Method for determining a tilt angle of an optical pickup head

Details Method for determining a tilt angle of an optical pickup head Method for determining a tilt angle of an optical pickup head

2004-02-17

2004-12-14

Le, Que T. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

With circuit for evaluating a web, strand, strip, or sheet

C250S559300

Reexamination Certificate

active

06831286

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for determining a tilt angle of an optical head, and in particular to a method of calculating a minimum jitter value and an optimum tilt angle of an optical pickup head.
2. Description of the Related Art
As shown in
FIG. 1
, the optical path of an optical pickup head
1
a
is not perpendicular to datum plane
2
a
because of component size and improper assembly, resulting in tilt angle &thgr;. In conventional methods, manufacturers perform a measuring process, in radial and tangential directions separately, gauging the relationship between jitter values and tilt angles to obtain an optimum tilt angle for the optical pickup head
1
a
, in which the jitter value and its limit value are defined in CD and DVD standards. As shown in
FIG. 2
, the jitter value is generated by measuring the time gap between both semiperiods of data signal (T1) and clock signal (T2), calculated by Jitter=T1—T2in accordance with the CD-ROM standard and by Jitter=(T1—T2)/T1 in accordance with the DVD standard. Another method of generating the jitter value is measurement of the pulse width (or pulse period of a Magneto-Optical Disk Drive). In addition, the jitter value and tilt angles are calculated by Jitter(x)=a1x
2
+b1x+c1 and by Jitter(y) =a2y
2
+b2y+c2, where x is the tilt angle in radial direction, y is the tilt angle in tangential direction, and a1, a2, b1, b2, c1 and c2 are unknown constants. The value of the tilt angle in tangential direction must be initialized to zero before the equation of Jitter(x) is obtained, and the tilt angle in radial direction is measured three times. Similarly, the value of the tilt angle in radial direction must be initialized to zero before the equation of Jitter(y) is obtained, and the tilt angle in tangential direction is measured three times.
Equations Jitter(x)=a1x
2
+b1x+c1 and Jitter(y)=a2y
2
+b2y+c2 are obtained by measuring three data points in one direction (radial or tangential) separately to obtain the values of a1, a2, b1, b2, c1 and c2, whereby the function “Jitter” can be completely achieved and the minimum point thereof can be determined, as shown in FIG.
3
and
FIG. 4
, and thereby optimum tilt angle for both directions is obtained separately. In addition, calculating of optimum tilt angle in radial or tangential direction requires measurement at least six data points, and, when the tilt angle in one direction is determined, the value of the tilt angle in another direction has to be initialized to zero.
FIG. 5
is a flowchart showing the detailed steps of conventional determination of a title angle of an optical pickup head of an optical drive, requiring much time for necessary measurement.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for determining the tilt angle of an optical pickup head of an optical drive, utilizing a quadratic surface equation to measure only five data points without initializing the values of tilt angles in radial and tangential directions separately, so that a minimum jitter value and an optimum tilt angle of the optical pickup head are more easily.
According to the object described above, the present invention provides a method for determining tilt angle of the optical pickup head of an optical drive, applied in a jitter inspection device comprising a jig for simulating and adjusting a tilt angle of the optical pickup head, and a jitter meter installed on the jig for inspecting jitter values of the optical pickup head at different tilt angles, the method comprising the following steps.
The optical pickup head is measured with the jitter meter utilizing a quadratic surface equation Z=ax
2
+by
2
+cx+dy+e using the jitter inspection device. Next, five sets of tilt angles of (x1, y1), (x2, y2), (x3, y3), (x4, y4), and (x5, y5), for the optical pickup head are obtained by adjusting the jig five times. A simultaneous equation is created according to the five sets of the tilt angles and their corresponding jitter values Z1, Z2, Z3, Z4 and Z5, and then, the simultaneous equation is solved to obtain the result of a1, b1, c1, d1 and e1. Next, the values of a1, b1, c1, d1 and e1 are substituted in the quadratic surface equation to create a quadratic surface equation Z=a1x2+b1y
2
+c1x+d1y+e1. The quadratic surface equation is solved to obtain a minimum jitter value and an optimum tilt angle. Finally, a barcode is produced in accordance with the minimum jitter value as a basis for adjusting the emitting angle of the optical pickup head.
A detailed description is given in the following embodiments with reference to the accompanying drawings.


REFERENCES:
patent: 6282161 (2001-08-01), Son et al.

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