Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR RF,PRODUCING DESIGNATED
INFORMATIOM FROM A RECORDED DISC
BACKGROUND OF THE INVENTION
Field of the Invention
The presen~ invention relates to apparatus for
reproducing information from a disc-shaped recording medium
and, more particularly, to apparatus for reproducinq
designated information from such a medium.
Description of the Prior Art
Disc-shaped recording mediums contalning program
information recorded in diyital form enable very high
Eidelty sound reproduction. The many problems inherent in
analog records are eliminated with discs recorded in digital
form. However, digital discs do no~ as easily lend
themselves to finding particular parts of the recorded
program information as do analo~ discs, which provide a
visual indication of the beginnings of different program
sections.
A convenient and well-known form of digitally
recorded disc uses a series of microscopic pits in the disc
surface to represent the recorded information. The pi~s are
arranged in a spiral track and, as the disc rotates, a laser
beam is focussed on the spiral track. Variations in the
re1ected or transmitted laser beam cau6ed by the pits are
sensed and the digital information thus derived is supplied
to suitable decoding circuitry to convert the digital
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information into the signal's original analog form for
supply to headphones or loudspeakers.
A common ~echnique for digital recording employs
pulse code modulation, or PCM. PCM recording "samples" the
original signal and converts each sample in~o digital form.
Error correction and other digltal inforrnation is added to
the PCM data and recorded on the disc. A typical ormat for
arranging the digital data employs a series of frames, each
of which contains~ among other information, program
information (the original signal) and address information.
The address information included in the digital
data recorded on the d sc identifies par~icular program
information. For example, the address information might
contain data identifying the particular section of program
information, data identifying the particular part of that
section and data representing the playing time required to
reach that part of the program information from the
beginning of that particular program section when the disc
player is opexating in the normal reproducing mode.
In any case, the digital data is reproduced from
the disc by tracing the spiral track of pits in the disc
outwardly from the radially innermost end of the ~rack. At
the beginning of the spiral track a 7'table of contents" is
provided. The table of contents~ contains in digital form,
the running time in the normal playback mode of the disc
player to the beginning of each segment of program
information.
To find a designated part of the progxam
information in prior art devices~ the laser picX-up device
moved transverse to the track a given amount and -then traced
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the trackO The address information at that point was
reproduced and used to determine how far the pick~up was
~rom the designated location. That searching operation
would then be repeated until the reproduced address
information matched the designated address information.
That approach inherentlv requires repeated
reproduction, at the normal playback speed, of address
information from the disc. As a resul~, the search time can
be lengthy. The resulting inconvenience will be even
greater when the designated program information is n~arer
the end of the track because it will take even longer to
reach it.
SUMl!lARY OF THE INVENTION
It is an object of the present invention to
provide an apparatus for reproducing information from a
designated location on a recorded disc that avoids the
aforementioned shortcomings of the prior art.
It is a further object of the present invention to
move the pick-up means of the reproducing apparatus
transversely across adjacent tracks using driving pulses
provided in a number proportional to the distance across
adjacent tracks to the designated location~ /
In accordance with an aspect of the present
in~ention/ an apparatus is provided for reproducing program
information from a designated location on a disc having
recorded thereon program information in a spiral track using
a pick-up means movable along the track in a normal playback
mode for reproducing the program information and
transversely across adjacent tracks generally radially of
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the disc. The apparatus comprises driving means for moving
the pick-up means from a reerence location transversely
across adjacent tracks on the disc in response to driving
pulses supplied thereto, counter means for providing an
actual count of driving pulses supplied to the driving
means, and system control means for providing a designated
count of driving pulses representing the distance
transversely across adjacent tracks between -the reference
loca~ion and the designated location and producing a driving
signal including a predetermined number of driving pulses
representing the difference between the designated count and
the actual count for supply to the driving means.
The above and other objects, features and
advantages of the present invention will be apparent when
the following detailed description of a preferred embodiment
of the invention is considered in connection with the
accompanying drawings.
BRIEF DESCRXPTION OF THE DRAWINGS
Fig. 1 i5 a schematic block diagram of a disc
player incorporating an embodiment of the present invention.
Fig. 2 is a flow chart illustrating the opexation
of the disc player shown in Fig. 1~
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Fig. 1 shows a digitally rec~rded disc 1 loaded on
a disc player for rotation. The disc 1 has program, address
and other informatlon recorded on it by means of a series of
pits Inot shown) formed in a spiral track in the surface of
the disc. The track is traced by an optical pick-up head 2.
