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Description  |
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FIELD OF THE INVENTION
This invention relates to optical information storage disks, and more
particularly, to providing a machine-readable serial number code on such
disks.
BACKGROUND OF THE INVENTION
It has been proposed to increase efficiency in the distribution of computer
software by distributing many software programs on a single CD-ROM instead
of distributing each program on a separate floppy disk or set of floppy
disks. In this proposed distribution system, a customer who has the CD-ROM
(hereinafter sometimes referred to as "the disk") in his possession and
desires to obtain access to one of the programs on the disk purchases an
access code which may be used to gain access to the desired program.
In order to carry out this software distribution system, it is desirable to
provide a serial number or identification number on the disk in
machine-readable form so that access codes can, through encryption, be
limited to use with only one disk serial number, thereby preventing
unauthorized use of the access code on more than one disk. However, the
most efficient manner of producing CD-ROMs is by molding each disk from a
master, which results in each disk containing identical recorded
information. In other words, if a conventional mastering process is used
to record a "serial" number on the disk, each disk formed from a given
master will have the same "serial" number. It has been proposed to use
approximately 20 different masters to produce compact disks which contain
identical software program information, with each master respectively used
to produce disks having an identification number that is different from
the identification numbers of disks produced using different masters.
However, this approach suffers from two drawbacks: First, the cost of
mastering is significantly increased, and secondly, the number of
different disk identification numbers is the same as the number of
different masters, i.e. about 20, which makes it relatively easy for
unscrupulous persons to locate disks having the same identification number
and then to use a single access code to "unlock" the same program on all
of the disks which have the same identification code.
It is also possible to use disk manufacturing processes without molding
from a master, with a unique serial number being recorded on each disk at
the same time the program software is recorded, for example by
magneto-optical recording, but such processes are substantially more
expensive than molding CD-ROMs from a master.
Another constraint on provision of serial numbers on CD-ROMs is the need
for the serial number to be readable using conventional hardware such as
generally available CD-ROM drives interfaced to personal computers.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method
of manufacturing an optical information storage disk having a
machine-readable identification number, in which each disk which contains
the same program information is formed by molding with the same master.
It is another object of the present invention that a large number of
different identification numbers be provided on the respective disks.
It is still another object of the invention that the disk identification
number be readable using conventional personal computer peripheral
hardware.
In accordance with the invention, there is provided a method of forming a
machine-readable code on an optical disk including the steps of forming a
disk-shaped molded substrate which includes an information recording area
in which information is represented by pits formed in the information
recording area, applying a reflective coating to the information recording
area, and removing the reflective coating from selected portions of the
information recording area to form a code pattern.
According to another aspect of the invention, there is provided an
apparatus for forming a machine-readable code pattern on a pre-recorded
compact disk that includes a reflective coating on an information bearing
substrate, the apparatus including means for rotating the disk about a
center of rotation of the disk, a laser for selectively emitting a cutting
beam, means for directing the cutting beam to a point at a selected
distance from the center of rotation of the disk, and means for
controlling the laser and the means for directing so that the reflective
coating is removed from selected portions of the information bearing
substrate to form the machine-readable code pattern.
According to still another aspect of the invention, there is provided an
optical information storage disk in which a reflective coating is formed
on a molded information bearing substrate and wherein the reflective
coating is removed in a predetermined pattern from selected portions of
the substrate to form a machine-readable code.
According to yet another aspect of the invention, there is provided a
method of applying a human-readable serial number to an optical
information storage disk having a machine-readable code formed thereon,
the method including the steps of reading the machine-readable code formed
on the disk, performing an encryption algorithm with respect to the
machine-readable code to obtain an encrypted code, and applying the
encrypted code to the disk in human-readable form.
According to a further aspect of the invention, there is provided a method
of forming a machine-readable code on an optical information storage disk
including the steps of forming a plurality of addressable information
storage locations on the disk, with at least some of the storage locations
containing program information, and creating defects in some of the
information storage locations in a predetermined pattern so as to form a
machine-readable code.
