Devices for detecting defects of disc-shaped record media

A defect in an information signal recorded in a spiral track on an optical disc is detected based on a low level portion of an envelope of a reproduced information signal. When periods between detection output pulses each measured from the leading edge of the detection output pulse are equal to each other, a pulse having its leading edge at a time point after the leading edge of said detection output pulse and its trailing edge at a time point of the trailing edge of said detection output pulse or a time point after the trailing edge of said detection output pulse is produced to be used as a defect detection signal. The defect detection signal is used for preventing tracking servo-control and focus servo-control for an optical head from being performed abnormally.

TECHNICAL FIELD 
The present invention relates to a device for detecting a defect of a 
disc-shaped record medium, which generates a defect detection output 
signal at the time when the defect of the disc-shaped record medium comes 
to a reading position during reproduction of an information signal 
recorded in a spiral recording track on the disc-shaped record medium. 
TECHNICAL BACKGROUND 
In a disc player for reproducing an information signal from an optical 
disc, such as an optical digital audio disc, on which the information 
signal is recorded in the form of small pits arranged in a spiral track, a 
light beam is used for reading the information signal from the spiral 
track. The light beam is emitted from an optical head which is moved in 
the direction of the radius of the optical disc so as to scan the spiral 
track on the optical disc which is in a state of revolutions at a 
predetermined speed, and the light beam is required to trace correctly the 
spiral track and to be focused correctly on the surface of the optical 
disc on which the spiral track is formed. To make the light beam comply 
with these requirements, tracking servo-control and focus servo-control 
are performed. In the tracking servo-control, the position of a beam spot 
formed by the light beam on the optical disc in relation to the spiral 
track is detected to produce a tracking detection output and an optical 
element, such as a focusing lens, in the optical head or the optical head 
in its entirety is moved in the direction of the radius of the optical 
disc in response to the tracking detection output so as to cause the 
position of the beam slot to be placed correctly on the spiral track. In 
the focus servo-control, a focus condition of the light beam on the 
optical disc is detected to produce a focus detection output and the 
focusing lens in the optical head or the optical head in its entirety is 
moved in the direction of an axis of rotation of the optical disc in 
response to the focus detection output so as to cause the light beam to be 
focused correctly on the optical disc. 
The tracking detection output is obtained in the form of a tracking error 
signal representing deviations of the beam spot on the optical disc from 
the center of the spiral track and the focus detection output is obtained 
in the form of a focus error signal representing defocus of the light beam 
on the optical disc. The tracking error signal and the focus error signal 
are usually derived from an information signal reproducing section 
together with a reproduced information signal. In the information signal 
reproducing section, a reading light beam, which comes from a portion of 
the optical disc on which the light beam emitted from the optical head is 
caused to impinge and modulated in intensity, is detected by a plurality 
of light detecting elements forming together a photodetector and detection 
output signals obtained from the light detecting elements in the 
photodetector are calculated at a signal processing circuit. Then, control 
signals are produced respectively based on the tracking error signal and 
the focus error signal which are derived from the information signal 
reproducing section containing the photodetector and the signal processing 
circuit, and supplied to driving means for moving the optical element such 
as the focusing lens in the optical head or the optical head in its 
entirety in the direction of the radius of the optical disc or the 
direction of the axis of rotation of the optical disc. As a result, the 
optical element such as the focusing lens in the optical head or the 
optical head in its entirety is moved in the direction of the radius of 
the optical disc or the direction of the axis of rotation of the optical 
disc in response to each of the tracking error signal and the focus error 
signal. 
