1. Method for controlling an optical disc drive apparatus (1), the apparatus comprising:
an optical system (30) for scanning a disc (2), comprising:
light beam generating means (31) adapted to generate a plurality of N optical beams (32(i));
means (33, 34, 37) for focusing said beams (32(i)) in respective focus spots (F(i));
at least one adjustable member (34) for axially displacing said focus spots (F(i));
the method comprising the step of:
calculating an optimum setting (ZOPTIMUM) for the adjustable member (34), such that the out-of-focus condition for the optical system (30) as a whole, i.e. all beams (32(i)) considered together, is as small as possible.
2. Method according to claim 1, wherein the adjustable member (34) is an axially displaceable objective lens.
3. Method according to claim 1, wherein the out-of-focus condition for the optical system (30) as a whole is defined as MAX(\u0394z(i)),
wherein \u0394z(i) indicates the axial distance between the actual position of the i-th focus spot (F(i)) and the ideal position of the i-th focus spot (F(i)),
and wherein MAX(\u0394z(i)) indicates the maximum value of the collection of values \u0394z(i).
4. Method according to claim 1, wherein the focus spots (F(i)) are located in a focal plane (FP) intersecting the optical axis at a position z0;
wherein N is an odd number;
and wherein the optimum setting (ZOPTIMUM) for the adjustable member (34) satisfies the formula
ZOPTIMUM\u2212z0=\u2212(N\u22121)2\xb7d2(16R)
wherein R indicates a radius of curvature of the focal plane (FP) near the optical axis.
5. Method according to claim 1, wherein the focus spots (F(i)) are located in a focal plane (FP) intersecting the optical axis at a position z0;
wherein N is an even number;
and wherein the optimum setting (ZOPTIMUM) for the adjustable member (34) satisfies the formula
ZOPTIMUM\u2212z0=\u2212(N2\u22122N+2)\xb7d2(16R)
wherein R indicates a radius of curvature of the focal plane (FP) near the optical axis.
6. Method according to claim 1, wherein the position of the adjustable member (34) is controlled to be substantially equal to the said optimum setting (ZOPTIMUM)
7. Method according to claim 1, the method further comprising the step of:
calculating an optimum beam number (mOPT), such that the out-of-focus condition for the optical system (30) as a whole, i.e. all beams (32(i)) considered together, is as small as possible when this specific optical beam is in an accurate focus condition.
8. Method according to claim 1;
wherein N is an odd number larger than 3;
and wherein an optimum beam number (mOPT) satisfies the formula
mOPT=\xb1INTEGERSQUARE{(N\u22121)(2\u221a2)}
wherein the function y=INTEGERSQUARE{x} is defined as the integer y whose square y2 is closest to x2;
and wherein m=0 corresponds to the central beam.
9. Method according to claim 1, wherein N=3, and wherein an optimum beam number mOPT=0 or wherein mOPT=\xb11
10. Method according to claim 1;
wherein N is an even number larger than 4;
and wherein an optimum beam number (mOPT) satisfies the formula
mOPT=\xb1INTEGERROUND{N\xb7(N\u22122)8}
wherein the function z=INTEGERROUND{x} is defined as the integer z for which z\xb7(z\u22121) is closest to x;
and wherein m=\xb11 corresponds to the inner beams.
11. Method according to claim 1, wherein N=4, and wherein an optimum beam number mOPT=\xb11 or wherein mOPT=\xb12
12. Method according to claim 1, the method further comprising the step of:
receiving reflected light from a light beam having an optimum beam number (m=mOPT or m=\u2212mOPT);
deriving a focus error signal from this reflected light beam;
controlling the positioning of said adjustable member (34) on the basis of this focus error signal.
13. Method according to claim 1, the method further comprising the step of:
receiving reflected light from the two light beams having an optimum beam number (m1=mOPT and m2=\u2212mOPT);
deriving a focus error signal from these reflected light beams, averaging the contribution of both light beams;
controlling the positioning of said adjustable member (34) on the basis of this focus error signal.