According to still a further aspect of the invention, there is provided a
method of providing access to a selected one of a plurality of software
programs stored in a CD-ROM, including the steps of inserting the CD-ROM
into a CD-ROM drive interfaced to a personal computer, entering into the
personal computer an access code for providing access to the selected one
of the plurality of software programs, examining a plurality of
information storage locations on the CD-ROM to detect defects in the
information storage locations, establishing a disk identification code on
the basis of results of examining the plurality of information storage
locations, and verifying the entered access code on the basis of the
established disk identification code.
By providing the methods and apparatus described above, a large number of
software programs can be distributed on a single CD-ROM, using access
codes for accessing each of the programs on the CD-ROM, with the codes
being formed on the basis of serial numbers that are, for practical
purposes, unique to each respective CD-ROM. Each CD-ROM which is to
include identical information content can be formed using the same master,
with the substantially unique serial number being formed on the disk after
mastering and at a relatively low cost. Software provided in accordance
with the invention allows the serial numbers to be read by conventional
hardware including a standard PC connected to a conventional CD-ROM drive.
The above, and other objects, features and advantages of the present
invention will be apparent from the following detailed description thereof
which is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are schematic illustrations of a CD-ROM having a
machine-readable code pattern formed thereon in accordance with the
present invention;
FIG. 2A is a block diagram of an apparatus for forming a machine-readable
code pattern on a CD-ROM;
FIG. 2B is a block diagram of an alternative embodiment of an apparatus for
forming a machine-readable code pattern on a CD-ROM;
FIG. 3 is an illustration of a band format used for forming a
machine-readable code on a CD-ROM in accordance with a preferred
embodiment of the invention;
FIG. 4 is a block diagram of an apparatus for reading a machine-readable
code pattern from a CD-ROM and applying a human-readable serial number to
the CD-ROM, in accordance with the present invention;
FIG. 5 is a schematic illustration of computer hardware in which a CD-ROM
is loaded for controllably accessing software packages stored on the
CD-ROM in accordance with the present invention;
FIG. 6 is a flow chart which illustrates a software routine for
controllably accessing a software package stored on a CD-ROM in accordance
with the present invention; and
FIG. 7 is a flow chart which illustrates a subroutine for reading an ID
code from a CD-ROM, and which is part of the routine illustrated in FIG. 6
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There will first be described, with reference to FIGS. 1A and 1B, an
optical recording disk having a machine-readable code pattern formed
thereon in accordance with the present invention.
In FIG. 1, reference numeral 10 indicates an optical recording disk. The
disk 10 is, except for the machine-readable code pattern and the code
pattern area to be described below, preferably a conventional CD-ROM which
is used for storing computer programs, digital data and the like for
reproduction by a conventional CD-ROM drive provided as a peripheral
device in a personal computer system.
The surface of the disk 10 is divided into a circular hub area 12, a
relatively wide annular program or information storage area 14 that
surrounds and is concentric with the hub area 12, and an outer mirror area
16 in the form of a rather narrow ring surrounding the program area 14. A
circular boundary 18 is formed where the program area 14 meets the mirror
area 16.
The CD-ROM 10 is preferably of the type, well known to those skilled in the
art, which is manufactured by molding a polycarbonate disk-shaped
substrate with a master to form a pattern of information storage bits in
the program area 14. After molding, a reflective aluminum coating is
applied to the polycarbonate substrate and then a protective layer of
transparent ink is formed on top of the reflective coating.
The pits which represent the stored information are arranged in spiral or
concentric tracks with a track pitch that is typically about 1.6 microns.
Storage location addressing information or the like is arranged at regular
intervals along the tracks.
In accordance with the invention, the program area 14 includes a code
pattern area 20 near or adjacent to the boundary 18 between the program
area 14 and the mirror area 16. A machine-readable code pattern 22 is
formed in the code pattern area 20.
