The invention relates to a device for reading information
represented by marks on an information carrier, the device comprising a scanning
unit for generating a read signal from the marks, a radiation source and optical
elements for generating a beam of radiation, focusing means for controlling at least
one of the optical elements for creating a spot by focusing the beam, and cleaning
means for cleaning a surface of the information carrier.
The invention further relates to an information carrier
for use in the device, which information carrier is provided with a protective cartridge.
A device for scanning an information carrier is known from
. The information carrier carries information represented by marks, e.g.
optically readable effects in a track on a disc shaped information carrier. The
device comprises a drive unit for rotating the information carrier. For scanning
the track a head constituted by optical elements is positioned opposite the track
by a positioning unit, while the information carrier is rotated. The problem of
contaminants on the surface of the information carrier is discussed. Contaminants
can be removed by several methods, e.g. by hand or by inserting a special cleaning
disk in the device for removing contaminants from within the device. A cleaning
system is described having a cleaning pad or brush build in the device for cleaning
the surface of the information carrier. Further the cleaning system includes a pad-cleaning
component for removing the contaminants from the pad. A problem of the known system
is that it is mechanically complex and not suitable for removing stubborn contaminants.
Such contaminants are particularly disturbing for reading information from high
density information carriers.
describes cleaning and inspecting a surface of a magnetic recording medium.
The surface is subjected to the output of a laser source for applying a cleaning
energy to the surface and removing contaminants on the surface. The laser source
is also used for inspecting the surface being cleaned and to measure the effect
of the cleaning.
describes an optical disk device having an optical pickup provided with
an objective lens. Further a cleaning member for removing dust, stuck foreign matter
or the like on the surface of the disk is provided near the objective lens. When
cleaning, the cleaning member is brought into contact with the surface of the disk
by an actuator to clean the surface of the disk.
describes a magnetic disk cartridge, which provides reliable operation
by protecting the magnetic disk media from dust. The cartridge is provided with
ribs on the inner surface near the magnetic disk media. The ribs for at least one
corner area are cut to form vents, and an adhesive trap for collecting dust is attached
to the inner surface in the corner area.
describes a disk cartridge that prevents rubbish such as dust to adhere
to a disk. In the disk cartridge, a magneto-optical disk is accommodated, and an
electrostatic charged body is provided for attracting rubbish adhering to the magneto-optical
disk by generating static electricity.
describes removing dust in a cartridge by a dust collecting part for collecting
dust scattered by rotating the discoid recording medium in the cartridge. The dust
collecting part has a dust take-in hole and a dust discharge hole. When the disk
is rotated, an airflow is generated in the cartridge, and dust is given centrifugal
force and is moved to the outer side of the cartridge to enter the dust collecting
part, and is then discharged from the dust discharge hole to the outside. Thus,
air in the disk housing chamber can be cleaned.
describes collecting fine dust particles by a dust collecting sheet on
the inner surface side of a cartridge body. The sheet collects dust particles contained
in an air current generated due to the rotation of a disklike recording medium.
The dust collecting sheet may be a resin sheet such as a polyimide sheet or the
like or a nonwoven fabric such as a nylon fabric, a polyester fabric, a rayon fabric
or the like which is coated with various adhesives.
It is an object of the invention to provide a scanning
device having a cleaning system that is more efficient in removing stubborn contaminants.
For this purpose, a device is provided as defined in claim
1. An information carrier is provided as defined in claim 10. The measures have
the effect that the surface of the information carrier is cleaned by locally heating
the contaminated area and/or the contaminating particle itself. Due to the available
power being focused on the small area constituting the spot said contamination is
effectively removed from the surface. Particles removed from the surface can be
prevented from again contaminating the surface by providing a material to which
particles strongly adhere on the inner walls of the cartridge or disc drive.
The invention is based on the following recognition. First
the inventors have seen that mechanical cleaning methods are not effective for removing
smaller contaminating particles and stubborn surface contamination. Secondly the
inventors have seen that industrial laser cleaning techniques, for example for semiconductor
device fabrication, etc. known from "
Laser cleaning of polymer surfaces; T. Fourier et al., Applied Physics A 72,
), Materials Science & Processing", can be build into a scanning device
like a home-use disc drive. Using a semiconductor radiation source and focusing
a spot on the surface of the information carrier, and controlling the power of the
radiation source provides just enough power to achieve the cleaning effect.
