Tension Control System for Deformable Nip Rollers
A method and apparatus for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set driven by a separate driver, the web passing sequentially through each set of deformable nip rollers and forming a web segment therebetween. The driver of a downstream set of deformable nip rollers is adjusted to set the tension of a first web segment and a controller adjusts a first characteristic of the driver of the upstream set of deformable nip rollers to maintain the tension of a second web segment constant. Alternatively, a sensor measures a second characteristic of the second web segment and the controller adjusts the first characteristic of the driver of the upstream set of deformable nip rollers based on the measurement from the sensor.
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The present invention relates generally to web printing presses and more particularly to a method and apparatus for controlling the tension of the web in a printing press including two or more sets of nip rollers with deformable covers.
Web printing presses print a continuous web of material, such as paper. The web travels through nips formed by opposing nip rollers. The web is moved on its way by driven nip rollers which are driven by respective nip roller drivers.
Tension in the web must be maintained within a desired range in order to achieve smooth operation of the printing press. At the same time, the velocity of the web, and hence the rotational speed of nip rollers, must be held relatively constant to achieve good print product quality. Tension in a web span between two nips can be adjusted by controlling the speed of the nip roller driver in the downstream nip.
Multiple types of nip rollers have been used in conventional web printing presses. Some nip rollers were formed with a deformable surface layer such as urethane. Nip rollers with a deformable surface were found to provide less than ideal operation because of uneven ribbon-to-ribbon tension in upstream web spans.
As a result, nip rollers formed with a deformable surface such as microcellular foamed urethane were introduced (see, U.S. Patent Publication No. 2006/0157924 A1 published on Jul. 20, 2006 and incorporated herein by reference). Nip rollers with this type of deformable surface layer were found to overcome the uneven ribbon-to-ribbon tension problem of the earlier nip rollers. However, it was found that any nips with non-rigid covers have an effective gain that is a function of the tension difference across the nip roller, so that if the tension of the web downstream from the nip roller is changed, the tension of the upstream web will also change requiring an additional tension adjustment.
BRIEF SUMMARY OF THE INVENTIONAn object of the present invention is to provide a method and apparatus which allows for adjustment of the tension of a downstream span of web without affecting the tension of an upstream span of web.
The present invention provides a method for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set of deformable nip rollers driven by a separate driver, the web passing sequentially through each set of deformable nip rollers, each adjacent set of deformable nip rollers forming a web segment therebetween. A first characteristic of the driver of a downstream set of deformable nip rollers is adjusted to set the tension of a first web segment which is between the downstream set of deformable nip rollers and an upstream set of deformable nip rollers. Then, a first characteristic of the driver of the upstream set of deformable nip rollers is adjusted to maintain a constant tension on a second web segment which is immediately preceding the upstream set of deformable nip rollers.
In an alternative embodiment, a second characteristic of the second web segment is measured and the first characteristic of the driver of the upstream set of deformable nip rollers is adjusted based on the measurement of the second characteristic.
The present invention also provides an apparatus for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set of deformable nip rollers driven by a separate driver, the web passing sequentially through each set of deformable nip rollers, each adjacent set of deformable nip rollers forming a web segment therebetween. The apparatus includes a circuit for adjusting a first characteristic of the driver of a downstream set of deformable nip rollers to set the tension of a first web segment which is between the downstream set of deformable nip rollers and an upstream set of deformable nip rollers. The apparatus also includes a controller for adjusting a first characteristic of the driver of the upstream set of deformable nip rollers to maintain a constant tension on a second web segment which is immediately preceding the upstream set of deformable nip rollers.
In an alternative embodiment, the apparatus also includes a sensor for measuring a second characteristic of the second web segment and the controller adjusts the first characteristic of the driver of the upstream set of deformable nip rollers based on the measurement from the sensor.
The first characteristic may be the rotational speed of the driver. The second characteristic may be the tension of the second web segment, the speed of the second web segment, or the amount of torque in the driver of a set of deformable nip rollers immediately preceding the upstream set of deformable nip rollers.