As best seen in FIG. 1B, the code pattern 22 is formed by a plurality of
code pattern bands 24 which extend in parallel to each other in the
circumferential direction of the disk 10. The code pattern bands are
formed by removing the aluminum coating from the program area 14 at the
places indicated by the bands 24, according to a method to be described
below. The bands 24 are, in a preferred embodiment, rather narrow, having
a width (in the radial direction of the disk 10) of approximately 25
microns. Preferably all of the bands 24 are of substantially the same
width. The length of the bands 24 (in the circumferential direction of the
disk 10) is determined in accordance with what is required for reliable
reading of the code pattern by methods to be described below. In a
preferred embodiment of the invention, the length of the bands 24 is
around 5 to 10 millimeters.
The code pattern 22 illustrated in FIG. 1B represents a seven digit binary
code in which the presence of a band in a particular location (i.e., the
absence of the reflective coating at that location) is taken to represent
the value "1", whereas the absence of the band (i.e., the presence of the
reflective coating) at such a location is taken to represent the value
"0". (It will be appreciated that the opposite convention could be used,
in which the presence of a band was accorded the value "0", and the
absence of the band was considered to indicate a "1".) Also, according to
the convention to be used in the example of FIG. 1B, the bands are read
proceeding radially outwardly from the innermost band. Thus, the code
pattern 22 of FIG. 1D represents the binary number "1101101" (that is, 109
in decimal numerals), with the two innermost bands each respectively
representing a "1" and being followed by a gap representing a "0", which
is in turn followed by two bands representing "1"s, followed again by a
gap for a "0" and concluding with an outermost band representing the final
"1".
It will be recognized that by using a seven-bit code pattern as shown in
FIG. 1B, up to 128 distinct machine-readable ID codes may be formed.
However, it is within the contemplation of the invention to provide a
larger number of distinct ID codes, utilizing eight or more binary bits,
and in a preferred embodiment a sixteen-bit binary code is used.
FIG. 2 illustrates in block diagram form an apparatus 100 used for forming
a machine-readable code pattern on a CD-ROM in accordance with the present
invention.
Major portions of the apparatus 100 include a control and display section
102, an optical section 104 and a signal processing section 106. The
apparatus 100 also includes a turntable 108 for receiving thereon and
rotating a disk 10.
The control and display section 102 includes a motor 110 which is connected
via a connecting mechanism 112 for controllably rotating the turntable 108
and the disk 10. The control and display section 102 also includes a
control system 114 which is connected for controlling motor 110.
The control system 114 also performs a number of other functions, as
described below, and preferably includes a conventional personal computer
or the like, including a display 116 and a keyboard 118, by which a user
interface is provided.
The optical section 104 includes a laser 120, which is preferably a
conventional medium power device of the type designed for micro-machining,
such as a Nd:YAG laser. The laser 120 emits a beam 122 that is adjustably
directed via a beam deflector 124 and a lens system L1 onto the program
area 14 of the disk 10. The laser 120 is selected, and the lens system L1
is arranged, so that the beam is focused on the surface of the program
area 14 in a spot having a diameter of about 25 microns, and with
sufficient power to vaporize the aluminum coating. The beam deflector 124
is selectively movable in directions indicated by arrows A for adjusting
the point on the surface of disk 10 to which the focused beam 122 is
directed. In a preferred embodiment of the invention the point of focus of
beam 122 is adjustable among selected radial positions relative to a
center of rotation of the disk 10. In other words, the axis along which
the focused beam may be deflected preferably coincides with a radius of
the disk 10.
The beam deflector 124 may take the form of a rotating mirror, an
acousto-optic modulator, or a low-inertia scanning device such as a
galvanometer.
The optical section 104 further includes a laser power control and
modulation circuit 126, which provides on/off control, power level control
and modulation of laser 120. The laser control circuit 126 is connected to
receive control signals from control system 114 of control and display
section 102.
As will be seen, the apparatus 100 is operable in a "read back" mode, and
for this purpose a read back detector 128 and a beam splitter 130 are
provided. The beam splitter 130 is positioned so as to direct to read back
detector 128 a reflected beam 122' that is reflected back from the surface
of disk 10 via the beam deflector 124.