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The spiral track begins radially inwardly of the edye of the
disc 1 and is traced as the di~c 1 rotates by xadial].y
outward movement of the pick-up head 2. The program
informat~.on on the disc 1 .is arranged in segments and -the
spiral track begl.ns with a table of conten-ts which contains
data indicating the running time, in minutes and seconds, to
the beginning of each segment. Typically, the information
.in the table of contents is also printed on the disc in
human-readable form.
The pick-up head 2 ~irects a laser beam agalnst
~he disc 1. The head ~ includes a photodetector -that
detects the modulation by the pits of the laser's
reflection. ~lternatively, the laser can be transmit~ed
through the disc, in which case the photodetector detects
the modulation by the pits of the laser beam as it is
transmitted t'nrough the disc. The photodetector in either
case provides an electrical output that represents the
digital information on the disc 1, in a well-known fashion.
The point where the laser beam impinges on the
disc 1 must be precisely controlled so that the pits are
read in the proper order. The optical head 2 thus includes
a tracking device that directs the laser beam against the
surface of the disc. The disc player includes a tracking
error detection circuit 3 that provides an error signal
which indicates mistracking of the l.aser beam in response to
the output of the photodetectorO The error signal is fed to
a tracking control circuit 4 which positions the optical
head using the tracking device. The direction in which the
laser beam i.s pointed is thus controlled by a servo-control
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system to maintain proper tracing of the spiral track of
pits in the disc 1.
For larger movement of the optical head 2, a
stepping motor 5 moves the optical head 2 radially lnwardly
and outwardly relatlve to the disc 1, depending on the
direction of rotation of the motor 5. A system control
circui~ 6 provides the input signals to a motor con~rol
circuit 7 which in turn provides signals to actlvate the
stepping motor 5. The motor actuation signals from the
motor control circuit 7 take the form of stepping pulses
which drive the stepping motor 5 a predetermined number of
steps either radially inwardly or outwardly relative to the
disc 1 depending on the polarity of the stepping pulses. In
the embodiment shown, each s~epwise rotation of the stepping
motor 5 moves the optical head 2 a constant distance
radially of the disc 1.
A counter 8 has three input terminals, U/D~ CK and
CR, and a single output terminal CO. The clock terminal CK
receives pulses and adds or subtracts them to the number
already in the counter 8. The up/down terminal U/D receives
a signal the polarity of which determines whether the pulses
received by the terminal CX will be added or subtracted from
the number in the counter~ The clear terminal CR sets the
number in the coun*er to a reference value, typically 2ero,
when it receives a signal. ~he output terminal CO provides
a signal that represents the number in t~e counter 8.
A start detector 9 provides a start signal when
the optical head ~ is at the beginning of the spiral track
on the disc 1. The start detector can either be a
mechanical device that provides a signal when contacted by
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~he op-tical head 2 or can be arranged to operate optically.
:~n any case, the start signal is provided to the CR terminal
of the counter 8 to set the counter to the zero reference
count when the optical. head 2 is set to begln tracing the
spiral track. As shown in Fi.g. 1, the system control
circuit 6 has two output termlnals tl and t2 at which are
provided signals Ps and Pd, respectively/ which together
comprise a driving signal. The signal Ps is applied to the
CK terminal of the counter 8 and the motor control circuit
7. The signal PD is applied to the U/D terminal of the
counter and also to the motor control circuit 7. The signal
Ps comprises driving pulses that are used by the motor
control circuit 7 to provide the stepping pulses to the
stepping motor 5 to cause it to rotate a predetermined
number of steps depending on, for example, the number of
pulses comprising the signal Ps. The signal PD is a
direction signal, the state (here its polarity) of which is
sensed by the motor control circuit 7 to determlne in which
direction the motor 5 is to be rotated. For example, if PD
is negative, the motor 5 is actuated in a directi~n that
moves the optical head 2 radially inwardly toward the
beginning of the spiral track and, if PD is posltive, the
motor 5 is rotated in the other direction.
: Meanwhile, the number stored in the counter 8
indicates the position of the optical head 2 relative to a
reference location, which in the illustrated embodiment is
the beginning of the spiral track, because the number of
driving pulses in the signal P~ is added to or subtracted
from, depending the polarity of the direction signal PD, the
number in the counter 8~ Thus, the signal dp at the output
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~erminal CO of the counter 8 comprises the actual count in
the counter 8 and represents the distance of the optical
head 2 from the reference location. The ac-tual count signal
dp is provided to an input ~erminal nl of the system control
circuit 6~
The output of the optical head 2 is supplied to a
digital signal detection circui~ 10 that conditions the
digital signal reproduced from the disc 1 for further use.
