disclosure may be made without departing from the scope of the invention as set out in the appended claims.

The invention may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which:.

When introducing elements of the current invention or the preferred embodiment(s) thereof, the articles "a", "an", and "the" are intended to mean that there are one or more of the elements.

In the past, manufacturers of web materials have carefully controlled the manner in which the web materials were produced and have carefully controlled the conditions under which the out-of-round (OOR) rolls were stored in order to avoid the necessity of having to process OOR rolls. For example, manufacturers of paper, nonwoven or similar webs thereof typically use great amounts of energy to make sure that the web is completely dried before the web is wound onto a core to prevent the wound roll from becoming OOR. A drier web material will generally produce less OOR rolls and provides for a better material for use in converting processes. Consequently, paper or nonwoven webs are typically dried so that the moisture content in the web is no greater than about <NUM>% by weight. Requiring the webs to be dried to such extreme amounts, however, slows processing speeds significantly and may greatly increase the cost of producing the product.

In addition to thoroughly drying the webs, manufacturers also carefully handle and store the rolls prior to being used in a converting process in order to prevent OOR rolls. For instance, storing the rolls on a flat surface or stacking the rolls may create flat surfaces which may create problems when the rolls are unwound into a process. In other words, large, high-bulk, through-air dried parent rolls of material are subject to distortion from handling and storage. Large diameter parent rolls are desired because this minimizes the roll change time and improves the efficiency of the converting process. Distortion is particularly evident after the rolls have been stored, where the weight of the roll compresses one side of the roll resulting in rolls having an oval or eccentric shape. These OOR rolls cause tension fluctuations when the roll is unwound by a center driven unwind that can lead to web breaks and variable density logs of material.

To improve the unwinding of OOR rolls, the current invention provides a rotary dancer mechanism for controlling tension and tension disturbances of the web as it is unwound. Unlike prior art dancer devices, the current invention provides a dancer having a rotatable arm and a non-driven roller to support the web as it is unwound. The instant rotary dancer mechanism has extremely fast response times to tension variations. As such, processes incorporating the apparatuses are capable of processing rolls that have a greater degree of eccentricity compared to prior art dancers. The faster response time also enables OOR rolls to be processed at faster speeds in comparison with past apparatuses. Having the capability to process OOR rolls allows manufacturers to produce web materials that contain a greater amount of moisture. Allowing the machines to produce a wetter roll allows for higher processing speeds and greater throughput to make the web. An additional benefit is that the OOR rolls produced may potentially be double stacked in a warehouse prior to converting. By increasing warehouse capacity, less machine grade changes may be needed.

In certain embodiments, the invention provides an improved method of controlling tension variation in a web unwound from an OOR roll using a rotary dancer mechanism having a non-driven roller that is moveable along the longitudinal axis of a rotatable arm. In-use, the rotatable arm has a rotational speed roughly equivalent to two times the rotational speed of the OOR roll and may be phased to the variation in web tension caused by the eccentricity of the OOR roll. In certain instances the arm may rotate continuously as the OOR roll is unwound and this continuous motion may reduce the acceleration required and therefore the load on the system.

With reference now to <FIG>, one embodiment of a rotary dancer mechanism <NUM> useful in the present invention is illustrated. Generally, the rotary dancer mechanism is provided downstream of a parent roll to control the tension of a web material being unwound from the roll, such as illustrated in <FIG>. The rotary dancer mechanism <NUM> comprises a linkage, referred to herein as a rotatable arm <NUM>, having first and second ends <NUM>, <NUM> and rotatable about a pivot point <NUM>. At a first end <NUM> of the rotatable arm <NUM> is a roller <NUM>, which is preferably light weight, low inertia and non-driven. The non-driven roller <NUM> is generally configured to support the web material <NUM> as it is unwound from a roll. A counterweight <NUM> is disposed opposite the non-driven roller <NUM> at the second end <NUM> of the rotatable arm <NUM>.

The arm <NUM> is rotated by a rotary drive (not illustrated), which may rotate the arm <NUM> about a rotary pin. As the arm <NUM> rotates, the rotary dancer mechanism <NUM> stores a certain length of sheet-material web and/or generates a desired level of tensioning in the sheet-material web supported by the roller non-driven roller <NUM>. As will be readily clear to a person skilled in the art, the length of sheet material stored depends on the angle of rotation of the rotatable arm <NUM> between <NUM> and more or less <NUM>°. As already explained, the rotatable arm <NUM> is driven by means of a motor. This motor may be a servomotor, or actuating motor, or a stepping motor or a pneumatic drive. In the case of the pneumatic drive, the pressure by which the drive is driven is regulated preferably in dependence on the angular position of the rotatable arm <NUM>. Starting from the zero position (cf. <FIG>), in which the rotary dancer mechanism <NUM> stores barely a minimal length of web material <NUM>, if any at all, and the rollers <NUM>, <NUM> are located, in the present case, below the non-driven roller <NUM>. The rotatable arm <NUM> may be advanced by the motor to a second position (cf. <FIG>) more or less <NUM>° from the first position. In the second position the angle of the web material <NUM> passes over the rollers <NUM>, <NUM> and the non-driven roller <NUM> decreases relative to the first position. In other words, as the rotary dancer mechanism <NUM> rotates from the first position to the second position, the rollers <NUM>, <NUM> move away horizontally from each other and become closer to the non-driven roller <NUM>. During dynamic operation, the position of the rotatable arm <NUM> may be continuously changed between the first and the second positions in phase with an OOR roll <NUM> that is being unwound.

