SYSTEMS AND METHODS FOR PROVIDING DOCTOR BLADE HOLDERS WITH VIBRATION MITIGATION
A self-compensating tube assembly is disclosed for use in a doctor blade holder. The self-compensating tube assembly includes a tube including a membrane that encloses a liquid with a substantially invariable bulk modulus of elasticity, density and viscosity; and chatter responsive for providing any of monitoring means of blade chatter through pressure, damping of blade chatter, and minimizing blade chatter.
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The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/816,367 filed Apr. 26, 2013, the disclosure of which is hereby incorporated by reference in its entirety.
BACKGROUNDThe present invention generally relates to doctoring systems, and relates in particular to doctor blade holders that provide improved performance of doctoring systems during the production of tissue and paper.
In certain applications, it is desirable to provide Yankee coating and creping systems having improved reliability within the tissue industry. Yankee dryer blade holders are required to provide near uniform loading across the sheet width, while not causing maintenance issues such as Yankee surface chatter marks. Yankee dryer doctor blade holders are typically comprised of a working blade, and supporting components such as a backup blade and a self-compensating load tube.
U.S. Pat. No. 3,529,315 for example, discloses a liquid filled tube that has a means of assisting the working blade to conform to a roll crown by displacing liquid along its length, and the liquid, being provided at uniform pressure, should result in near uniform blade load. U.S. Pat. No. 3,529,315 also teaches us that the conforming tube may negotiate or follow a high spot on the roll circumference without affecting load to any significant extent. As discussed further below however, such a characteristic encourages low machine direction (MD) stiffness, which is, however, not desirable with regard to unwanted chatter.
U.S. Pat. Nos. 3,688,336; 3,711,888; 3,778,861 and 4,630,328 disclose holder inventions that utilize a liquid tube. U.S. Pat. No. 3,688,336 and U.S. Pat. No. 3,711,888 disclose a cartridge assembly of which the tube is a component. U.S. Pat. No. 3,778,861 discloses a protective metal sheath for the tube. U.S. Pat. No. 4,630,328 discloses a sealing means to address seal failures during the time period of that patent. The increasingly demanding challenges of Yankee doctoring systems, however, may not be met by the end sealing means that are disclosed in U.S. Pat. No. 4,630,328. If the seal fails, there is loss of liquid, and ingress of air is possible, reducing dynamic stiffness. Thus there becomes a need for improved sealing of the self compensating tube.
It is important that a liquid tube offer load self-compensation to negotiate crown, but it should also maintain suitable local and lengthwise MD stiffness in order to negotiate dynamic changes on the roll circumference. A Yankee blade holder with high dynamic stiffness over an extended frequency range will be able to negotiate a roll surface defect feature. Further, the absence of suitable stiffness will increase the likelihood of self-excited vibration leading to the creation of chatter marks.
The present commercially available tube has numerous features which influence local MD stiffness as well as overall (lengthwise) MD stiffness. The tube assembly is comprised of the tube and the enclosed liquid, and both of these contribute greatly to the MD stiffness; 1) the tube through its material elastic modulus and strength, along with its geometry (thickness, height, width, shape), and 2) the liquid through its bulk modulus of elasticity.
The operating conditions of Tissue machines are increasingly demanding as speed, temperature and loads increase, and Yankee hardness of surface coatings increase. Beyond the conventional approach of improved materials, there becomes a need for additional features in the tube to increase its dynamic stiffness and damping, while retaining the self-compensating features.
The presence of entrained air will reduce the effective bulk modulus of the liquid. Only a small percentage of air by volume will reduce the bulk modulus by as much as two orders of magnitude. Since the tube assembly stiffness is dictated primarily by development of pressure, a lowered bulk modulus is devastating on stiffness.
The tissue industry has placed more emphasis on improved performance of numerous coating and creping parameters. Thus there is a need for improved and additional means of measuring blade load behavior. A typical industry practice is to mount vibration sensors on the doctor beam. These locations however, are removed from the blade tip, and thus unique vibration signatures present in the blade tip may be undetected.
