1. A bistable liquid crystal device comprising: a first cell wall and a second cell wall enclosing a layer of nematic liquid crystal material; electrodes on at least one cell wall for applying an electric field across at least some of the liquid crystal material; a grating alignment structure on the inner surface of the first cell wall; a thin film coating of a polymeric material locally on the said grating alignment structure but not on the alignment structure of the second cell wall, a surface of the thin film coating of the polymeric material contacting the liquid crystal material and substantially insoluble therein; the arrangement being such that two stable molecular configurations can exist within the nematic layer in response to suitable electrical signals applied to the electrodes.
2. A device as claimed in claim 1, wherein the said polymeric material is chemically different from the material of the grating alignment structure.
3. A device as claimed in claim 1, wherein the inner surface of the second cell wall includes a similar or identical grating alignment structure to that on the first wall but without the thin film polymeric coating.
4. A device as claimed in claim 3, wherein the polymeric material is a glassy or crystalline material at the operating temperature range of the device.
5. A device as claimed in claim 3, wherein the polymeric material has a glass transition temperature above 30.degree. C.
6. A device as claimed in claim 3, wherein the polymeric coating is polymerised ethoxylated bisphenol A diacylate.
7. A device as claimed in claim 3, wherein the grating alignment structure on both walls has a grating depth less than 1 .mu.m.
8. A device as claimed in claim 7, wherein the grating depth on both walls is in the range 100 to 600 nm.
9. The device of claim 1 wherein the thin film polymer layer has a higher resistivity than the liquid crystal material in the volume of a cell of the device so that in response to an electric field applied to the cell, the applied field is concentrated in the region of the thin film polymer layer to enable breaking anchoring of molecules in the liquid crystal material in the cell to the thin film surface in response to a smaller voltage applied to the cell than if the thin film polymer were not on the grating alignment structure.
10. A device as claimed in claim 1, wherein the inner surface of the second cell wall includes a similar or identical grating alignment structure to that on the first wall but without the thin film polymeric coating, the thin film polymer layer having a higher resistivity than the liquid crystal material in the volume of a cell of the device so that in response to an electric field applied to the cell, the applied field is concentrated in the region of the thin film polymer layer to enable breaking anchoring of molecules in the liquid crystal material in the cell to the thin film surface in response to a smaller voltage applied to the cell than if the thin film polymer were not on the grating alignment structure.
11. A bistable liquid crystal display device comprising a first cell wall and a second cell wall enclosing a layer of nematic liquid crystal material; electrodes on both cell walls for applying an electric field across at least some of the liquid crystal material; substantially identical grating alignment structures formed on the inner surface of both cell walls; and a coating of a thin film polymeric material (a) locally on the alignment structure of the first cell wall but not on the alignment structure of the second cell wall, and (b) in contact with the liquid crystal material; the arrangement being such that two stable molecular configurations can exist within the nematic layer in response to suitable electrical signals applied to the electrodes.
12. A device as claimed in claim 11, wherein the polymeric material is a glassy or crystalline material at the operating temperature range of the device.
13. The device of claim 11 wherein the thin film polymer has a higher resistivity than the liquid crystal material in the volume of a cell of the device so that in response to an electric field applied to the cell, the applied field is concentrated in the region of the thin film polymer layer to enable breaking anchoring of molecules in the liquid crystal material in the cell to the thin film surface in response to a smaller voltage applied to the cell than if the thin film polymer were not on the grating alignment structure.
14. A bistable liquid crystal display device comprising a first cell wall and a second cell wall enclosing a layer of nematic liquid crystal material; electrodes on both cell walls for applying an electric field across at least some of the liquid crystal material; a grating alignment structure formed on the inner surface of the first cell wall; and a coating of a thin film polymeric material locally on the alignment structure of the first cell wall but not on the alignment structure of the second cell wall, the coating of polymeric material being in contact with the liquid crystal material, the polymeric material being crystalline or glassy at the operating temperature range of the device; the arrangement being such that two stable molecular configurations can exist within the nematic layer in response to suitable electrical signals applied to the electrodes.
15. A device as claimed in claim 14, wherein the polymeric coating is substantially insoluble in the liquid crystal material.
16. A device as claimed in claim 14, wherein the polymeric material has a glass transition temperature above 30.degree. C.
17. A device as claimed in claim 14, wherein the grating alignment structure has a depth less than 1 .mu.m.
18. A device as claimed in claim 17, wherein the grating depth is in the range 100 to 600 nm.
19. The device of claim 14 wherein the thin film polymer has a higher resistivity than the liquid crystal material in the volume of a cell of the device so that in response to an electric field applied to the cell, the applied field is concentrated in the region of the thin film polymer layer to enable breaking anchoring of molecules in the liquid crystal material in the cell to the thin film surface in response to a smaller voltage applied to the cell than if the thin film polymer were not on the grating alignment structure.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method for detecting the onset of hard disk drive failure, comprising:
measuring vibrations from the hard disk drive to produce one or more vibration signals during an idle phase for the hard disk drive;
generating a vibration signature for the hard disk drive from the measured vibration signals;
determining if the vibration signature indicates the onset of hard disk failure by comparing the vibration signature with a reference vibration signature for the hard disk drive, and
if so, generating a warning or taking a remedial action.
