Rotational inductive accelerometer

Details Rotational inductive accelerometer Rotational inductive accelerometer

2000-03-24

2001-11-20

Moller, Richard A. (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

Reexamination Certificate

active

06318176

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a disc drive system. More particularly, the present invention relates to an apparatus for detecting and measuring rotational vibrations impacting a disc drive in order to improve track following.
BACKGROUND OF THE INVENTION
In a contemporary disc drive, a transducer records information onto a magnetic disc in concentric tracks. Each piece of data that is recorded on the magnetic disc is assigned a location. When the information is needed, the transducer must return to the exact location and track where the piece of data has been stored.
As track densities have increased, disc drives have become more sensitive to vibrations which deflect the transducer from the track it follows or which cause the magnetic disc to vibrate beneath the transducer. In effect, vibrations within the disc drive cause the disc to move or slip underneath the transducer. Motion of the magnetic disc relative to the transducer can cause the transducer to slip further along the track producing read/write errors. Furthermore, a contemporary disc drive needs to meet exacting standards with respect to the speed with which data can be accessed and recorded. Movement of the magnetic disc relative to the transducer slows down both information retrieval times and data recording times for the system. There exists a need to detect and compensate for these vibrations before they cause slipping of the magnetic disc.
Rotational accelerations as low as 21 radians/second
2
can cause track slipping. One source of rotational vibration involves disc drives stacked in close proximity to each other. An actuator arm controls the movement of the transducer relative to the magnetic disc for each disc drive. During a seeking mode, the actuator arm of a disc drive will move the transducer rapidly over the surface of the magnetic disc. The rapid movement of the actuator arms in such close proximity to other disc drives can cause rotational vibrations which affect the track following performance of nearby disc drives. When dozens of disc drives are stacked together, the effect can be significant.
Several solutions to this problem have been suggested. Dedicated servo surface systems attempt to maintain constant information regarding the transducer's position relative to the magnetic disc by dedicating a portion of the magnetic disc space to storing this information. This information is then used by a servo control system to compensate for track skipping during use. This solution suffers from the obvious disadvantage of consuming disk space which would otherwise be available for other data.
Embedded servo surface systems embed periodic reference points on the surface of the magnetic disk to provide the system with position information. This system requires less disc surface space than the dedicated servo surface systems, but they do not provide constant position information. Embedded reference points only provide position information periodically as the transducer passes over a reference point. Therefore, embedded servo surface systems do not provide instantaneous and constant position information.
SUMMARY OF THE INVENTION
The use of accelerometers to detect and measure rotational vibrations offers the advantage of requiring little magnetic disc space while at the same time providing constant information to the servo control system enabling the servo control to compensate for rotational vibrations.
The present invention relates to an inductive accelerometer for detecting and measuring rotational vibrations in a disc drive. In accordance with one embodiment of the present invention there is provided a rotational mass disposed on a pin having two ends. The pin is held at its ends by a top frame member and a bottom frame member. Both frame members are secured to the hard disc drive. The pin and rotational mass act as a torsional mass-spring system. Disposed on the rotational mass are ferro-magnetic blocks. The ferro-magnetic blocks overlap the bottom frame member. Together the rotational mass, the ferro-magnetic blocks, and the bottom frame member make a path for magnetic flux. A wire coil is disposed around the bottom frame member. Rotational accelerations cause the rotational mass to twist the pin and rotate momentarily relative to the bottom frame member. This rotation causes a portion of the ferro-magnetic blocks not to overlap the bottom frame member. A change in the magnetic flux will result which induces a change in the inductance of the wire coil. The change in inductance of the wire coil is proportional to the rotational acceleration applied to the hard disc drive. By measuring the change in inductance of the wire coil, the system can supply a servo control system with information necessary to compensate for the rotational acceleration so detected.


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