When the information signal is reproduced from the spiral track on the 
optical disc under the tracking servo-control and the focus servo-control 
performed as mentioned above in the disc player, and in the case where the 
optical disc has a defect where the surface or inside thereof is damaged 
or stained, the defect is read by the light beam emitted from the optical 
head to impinge thereon and the detection output signals obtained from the 
light detecting elements forming the photodetector are provided with 
variations caused in response to the defect of the optical disc. These 
variations in the detection output signal obtained from the light 
detecting elements bring about a missing portion of the reproduced 
information signal obtained from the signal processing circuit, which has 
such an extraordinarily low level as to be out of a predetermined range of 
the amplitude of the reproduced information signal, and further give rise 
to a relatively large noise in the form of a pulse in each of the tracking 
error and focus error signals derived from the signal processing circuit. 
That is, the defect of the optical disc results in the missing portion of 
the reproduced information signal and the relatively large noise in each 
of the tracking error and focus error signals. 
The relatively large noise in the tracking error signal or the focus error 
signal resulting from the defect of the optical disc causes the control 
signal, which is supplied to the driving means for moving the optical 
element such as the focusing lens in the optical head or the optical head 
in its entirety in the direction of the radius of the optical disc or the 
direction of the axis of rotation of the optical disc, to take up an 
extraordinary level. Then, In the case where the control signal taking up 
such an extraordinary level is supplied to the driving means, the optical 
element such as the focusing lens in the optical head or the optical head 
in its entirety is moved abnormally so that the tracking servo-control or 
the focus servo-control is not properly carried out. 
In the manner as mentioned above, an undesirable operation state wherein 
the tracking servo-control or the focus servo-control is not properly 
performed is easily caused in the disc player when the defect portion of 
the optical disc is read by the light beam emitted from the optical head. 
To avoid such an undesirable operation state caused in the disc player, 
there has been proposed to provide a disc player with an arrangement for 
conducting a defect detection by which an operation state wherein the 
defect of the optical disc is read is detected in an information signal 
reproducing section including a photodetector and a signal processing 
circuit and for preventing both the tracking servo-control and the focus 
servo-control from being carried out abnormally when an output of the 
defect detection, namely, a defect detection output is obtained. In this 
arrangement proposed previously, the defect detection is carried out based 
on the reproduced information signal derived from the signal processing 
circuit in such a manner as mentioned below. 
When the defect of the optical disc is read, a reproduced information 
signal Si comprises missing portions d each having a width corresponding 
to the width of the defect, as shown in FIG. 1A. Since the defect of the 
optical disc extends usually over several convolutions of the spiral track 
formed on the optical disc, the missing portions d occur periodically 
during a period of time depending on the size of the defect. The 
reproduced information signal Si containing the missing portions d is 
supplied to an envelope detector and a detection output signal Sv having a 
voltage level which corresponds to the envelope level of the reproduced 
information signal Si, as shown in FIG. 1B, is obtained from the envelope 
detector. 
The detection output signal Sv has low level portions d' corresponding to 
the missing portions d contained in the reproduced information signal Si. 
Then, the level of the detection output signal Sv is compared with a 
reference voltage level Vo set as shown in FIG. 1B, and as a result, 
pulses Sp each taking up a high level in response to a portion of the 
detection output signal Sv which has a voltage level lower than the 
reference voltage level Vo, namely, the low level portion d' of the 
detection output signal Sv, as shown in FIG. 1C, are obtained. 
In the case where pulses Sp thus obtained are used directly as the defect 
detection output successively from the first one thereof, false detection 
of the defect of the optical disc is apt to be caused. Accordingly, on the 
basis of the fact that the pulse Sp which result actually from the defect 
of the optical disc occurs for every revolution of the optical disc during 
a certain period of time in the same manner as the missing portion d in 
the reproduced information signal Si, the pulses Sp are supplied to an 
integration circuit having a predetermined integration time constant to be 
integrated in level and the defect detection output is destined to be made 
based on each of the pulses Sp which are obtained after an output level of 
the integration circuit reaches a predetermined voltage level. 
