Winding – tensioning – or guiding – Material guide or guard – Fluid suspension
Reexamination Certificate
2000-02-29
2002-01-08
Mansen, Michael R. (Department: 3653)
Winding, tensioning, or guiding
Material guide or guard
Fluid suspension
C226S097100, C242S615200
Reexamination Certificate
active
06336608
ABSTRACT:
BACKGROUND—CROSS REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
1. Background Field of Invention
This invention applies to the computer magnetic tape data recorder product industry and more specifically to the development of the mechanical tape (media) path portion of the product. However it can be applied to any industry that rolls webs of any width onto reels for further processing or storage purposes.
2. Background Prior Art
A search of the U.S. Patent Office Patent Records does not reveal a Roller Guide Assembly of any design that incorporates an integral Centrifugal Air Pump within it's basic outline. The Durbeck U.S. Pat. No. 3,078,022, entitled FLUID BEARING, which was issued in 1960 was the only patent found that utilized a rotating pump to generate air flow to an Hydrostatic air bearing assembly. Looking at FIG.
1
-PRIOR ART one can see the use of a Reaction Air Pump in this patent to push air into the air bearing insides. This patent teaches the problem with air bearings that uncovering ports that feed the air film generated can affect the operation of the bearing supporting a film. It teaches the use of a vane-like wall that does not rotate with the pump itself. But rather it is selectively positioned to cover the air bearing ports that may be uncovered depending upon the wrap angle of the media. The wrap can change when media is transferred from reel to reel during the data recording or reproducing process. The outside air bearing surface does not rotate. The wall position is controlled by a separate mechanism to set it where desired. It is believed that this pump design will not easily push air into the air bearing because of long, narrow air passages shown in FIG.
1
. It is a very complicated design and there would be problems placing the design into any medium, or smaller sized, magnetic tape recorder. It is not obvious how to conceive of the Present Invention (described herein) based upon the Durbeck patent.
The only other patent that touches upon the Present Invention is the DAVISON et al U.S. Pat. No. 3,122,295, entitled WEB TRANSPORT, issued in 1964. The Davison Patent teaches driving
2
rotating capstans continuously using a single motor, belt and pulleys; in both CW and CCW directions at the same time. The function of the magnetic tape unit that uses this system is to allow the capstans to spin up to speed and hold this speed for the duration. Then a brake between the capstans is applied fully at all times. To start the media in either direction an external air pressure source is engaged to push down upon the media being supported by a Hydrodynamic Air Film generated by the spinning wheels. The two Capstan's outer surfaces that the air film is generated upon have ports and exterior grooves. There are also a ring of sub-tunnels leading from these ports to the atmosphere at the sides of the wheels. The Patent states that the air film is allowed to collapse when the overhead air pressure is applied so the friction would cause the media and the capstan of choice to move together. No vacuum or pressure head is generated inside these capstan wheels. It teaches that the ports on the Capstan surface are exposed to atmospheric pressure through the surface grooves that intercept the ports, down through the cross-holes to the side. It teaches the fact that Hydrodynamic air film can be generated on a moving roller shaped surface but can be easily deflated by a design described in the Davison Patent. It does very effectively teach the use of an external motor and belt system to continuously rotate the subject wheels continuously. It does not teach the generation of Hydrostatic Air Films.
There are many examples in the U.S. Patent Record that teach both Hydrodynamic Air Film effects and Hydrostatic Air Film effect, but not at the same time. It may be possible that the Davison Patent does generate some Hydrostatic Air Film while rotating but it is not obvious. There is no effort to make the internal holes large enough or the internal spaces large enough so air could easily flow from the sides to the surface ports. The surface grooves would destroy any Hydrostatic Air Film with the bleeding off the pressure that may be generated. In fact it is hard to understand how even a Hydrodynamic Air Film could be generated with this invention.
A discussion of the difference relative to Magnetic Tape Unit design of Hydrodynamic and Hydrostatic pressures is presented here as an aid to understand the Prior Art better. Hydrodynamic Guides are very smooth guiding surfaces with very small wrap angles of the media entering and exiting the guide. They self generate an air film by pulling air into the space between the media supported over the guide and the guide exterior surface. The Hydrodynamic Principle applies to both when the guide is fixed, or if it rotates as in a roller design. The pressure is positive for a time before exiting the guide and at the trailing end it goes negative for a short time before the media leaves the surface. This is shown in FIG.
6
-PRIOR ART. This figure shows a Hydrodynamic Guide supporting media traveling (V) across the top surface. Below, in
FIG. 9
is a plot of the pressure developed in the interface between the media and guide surface. One can see the vacuum being generated at the left side due the conservation of energy that takes place during this operation. This vaccum causes contact between the media and roller surface. Note that the Pressure Area Al Equals A
2
. The pressure head (P) generated with this kind of guide is a direct function of speed of the media (V), tension of media moving across (T), radius of the guide (R), and the wrap angle (W) of the media being stretched over the guide's top surface. An important aspect of using a Hydrodynamic Guide is to insure that the Wrap Angle is not too high. This would lead to stiction in high humidity conditions for the recorder and would produce operational errors for the machine. Also very small wrap angles will just fly the media over the guide surface without making contact. This might be preferable in tape unit design but probably not possible due to space limitations where the media must leave a reel and be wound up onto another reel in a very small space.
Hydrodynamic Guides are beneficial because of:
1) the Recorder Design can make severe direction changes when placing the tape path design into a small volume,
2) have been lower cost (up to this Invention) to use in low cost Tape Recorders, and
3) are simple in design and higher in reliability than air bearings (again up to this Invention).
A Hydrostatic Air Film is created when external pressure is applied to the insides of a guide with a number of small ports allowing the pressurized air to bleed to the top surface. If there were media with tension placed upon this surface then the bleeding air would be trapped and would develop a pressure. The U.S. Patent Record has numerous examples of Air Bearing design and improvements over the past 30 years, and it is a common, well know phenomena. The actual pressure generated in the space between the media and the guide outer surface is a direct function of the:
1) external supply pressure head,
2) the amount of air flow through the bearing ports due to leakage,
3) the tension applied to the media,
4) the wrap angle of the media,
5) are there any uncovered air bleed ports?, and
6) the amount of side leakage at the media edges.
In a Magnetic Tape Recorder it is preferable to use Hydrostatic Air Bearings as they allow:
1) little, or no, friction in the tape path,
2) do not engage the inertia properties of rollers that lead to tension spikes with starting and stopping the media,
3) do not have problems with any environmental conditions that would tend to produce humidity generated friction buildup between media and guide surfaces, and
4) will result in low power consumption for the entire recorder. Continuing with the Prior Art found in the U.S. Patent Record STAHLER's U.S. Pat. No. 4,337,885, entitled APPARATUS FOR GUIDING TAPE, and issued in 1982, is shown in
FIG. 3
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