In an embodiment of the device the control means are arranged
for controlling the power of the radiation source in pulses. The effect of using
short pulses is that the radiation source can deliver a peak power that is substantially
higher than the average power, because the power dissipation is based on average
power. The peak power increases the cleaning efficiency.
A further embodiment of the device comprises detection
means for detecting possible contamination of the surface, and the control means
are arranged for cleaning parts of the surface where said possible contamination
is detected. This has the advantage that only contaminated parts of the surface
have to be cleaned, and this reduces the cleaning time.
These and other aspects of the invention will be apparent
from and elucidated further with reference to the embodiments described by way of
example in the following description and with reference to the accompanying drawings,
Corresponding elements in different Figures have identical reference numerals.
- Fig. 1a shows an information carrier (top view),
- Fig. 1b shows an information carrier (cross section),
- Fig. 2 shows an information carrier in a cartridge,
- Fig. 3 shows a radiation beam for reading a track,
- Fig. 4 shows a radiation beam focused on the surface for cleaning,
- Fig. 5 shows a reading device having laser control for cleaning, and
- Fig. 6 shows a recording device having laser control for cleaning.
Fig. 1a shows a disc-shaped information carrier 11 having
a track 9 and a central hole 10. The track 9, being the position of the series of
(to be) recorded marks representing information, is arranged in accordance with
a spiral pattern of turns constituting substantially parallel tracks on an information
layer. The information carrier is optically readable, called an optical disc, and
has an information layer of a read-only or recordable type. Examples of read-only
discs are CD or DVD, and of a recordable disc are the CD-R and CD-RW, and writable
versions of DVD, such as DVD+RW and DVD+R, and the high density writable optical
disc using blue lasers, called Blue-ray Disc (BD). Further details about the DVD
disc can be found in reference:
ECMA-267: 120 mm DVD - Read-Only Disc - (1997
). The information is represented on the information layer by recording optically
detectable marks along the track, e.g. crystalline or amorphous marks in phase change
material. The surface of the information carrier is suitable for cleaning by laser
power as described below. It is noted that the laser cleaning of the surface can
be used for discs with cartridge, but also for discs without cartridge. Reliability
for both reading and writing can be improved.
Fig. 1b is a cross-section taken along the line b-b of
the information carrier 11 of the recordable type, in which a transparent substrate
15 is provided with a recording layer 16 and a protective layer 17. In an embodiment
of a multi-layer storage medium the protective layer 17 comprises one or more substrate
layer(s) and/or recording layer(s), for example as in DVD where the recording layer
is at a 0.6 mm substrate and a further substrate of 0.6 mm is bonded to the back
side thereof. The track 9 on the recordable type of information carrier may be indicated
by a pre-embossed track structure provided during manufacture of the blank information
carrier. The track structure is constituted, for example, by a pregroove 14 which
enables a read/write head to follow the track during scanning. The track structure
comprises position information, e.g. addresses, for indication the location of units
of information, usually called information blocks. The position information includes
specific synchronizing marks for locating the start of such information blocks.
The pregroove 14 may be implemented as an indentation or an elevation of the substrate
15 material, or as a material property deviating from its surroundings.
The information carrier 11 may, for example, be for carrying
information representing digitally encoded video according to a standardized format
Fig. 2 shows an information carrier in a cartridge. The
information carrier 11 is enclosed by a cartridge 21. The cartridge is closable
by a slider 22, which slider is moved away when the cartridge is inserted in a device
for making the information carrier surface accessible for a read head. The centre
hole 10 is visible for coupling to a driving unit in the device, but may alternatively
be covered by the slider 22. The cartridge and slider constitute a substantially
closed box around the information carrier 11 when not inserted in a device. The
cartridge is provided with a contamination collecting unit 23 for collecting contamination
which has been separated from the surface of the information carrier by laser cleaning
as described below. In an embodiment the contamination collecting unit 23 is constituted
by the inner walls of the cartridge being covered with a layer of material to which
particles adhere, e.g. a material with a high surface energy being highly reactive
such as (chemically treated) activated carbon.