2. The method of claim 1, wherein generating the vibration signature for the hard disk drive from the measured vibration signals involves:
phase-aligning the vibration signals;
computing the average of the vibration signals;
computing an envelope for the average of the vibration signals; and
computing the Fourier transform of the envelope for the average of the vibration signals.
3. The method of claim 2, wherein computing the average of the vibration signals involves:
computing the average of the vibration signals;
discarding two vibration signals that are farthest from the average; and
computing the average of the vibration signals without the two discarded vibration signals.
4. The method of claim 2, wherein computing the envelope for the average of the vibration signals involves:
computing the Hilbert transform of the average of the vibration signals to produce an analytic vibration signal; and
computing the envelope for the analytic vibration signal.
5. The method of claim 1, wherein prior to measuring the vibration signals, the method further comprises:
generating the reference vibration signature for the hard disk drive; and
storing the reference vibration signature for the hard disk drive for future comparison with vibration signatures generated during subsequent operation of the hard disk drive.
6. The method of claim 1, wherein determining if the vibration signature indicates the onset of hard disk failure involves determining if a difference between the vibration signature and the reference vibration signature is greater than a tolerance.
7. The method of claim 1, wherein the vibration signals are measured by an accelerometer.
8. An apparatus for detecting the onset of hard disk drive failure, comprising:
a hard disk drive;
an accelerometer; and
a failure-detection mechanism;
wherein the failure-detection mechanism is configured to:
measure vibrations from the hard disk drive to produce one or more vibration signals during an idle phase for the hard disk drive;
generate a vibration signature for the hard disk drive from the measured vibration signals;
determine if the vibration signature indicates the onset of hard disk failure by comparing the vibration signature with a reference vibration signature for the hard disk drive, and
if so, to generate a warning or take a remedial action.
9. The apparatus of claim 8, wherein while generating the vibration signature for the hard disk drive from the measured vibration signals, the failure-detection mechanism is configured to:
phase-align the vibration signals;
compute the average of the vibration signals; compute an envelope for the average of the vibration signals; and to
compute the Fourier transform of the envelope for the average of the vibration signals.
10. The apparatus of claim 9, wherein while computing the average of the vibration signals, the failure-detection mechanism is configured to:
compute the average of the vibration signals;
discard two vibration signals that are farthest from the average; and to
compute the average of the vibration signals without the two discarded vibration signals.
11. The apparatus of claim 9, wherein while computing the envelope for the average of the vibration signals, the failure-detection mechanism is configured to:
compute the Hilbert transform of the average of the vibration signals to produce an analytic vibration signal; and to
compute the envelope for the analytic vibration signal.
12. The apparatus of claim 8, wherein prior to measuring the vibration signals, the failure-detection mechanism is configured to:
generate the reference vibration signature for the hard disk drive; and to
store the reference vibration signature for the hard disk drive for future comparison with vibration signatures generated during subsequent operation of the hard disk drive.
13. The apparatus of claim 8, wherein while determining if the vibration signature indicates the onset of hard disk failure, the failure- detection mechanism is configured to determine if a difference between the vibration signature and the reference vibration signature is greater than a tolerance.
14. The apparatus of claim 8, wherein the vibration signals are measured by an accelerometer.
15. A computer system for detecting the onset of hard disk drive failure, comprising:
a hard disk drive;
an accelerometer; and
a failure-detection mechanism;
wherein the failure-detection mechanism is configured to:
measure vibrations from the hard disk drive during an idle phase for the hard disk drive to produce one or more vibration signals;
generate a vibration signature for the hard disk drive from the measured vibration signals;
determine if the vibration signature indicates the onset of hard disk failure by comparing the vibration signature with a reference vibration signature for the hard disk drive, and
if so, to generate a warning or take a remedial action.
16. The computer system of claim 15, wherein while generating the vibration signature for the hard disk drive from the measured vibration signals, the failure-detection mechanism is configured to:
phase-align the vibration signals;
compute the average of the vibration signals;
compute an envelope for the average of the vibration signals; and to
compute the Fourier transform of the envelope for the average of the vibration signals.
17. The computer system of claim 16, wherein while computing the average of the vibration signals, the failure-detection mechanism is configured to:
compute the average of the vibration signals;
discard two vibration signals that are farthest from the average; and to
compute the average of the vibration signals without the two discarded vibration signals.
18. The computer system of claim 16, wherein while computing the envelope for the average of the vibration signals, the failure-detection mechanism is configured to:
compute the Hilbert transform of the average of the vibration signals to produce an analytic vibration signal; and to
compute the envelope for the analytic vibration signal.