1. A rust-preventive steel sheet for fuel tanks, excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.01% of C, up to 0.2% of Si, less than 0.6% of Mn, up to 0.04% of P, up to 0.1% of soluble Al, up to 0.01% of N, at least one of Ti and Nb in a total amount of at least the atomic equivalent of (CN) and up to 0.2%, 0.0001 to 0.0030% of B, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet.
2. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.01% of C, up to 0.2% of Si, less than 0.6% of Mn, up to 0.04% of P, up to 0.1% of soluble Al, up to 0.01% of N, one or at least two of Ti and Nb in a total amount of at least the atomic equivalent of (CN) and up to 0.2%, 0.0003 to 0.0030% of B, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet.
3. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.003% of C, up to 0.1% of Si, up to 0.4% of Mn, up to 0.02% of P, up to 0.1% of soluble Al, up to 0.01% of N, at least one of Ti and Nb in a total amount of at least the atomic equivalent of (CN) and up to 0.2%, 0.0003 to 0.0030% of B, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet.
4. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.003% of C, up to 0.03% of Si, up to 0.3% of Mn, up to 0.02% of P, up to 0.006% of soluble N, up to 0.1% of Ti, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet,
the steel sheet showing a total elongation of at least 45% after plating.
5. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 4, wherein the steel sheet comprises at least one element selected from the following group in the following amounts: 0.5 to 7% of Cr, 0.05 to 0.5% of Cu, 0.05 to 0.5% of Ni and 0.05 to 0.5% of Mo.
6. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 5, wherein the amount of the Al plating layer is up to 50 gm2 per side.
7. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises a steel sheet substrate for plating, an AlFeSi intermetallic compound layer thereon and a plating layer comprising Al and unavoidable impurities on the intermetallic compound layer, the difference between the immersion potential of the steel sheet substrate for plating and that of the intermetallic compound layer in a solution comprising 100 ppm of formic acid and the balance water and unavoidable impurities being up to 0.35 V.
8. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to claim 7, wherein the AlSi plating layer comprises 2 to 13% of Si, 0.5 to 5% in total of one or at least two elements selected from the group consisting of Sn, Zn, Sb and Bi, and the balance Al and unavoidable impurities.
9. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 8, wherein the rust-preventive steel sheet comprises a chromate coating layer in an amount of 5 to 100 mgm2 as Cr per side at least on one side of the Al plating layer.
10. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 9, wherein the rust-preventive steel sheet comprises an organic resin coating layer on the top surface at least on one side thereof.
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. An optical pickup for recording andor reproducing data with respect to a multilayer recording medium having a plurality of recording layers, the optical pickup comprising:
a light source emitting a beam having a predetermined wavelength;
a diffraction unit separating the beam emitted from the light source into a main beam and a sub-beam; and
a photo-detector having a main photodetector, detecting the main beam reflected from the multilayer recording medium, and a sub-photodetector detecting the sub-beam,
wherein the main photodetector and the sub-photodetector are separated a predetermined distance Ds from each other so that a beam spot formed by the beam reflected from a defocus recording layer of the multilayer recording medium is not detected by the sub-photodetector, and
wherein the predetermined distance Ds between the main photodetector and the sub-photodetector satisfies the following inequality:
Ds\u2267A2+QR
wherein \u201cR\u201d is a radius of the beam spot formed by the beam reflected from the defocus recording layer, \u201cA\u201d is a width of the sub-photodetector, and \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, and
wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
2. The optical pickup as claimed in claim 1, wherein the radius R satisfies the following equation:
R
=
2
\xd7
d
sp
n
sp
\xd7
M
\xd7
NA
,
wherein, \u201cdsp\u201d is a thickness of a spacer layer between the defocus recording layer and a recording layer that is subject to recording andor reproduction, \u201cnsp\u201d is a refractive index of the spacer layer, \u201cM\u201d is a magnifying power of the optical pickup, and \u201cNA\u201d is a numerical aperture of an objective lens used in the optical pickup.
3. The optical pickup as claimed in claim 1, wherein the main photodetector is a four-section photodetector.
4. The optical pickup as claimed in claim 1, wherein the sub-photodetector is a two-section photodetector.
5. The optical pickup as claimed in claim 1, further comprising a calculation portion calculating signals detected by the main photodetector and the sub-photodetector and outputting a differential push-pull signal.