The above and related objects, features and advantages of the present invention will be more fully understood by reference to the following detailed description of the presently preferred, albeit illustrative, embodiments of the present invention when taken in conjunction with the accompanying drawings wherein:
Nip rollers 20, 26 and 32 in
Upstream web span 16 is formed between nips 22 and 28, while downstream web span 18 is formed between nips 28 and 34. As one of ordinary skill in the art will readily recognize, additional nips may be provided in the printing press 10 within the context of the present invention, and the principles of this invention apply in that event as well. A tension sensor 92 directly measures the tension in upstream web span 16 and provides a corresponding output signal on line 93 to controller 70. Controller 70 also includes an input 60 which is used by an operator to set the tension of downstream web span 18 according to principles of the invention.
In the embodiment of
Although the embodiment of
While the present invention has been particularly shown and described with reference to the preferred embodiments and various aspects thereof, it will be appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the appended claims be interpreted as including the embodiments described herein, the alternatives mentioned above, and all equivalents thereto.
Claims
1. A method for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set of deformable nip rollers driven by a separate driver, the web passing sequentially through each set of deformable nip rollers, each adjacent set of deformable nip rollers forming a web segment therebetween, comprising the steps of:
- adjusting a first characteristic of the driver of a downstream set of deformable nip rollers to set the tension of a first web segment which is between the downstream set of deformable nip rollers and an upstream set of deformable nip rollers; and
- adjusting a first characteristic of the driver of the upstream set of deformable nip rollers to maintain a constant tension on a second web segment which is immediately preceding the upstream set of deformable nip rollers.
2. The method of claim 1, further comprising the step of:
- measuring a second characteristic of the second web segment; and
- wherein the step of adjusting a first characteristic of the driver of the upstream set of deformable nip rollers is based on the measurement of the second characteristic.
3. The method of claim 2, wherein the first characteristic is the rotational speed of the driver.
4. The method of claim 2, wherein the second characteristic is the tension of the second web segment.
5. The method of claim 2, wherein the second characteristic is the speed of the second web segment.
6. The method of claim 2, wherein the second characteristic is the amount of torque in the driver of a set of deformable nip rollers immediately preceding the upstream set of deformable nip rollers.
7. An apparatus for controlling web tension in a web printing press having a plurality of sets of deformable nip rollers, each set of deformable nip rollers driven by a separate driver, the web passing sequentially through each set of deformable nip rollers, each adjacent set of deformable nip rollers forming a web segment therebetween, comprising:
- means for adjusting a first characteristic of the driver of a downstream set of deformable nip rollers to set the tension of a first web segment which is between the downstream set of deformable nip rollers and an upstream set of deformable nip rollers; and
- a controller for adjusting a first characteristic of the driver of the upstream set of deformable nip rollers to maintain a constant tension on a second web segment which is immediately preceding the upstream set of deformable nip rollers.
8. The apparatus of claim 7, further comprising:
- a sensor for measuring a second characteristic of the second web segment; and
- wherein the controller adjusts the first characteristic of the driver of the upstream set of deformable nip rollers based on the measurement from the sensor.
9. The apparatus of claim 7, wherein the first characteristic is the rotational speed of the driver.
10. The apparatus of claim 8, wherein the sensor measures the tension of the second web segment.
11. The apparatus of claim 8, wherein the sensor measures the speed of the second web segment.
12. The apparatus of claim 8, wherein the sensor measures the torque in the driver of a set of deformable nip rollers immediately preceding the upstream set of deformable nip rollers.
Type: Application
Filed: Jan 22, 2009
Publication Date: Jul 22, 2010
Applicant: GOSS INTERNATIONAL AMERICAS, INC. (Durham, NH)
Inventors: Daniel Matthew Perdue (Rochester, NH), Douglas Joseph Dawley (Dover, NH), Michael Raymond Rancourt (Merrimack, NH)
Application Number: 12/357,718
International Classification: B65H 23/192 (20060101); B65H 23/188 (20060101); B65H 23/18 (20060101);