A defect detecting part of the previously proposed arrangement which is 
operative to detect the operation state wherein the defect of the optical 
disc is read in such a manner as aforementioned comprises a circuit block 
including the integration circuit and produces the defect detection output 
after the defect of the optical disc is read and thereby the pulse Sp is 
obtained within a period of time of each one revolution of the optical 
disc. Therefore, the defect detection output derived from the defect 
detection part is delayed compared with a time point at which the defect 
of the optical disc is read actually. The time-lag arising thus on the 
defect detection output results in a problem that each of the tracking 
servo-control and the focus servo-control are not prevented effectively 
from being carried out abnormally in the operation state wherein the 
defect portion of the optical disc is read. Further, reliability in 
producing the defect detection output in response to the pulse Sp at the 
defect detection part is deteriorated due to the delay of the defect 
detection output. 
DISCLOSURE OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a device 
for detecting a defect of a disc-shaped record medium, which generates a 
defect detection output signal without time-lag surely and precisely when 
the defect formed in or on the disc-shaped record medium is read during 
reproduction of an information signal recorded in a spiral recording track 
on the disc-shaped record medium performed in a disc player. 
To achieve the end described above, the device for detecting a defect of a 
disc-shaped record medium according to the present invention comprises, as 
a fundamental configuration thereof is shown in FIG. 2, period detecting 
means 1 for measuring a period of input pulses Sp which are obtained 
whenever the defect of the disc-shaped record medium is read, period 
setting means 2 for setting up a period of time shorter than the period of 
the input pulses Sp detected by the period detecting means 1, leading edge 
fixing means 3 for fixing a time point of a leading edge of an output 
pulse Sd at a first time point at which the period of the input pulses Sp 
is detected by the period detecting means 1 or a second time point to 
which a time corresponding to the period of time set up by the period 
setting means 2 elapses from a time point of a leading edge of one of the 
input pulses Sp appearing after the first time point, trailing edge fixing 
means 4 for fixing a time point of a trailing edge of the output pulse Sd 
at a time point of a trailing edge of one of the input pulses Sp appearing 
after the time point of the leading edge of the output pulse Sd set up by 
the leading edge fixing means 3 or a third time point to which a 
predetermined time elapses from the time point of the leading edge of the 
output pulse Sd fixed by the leading edge fixing means 3, and output pulse 
generating means 5 for producing the output pulse Sd having its pulse 
width corresponding to a period of time from the time point fixed by the 
leading edge fixing means 3 to the time point fixed by the trailing edge 
fixing means 4 and sending out the output pulse Sd as a defect detection 
output signal in relation to the disc-shaped record medium. 
In the device for detecting a defect of a disc-shaped recording medium thus 
constituted according to the present invention, first the period of the 
input pulses Sp is measured by the period detecting means 1 when the input 
pulses Sp are supplied, and then the period of time which is shorter than 
the period of the input pulses Sp measured by the period detecting means 1 
is set up by the period setting means 2. Next, the time point of the 
leading edge of the output pulse Sd is fixed at the first time point or 
the second time point by the leading edge fixing means 3, and further the 
time point of the trailing edge of the output pulse Sd is fixed at the 
time point of the trailing edge of one of the input pulses Sp appearing 
after the time point fixed by the leading edge fixing means 3 or the third 
time point by the trailing edge fixing means 4. Then, the output pulse Sd 
is generated by the output pulse generating means 5 so as to have its 
leading edge at the time point fixed by the leading edge fixing means 3 
and its trailing edge at the time point fixed by the trailing edge fixing 
means 4, and sent out as the defect detection output signal from the 
output pulse generating means 5. 
Through the operation mentioned above, the output pulse Sd is formed to 
have its leading edge at a time point before the leading edge of one of 
the input pulses Sp and its trailing edge at a time point of the trailing 
edge of the same input pulse Sp or a time point thereafter, and surely 
sent out without time-lag as the defect detection output signal when the 
defect formed on or in the disc-shaped record medium is read. As a result, 
the defect detection output signal Sd is obtained with improved precision 
in time when the defect of the disc-shaped record medium is read. 