Also included in the optical section 104 is an eccentricity compensator
132. As will be described below, the eccentricity compensator 132
cooperates with the control system 114 to provide precise positioning of
the focused beam 122 on the surface of disk 10 relative to the
program/mirror boundary 18.
The eccentricity compensator 132 includes a laser diode 134, a beam
splitter 136, a lens system L2 and a photo detector 138. As will be
discussed in more detail below, a beam 140 emitted by laser diode 134 is
directed by beam splitter 136 and lens L2 to the nominal position of the
boundary 18 on the surface of disk 10 and the beam 140 is reflected back
from the surface of disk 10 to the photo detector 138. Although not shown
in the drawing, it should be understood that a signal path is provided
between the control system 114 and the laser diode 134 for on/off control
of laser diode 134 by the control system 114.
The signal processing section 106 includes a signal conditioning and
processing circuit 142, a deflector driving circuit 144 and a signal
conditioning circuit 146. The signal conditioning and processing circuit
142 is connected to receive an output signal from the read back detector
128. The signal conditioning and process circuit 142 conditions and
processes the detector output signal and provides a detection signal to
the control system 114.
The deflector driving circuit 144 provides a driving signal to the beam
deflector 124 for the purpose of controlling the positioning of the beam
deflector 124 (and hence also the focusing point of the beam 122 with
respect to the surface of the disk 10). The driving signal output from the
deflector driving circuit 144 is based upon two input signals provided to
the driving circuit 144. The first of the input signals is a radial
position control signal provided from the control system 114, and is
indicative of a selected radial position on the disk 10 to which the beam
122 is to be directed. As will be seen, in a preferred embodiment of the
invention, the signal provided from the control system 114 to the driving
circuit 144 is such as is required to direct the beam 120 to a selected
one of 16 different radial positions relative to the center of rotation of
the disk 10.
The other input signal received by the driving circuit 144 is a
compensation signal provided from signal conditioning circuit 146. The
signal conditioning circuit 146 is connected to receive an output signal
provided from the photodetector 138 of the eccentricity compensator 132.
Because all CD-ROM's are eccentric to some extent, it is necessary to
provide eccentricity compensation to achieve the desired accuracy in
forming the code pattern on the disk 10.
As will be described in more detail below, the photodetector 138 outputs a
signal indicative of the degree of eccentricity of the disk 10. The signal
output from the photodetector 138 is conditioned by signal conditioning
circuit 146 to provide a compensation signal which is added at the driving
circuit 144 to the radial position control circuit provided by the control
system 114. As a result, the output signal from the driving circuit 144
provides desired radial positioning of the beam 122 on the surface of the
disk 10, with compensation for the eccentricity of the disk 10.
In operation, a disk 10 which has been molded to form the information
bearing pits in the aforementioned track arrangement, with the aluminum
reflective coating having been applied to the molded substrate, is placed
on the turntable 108 of the apparatus 100. Via the keyboard 118 an
operator enters a command to start the process of forming the
machine-readable code pattern and the control system 114 determines a
serial number that is to be applied to the disk 10. For example, a serial
number applied to an immediately preceding disk may be incremented to
generate the serial number to be applied to the present disk 10. The
serial number is either generated in binary form or is converted to binary
form by the control system 114.