In addition to rotating the arm <NUM> between a first and second position to control the length of web material <NUM> being taken up by the system, the position of the non-driven roller <NUM> relative to the pivot point <NUM> of the rotatable arm <NUM> may be adjusted. In this manner, the rotary dancer mechanism <NUM> may comprise an arm <NUM> having a longitudinal axis <NUM> and rotatable about a pivot point <NUM> and a non-driven roller <NUM> disposed near the first end <NUM> thereof and movable between the first end <NUM> and the pivot point <NUM> along the longitudinal axis <NUM>. In operation, the position of the non-driven roller <NUM> may be adjusted as the shape of the roll being unwound changes. For example, as discussed in more detail below, during the initial stages of unwinding an OOR roll <NUM> the non-driven roller <NUM> may be disposed near the first end <NUM> of the rotatable arm <NUM>. As the OOR roll <NUM> is unwound and the difference between the lengths of the major and minor lobes decreases, the non-driven roller <NUM> may be moved along the longitudinal axis <NUM> of the rotatable arm <NUM> towards the pivot point <NUM>.

Referring to <FIG>, web displacement on the rotary dancer mechanism <NUM> is illustrated as the rotary dancer mechanism <NUM> rotates. <FIG> shows different positions as the rotary dancer mechanism <NUM> rotates in a continuous clockwise motion. At the beginning of the unwind process, shown in <FIG>, the non-driven roller <NUM> is positioned adjacent to the first end <NUM> of the rotatable arm <NUM>. As OOR becomes less severe as the OOR roll <NUM> is unwound, the offset of the non-driven roller <NUM> will adjust toward the rotating assembly center. The portion of the non-driven roller <NUM> relative to the pivot point <NUM> of the rotatable arm <NUM>, referred to herein as the offset magnitude (D), may be adjusted based on the difference between the major and minor lobe distances. Further, as the OOR roll <NUM> is unwound and the difference between the major and minor lobe distances changes, the offset magnitude may be adjusted. Eventually, the major and minor lobe distances may be approximately equal and the rotatable arm <NUM> may stop rotating and the non-driven roller <NUM> may be fixed in given position.

With reference now to <FIG>, the OOR roll <NUM> comprises a web material <NUM> spirally wound about a core <NUM>. The OOR has major and minor axis <NUM>, <NUM>, also referred to herein as major and minor lobes. A high point of the OOR roll <NUM> is defined by a major lobe tangency <NUM> and a low point of the OOR roll <NUM> is defined by a minor lobe tangency <NUM>. The major and minor lobe tangencies <NUM>, <NUM> may be measured using any suitable distance measuring devices including, but are not limited to, lasers, ultrasonic devices, conventional measurement devices, combinations thereof, and the lengths of the major and minor lobes <NUM>, <NUM> may be determined. The lengths of the major and minor lobes <NUM>, <NUM> may then in-turn be used to calculate the effective diameter of the OOR roll <NUM> using Equation <NUM> below, where X is the major lobe length and Y is the minor lobe length.

While the current invention is particularly well suited for controlling the tension of a web <NUM> as it is unwound from an OOR roll <NUM> it may also be useful in unwinding a substantially round roll such that the major and minor lobe lengths are equal and the OOR roll <NUM> has an aspect ratio approximately equal to <NUM>.

At the start of unwinding an OOR roll <NUM>, a position sensor (not shown) measures the major and minor lobe tangencies <NUM>, <NUM> and the effective diameter of the roll is determined using Equation <NUM> shown above. A position sensor <NUM> senses the position of the rotatable arm <NUM> and the arm <NUM> is rotated to lock the rotary dancer mechanism <NUM> to an unwind position. A phase offset is calculated dividing the length of web between the major lobe tangency <NUM> and the non-driven roller <NUM> by the effective radius. The final phasing is a closed loop control based on feedback from a load cell <NUM> at the discharge of the rotary dancer mechanism <NUM>.

