Patent Application
20090159631
The invention relates to a sheet material feeder and, more particularly, to maintaining tension of a sheet material web in a sheet material feeder.
Web tension is an important factor in providing an accurate sheet length cut in a high speed web cutter. In order to handle the web properly, the web must be under tension. Maintaining a web under tension in the cutter becomes even more challenging due to the rapid start/stop motion of the web. During rapid deceleration, inertia loading on the web is significantly larger than the tension force provided by devices commonly used as a tensioning device in a high speed pinfeed cutter, such as a vacuum box, for example. Attempts to solve the web tensioning problem by simply increasing the vacuum level in the vacuum box have been unsuccessful because increased web tension during web acceleration causes the web to break.
There is a desire to provide a sheet material feeder that can maintain the web tension of a sheet material web during rapid deceleration of the web without causing the web to break during web acceleration. This may be of particular interest in a high speed apparatus having a sheet material cutter that requires the sheet material web to be stopped for cutting.
In the following description, certain aspects and embodiments of the present invention will become evident. It should be understood that the invention, in its broadest sense, could be practiced without having one or more features of these aspects and embodiments. It should also be understood that these aspects and embodiments are merely exemplary.
In one aspect, the invention relates to a sheet material feeder comprising a sheet material web, a vacuum box applying a tension force to a portion of the sheet material web extending into the vacuum box by applying a first vacuum force on the sheet material web, a first drive feeding the sheet material web into the vacuum box, a second drive pulling the sheet material web out of the vacuum box, and a system for applying a braking force to the sheet material web proximate to the vacuum box only during a decelerating movement of the sheet material web at the second drive.
In another aspect, the invention relates to a method of maintaining web tension in a sheet material feeder comprising feeding a sheet material web from a first drive, through a vacuum box, to a second drive, and applying a braking force to the sheet material web proximate to the vacuum box only during a decelerating movement of the sheet material web at the second drive, wherein the braking force supplements a vacuum force applied to the sheet material web in the vacuum box to maintain a web tension of the sheet material web between the vacuum box and the second drive.
In yet another aspect, the invention relates to a method of maintaining web tension in a sheet material feeder comprising feeding a sheet material web from a first drive, through a vacuum box, to a second drive, applying a force to the sheet material web proximate to the vacuum box only during a decelerating movement of the sheet material web at the second drive to thereby form a frictional brake to maintain a web tension of the sheet material web between the vacuum box and the second drive, and adjusting the force based on a coefficient of friction of the sheet material web to provide a substantially uniform friction force for sheet material webs comprising different compositions of materials.
In accordance with another aspect of the invention, a sheet material feeder is provided comprising a vacuum box adapted to apply a vacuum force to a sheet material web extending into the vacuum box; and a system for applying a friction force to the sheet material web proximate an exit from the vacuum box. The system for applying the friction force is adjustable to allow a substantially same friction force value to be applied to different compositions of the sheet material webs having different coefficients of friction.
In accordance with another aspect of the invention, a method of maintaining web tension in a sheet material feeder is provided comprising feeding a sheet material web from a first drive, through a vacuum box, to a second drive; and applying a brake force to the sheet material web proximate the vacuum box during a decelerating movement of the sheet material web at the second drive. The brake force supplements a vacuum force applied to the sheet material web in the vacuum box to help maintain the web tension of the sheet material web between the vacuum box and the second drive.
Aside from the structural and procedural arrangements set forth above, the invention could include a number of other arrangements, such as those explained hereinafter. It is to be understood that both the foregoing description and the following description are exemplary only.
The foregoing aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawings, wherein:
Referring to
The apparatus 10 is a continuous web cutting apparatus. Typically, a continuous web cutting apparatus is used to cut a continuous sheet material web into cut sheets and to provide the sheets to an accumulator. The accumulator takes the sheets and moves them to an insertion station in a mass mailing inserting system. In the embodiment shown in
In the illustrated embodiment, the sheet material 12 comprises a substrate, such as paper, which may include information printed on the substrate. In an alternative embodiment, the apparatus could comprise a printer (not shown) between the roll 14 and the feeder 16 for printing information on the substrate. The sheet material 14 enters the feeder 16 as a continuous sheet material web 18. The feeder 16 is adapted to feed the web 18 into the cutter 20. In one embodiment, the cutter 20 comprises a guillotine cutter for cutting the web 18 into individual sheets. Other cutters may also be used. A simplified model of a pinless cutter 20 is shown in
Referring also to
In the illustrated embodiment, the transport mechanism (e.g., feeder 16) for the cutter comprises two sets of drive nips forming the first and second drives. The vacuum box 26 is located between the drives 24, 30 to provide tension in the web 18 between the drives 24, 30. During steady state cutter operation, the upstream first drive 24 moves with relatively constant velocity feeding the web 18 into the vacuum box 26 creating a loop 32, as shown in
The vacuum box 26 comprises a frame 34 containing several fans 36 at its base. The loop 32 can lengthen and shorten inside the vacuum box 26 due to the motion differential between the two drives 24, 30. The fans 36 create a low pressure zone under the loop 32 which provides web tension of the web 18 between the two drives 24, 30. The feeder 16 includes an entrance support surface or deck 38 into the vacuum box 26 for the web 18 to slide along. The feeder 16 also includes an exit support surface or deck 40 out of the vacuum box 26 for the web 18 to slide along. The two surfaces 38, 40 are curved to provide for a smooth motion of the web 18 along the surfaces 38, 40.