Fig. 3 shows a radiation beam for reading a track. A radiation
source 34, e.g. a semiconductor laser, generates radiation which is guided via optical
elements like objective lens 32 for constituting a radiation beam 35. The radiation
beam enters the surface 36 of an information carrier, which is constituted by a
substrate 37 of a predefined thickness as indicated by the arrow, e.g. 0.6 mm for
DVD or 0.1 mm for a BD. Behind the substrate 37 there is located a recording layer
having a track constituted by marks 38. A second substrate supports the structure
for mechanical stability, or provides a second surface for reading and recording
information. The radiation beam 35 is focused to form a spot 66 on the marks. Radiation
is reflected to a detector 33 for generating a read signal. The surface 36 of the
information carrier is contaminated by a dust particle 31. The optical beam 35 may
be disturbed by the particle. The excellent reliability of the compact disc (CD)
can be highly attributed to the presence of a 1.2 mm thick transparent substrate
on top of the data layer. During reading and writing, the laser beam is focused
through the thick substrate onto the data layer. The laser beam is out-of-focus
on the surface of the disc, making the CD system rather insensitive to dust and
fingerprints. The increase in data capacity of optical storage systems beyond CD
(i.e. DVD and BD) has been realized using an objective with a higher numerical aperture
and a laser with a shorter wavelength. However, in order to limit optical aberrations
and to achieve sufficient optical tolerances, the thickness of the transparent substrate
is reduced to 0.6 mm for DVD and 0.1 mm for BD. Hence DVD and BD, as well as future
optical storage generations, are more vulnerable to dust and fingerprints, which
may endanger their reliability. According to the invention laser cleaning as described
below is built in the reading and/or recording device to increase the reliability.
The disturbance, e.g. change in the intensity of the read signal, change in tracking
signals or read errors, may be detected for determining the presence and location
of the particle 31.
Fig. 4 shows a radiation beam focused on the surface for
cleaning. The same optical elements are shown as in Fig. 3. The optical system is
arranged for focusing the radiation beam 35 on the surface or near the surface,
e.g. above the surface near the particle 31. By applying sufficient power to the
radiation source 34 the dust particle is either loosened from the surface or evaporated.
Instead of focussing the laser beam on the data layer, as is done during reading
and writing, the laser is focussed on the top surface of the disc for cleaning.
Short laser pulses (typically ~ 20 ns) of sufficiently high fluence (typically ~
100 mJ/cm2) can remove contaminants, such as dust and fingerprints, due
to rapid thermal expansion, ejecting the contaminants from the disc surface. The
following calculation uses a practical laser of a maximum laser power of 250 mW
(pulsed). A pulse width of 20 ns and a spot size of 1x5 µm2 result
in a fluence of 100 mJ/cm2. Assuming a linear disc velocity of 10 m/s
(which is about 3x the normal speed of DVD) and a pulse frequency of 10 MHz, a cleaning
rate of 0.5 cm2/s is obtained. The laser power of 250 mW is not a strict
requirement; the only requirement is that a fluence of approximately 100 mJ/cm2
is obtained during a pulse of the order of tens of nanoseconds. The maximum laser
power of current high-speed CD-R drives is approximately 200 mW (pulsed). The efficiency
of the light path (usually around 40%) has to be taken into account. Therefore,
using a laser power of 80 mW on the disc, a pulse width of 20 ns and a spot size
of 1x1.6 µm2, a fluence of 100 mJ/cm2 can be obtained.
Again assuming a linear disc velocity of 10 m/s and a pulse frequency of 10 MHz,
a cleaning rate of 0.16 cm2/s is obtained. Dust particles which affect
the read out or writing of a disc will generally cover an area much smaller than
one square centimetre, and can thus be quickly removed.