6. A method of setting an optical pickup including a light source emitting a beam having a predetermined wavelength, a diffraction unit separating the beam emitted from the light source into a main beam and a sub-beam, and a photodetector having a main photodetector, detecting the main beam reflected from a multilayer recording medium, and a sub-photodetector detecting the sub-beam, the method comprising:
setting a distance Ds between the main photodetector and the sub-photodetector to satisfy the following inequality, to prevent a beam spot formed by the main beam from being detected by the sub-photodetector:
D
s
\u2265
A
2
+
QR
,
wherein \u201cR\u201d is a radius of the beam spot formed by the beam reflected from a defocus recording layer, \u201cA\u201d is a width of the sub-photodetector, and \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, and
wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
7. The method as claimed in claim 6, wherein the radius R satisfies the following equation:
R
=
2
\xd7
d
sp
n
sp
\xd7
M
\xd7
NA
,
wherein, \u201cdsp\u201d is a thickness of a spacer layer between the defocus recording layer and a recording layer that is subject to recording andor reproduction, \u201cnsp\u201d is a refractive index of the spacer layer, \u201cM\u201d is a magnifying power of the optical pickup, and \u201cNA\u201d is a numerical aperture of an objective lens used in the optical pickup.
8. An optical pickup for use with a multilayer recording medium having a plurality of recording layers that are subject to recording andor reproduction, the optical pickup comprising:
a photodetector having a main photodetector and a sub-photodetector, wherein, when a distance between the main photodetector and the sub-photodetector is Ds, the distance Ds satisfies the following inequality:
d
sp
\u2264
(
D
s
–
A
2
)
\xd7
n
sp
2
\u2062
Q
\xd7
M
\xd7
NA
,
wherein \u201cA\u201d is a width of the sub-photodetector, \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, \u201cnsp\u201d is a refractive index of a spacer layer between the plurality of recording layers, \u201cM\u201d is a magnifying power of the optical pickup, and \u201cNA\u201d is a numerical aperture of an objective lens used for the optical pickup.
9. The optical pickup as claimed in claim 8, wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
10. The optical pickup as claimed in claim 8, wherein the optical pickup performs a tracking servo control using a differential push-pull method.
11. The optical pickup as claimed in claim 9, wherein the coefficient indicating the allowable range of the DC offset is determined based on the range of the DC offset of the sub-push-pull signal.
12. The optical pickup as claimed in claim 1, wherein the light source is configured to emit a beam in a blue wavelength range.
13. The optical pickup as claimed in claim 1, wherein the optical pickup uses a differential push-pull (DPP) method for tracking servo control.
14. The optical pickup as claimed in claim 2, wherein the numerical aperture of the objective lens is approximately 0.85.
15. The method of claim 6, comprising detecting a radial tilt signal from the multilayer recording medium, preventing crosstalk created by the beam reflected from the defocus layer.
16. An optical pickup for recording andor reproducing data with respect to a multilayer recording medium having a plurality of recording layers, the optical pickup comprising:
a light source emitting a beam having a predetermined wavelength;
a diffraction unit separating the beam emitted from the light source into a main beam and at least one sub-beam; and
a photodetector having a main photodetector, detecting the main beam reflected from the multilayer recording medium, and at least one sub-photodetector detecting the at least one sub-beam,
wherein the main photodetector and the at least one sub-photodetector are separated a predetermined distance from one another preventing a defocus spot, formed by the beam reflected by a defocus recording layer adjacent to a recording layer that is subject to recording andor reproduction, from being detected by the at least one sub-photodetector, and
wherein an outer border of the defocus spot is tangential to an outer area of the sub photodetector that is not contacted by the sub-beam, and
wherein the predetermined distance between the main photodetector and the at least on sub-photodetector satisfies the following inequality:
Ds\u2267A2\u2212QR
wherein \u201cR\u201d is a radius of the beam spot formed by the beam reflected from the defocus recording layer, \u201cA\u201d is a width of the sub-photodetector, and \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, and
wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
17. The optical pickup as claimed in claim 16, wherein the radius R of the beam spot satisfies the following equation:
R
=
2
\u2a2f
d
sp
n
sp
\u2a2f
M
\u2a2f
NA
,
wherein, \u201cdsp\u201d is a thickness of a spacer layer between the defocus recording layer and a recording layer that is subject to recording andor reproduction, \u201cnsp\u201d is z refractive index of the spacer layer, \u201cM\u201d is z magnifying power of the optical pickup, and \u201cNA\u201d is z numerical aperture of an objective lens used in the optical pickup.
18. The optical pickup as claimed in claim 16, wherein the DC offset of the sub-push-pull signal decreases as the predetermined distance between the main photodetector and the at least one sub-photodetector increases.