The apparatus then proceeds to form the code pattern 22 on the disk 10 by
removing the reflective coating band by band with respect to the binary
digits having the value "1" in the serial number to be applied to the
disk. Before forming the first band, the disk 10 is rotated an initial
time by means of turntable 108 and motor 110, and during the initial
rotation of the disk the eccentricity compensator 132 is operated in a
calibration mode. More specifically, the laser diode 134 is turned on, and
the beam 140 emitted by the laser 134 is directed via the splitter 136 and
the lens L2 onto a location on the surface of disk 10 that is selected to
be the nominal position of the program/mirror boundary 18. The beam 140 is
reflected back from the surface of disk 10 through the beam splitter 136
to the photodetector 138, which outputs a signal that represents the
intensity of the reflected beam at the photodetector 138. Because disk 10
is eccentric, and the mirror area 16 is more reflective than the program
area 14, the intensity of the reflected beam fluctuates over the period of
rotation of the disk 10, and the output signal of the photodetector 138
fluctuates accordingly. The slope of the fluctuation indicates the phase
and the degree of the eccentricity, and is used at the signal conditioning
circuit 146 to form a compensation signal which compensates for the
eccentricity in the disk 10.
The initial rotational period of the disk 10 also allows the operation of
the turntable 108 and the control and display section 102 to become
stabilized.
On the second rotation of the disk 10, the control system 114 outputs a
radial position control signal to drive the beam deflector 124 to an
appropriate position for directing the beam 122 of the laser 120 to a
radial position on the disk 10 that corresponds to the first "1" bit of
the binary serial number. The radial position control signal output from
the control system 114 is provided to the deflector driving circuit 144,
which adds the compensation signal from the signal conditioning circuit
146 and the radial position control signal from the control system 114 to
form a driving signal that appropriately positions the beam deflector 124
to direct the beam 122 to the desired radial location on the disk 10,
taking into account the eccentricity of the disk 10.
After the positioning of the beam deflector as just described, and during
the second rotation of the disk, the control system 114 outputs a signal
to the laser control circuit 126, which in turn drives the laser 120 so
that it emits a beam 122 at a sufficient intensity to form a band in which
the reflective coating is removed and for a predetermined period of time
that is sufficiently long to form the band in a desired length, which may
be from 5-10 mm, for example. At the end of the predetermined time, the
laser beam 122 is turned off.
During the period in which the beam 122 is forming the first band, the
radial position control signal remains constant, but the compensation
signal from the signal conditioning circuit may be changed to compensate
for eccentricity in the disk 10, so that the position of beam deflector
124 is adjusted to maintain the beam 122 at the desired radial position on
the surface of disk 10 relative to the boundary 18.
During the next (i.e., the third) rotation of the disk, the control system
outputs another radial position control signal to reposition the beam
deflector so that the beam 122 will be directed to a radial position
corresponding to the band for the next "1" bit. Again the beam 122 is
turned on for the predetermined time period to form a band of the desired
length. The time at which the beam is initially turned on to start forming
the next band is controlled by the control system 114 to be substantially
one period of rotation of the disk after the time at which the beam 122
was initially turned on to form the first band. The timing may be
established by control system 114 on the basis of a known period of
rotation of turntable 108, or alternatively may be based upon code pulses
provided from an encoder (not separately shown) associated with motor 110.
Each of the bands corresponding to the remaining "1" bits of the binary
serial number is formed in the manner just described. It will be
understood that the period of the laser "burn" for forming each band is
commenced at substantially the same phase of rotation of the disk 10, and
continues for the same amount of time, so as to produce the code pattern
22 confined to the code pattern area 20 as shown in FIG. 1B.
Although the bands are shown in FIG. 1B as being substantially continuous,
it should be noted that such bands could be produced by rapid pulsing of
the engraving beam 122 as well as by continuous application thereof.
Moreover, it is also within the contemplation of the invention that the
bands consist of discrete engraved spots, which could be produced by
pulsing the beam 122 less rapidly than a pulsing rate which produces
continuous bands.
After the formation of the code pattern bands has been completed, the
apparatus 100 preferably proceeds to a "read after write" mode, in which
the satisfactory formation of the code pattern is checked. In this mode,
the control system 114 sequentially controls the beam deflector 124 to
deflect the beam 122 to positions corresponding to each of the 16
potential band locations and while the beam deflector is positioned for
each potential band location, the control circuit 114 causes the disk 10
to be rotated through one or more rotations, while controlling the laser
120 to output a beam 122 in a relatively low power continuous wave mode.