Referring to <FIG>, one embodiment of a system for controlling the tension of an OOR roll <NUM> using a rotary dancer mechanism <NUM> in accordance with the present invention is shown. In <FIG>, the rotary dancer mechanism <NUM> is shown as part of a process by which a web material <NUM> is unwound from the OOR roll <NUM> and fed downstream. The OOR roll <NUM> in <FIG> is an elliptical shape and as the OOR roll <NUM> is unwound it becomes substantially circular as depicted in <FIG>. The rotary dancer mechanism <NUM> is configured to respond to tension variations in the web material <NUM> so that the web material <NUM> is fed downstream at a relatively constant tension.

As shown in <FIG>, the OOR roll <NUM> is unwound from a core <NUM> using an unwind device <NUM>, such as a motor. Speed of advance of the web material <NUM> is controlled by the unwind device <NUM>. The rotary dancer mechanism <NUM> includes a non-driven roller <NUM> disposed on a rotatable arm <NUM> having a longitudinal axis <NUM>. The rotatable arm <NUM> is attached to a motor, not shown, configured so that a controlled amount of torque is applied to the arm <NUM> and rotates the arm <NUM> <NUM>° about a pivot point <NUM>. The non-driven roller <NUM> preferably has a low inertia and low weight. The low inertia and weight of the non-driven roller <NUM> minimizes the drive power to turn the rotatable arm <NUM>. A counterweight <NUM> is disposed on the rotatable arm <NUM> opposite the non-driven roller <NUM> so as to balance the rotatable arm <NUM> as it rotates. The counterweight <NUM> is moveable along the longitudinal axis <NUM>. In embodiments, the counterweight <NUM> is moved in a direction opposite that of the non-driven roller <NUM> so as to balance the arm <NUM> as it is rotated.

The rotary dancer mechanism <NUM> may also be placed in association with a first fixed roll <NUM> and a second fixed roll <NUM>. The fixed rolls <NUM> and <NUM> may facilitate web displacement when the rotary dancer mechanism <NUM> rotates. The fixed rolls <NUM> and <NUM> may be provided with a load sensor and used to facilitate measurements of tension in the web <NUM>. In certain embodiments, such as the embodiments illustrated in <FIG>, the fixed rolls <NUM>, <NUM> and non-driven roller <NUM> are arranged such that the web material <NUM> assumes a serpentine travel path through the rotary dancer mechanism <NUM>.

Once tension disturbance is experienced, torque may be delivered to the rotatable arm <NUM> and the speed at which the arm <NUM> rotates may be varied or controlled such that the rotatable arm <NUM> rotates <NUM>° continuously and tension of the web material <NUM> is maintained. For instance, in view of <FIG>, the position of the rotatable arm <NUM> may be constantly monitored by a position sensor <NUM>. When the rotatable arm <NUM> rotates in response to tension variations, the position sensor <NUM> may send signals to a controller <NUM> such as a computer. A controller <NUM> may be used to control the amount of torque applied to the rotary dancer mechanism <NUM> so as to control the position of the rotatable arm <NUM>. The controller <NUM> may also be configured to receive information regarding tension and velocity of the rotatable arm <NUM>.

The controller <NUM> may be in communication with the rotary dancer mechanism <NUM> and/or the unwind device <NUM>. Based on information received from the position sensor <NUM>, the controller <NUM> may then send a corrective signal to the unwind device <NUM> and/or the rotary dancer mechanism <NUM>.

The amount that the web material <NUM> displaces as the dancer mechanism <NUM> rotates depends on various dimensions. For example, as the rotary dancer mechanism <NUM> rotates, the amount of web displacement changes as a function of the rotary position of the dancer mechanism <NUM> and offset magnitude. For instance, <FIG> shows a maximum web displacement for the rotary dancer mechanism <NUM> wherein the OOR roll <NUM> is in a major lobe position.

When the OOR roll <NUM> is in the major lobe position as shown in <FIG>, the web displacement corresponding equation is as follows: <MAT> wherein.

<FIG> illustrates a minimum web displacement for the rotary dancer mechanism <NUM> where the OOR roll <NUM> lies in a minor lobe position. The OOR roll is rotated <NUM>° and the dancer mechanism <NUM> is rotated <NUM>°.

When the OOR roll <NUM> is in the minor lobe position as illustrated in <FIG>, the web displacement corresponding equation is as follows: <MAT> wherein.

The web displacement calculations above are an example of one aspect of the current invention.

A controller <NUM>, such as a programmable device (i.e. a computer) may be configured to receive various information and to calculate an output that controls the offset speed and the amount of torque applied to the pivot location <NUM> of the rotary dancer mechanism <NUM>. In one embodiment, the controller <NUM> may be programmed with various algorithms for controlling the different system parameters. For instance, the phasing and magnitude control systems, such as those illustrated in <FIG> and <FIG>, respectively, may be programmed into the controller <NUM>. The variables for equations <NUM> and <NUM> are illustrated in <FIG> and <FIG>, respectively. The following equation for the phasing control system shown in <FIG> may be derived as: <MAT> wherein.