Accordingly, in the case where the defect detection output signal which is 
generated by the device according to the present invention is used for 
restraining the tracking servo-control or the focus servo-control when the 
defect of the disc-shaped record medium is read in the disc player, the 
tracking servo-control or the focus servo-control is prevented timely and 
effectively from being carried out abnormally in response to the defect 
detection output signal obtained by the device according to the present 
invention.

AN EMBODIMENT MOST PREFERABLE FOR WORKING OF THE INVENTION 
FIG. 3 shows an example of a device for detecting a defect of a disc-shaped 
record medium according to the present invention, together with a part of 
a disc player to which the example is applied. The disc player is 
operative to reproduce an information signal recorded in a spiral track 
formed on a recording plane of an optical disc, as aforementioned. 
In the example shown in FIG. 3, a reading light beam, which emerging from a 
portion of the optical disc revolving at a constant linear velocity on 
which a light beam emitted from an optical head is caused to impinge and 
modulated in intensity, is guided through an objective lens to four light 
detecting elements 10a, 10b, 10c and 10d which form a photodetector 10 to 
form a beam spot on the light detecting elements 10a to 10d. The light 
detecting elements 10a to 10d produce respective output signals Ia, Ib, Ic 
and Id each corresponding to a portion of the beam spot formed on each of 
the light detecting elements 10a to 10d, and the output signals Ia to Id 
are supplied to a signal processing circuit 12. In the signal processing 
circuit 12, the output signals Ia to Id are subjected to arithmetic 
operation so as to produce a reproduced information signal Si 
corresponding to the information signal recorded in the spiral track on 
the optical disc, a tracking error signal St representing deviations of a 
beam spot formed on the optical disc by the light beam emitted from the 
optical head from the center of the spiral track, and a focus error signal 
Sf representing defocus of the light beam on the optical disc. 
The reproduced information signal Si is supplied to an information signal 
processing circuit 14 and a demodulated or decoded information signal Sa 
is derived from the information signal processing circuit 14 to an output 
terminal 15. The reproduced information signal Si is supplied also to an 
envelope detecting circuit 16 and a detection output signal Sv having a 
voltage level corresponding to the envelope of the reproduced information 
signal Si is obtained from the envelope detecting circuit 16. The 
detection output signal Sv is supplied to one of input terminals of a 
level comparator 18 which has the other of the input terminals thereof 
supplied with a reference voltage Vo from a voltage source 17, and a pulse 
Sp which takes up a high level when the voltage level of the detection 
output signal Sv is lower than the reference voltage Vo is obtained from 
the level comparator 18. This pulse Sp is supplied to a defect detecting 
section 20. 
The defect detecting section 20, to which the pulse Sp is supplied as an 
input pulse, comprises one example of the device detecting a defect of a 
disc-shaped record medium according to the present invention, generates an 
output pulse Sd and sends out it as a defect detection output signal as 
described later when a defect of the optical disc is read by the light 
beam emitted from the optical disc. The output pulse Sd obtained from the 
defect detecting section 20 is supplied to both a switch 30 provided in a 
tracking servo-control section and a switch 32 provided in a focus 
servo-control section. 
The tracking error signal St and the focus error signal Sf obtained from 
the signal processing circuit 12 are supplied through variable resistors 
22 and 24 for level adjustment to a fixed contact 30a of the switch 30 and 
a fixed contact 32a of the switch 32, respectively. The tracking error 
signal St obtained through the variable resistor 22 is supplied also to a 
restraining signal generating circuit 26 for tracking servo-control, which 
comprises a capacitor 26a and a resistor 26b, and a restraining signal St' 
is produced based upon the tracking error signal St in the restraining 
signal generating circuit 26 to be supplied to a fixed contact 30b of the 
switch 30. Further, the focus error signal Sf obtained through the 
variable resistor 24 is supplied also to a restraining signal generating 
circuit 28 for focus servo-control, which comprises a capacitor 28a and a 
resistor 28b, and a restraining signal Sf' is produced based upon the 
focus error signal St in the restraining signal generating circuit 28 to 
be supplied to a fixed contact 32b of the switch 32. 