There remains a need therefore, for a system and method for measuring and/or mitigating vibration in certain doctor blade holder systems.
SUMMARYIn accordance with an embodiment, the invention provides a self-compensating tube assembly for use in a doctor blade holder. The self-compensating tube assembly includes a tube including a membrane that encloses a liquid with a substantially invariable bulk modulus of elasticity, density and viscosity; and chatter responsive means for providing any of monitoring of blade chatter through pressure, damping of blade chatter, and minimizing blade chatter.
In accordance with a further embodiment, the invention provides a self-compensating tube assembly for use in a doctor blade holder. The self-compensating tube assembly includes a tube including a membrane that encloses a liquid with a substantially invariable bulk m modulus of elasticity, density and viscosity; and dynamic means for enhancing dynamic stiffness and damping.
In accordance with a further embodiment, the invention provides a method of providing a self-compensating tube assembly for use in a doctor blade holder. The method includes the steps of: providing a tube including a membrane that encloses a liquid with substantially invariable bulk modulus of elasticity, density and viscosity; and providing any of monitoring of blade chatter through pressure, damping of blade chatter and minimizing of blade chatter
The following description may be further understood with reference to the accompanying drawings in which:
The drawings are shown for illustrative purposes only and are not to scale.
DETAILED DESCRIPTIONThe present invention is concerned with providing an improved self-compensating support element for a doctor blade system that operates at higher loads and promotes reduction of blade vibration during the production of tissue and paper. Devices of the invention further may be used as a process monitoring device, in particular as it applies to tissue production and Yankee chatter. Since the tube is in communication with the blade, applicants have discovered that the tube's pressure may be used as an indicator of time variant blade forces associated with chatter events.
Chatter is a dynamic event, involving dynamic motion of blade holder components. Damping, if introduced within degrees of freedom that are participating in the chatter event, will likely decrease motion and therefore decrease the magnitude of chatter. Introducing damping in the self-compensating tube, will likely reduce chatter for those cases in which the tube is part of the vibration mode participating in the chatter event. Conventional devices do not provide damping means nor any measurement using the tube. The tube provides a reactive force against a guide plate that varies along the cross machine direction (CD) to accommodate variations in load during tissue processing.
In the present invention, it is disclosed how to take advantage of the self-compensating element and implement means for proper tube assembly stiffness, blade vibration measurement, and blade vibration mitigation. The present invention provides an improved self-compensating tube for use in Yankee Dryer blade holders, that addresses shortcomings of present designs and adds additional benefits such as vibration monitoring and vibration mitigation means.
The self-compensating load tube assembly 26 includes a synthetic tube 28 that encloses a liquid 30 as shown in
Preferably the tube behaves very stiff in membrane behavior, less so in bending. To meet this, the tube thickness shall be generally thin, and may include fiber reinforcement added near the neutral axis of the tube wall, so as to maximize membrane stiffness and limit bending stiffness. In the limit, it is observed that too much bending stiffness, such as with a metal tube, will not allow for self-compensation; the tube will be too rigid.
Blade chatter is a dynamic event, and associated with it are time fluctuating forces. The addition of system damping would generally reduce chatter and chatter development, so if blade chatter involves a mode of which the tube is a part, chatter may be avoided or reduced. Typically, damping within the liquid may be provided via inertial restriction, or viscous restriction (including squeeze film damping effects). Inertial restriction would require substantial density (e.g., air not suitable), viscous restriction would require substantial viscosity.
