Electricity: motive power systems – With particular motor-driven load device – Tension-maintaining type of motor-control system
Reexamination Certificate
2002-08-30
2004-07-06
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
With particular motor-driven load device
Tension-maintaining type of motor-control system
C318S480000, C242S334000
Reexamination Certificate
active
06759816
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to tape drives, and more particularly to a magnetic recording tape drive with an improved system for detecting and controlling tape tension.
BACKGROUND OF THE INVENTION
In tape recording systems, such as reel-to-reel type magnetic recording tape drives, the tape tension and velocity are controlled to provide a stable recording speed as well as a stable distance between the recording head and the recording surface of the tape. In low performance tape drives with relatively low accelerations to bring the tape up to the desired velocity, direct measurement of tape tension is not required. This is because a tape tension signal can be derived from the motor torque vs. current characteristics for the supply and take-up motors and from the supply and take-up reel speeds, which are inversely proportional to the diameters of the tape packs on the tape reels.
A typical magnetic recording tape drive, wherein tape tension and velocity are controlled, is shown schematically in FIG.
1
. The tape drive includes a tape supply reel
15
containing tape pack
13
and driven by supply motor
16
, a tape take-up reel
17
containing tape pack
14
and driven by take-up motor
18
, a recording head
20
and guides,
22
,
24
for guiding the tape
25
past the recording head
20
. Tachometers
26
a
,
26
b
for the supply motor
16
and take-up motor
18
, respectively, continually sense the supply and take-up motor speeds. A controller
30
provides output signals
23
,
27
to control the motor currents to supply motor
16
and take-up motor
18
, respectively. An estimator
34
is used to provide the required tape tension signal
35
and tape velocity signal
37
which are input into controller
30
. The estimator
34
receives motor speed signals
31
,
33
from tachometers
26
a
,
26
b
respectively, and motor current signals
23
,
27
from controller
30
. The estimator
34
uses the motor speed inputs (to determine the diameters of the tape packs
13
,
14
) and the motor current inputs (with known motor torque vs. current characteristics) to estimate the tape tension, which is fed back as signal
35
into controller
30
. The estimator
34
also provides an estimate of tape velocity as signal
37
input to controller
30
. A tape tension control system that estimates tape pack diameters to control motor currents is described in U.S. Pat. No. 4,408,144.
Tape drives like those depicted in
FIG. 1
, such as the current linear-tape-open (LTO) tape drives, do not require direct measurement of tape tension and thus do not have a separate tape tension sensor. However, future generations of type drives, especially high performance tape drives with high acceleration to bring the tape up to the desired velocity, will require direct measurement of tape tension to handle the thinner tapes that will be used. Some tape drives, like the IBM 3590, use a fixed pin tape guide in the tape path and measure tape tension directly by measuring the air pressure between the tape and the fixed pin guide. This type of direct tape tension measurement is described in U.S. Pat. No. 4,842,177. However, in tape drives such as the IBM LTO tape drive that use rollers as tape guides in the tape path instead of fixed pins, it is not possible to measure air pressure between the tape and the rollers.
Other alternatives for directly measuring tape tension have been proposed that require physical contact with the tape and/or additional components in the tape path. These include tension arms, strain gauges on roller mounts, and optical measurement of tape displacement in a flat region of the tape path. The use of an optical sensor to measure tape displacement in a flat region of the tape path is described in “Vacuum Puffer Head to Prevent Tape Stick on Magnetic Head”,
IBM Technical Disclosure Bulletin
, May 1988, pp. 242-243 and “Tape Tension Detection”,
IBM Technical Disclosure Bulletin
, November 1983, pp. 2990-2991, both of which require the use of a vacuum region in the tape path, in Japanese published patent application JP-08122176A (May 17, 1996) that requires an air blower in the tape path, and in Japanese published patent application JP-2001035046A (Feb. 9, 2001) that measures tape width.
What is needed is tape drive with a tape tension sensor that does not require physical contact with the tape or additional rollers, guides or other components in the tape path.
SUMMARY OF THE INVENTION
The invention is a non-contact optical tape tension sensor for a tape drive. A light source directs an incident beam to the tape in a region of the tape path near where the tape bends. The amount of divergence of the reflected light is related to the curvature of the tape, and thus to the tape tension. The reflected light is passed through an aperture to a photodetector that detects the amount of the divergent beam passing through the aperture. The photodetector output is input to the tape drive controller that controls the currents to the supply and take-up motors to thereby maintain the tape tension within the desired range.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.
REFERENCES:
patent: 4408144 (1983-10-01), Lukes
patent: 4501642 (1985-02-01), Wells
patent: 4557435 (1985-12-01), Reishus
patent: 4842177 (1989-06-01), Callendar et al.
patent: 6543288 (2003-04-01), Blouin et al.
patent: 6564983 (2003-05-01), Ludwig
patent: 08122176 (1996-05-01), None
patent: 2001035046 (2001-02-01), None
“Vacuum Puffer Head to Prevent Tape Stick on Magnetic Head”, IBM Technical Disclosure Bulletin, May 1988, pp. 242-243.
“Tape Tension Detection”, IBM Technical Disclosure Bulletin, Nov. 1983, pp. 2990-2991.
Berthold Thomas R.
Johnson Daniel E.
Ro Bentsu
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