The system in <FIG> is trimmed to the phase angle of a load cell control loop as shown in <FIG>.

The following equation for the offset control system shown in <FIG> may be derived as: <MAT> wherein.

The distance between the non-driven roller and the pivot point of rotating arm, referred to herein as the offset magnitude (D), may be based on the measurement of the OOR roll. As the roll is unwound and the difference in the major and minor lobe lengths is reduced, the offset magnitude will decrease as the non-driven roller is moved towards the pivot point. The In certain instances, the offset magnitude may be trimmed by the magnitude component of a load cell measuring tension of the web before and/or after the rotary dancer mechanism.

In one embodiment, for the closed loop control system, the apparatus may include a position sensor <NUM> that senses the position of the rotary dancer mechanism <NUM>. The apparatus may also include a first load cell <NUM> that measures tension in the web material <NUM> upstream from the rotary dancer mechanism <NUM> and a second load cell <NUM> that measures tension in the web material <NUM> downstream from the rotary dancer mechanism <NUM>. The position sensor <NUM>, the first load cell <NUM>, and the second load cell <NUM> may all be configured to send information (i.e. the sensed variable) to the controller <NUM>.

The block diagrams shown in <FIG> are directed to controlling the amount of torque applied to the rotary dancer mechanism <NUM>. In order to control tension variations, the controller <NUM> may also be configured to control the unwind device <NUM> for controlling the speed at which the web <NUM> is unwound. <FIG> illustrate one embodiment of a block diagram for controlling web acceleration. In this manner, the controller <NUM> may be configured not only to control the speed or acceleration at which the web material <NUM> is unwound but also control the torque applied to the rotary dancer mechanism <NUM> in a closed loop fashion.

Referring to <FIG>, the box <NUM> represents the calculations that occur inside the controller <NUM>. The controller <NUM> calculates a resultant output, Tapp, which is the amount of torque applied to the rotary dancer mechanism <NUM> by the rotatable arm <NUM>. The circle to the right of the box <NUM> represents the rotary dancer mechanism <NUM>. Also shown are the forces which act on the rotary dancer mechanism <NUM>.

In view of <FIG>, the position of the rotary dancer mechanism <NUM> is monitored by a position sensor <NUM> and continuously fed to the controller <NUM> along with web tension monitored by load cells <NUM>, <NUM> prior to and after the rotary dancer mechanism <NUM>. During operation, the controller <NUM> compares the web tension before the rotary dancer mechanism <NUM> and after the rotary dancer mechanism <NUM> to determine a web tension value. If the web tension value is out of a specified limit, the controller <NUM> may then calculate the amount of torque to apply to the rotary dancer mechanism <NUM>. This signal is fed to the motor driving the rotatable arm <NUM> which adjusts the amount of torque applied to the rotary dancer mechanism <NUM>. As described above, this may be a closed loop system such that these calculations may occur continuously as the web is processed.

The rotary dancer mechanism of the present disclosure may provide numerous benefits and advantages in relation to conventional linear dancer devices that move up and down. For instance, as shown by the equations above, the product of the mass of a rotary dancer mechanism and gravity are no longer forces that need to be accounted for in adjusting web tension. Consequently, the rotary dancer mechanism is extremely responsive to web tension variations and has a very fast reaction time.

Claim 1:
A method for controlling tension in a web being unwound from an out-of-round roll (<NUM>) of spirally wound web material (<NUM>) having a major lobe (<NUM>) and a minor lobe (<NUM>), the method comprising the steps of:
a. determining the major and minor lobe lengths;
b. determining effective diameter of the out-of-round roll (<NUM>);
c. determining distance between the out-of-round roll and a rotary dancer mechanism (<NUM>) comprising a non-driven roller (<NUM>) disposed on a rotatable arm (<NUM>) having a longitudinal axis (<NUM>), the rotatable arm (<NUM>) attached to a motor configured to apply a controlled amount of torque to the arm (<NUM>) and rotate the arm <NUM>°;
d. unwinding web material from the out-of-round roll;
e. feeding unwound web material over the non-driven roller (<NUM>) disposed on the rotatable arm (<NUM>);
f. rotating the arm <NUM>°;
g. repeating steps a) - d) to determine an offset magnitude; and
h. moving the non-driven roller (<NUM>) along the longitudinal axis of the rotatable arm (<NUM>) based on the determined offset magnitude;
wherein the rotary dancer mechanism (<NUM>) further comprises a counterweight (<NUM>) disposed on the rotatable arm (<NUM>) and movable along the longitudinal axis.