The conditioned digital signal is provided ~o a decoder ll.
The decoder 11 provides three outputs. ~irst, the program
information Sp is provided by the decoder 11 to a program
information processing circuit 12 that provides the program
information as an analog signal A corresponding to the
original signal. The analog signal A can be used in the
conventional manner to drive loudspeakers or headphones.
The decoder 11 also provides address in~ormation
Q' reproduced from the disc. The address information Ql is
converted by a deciphering circuit 13 into a resulting time
signal TQ. The resulting time signal TQ represents the
resulting time that would be required for the optical head 2
to reach the particular address represented by the signal Q'
when operated fxom the beginning of the splral track in the
normal playback mode. The resulting time signal TQ is
provided to a second input terminal n2 of the system control
circuit 6 .
Finally, the decoder 11 provides the table of
contents as a signal Toc to an input terminal n3 of the
system control circuit 6, which stores the information
represented by the signal Toc.
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As Fig. 1 shows, the system control circuit 6 has
a third output -terminal t3 which provides jump signal J to a
jumping pulse generating circuit 14. In response to the
signal J the circuit 14 provides a jumping pulse Pj to the
tracking control circuit 4. The -tracki.ng control circuit 4
moves the optical head 2 radially of the disc 1 in response
to the jumping pulse Pj, The output of the tracking control
c.ircuit 4 is also provided through a low pass filter 15 to a
fourth input terminal n4 of ~he system control circuit 6.
The disc player incorporating -~he present
invention also includes a command signal generating circuit
16 that provldes a designating .signal I to a f.ifth lnput
terminal n5 of the system control circuit 6. An operator
uses the generating circuit 16 as a designating means to
select a position on the disc 1 from which the reproduction
of program information is to begin. For example, by using
the printed table of contents on the disc, the operato.r can
choose the desired time, in minutes and seconds from the
beginning of a parti.cular program segment, from which
.reproduction is to begin. The generating circuit 16
provides the designating signal I representing that
designated information to the system control circuit 6.
The operation of the apparatus of the presen~
.Lnvention can be understood by referring to both F.igs. 1 and
.
Assume that the operator wishes reproduction of
program information from the disc 1 to begin at x minutes
and ~ seconds from the beginning of the Mth program segment.
Assume also that the disc 1 has been loaded on the disc
player and that the table of contents has been read from the
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disc and provided to the system control circuit 6 as the
slgnal Toc and is stored therein.
The operator provides the informatlon concerning
the clesignated location from which reproduction is to begin.
As shown in Fig. 2, the first calculation step C1, performed
by the system control circuit 6, converts the designating
signal I into time data in the proper form. The system
control circuit 6 has, in the table of contents inEormation
stored ~herein, sufficient data to calculate the -time, in xO
minutes and yO seconds, irom the heginning of the spiral
track to the beginning of the Mth prograrn section. With
that information, the system control circuit 6 calculates
the normal reproducing time T in X minutes Ix ~ x ) and Y
~ o
seconds (y -~ yO) it would require to reach the designated
]o~ation from the beginning of the spiral track.
In calculation step C2, the time Ti is converted
into a signal dil so that the time Ti actually represents
the radial distance from the beginning of the spiral ~rack
to the designated location. Generally,`the radial distance
dr fron the beginning of the spiral track to any given
point, which takes the optical head 2 a time Tx to ~each
when in a normal playback mode, can be expressed:
dr = flTX) ~ a constank.
Thusl if the function f(Tx) is known and programmed into the
system control circuit 6, the signal di can be calculated
from Ti.
The signal di calculated by skep C2 is in the same
form as the actual count dp provided from the counter 8
output terminal CO. That is, di is expressed as a number
that corresponds to the distance represented by Ti, can be
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time regarded as a designated count. So, if di and dp have
the same value, the actual radial distance (dp) of the
optical head 2 from the beginning of ~he spiral track is the
same as the dlstance calcu].ated uslng the time Tl.
In steps C4 and C5 the system control circuit 6
uses a difference signal di to generat.e the pulse signal
Ps and the direction signal Pd, which are provided to the
motor control circuit 7 and the counter 8. The pulse signal
Ps comprises a predetermined number of driving pulses and
the direction signal Pd has a polarity which depends on the
comparison of di and dp. The motor control circuit 7
generates the stepping pulses with the pro~er polarity to
move the optical head 2 radially of the disc 1 and, at the
same time, the count in the counter 8 changes to provide a
different actual count dp which represents the new position
of the optical head 2. That movement of the optical head is
shown in the block in Fig. 2 following step C5.