Rapid deceleration of the web 18 by the second drive 30, such as that encountered in a high speed cutter system, may create a peak inertia load on the web 18 that is significantly larger than the tension force provided by a vacuum box 26. For example, the peak inertia load might be 3.5 lb. and the tension force provided by the vacuum force 42 in the vacuum box may only be 0.5 lb. The vacuum force 42 cannot be increased because that may cause the web 18 to break. Intermediate changing of the vacuum force 42 will not work because the response time of the fans 36 and air pressure change inside the vacuum box 26 would likely be too slow. The brake 28 has been added to provide a fast responding supplement to the vacuum force 42 during rapid deceleration to maintain sufficient web tension on the web 18 between the brake 28 and the second drive 30. With the web 18 properly tensioned, this allows proper tracking of the web and provides an accurate sheet length cut with the high speed cutter 20.
The brake 28 is located proximate to the exit from the vacuum box 26. Referring also to
During the web advance acceleration motion, the valve 46 is closed (i.e., turned off) and is opened (i.e., turned on) just as the web 18 begins deceleration. The apparatus 10 includes a controller 52 that is adapted to actuate the valve. When the valve is turned on, the air starts passing through the venturi generator 48, which creates vacuum air flow through the slots 50, thereby acquiring and creating a retarding friction force on the web 18.
The friction force is created between the web 18 and the deck section 40. The slots 50 are provided only in the middle section of the width of the frame 34, as seen best in
In one example, the invention may be used in a pneumatic tensioning mechanism and control for a pinless cutter. In such an application, a brake is applied to the web during the deceleration portion of the motion, keeping the web under tension. Moreover, the web tension is controlled by an additional friction force applied to the web only during the deceleration part of the web advance motion.
In one example, the force generated by the brake may be amplified by the geometry of the curved deck 40 by an amount [eĢ(f*alpha)], where f is the coefficient of friction between the web 18 and curved deck 40, and alpha is the angle the web wraps around the guide (expressed in radians). To avoid web breaks and excessive tension, this amplified force need not be much higher than the maximum inertia force of the web, Fin-max, experienced during deceleration.
In practice, the coefficient of friction depends on many factors, such as paper type, paper quality, amount of ink or toner on the surface of the paper, type of ink or toner, etc. For example, it is well known that the coefficient of friction of printed material can vary significantly from one type of material to another. The friction force generated by the vacuum brake and applied to the moving web can be determined by the following expression:
F=f*N=f*Svs*Pv āā(Eq. 1)
where:
f=the dynamic coefficient of friction between the paper and the deck
N=the normal force
Svs=the total area of the vacuum slots
Pv=pressure generated by the vacuum
alpha=the angle the web wraps around guide
The normal force N is the vacuum force provided by the brake 28. To keep the friction force relatively constant for all paper applications, the vacuum pressure in the brake can become a function of the paper coefficient of friction on the deck. Referring also to
In a further example, one way to calibrate the tension force for a specific web application is to advance the web slowly at constant velocity while recording the digital-to-analog converter (DAC) value of the second drive 30. That value is proportional to the torque generated by the drive motor. The value can be communicated to the controller 52 as indicated by line 58. The acquired DAC value can next be compared against the required tension force value and the difference can be converted into the voltage or current to be applied to the pressure regulator 56. However, in alternative embodiments, any suitable method could be provided. In an alternative embodiment and method, the apparatus could have a separate sensor 60 to sense or detect web tension.
Referring also to
Alternative embodiments of the invention can include, for example, replacing the venturi vacuum generator with a vacuum pump. In another embodiment, the passive friction tensioning device may be replaced with a servo driven nip, which may assist in conveying the web during acceleration, but may impart a retarding force during deceleration of the web, thereby maintaining consistent tension. An example of this can be seen in
Embodiments of the invention provide a method and device for keeping a web under tension to achieve an accurate sheet length cut in a pinless high speed cutter. In some embodiments, a web tensioning force is provided by a vacuum box and an additional friction force is applied to the web only during the deceleration portion of the web advance motion profile using a web brake. The friction force applied by the brake may be automatically adjusted to be a function of the sheet material coefficient of friction using a proportional air pressure regulator.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure and methodology described herein. Thus, it should be understood that the invention is not limited to the examples discussed in the specification. Rather, the present invention is intended to cover modifications and variations.