Figs. 5 and 6 show apparatuses according to the invention
for scanning an information carrier 1, which have laser control for cleaning. The
apparatus of Fig. 5 is arranged for reading the information carrier 1, which information
carrier is identical to the information carriers shown in Fig. 1 or 2. The device
is provided with read means comprising a read head 52 for scanning the track on
the information carrier, a drive unit 55 for rotating the information carrier 1,
a read signal processing unit 53 for example comprising a channel decoder and an
error corrector and a system control unit 56. The read head comprises an optical
system of a known type for generating a radiation spot 66 focused on a track of
the recording layer of the information carrier via a radiation beam 65. The radiation
beam 65 is generated by a radiation source, e.g. a laser diode. The read head 52
further comprises a focusing actuator 59 for focusing the radiation beam 65 on the
recording layer and a tracking actuator (not shown) for fine positioning of the
spot 66 in radial direction on the center of the track. The radiation reflected
by the recording layer is detected by a detector of a usual type, e.g. a four-quadrant
diode, for generating detector signals 57 including a read signal, a tracking error
and a focusing error signal. During reading, the read signal is converted into output
information, indicated by arrow 64, in the read signal processing unit 53. The apparatus
has positioning means 54 for coarsely positioning the read head 52 in the radial
direction on the track, the fine positioning being performed by the tracking actuator.
The tracking actuator may comprise coils for radially moving an optical element
or may be arranged for changing the angle of a reflecting element on a movable part
of the read head or on a part on a fixed position in the case part of the optical
system is mounted on a fixed position. The apparatus is provided with a cleaning
control unit 51 for focusing the beam on the surface of the information carrier
and for controlling the power of the laser for cleaning. For generating enough power
for effective cleaning the power of the laser is applied in pulses. The peak power
is delivered during said pulses, and the average power for the laser is kept sufficiently
low by the periods between the pulses. The device is further provided with a control
unit 56 for receiving commands from a controlling computer system or from a user
and for controlling the apparatus via control lines 58, e.g. a system bus connected
to the drive unit 55, the positioning means 54, the cleaning control unit 51 and
the read signal processing unit 53. To this end, the control unit comprises control
circuitry, for example a microprocessor, a program memory and control gates, for
performing the procedures described below. The control unit 56 may also be implemented
as a state machine in logic circuits. The cleaning control unit 51 may be arranged
for controlling the cleaning function via the firmware of the drive and be integrated
with control unit 56. As for the hardware, care should be taken that the focusing
actuator 59 has a sufficient moving range perpendicular to the disc surface, in
order to be able to focus both on the data layer and the disc surface. The optical
elements in the light path of an optical disc drive are generally designed to minimize
optical aberrations during focussing on the data layer through a substrate. If designed
for a thin substrate, the optical aberrations while focussing on the disc surface
will remain relatively small. Depending on the thickness of the substrate some of
the optical elements may be adapted for focussing on the surface.
In an embodiment of the device the device has a contamination
detection unit 50. In order to remove a contaminant particle from an optical disc
surface by laser cleaning, the location of the contaminant is determined. The basic
idea is that only contaminant particles which affect the optical reading and/or
writing process should be removed. Contaminants that have no effect on the optical
recording process will be left alone. In case of major contamination the user data
rate may be temporarily affected during cleaning, which is preferable over unrecoverable
data loss or write failure.
In a first embodiment of contamination detection unit 50
a contaminant is localized on a disc surface by detecting occurrence of unrecoverable
data error(s). The approach assumes that an unrecoverable data error is caused by
contaminants. When unrecoverable errors are detected and the tracking signal is
still present, the exact location of the unrecoverable data error(s) is known. The
area of the track involved is cleaned by focussing the laser on the surface. In
an embodiment by alternatingly focussing on the disc surface and the data layer,
the disc is laser cleaned by laser pulses focussed on the disc surface, while fully
remaining on track due to the alternating focussing on the data layer. In an embodiment
for a high density disc with a thin substrate contaminants are most harmful, and
switching quickly between focussing on the data layer and focussing on the disc
surface is possible because the distance between the data layer and the disc surface
In a second embodiment of contamination detection unit
50 a contaminant is localized on a disc surface by detecting occurrence of loss
of tracking signals. The actuator data at the moment of loss of tracking signal
can be stored. In this way, the radial position of the contaminant is known. Starting
from this radial position, the disc is laser cleaned by laser pulses focussed on
the disc surface.