The low power beam 122 is directed to the particular potential band
position by the deflector 124, with compensation for the disk's
eccentricity, and is reflected from the surface of the disk 10 to form a
reflected beam 122' which is directed to the read back detector 128 to
provide a signal level indicative of whether the reflective coating is
present or absent at the radial position on the disk 10 to which the beam
122 is directed. The output signal from the read back detector 128 is
conditioned and processed by the signal conditioning and processing
circuit 142 and the resulting signal is output to the control system 114.
In this way the apparatus 100 "reads" each of the 16 potential band
locations to determine for each location whether or not a band
representing a "1" bit is present. The apparatus then compares the result
of the reading to the binary number which was to be applied to disk 10 to
confirm that the code pattern was properly formed.
If the read back process fails to confirm that the code pattern was
properly formed, then appropriate action is taken, such as discarding the
disk. Otherwise, if the formation of the proper code pattern is confirmed,
the disk manufacturing process proceeds to completion.
An alternative approach to forming the code pattern shown in FIG. 1B is
embodied in an apparatus 100' illustrated in block diagram form on FIG.
2B. Elements shown in FIG. 2B which correspond to the elements of FIG. 2A
are given like reference numerals and will not be described in detail.
Like the apparatus 100 shown in FIG. 2A, the apparatus 100' of FIG. 2B has
a turntable 108 for rotating the disk 10, a control and display section
102, and an engraving laser 120' with its associated laser control circuit
126.
The apparatus 100' also includes a rotating mirror assembly 160 which
functions as a beam deflector, and which, together with lens system L1,
selectively directs the beam 122 from engraving laser 120' to desired
radial positions on the surface of the disk 10. The rotating mirror
assembly 160 includes a motor (not separately shown) for rotationally
driving the mirror assembly 160 and an encoder 162 associated with the
motor for providing encoder pulses to the system 114.
The eccentricity compensation function of the apparatus 100 (FIG. 2A) is
performed in a different manner by the apparatus 100'. More specifically,
the laser beam 140 produced by laser diode 134 and used for eccentricity
compensation in the apparatus 100' (FIG. 2B) is directed to varying radial
positions on the disk 10 by the rotating mirror 160 and lens L1 in a
similar manner to the beam 122 of the engraving laser 120'. The optical
path for the beam 140 from the laser diode 134 to the rotating mirror 160
includes a polarized beam splitter 164, a quarter wave plate 166, and a
dichromatic mirror 168. The dichromatic mirror 168 is selected so as to be
highly reflective at the wavelength of the beam 140 and highly
transmissive at the wavelength of the beam 122. A return path for a beam
140' produced by reflection of the beam 140 from the disk 10 is provided
via the lens L1, the rotating mirror 160, the dichromatic mirror 168, the
quarter wave plate 166 and the polarized beam splitter 164, so that the
reflected beam 140' is directed to a read back detector 138'. A signal
output from the read back detector 138' is provided to a signal
conditioning and processing circuit 146', which provides a detection
signal to the control system 114.
The control system 114 is connected through signal paths which are not
shown in the drawing to provide on/off control of the laser diode 134 and
of the motor for the rotating mirror assembly 160.
In operation, a binary serial number to be applied in machine-readable form
to the disk 10 is generated in the same manner as in the apparatus 100 of
FIG. 2A. However, in the apparatus 100' (FIG. 2B) no initializing rotation
of the disk 10 is required. Rather, with the disk 10 at rest in an
arbitrary rotational position, the laser diode 134 and the motor in the
rotating mirror assembly 160 are both turned on, with the rotating mirror
assembly 160 being continually rotated at a constant rotational speed and
the laser diode remaining on throughout the code pattern engraving
operation now being described. The beam 140 emitted by the laser diode 134
is directed via the beam splitter 164, the quarter wave plate 166 and the
dichromatic mirror 168 for reflection by the rotating mirror 160.
Depending upon the instantaneous rotational position of the rotating
mirror 160, the beam 140 may or may not be reflected from the surface of
the disk 10 so that it is directed back to the read back detector 138'.
