Winding – tensioning – or guiding – Unwinding and rewinding a machine convertible information... – Carrier speed or tension control
Reexamination Certificate
1999-11-15
2001-10-23
Nguyen, John Q. (Department: 3653)
Winding, tensioning, or guiding
Unwinding and rewinding a machine convertible information...
Carrier speed or tension control
C242S334500, C360S074100
Reexamination Certificate
active
06305628
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to reel-to-reel tape drive systems and more particularly to control of such a system during a period in which application of normal power has been interrupted.
BACKGROUND
The use of tape drive systems as nonvolatile data storage for archival purposes, as well as for retrieval for data processing, has become increasingly commonplace. A tape drive system typically interacts with, and interfaces to, a computer or PC or the like through an application specific integrated circuit (ASIC) incorporated within or associated with the computer.
FIG. 1
is a simplified illustration of a tape path mapping between take-up and supply reels. The tape
18
passes through an assembly
16
of read and write heads structurally arranged to appropriately configure the tape path between supply reel
32
and take-up reel
34
. As indicated by the arrows, the tape can be driven bidirectionally so that each reel can perform both supply and take-up functions.
As can be appreciated, the requirements for accuracy in reading and writing of data on tape are much more critical than in analog applications in which tape recording and playback provide audio or video presentations. While a tape error in the latter systems may result in a momentary glitch in audio or video that may not even be noticed, the density of data bit storage and necessity for negligible bit rate error imposes potential disastrous effects on the data processing capability if a tape error should occur. Accuracy and consistency of the drive rate at which the tape traverses the read and write heads are of ultimate importance. Tape drive systems for data storage and retrieval thus have become highly sophisticated in controlling the motor drive characteristics of the drive motors for each reel motor, in maintaining appropriate tension in the tape path, and in controlling threading of the tape throughout the path to avoid diversion of the tape from its path position or breakage of the tape. These measures ensure accuracy in accessing the appropriate point in the tape during start-up, running and stopping conditions. During normal operations, precision stopping of the tape is accomplished by increasing back tension on the supply reel while reducing forward tension on the take up reel.
Stopping tape movement in a reel to reel application provides unique difficulties during a power loss situation. The implementation of braking by using motor back emf alone, during such a situation, does not necessarily prevent the loss of tape path integrity. Braking by using back emf on the supply reel is ineffective if the momentum of the supply reel is significantly greater than that of the take-up reel. Such an inequality would occur if the radius of the tape accumulated on the supply reel at the time of power interruption is greater than the radius of the tape accumulated on the take-up reel. The torque provided by braking using motor back emf on the supply reel would not then be sufficient to balance the rates of deceleration of both reels. As the take-up reel will be stopped sooner than the supply reel, the appropriate tension along the tape path can not be maintained. After the take-up reel is stopped, the continued rotation of the supply reel causes a tape run out, loosening tension in the tape path and subjecting the tape to destruction.
The need exists to maintain tape path integrity, in the event of power failure, with minimal or no tape becoming loosened, either around the reel which supplies the tape, the reel which takes up the tape, or the tape path from reel to reel, other than an amount which might occur during normal operations.
DISCLOSURE OF THE INVENTION
The present invention fulfills the above-described needs by stopping the movement of tape in a reel-to-reel tape system during a power loss situation without overrun by one of the tape reels and without causing undue stress upon the tape itself. These and other advantages of the invention are satisfied, at least in part, through the use of motor back emf for dynamically braking the supply reel while also driving the take-up reel in the direction of rotation in which it operated when the power source was discontinued. An appropriate amount of tension is maintained on the tape until the tape motion has come to a complete stop. The degree to which the take-up reel is driven during this time is dependent on the relative momentum, and tape radius, between the two reels as determined by appropriate sensing means. The necessary systems involved in tape movement are kept alive until the tape is stopped.
In one preferred embodiment, a capacitor large enough to supply the power needed to provide current to the power bridge of the motor drivers and other necessary circuitry is provided. The capacitor is charged upon power up of the drive and is not tapped unless and until the normal supply voltage of the motor drivers is turned off. At that point the system driving the motors will be powered by the capacitor. The supply reel motor is braked by the use of back emf voltage and the take-up reel motor is driven forward. The take-up reel motor is provided with optimum current to take up the loose tape that otherwise would have been produced in the tape path and around the reels, thus preventing a hazardous situation. The radii of the two reels, the direction of travel, and the speed at which the tape is moving contribute to determining which reel will be placed in either a dynamically braked, coast, or feed forward mode. In an alternative embodiment, a battery backup is provided to supply the take-up reel driving current upon loss of the primary power supply.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
REFERENCES:
patent: 3873896 (1975-03-01), Jennings
Redhead Kempton W.
Thompson Mark R.
McDermott & Will & Emery
Nguyen John Q.
Seagate Removable Storage Solutions LLC
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