Measuring and testing – Inspecting
Reexamination Certificate
2001-05-21
2003-05-27
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Inspecting
C702S155000, C356S141100
Reexamination Certificate
active
06568289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a planar shape characteristic measuring apparatus and a planar shape characteristic measuring method which measure, for example, characteristic values relating to the shape of a measured surface of a disk such as an optical disk.
2. Description of the Related Art
As shown in
FIG. 7
, a disk-shaped recording medium, that is, an optical disk
101
, comprises an optical disk substrate
103
made of an optically transparent plastic provided on one surface with a data recording surface
104
and provided with a data recording area
102
within a predetermined area in the data recording surface
104
.
Also, there are known an optical disk where the data recording area
102
in the data recording surface
104
is provided with, for example, as shown in
FIG. 8A
, a continuous groove
105
and a land
106
adjacent thereto provided spirally for every track by a predetermined track pitch
109
(1 to 2 &mgr;m) on the data recording surface
104
of one side of the disk substrate
103
and an optical disk where, as shown in
FIG. 8B
, the data recording surface
104
is provided with a series of pits
108
spirally for every track by a predetermined track pitch.
For example, in most data recordable optical disks of the phase-changing type or opto-magnetic type, a phase changing film or a magnetic film, a light reflecting layer, and a protective film layer (all not shown) are formed in that order on the data recording surface
104
on which the grooves
105
shown in
FIG. 8A
is provided. One of the grooves
105
and the lands
106
on the data recording surface
104
is used as a recording area, while the other is used as a light reflecting area for tracking.
Also, in most write-once (read-only) type optical disks, a light reflecting layer and a protective film layer (both not shown) are formed in that order on the data recording surface
104
on which the series of the pits
108
shown in
FIG. 8B
is provided. The series of the pits
108
on the data recording surface
104
is used as both a recording area and a diffraction grating for tracking.
In an optical disk having the above configuration, a laser beam condensed by an object lens (not shown) mounted on an optical pickup is fired from the non-data surface
107
at the side opposite to the data recording surface
104
of the optical disk substrate
103
while rotating the optical disk.
In a data recordable optical disk, information is optically recorded in a recording layer on the land
106
by the beam or the information optically recorded on the recording layer is read by the reflected light beam. Further, for example the light beam reflected from the groove
105
is detected for tracking so that the laser beam for recording or reproduction is always focused on a predetermined track.
In a write-once type (read-only) optical disk, information is read and tracking performed by detecting the reflected and diffracted beam from the surface
104
provided with the series of pits
108
due to the beam from the non-data surface
107
to the optical pickup.
On the other hand, in the high density optical disks being developed in recent years, as shown in
FIG. 9
, ones are known having an optical disk substrate
103
provided with grooves
105
and formed with a light reflecting surface
104
comprising a light reflecting layer and a phase change film or a magnetic film and a transparent layer
111
which has a constant thickness of about 0.1 mm in that order.
Similarly, in a write-once type (read only) optical disk, there is known an optical disk formed with a light reflecting surface
104
comprising a light reflecting layer and a transparent layer
111
having a constant thickness about 0.1 mm in that order.
In the case of an optical disk formed with a film in this way, an optical pickup (not shown) is arranged at the side of the transparent layer
111
formed on the surface
104
of the optical disk substrate
103
and fires a laser beam while the optical disk is being rotated.
Summarizing the problems to be solved by the present invention, the optical disk substrate
103
is generally formed by injection molding of plastic. In an optical disk substrate
103
formed by this method, it is known that warping occurs along with heat distortion at the time of molding and changes in the environment such as the air temperature or humidity. Further, undulation occurs at the surface of the disk due to warping of the molds at the time of molding.
If rotating the optical disk substrate
103
in a state with warping or unevenness of undulation, up-down vibration occurs at the surface of the optical disk substrate
103
leading to the focal position of a data reading lens deviating from the data recording surface of the disk (defocus state) or the data recording surface becoming tilted from a focal surface of the data reading lens (skew state).
At this time, a spot condensed by the optical pickup ends up being influenced by the aberration. The magnitude of the aberration depends on the numerical aperture (NA) of a pickup lens. The aberration caused by the defocus is proportional to the second power of the numerical aperture (NA), while the aberration caused by the skew is proportional to the third power of the numerical aperture (NA). That is, due to the larger numerical aperture (NA), the allowable defocus and skew become smaller.
On the other hand, the smaller the thickness from the surface of the disk to the data recording surface
104
, the smaller the aberration due to the defocus and the skew. For this reason, along with the recent higher density of optical disks, the numerical aperture (NA) has become higher and the thickness of the disk has become smaller.
For example, the high density optical disk such as shown in
FIG. 9
is structured with a thin transparent layer
111
of a thickness of about 0.1 mm placed on the data recording surface
104
on which the grooves and the lands or the series of pits of the disk substrate
103
are formed.
Thus, to decrease or avoid the influence of the aberration caused by the increase of the numerical aperture (NA), an optically thin disks are being developed. Recently, a high density disk having a short wavelength (&lgr;≦430) and a large numerical aperture (NA≧0.76) has been proposed.
Because the depth of focus becomes shallower along with the higher NA as stated above, stricter values are now demanded for the surface vibration permitted to the optical disk substrate
103
, that is, the magnitude of the unevenness of the surface of the optical disk substrate
103
.
For this reason, it is necessary to accurately measure the characteristics relating to the shape of the surface of the optical disk substrate
103
. For example, it is demanded to precisely and efficiently measure the unevenness of the surface of the optical disk substrate
103
, the amount of focus servo error making it impossible to track the unevenness of the surface of the optical disk substrate
103
generated at the time of focus servo control or the so-called “tangential skew”, and other planar shape characteristics.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a planar shape characteristic measuring apparatus and a planar shape characteristic measuring method which can precisely and efficiently measure characteristics relating to the shape of a measured surface of a disk such as a data recording surface of an optical disk.
According to a first aspect of the present invention, there is provided a planar shape characteristic measuring apparatus comprising a speed detecting means for detecting a perpendicular direction speed of a measured surface of a rotating disk and a tilt angle calculating means for calculating a tilt angle in the rotational direction of said measured surface relative to a reference surface at each measuring position based on the linear speed at each measuring position detected by said speed detecting means and the detected perpendicular direction speed.
Preferably, the planar shape characteris
Kananen, Esq. Ronald P.
Larkin Daniel S.
Rader & Fishman & Grauer, PLLC
Rogers David
Sony Corporation
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