The optical head 2 is then operated momentarilv in
the normal playback mode long enough to obtain address
information Q from the disc 1. That address information Q
is converted by the deciphering circuit 13 into the
resulting time signal TQ representing the time required to
reach that particular location on the disc in a normal
playhack modeO In step C6 the resulting time TQ is compared
with the designated time Ti to obtain a time difference
signal Ui Q (= Ti ~ TQ)'
The time difference signal Ui_Q is compared with a
first coarse-reference time Ul. The decision step Dl depicts
that comparison. If Ui Q is less than or equal to Ul~ steps
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C7, C8 and Cg are omitted and the next calculation step that
takes place is C10.
If Ui Q is greater than Ul, indicating that it
woulcl take longer than the coarse-reference time Ul of
playing time to reach the designated position on the disc
from the optical head's actual position, the step C7 is
performed. In step C~ the system control circuit 6 again
calculates the number of steps and the direction of rotation
required for the motor S to move the optical head 2 from the
location of the address information Q to the designated
location di, by using the resulting time TQ. The pulse and
direction signals Ps and Pd, as shown by step C8, again
cause the optical head 2.
Ps and Pd are also supplied to the counter 8, so
that the actual count dp provided by the counter output CO
still has a value that corresponds to the radial distance
from the reference location at the beginning of the spiral
track.
The disc 1 is again read long enough to obtain
again address information Q that represents the actual
position of the optical head 2 relative to the beginning of
the track on the disc 1. The time data TQ thus obtained
from Q by the deciphering circuit 13 is used to calculate
Ti TQ, as represented by step Cg. The magnitude of that
difference is used by the system control circuit 6 to
provide the signal J to the jumping pulse generating circuit
14, which pr~vides a jumping pulse Pj to the tracking
control circuit 4, as depicted by the step C10 in Fig. 2.
The tracking control circuit 4 generates a
fine-adjustment signal using the jumping pulse Pj. The
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fine-adjustment signal is in a form identical to the signal
provided by the tracklng con~rol circuit 4 in response to
the tracking error cletection circuit , that is, a direct
current signal. The fine-adjustment signal is provided with
a voltage which is proportional to the difference between
the designated time Ti and the resulting time T~ last read
from the disc.
The tracking device used to change the position of
the laser in the optical head 2 relative to the disc 1 has a
conventional and well-known configuration. For example, the
optical head 2 may be rotably mounted on an axis
substantially normal to the disc surface. The laser is
directed at the disc from a location on the optical head
displaced from that axis. A coil surrounds the optical head
such that the magnitude and polarity of a dc signal supplied
to the coil causes the optical head to rotate about the axis
and thereby move the location of the laser relative to the
disc surface.
In any case, the fine-adjustment signal causes the
optical head to direct the laser against the disc at a track
that is displaced from the location of the last-provided
address information Q, which is the track-jumping operation
depicted in Fig. 2. ~he address in_ormation Q is read from
the disc at that location and is converted by the
deciphering circuit 13 into another resulting time signal
r
TQ.
At the same time, the fine-adjustment signal is
provided through the low-pass filter 15 to the input
terminal n4 of the system control circuit 6. The system
control circuit 6 generates the driving signal (Ps and Pd~
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which causes ~he stepping motor 5 to move the optical head 2
and increments the counter 8 to change dpo
As shown in step C11, the designated time Ti and
~he result,ing time TQ are compa,red. The resul-t Ui Q of that
comparison is checked against a fine-reference time UO. If
the time difference signal Ui Q is less than or equal to UO,
then the search operation is ended. However, if Ui Q is
greater than UO, steps C10, C11 and D2 are repeated.
Thus, a ine~adjustment process is accomplished by
direct use of the address information aftex a coarse~
adjustment which initially uses driving pulses to quickly
move the optical head to a loca-~ion very close -to the
designated location and then indirectly uses address
information driving pulses if the initial movement of the
optical head is not to within an acceptable distance from
the designated location.
The present invention has been described by
reerring to a specific embodiment thereof. Those skilled
in -the art will recognize that modifications other than
those specifically referred to can be made in that
embodiment without departing from the spirit of the
invention. For that reason the scope of the in~ention is
not to be limited by the above description but instead is
defined solely by the claims which follow.
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