Moreover, the rotating mirror assembly 160 is positioned with respect to
the program/mirror boundary 18 of the disk 10 such that at some rotational
positions of the mirror 160 a reflected beam 140' is returned from the
mirror area 16 of the disk 10, and at other rotational positions of the
mirror 160, the reflected beam 140' is returned from the program area 14
of the disk 10.
The output signal of the read back detector 138' and the conditioned
detection signal by the signal conditioning and processing circuit 146'
are indicative of the intensity of light incident upon the read back
detector 138'. The intensity of light incident on the read back detector
138' is at a low level at times when the rotational position of the mirror
160 prevents the reflected beam 140' from reaching the read back detector
138'. The intensity of the light incident upon the read back detector 138'
is at a high level when the beam 140' is returned to the read back
detector 138' from the highly reflective mirror area 16, and the intensity
is at an intermediate level when the beam 140' is returned from the
moderately reflective program area 14. Accordingly, the detection signal
provided from the conditioning and processing circuit 146' to the control
system 114 is at one of three levels, namely a low level indicative of no
beam return, a high level indicative of beam return from the mirror area
16, and an intermediate level indicative of a beam return from the program
area 14. With constant rotation of the rotating mirror 160 in the
direction indicated by the arrow Ro, the path of the beam 140 is
continually changed from the rotating mirror 160 onward along an axis that
substantially coincides with a radius of the disk 10. When the beam is
incident upon the rotating mirror 160 at a rather acute angle, no
reflected beam 140' is present at the read back detector 138', with the
beam 140 being deflected to a position outboard from the disk 10. But with
continued rotation of the mirror 160 the beam 140 is directed radially
inwardly onto and across the mirror area 16, past the boundary 18 and on
to the program area 14. Accordingly, the intensity of light incident on
the read back detector 138' varies over time from a low level to a high
level to an intermediate level during the progressive deflection of the
beam 140 in a radially inward manner as just described. At the same times,
respective signals indicative of the low, high and intermediate detected
intensities are provided to control system 114. In particular, the control
system 114 is adapted to note the transition from high intensity to
intermediate intensity, which indicates the point in time at which the
beam path is deflected across the program/mirror boundary 18. The time at
which the deflected beam 140 crosses the boundary 18 is then used as a
benchmark for code pattern engraving using the laser 120', so that the
code pattern bands can be formed at a fixed distance from the boundary 18,
notwithstanding eccentricity in the disk 10. It will be noted that this is
possible because the engraving beam 122 shares the same beam deflection
path with the eccentricity compensation beam 140.
Accordingly, at a predetermined time interval after the beam path crosses
the boundary 18, the control system 114 causes the laser 120' to emit one
or more intense pulses of the engraving beam 122 so as to form an engraved
spot on disk 10 from which the reflective coating is removed. The
predetermined delay period between when the beam crosses the boundary 18
and the time at which the laser 120' is actuated to form the engraved spot
is selected so that the spot is formed in the code pattern band location
which corresponds to the first "1" bit in the binary serial number to be
applied to the disk 10. Then, after another predetermined delay, the laser
120' is again operated to engrave another spot at the radial location
corresponding to the band for the next "1" bit in the serial number. This
process continues during the same deflection pass of the beam path so that
a respective spot is formed for each of the bands required for the "1"
bits of the serial number. Although formation of all of the required spots
in a single deflection pass is preferred, it is also contemplated that
multiple passes, up to one deflection pass per spot, could be performed to
engrave all of the required spots along a single radius of the disk 10
(i.e., at the same rotational position of the disk 10). The timing for
establishing the delay periods after which engraved spots are formed may
be based on a timing circuit within control system 114 or upon code pulses
supplied to control system 114 from encoder 162.
After the respective spots have been formed at each of the "1" bit
positions, the control system 114 outputs a signal to the motor 110 so
that the disk 10 is rotated a very small distance by the turntable 108.