In an embodiment upon detection of a contaminant (either
by means of detecting an unrecoverable data error, loss of tracking signal, or deviant
reflectivity), the laser cleaning process is started from the respective radial
position in outward direction. The laser cleaning process will last for a fixed
time or fixed area. If only part of the contaminant has been removed (as detected
again by an unrecoverable data error, loss of tracking signal, or deviant reflectivity),
the laser cleaning process will again continue for a fixed time or fixed area.
In an embodiment of contamination detection unit 50 the
disc surface is scanned for contaminants before reading or writing. This can e.g.
be done by measuring the reflection of a laser beam focussed on the disc surface.
Using an actuator, the laser is scanned over the entire disc surface. Areas where
the reflectivity is different from the average value are likely contaminated. Upon
detection of an area with a deviant reflectivity value, the disc is laser cleaned
by laser pulses focussed on the disc surface. This approach will take more time
than the embodiment above in which errors are detected, because also particles which
do not (heavily) affect the optical reading and/or writing process will be removed.
However the cleaning will advantageously be preventing problems during future writing
or reading operations.
In an embodiment of the read device or the write device
the disc is scanned for contamination upon insertion of the disc into the drive.
Any contaminated part is cleaned immediately, or a background process is started
for cleaning when no user read or write of data is required.
In an embodiment of the read device or the write device
an oblong shaped laser spot for cleaning is obtained by putting a cylindrical lens
in the light path. An oblong shaped spot is used to increase the cleaning rate,
i.e. to reduce the cleaning time.
Fig. 6 shows a device for writing information on an information
carrier having laser control for cleaning. The information carrier is of a type
which is (re)writable in, for example a magneto-optical or optical manner (via phase
change or dye) by means of a beam 65 of electromagnetic radiation. The device is
usually also equipped for reading and comprises the same elements as the apparatus
for reading described above with Fig. 5, except that it comprises write means which
include a write/read head 62 and a write signal processing unit 60, which comprises
for example a formatter, an error encoder and a channel encoder. The write/read
head 62 has the same function as the read head 52 together with a write function
and is coupled to the write signal processing unit 60. The information presented
to the input of the write signal processing unit 60 (indicated by the arrow 63)
is distributed over logical and physical sectors according to formatting and encoding
rules and converted into a write signal 61 for the write/read head 62. The system
control unit 56 is arranged for controlling the cleaning function as described above
for the reading apparatus. During the writing operation, marks representing the
information are formed on the information carrier. Writing and reading of information
for recording on optical discs and usable formatting, error correcting and channel
coding rules, are well-known in the art, e.g. from the CD system. The apparatus
is provided with a cleaning control unit 51 for controlling the power of the laser
for cleaning, and in an embodiment provided with a contamination detection unit
50, having the same function as described above for the read device and its embodiments.
In an embodiment the read device or the write device is
provided with a data buffer (not shown) coupled to the read signal processing unit
53 or the write signal processing unit 60. The size of the data buffer is determined
such that a few seconds worth of data can be stored. Several square centimeters
of disc surface can be cleaned during reading and/or writing without affecting the
user data rate using the practical laser calculation given with Fig. 4.
The laser cleaning process will remove contaminant particles
from the disc surface. Once removed, the motion of the particles will be affected
by the air flow in the optical drive. In an embodiment the inside walls of the optical
drive can be (partly) covered by a material to which the particles strongly adhere,
in order to prevent the same particles from contaminating the disc surface again,
e.g. a material with a high surface energy which is highly reactive such as (chemically
treated) activated carbon.
Further in a combination drive, i.e. a device having at
least two laser sources for two different types of optical discs like CD-R and DVD,
the laser source used for cleaning may be a different laser than the laser used
for reading the information carrier. For example a powerful laser build in the device
for writing CD-R may advantageously be used for cleaning a DVD disc. It is noted,
that in this document the word 'comprising' does not exclude the presence of other
elements or steps than those listed and the word 'a' or 'an' preceding an element
does not exclude the presence of a plurality of such elements, that any reference
signs do not limit the scope of the claims, that the invention may be implemented
by means of both hardware and software, and that several 'means' may be represented
by the same item of hardware.