Another embodiment of a self-compensating load tube assembly 66 in accordance with an embodiment of the invention includes separate volumes with inertial restrictors as shown in
In accordance with a further embodiment of the invention, a self-compensating load tube assembly 96 includes an outer tube 98, as well as two stacked internal narrower tubes 100, 102 as shown in
In accordance with still another embodiment of the invention, a self-compensating load tube assembly 116 is shown in
In accordance with a further embodiment on the invention, self-compensating load tube assembly 136 may provide squeeze film damping as shown in
In
The aforementioned embodiments utilize fluid transport across restrictors (either discrete or continuous) that invoke inertial or viscous resistance. There will be other configurations in addition to those shown, that would be consistent with the scope and spirit of the invention.
The tube assembly may be used to assist in process monitoring. Blade vibration may involve modes that introduce motion at the self-compensating tube, as described above. Such dynamic motion will create fluctuating pressure inside the tube assembly. This pressure may be measured using a dynamic pressure sensor, suitable to extremely high frequency.
Contemporary load levels also challenge the sealing means at the tube ends, which currently utilizes a crimped elastomer insert, and prior to that crimped metal insert and heat sealing.
In accordance with another embodiment, a self-compensating load tube assembly 296 that includes an outer tube 298 as well as sealed ends 300. With reference to
Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the present invention.
Claims
1. A self-compensating tube assembly for use in a doctor blade holder, said self-compensating tube assembly comprising:
- a tube including a membrane that encloses a liquid with a substantially invariable bulk modulus of elasticity, density and viscosity; and
- chatter responsive means for providing any of monitoring of blade chatter through pressure, damping of blade chatter, and minimizing blade chatter.
2. The self-compensating tube assembly as claimed in claim 1, wherein said tube includes directional fiber reinforcement.
3. The self-compensating tube assembly as claimed in claim 1, wherein said self-compensating tube assembly includes dynamic means for enhancing dynamic stiffness and damping.
4. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping functions by inertial restriction.
5. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping functions by viscous restriction.
6. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping includes at least one inner tubular component.
7. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping includes at least one restrictor that limits liquid flow.
8. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping functions by squeeze film damping.
9. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping functions by viscous shear.
10. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping includes open cell material.
11. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping includes at least two inner tubular components, separated by restrictors.
12. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and provides damping via at least one of inertial or viscous restriction.
13. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping includes parallel compartments in the cross-machine direction.
14. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping includes discrete compartments along the cross-machine direction.
15. The self-compensating tube assembly as claimed in claim 3, wherein said means for enhancing dynamic stiffness and damping includes a magnetic field means inserted in adjacent blade holder components, and wherein the liquid is a magnetorheological fluid.
16. The self-compensating tube assembly as claimed in claim 1, wherein said chatter responsive means includes dynamic pressure sensors that are attached to either or both ends for dynamic pressure sensing.
17. The self-compensating tube assembly as claimed in claim 1, wherein ends of said tube are sealed by clamped means for clamping the ends of the tube.
18. The self-compensating tube assembly as claimed in claim 1, wherein ends of said tube are sealed by using o-rings.
19. A self-compensating tube assembly for use in a doctor blade holder, said self-compensating tube assembly comprising:
- a tube including a membrane that encloses a liquid with a substantially invariable bulk modulus of elasticity, density and viscosity; and
- dynamic means for enhancing dynamic stiffness and damping.
20. A method of providing a self-compensating tube assembly for use in a doctor blade holder, said method comprising the steps of:
- providing a tube including a membrane that encloses a liquid with substantially invariable bulk modulus of elasticity, density and viscosity; and
- providing any of monitoring of blade chatter through pressure, damping of blade chatter and minimizing of blade chatter.
Type: Application
Filed: Apr 28, 2014
Publication Date: Mar 19, 2015
Applicant: Kadant Inc. (Westford, MA)
Inventors: Robert P. Johnson (Sutton, MA), David Leeman (Worcester, MA), Allen Brauns (Sturbridge, MA)
Application Number: 14/263,700
International Classification: D21G 7/00 (20060101); F16F 9/50 (20060101); D21G 3/00 (20060101); F16F 9/30 (20060101);