In the switch 30, a movable contact 30c is connected to the fixed contact 
30a so that the tracking error signal St is obtained at the movable 
contact 30c when the output pulse Sd is not supplied thereto from the 
defect detecting section 20, and the movable contact 30c is connected to 
the fixed contact 30b so that the restraining signal St' is obtained in 
place of the tracking error signal St at the movable contact 30c when the 
output pulse Sd is supplied thereto from the defect detecting section 20. 
Similarly, in the switch 32, the movable contact 32c is connected to the 
fixed contact 32a so that the focus error signal Sf is obtained at the 
movable contact 32c when the output pulse Sd is not supplied thereto from 
the defect detecting section 20, and the movable contact 32c is connected 
to the fixed contact 32b so that the restraining signal Sf' is obtained in 
place of the focus error signal Sf at the movable contact 32c when the 
output pulse Sd is supplied thereto from the defect detecting section 20. 
The tracking error signal St or the restraining signal St' derived from the 
switch 30 is supplied to a tracking control signal generating circuit 34 
and a control signal Ct generated based on the tracking error signal St or 
the restraining signal St' is derived from the tracking control signal 
generating circuit 34 to a driving coil 40 for tracking control. The 
driving coil 40 supplied with the control signal Ct works for moving an 
optical element such as the objective lens in the optical head or the 
optical head in its entirety in the direction along the radius of the 
optical disc in accordance with the control signal Ct, so that the 
tracking servo-control is performed. In like manner, the focus error 
signal Sf or the restraining signal Sf' derived from the switch 32 is 
supplied to a focus control signal generating circuit 36 and a control 
signal Cf generated based on the focus error signal Sf or the restraining 
signal Sf' is derived from the focus control signal generating circuit 36 
to a driving coil 42 for focus control. The driving coil 42 supplied with 
the control signal Cf works for moving the optical element such as the 
objective lens in the optical head or the optical head in its entirety in 
the direction along the axis of rotation of the optical disc in accordance 
with the control signal Cf, so that the focus servo-control is performed. 
In such a configuration including an information signal reproducing 
section, a tracking servo-control section and a focus servo-control 
section as described above, the defect detecting section 20, which 
comprises one example of the device according to the present invention, 
performs a defect detection by which an operation state wherein a defect 
of the optical disc is read is detected. 
In the case where the optical disc has a defect thereon or therein and when 
the defect of the optical disc is read by the light beam emitted from the 
optical head, a missing portion d occurs repeatedly in the reproduced 
information signal Si obtained from the signal processing circuit 12 for 
every revolution of the optical disc during a period of time depending on 
the size of the defect, as aforementioned and shown in FIG. 1A. From the 
envelope detecting circuit 16 to which the reproduced information signal 
containing the missing portions d is supplied, the detection output signal 
Sv having low level portions d' corresponding to the missing portions d in 
the reproduced information signal Si, as shown in FIG. 1B, is obtained. 
Then, the pulse Sp taking up the high level in response to the low level 
portion d' of the detection output signal Sv, which has the voltage level 
lower than the reference voltage level Vo, as shown in FIG. 1B, is 
obtained from the level comparator 18 in which the voltage level of the 
detection output signal Sv is compared with the reference voltage Vo, and 
the pulse Sp is supplied to the defect detecting section 20. 
Accordingly, the pulse Sp which is obtained during a period of time 
corresponding to the missing portion d in the reproduced information 
signal Si, in other words, obtained when the defect of the optical disc is 
read is supplied to the defect detecting section 20 as the input pulse 
thereto, and in the defect detecting section 20, the defect detection is 
carried out and the output pulse Sd is sent out as the defect detection 
output signal, as described below. 