14. Optical disc drive apparatus (1), the apparatus comprising:
an optical system (30) for scanning a disc (2), comprising:
light beam generating means (31) adapted to generate a plurality of N optical beams (32(i));
means (33, 34, 37) for focusing said beams (32(i)) in respective focus spots (F(i));
at least one adjustable member (34) for axially displacing said focus spots (F(i));
an actuator system (50), comprising a controllable focus actuator (52) for axially displacing said adjustable member (34);
an optical detector arrangement (35), comprising a plurality of detector units (35(i)), each detector unit arranged for receiving reflected light from a corresponding beam (32(i)) and for generating an electrical output signal (SR(i)) representing the received light;
a control circuit (90), having signal inputs (95(i)) coupled to receive the electrical output signal (SR(i)) of the detector units (35(i)), and adapted to generate a focus control signal (SCF) for the focus actuator (52);
wherein the control circuit is adapted to perform the method of claim 1.
15. Apparatus according to claim 14, wherein a detector unit having an optimum number (35(m=mOPT) or 35(m=\u2212mOPT)) is subdivided into multiple detector segments, each segment for generating a corresponding detector segment output signal;
wherein the control circuit (90) is coupled to receive the detector segment output signals of said detector unit;
wherein the control circuit is adapted to process said detector segment output signals of said detector unit in order to derive a focus error signal;
and wherein the control circuit is adapted to generate its focus control signal (SCF) on the basis of the focus error signal thus obtained.
16. Apparatus according to claim 14, wherein both detector units having an optimum number (35(m=mOPT) and 35(m=\u2212mOPT)) are subdivided into multiple detector segments, each segment for generating a corresponding detector segment output signal;
wherein the control circuit (90) is coupled to receive the detector segment output signals of both of said detector units;
wherein the control circuit is adapted to process said detector segment output signals of said detector units in order to derive a focus error signal, averaging the corresponding contributions of both of said detector units;
and wherein the control circuit is adapted to generate its focus control signal (SCF) on the basis of the focus error signal thus obtained.
17. Apparatus according to claim 15, wherein N is an odd number larger than 3;
and wherein the optimum number (mOPT) satisfies the formula
mOPT=\xb1INTEGERSQUARE{(N\u22121)(2\u221a2)}
wherein the function y=INTEGERSQUARE{x} is defined as the integer y whose square y2 is closest to x2;
and wherein m=0 corresponds to the central beam.
18. Apparatus according to claim 15, wherein N=3, and wherein the optimum number mOPT=0 or wherein mOPT=\xb11
19. Apparatus according to claim 15, wherein N is an even number larger than 4;
and wherein the optimum number (mOPT) satisfies the formula
mOPT=\xb1INTEGERROUND{N\xb7(N\u22122)8}
wherein the function z=INTEGERROUND{x} is defined as the integer z for which z\xb7(z\u22121) is closest to x;
and wherein m=\u22131 corresponds to the inner beams.
20. Apparatus according to claim 15, wherein N=4, and wherein the optimum number mOPT=\xb11 or wherein mOPT=\xb12.
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 determining the length of a capillary gas chromatography column fabricated from a light guiding capillary tube material using an optical rangefinder, the method comprising:
coupling first and second ends of the gas chromatography column to an input and an output of the optical rangefinder using an adapter, the gas chromatography column being coiled;
operating the rangefinder to determine an uncorrected length of the column; and
calculating a corrected column length from the uncorrected length and from a correction factor, the correction factor being empirically determined by measurement of a length of a column of known length fabricated from the light guiding capillary tubing using the optical rangefinder.
2. A method as in claim 1, wherein the rangefinder is a digital rangefinder.
3. A method as in claim 1, wherein the rangefinder operates within the visible light spectrum.
4. A method as in claim 1, wherein the rangefinder operates within the invisible light spectrum.
5. A method as in claim 1, wherein the rangefinder operates at 635 nm.
6. A method as in claim 1, wherein the rangefinder operates in the range of 630 and 670 nm.