The rotation is such that the radius along which the spots were just
formed is at a very small angle to the disk radius which, after the
rotation, coincides with the axis of deflection of the beam. For example,
at the radial positions of the disk 10 at which the spots were formed, the
displacement between the radius upon which engraving was just performed
and the radius now coinciding with the beam deflection path may be in the
range of 5 to 100 microns, or more.
After the small rotation of the disk, another set of spots corresponding to
the "1" bit locations is then engraved along the new radius in the same
manner as just described (i.e., at the same time delays after the beam
deflection path crosses the boundary 18), and the disk is then rotated
again by the same small amount and the process is repeated until bands of
the desired length have been formed. With an engraved spot diameter of
approximately 25 microns, it will be appreciated that a substantially
continuous band is formed if the intermittent rotation between engraving
operations is in the lower end of the 5-100 micron range mentioned above,
whereas with rotation within or beyond the upper end of the range, bands
consisting of discrete spots will be formed.
The number of radii of the disk along which spots are formed depends on the
desired density of the spots and the desired length of the bands. For
example, the number of radii may be 50 or more, which implies that 50 or
more radial passes of the engraving beam are carried out.
It should be noted that in the beam path provided for the eccentricity
compensation beam 140, the quarter wave plate 166 increases the intensity
of the reflected beam 140' at the read back detector 138' by changing the
linear polarization of the outward bound beam 140 to a circular
polarization and by changing the resulting circular polarization of the
reflected beam back to a linear polarization in the return path of the
reflected beam 140'. However, the quarter wave plate 166 can be dispensed
with if the laser diode 134 is selected to have a more powerful output
beam and/or more sensitive detection circuitry is provided.
With the arrangement as shown in FIG. 2B, a relatively inexpensive Nd:YAG
laser, operable only in a pulsed mode, can be used. However, it is within
the contemplation of the invention to substitute a more expensive Nd:YAG
laser, which is operable in a continuous wave mode as well as a pulsed
mode. With such an Nd:YAG laser, the laser diode 134 and the quarter wave
plate 166 can both be dispensed with, and the Nd:YAG can be operated in a
low power continuous wave mode to provide the reflected beam used for
detecting the time at which the beam path crosses the boundary 18 on the
disk 10.
According to alternative embodiments of the invention, the formation of the
code pattern by vaporizing selected portions of the aluminum reflective
coating is performed either before or after application of the transparent
protective ink layer over the aluminum reflective coating. If the
vaporizing of the reflective coating is performed after the protective
layer has been applied, then the protective layer is vaporized along with
the reflective coating, but residual heat after removal of the laser beam
causes the protective layer to flow from adjacent areas to cover the
locations from which the material was vaporized, so that the protective
layer is reformed over the bands removed from the reflective coating.
FIG. 3 illustrates additional details concerning the format in which the
code pattern bands are formed. As mentioned before, in a preferred
embodiment of the invention a 16 bit machine-readable code is to be formed
so that 16 bands 150-1, 150-2, . . . , 150-16 are provided, respectively
corresponding to 16 bit locations. The bands 150-1-150-16 are arranged one
after the other, proceeding radially inwardly from a program read out area
152.
It should be understood that FIG. 3 is presented on a scale such that the
curvature of the bands 150 is negligible, and the bands 150 are presented
as being parallel in the circumferential direction of the disk 10, which
is indicated by the arrows C. Also, only a small portion of these bands
150 is shown in FIG. 3, inasmuch as the band format extends around the
entire circumference of the disk 10. The width of each band 150 (i.e., its
dimension in the radial direction indicated by the arrows R) is
approximately 100 microns. Thus all 16 of the bands 150 together make up
an annular region of the program area 14 having a width of about 1.6 mm.
Each of the bands 150 is divided approximately evenly in the
circumferential direction to form an engraving sub band 154 and an
information sub band 156, each having a width of about 50 microns.
Each engraving sub-band 154 is in turn divided into an engraving area 157
between safety areas 158. | | |