In the operation state wherein the defect of the optical disc is read, the 
pulse Sp is supplied periodically to the defect detecting section 20 for 
every revolution of the optical disc, as shown in FIG. 4. In the defect 
detecting section 20, first, a period of time from a time point t.sub.1 of 
the leading edge of the first one of the pulses Sp to a time point t.sub.2 
of the leading edge of the second one of the pulses Sp, namely, a period 
T.sub.1 of the pulses Sp is measured. Then, a period of time from a time 
point t.sub.2 of the leading edge of the second one of the pulses Sp to a 
time point t.sub.3 of the leading edge of the third one of the pulses Sp, 
namely, a period T.sub.2 of the pulses Sp is measured. After that, periods 
T.sub.3, T.sub.4, . . . T.sub.x-2 are measured successively at respective 
occurrences of the fourth one to the (x-1)th one of the pulses Sp. 
Further, a predictive pulse P.sub.1 which has its leading edge at a time 
point to which a time T.sub.1 -.alpha. shorter by a short time .alpha. 
than the period T.sub.1 elapses from the time point t.sub.2 of the leading 
edge of the second one of the pulses Sp and its trailing edge at a time 
point to which a predetermined time Tc longer than the width of the pulse 
Sp elapses from the leading edge thereof is formed after the measurement 
of the period T.sub.1. Then, a predictive pulse P.sub.2 which has its 
leading edge at a time point to which a time T.sub.2 -.alpha. shorter by 
the short time .alpha. than the period T.sub.2 elapses from the time point 
t.sub.3 of the leading edge of the third one of the pulses Sp and its 
trailing edge at a time point to which the predetermined time Tc elapses 
from the leading edge thereof is formed after the measurement of the 
period T.sub.2. After that, in like manner, predictive pulses P.sub.3 to 
P.sub.x-2 relating to a time T.sub.3-.alpha. to a time T.sub.x-2 -.alpha. 
respectively are formed successively. These predictive pulses P.sub.1 to 
P.sub.x-2 set up respectively a period of time T.sub.1 -.alpha. to a 
period of time T.sub.x-2 in relation to the measured periods T.sub.1 to 
T.sub.x-2, and the leading edges of the predictive pulses P.sub.1 to 
P.sub.x-2 are antecedent respectively to the leading edges of the third 
one to the (x-1)th one of the pulses Sp. 
Then, the period T.sub.2 is compared with the period T.sub.1, and it is 
judged that the pulse Sp obtained from the level comparator 18 results 
from the defect of the optical disc when the period T.sub.2 is 
substantially equal to the period T.sub.2. In the case where the period 
T.sub.2 is substantially equal to the period T.sub.2, a wide pulse signal 
Sw which has its leading edge at the time point t.sub.3 of the leading 
edge of the third one of the pulses Sp to keep a high level until a time 
point tx of the trailing edge of the last one of the predictive pulses 
P.sub.1 to P.sub.x-2 and its trailing edge at the time point t.sub.3 is 
produced as shown in FIG. 4. 
With the wide pulse signal Sw thus formed, a time point of the leading edge 
of the output pulse Sd is fixed at the time point of the leading edge of 
each of the predictive pulses P.sub.2 to P.sub.x-2 which are obtained when 
the wide pulse signal Sw takes up the high level, and a time point of the 
trailing edge of the output pulse Sd is fixed at the time point of the 
trailing edge of the pulse Sp which occurs first after each of the time 
points of the leading edges of the output pulses Sd or at the time point 
of the trailing edge of the predictive pulses P.sub.x-2. Consequently, the 
output pulses Sd each having the leading and trailing edges fixed in such 
a manner as escribed above are generated as shown in FIG. 4. 
To the contrary, in the case where the period T.sub.2 is not substantially 
equal to the period T.sub.2, it is judged that the pulse Sp obtained from 
the level comparator 18 does not result from the defect of the optical 
disc and the wide pulse signal Sw is not produced, and therefore the 
output pulse Sd is not generated. Then, when any combination of successive 
two of the periods T.sub.2 to T.sub.x-2, such as the periods T.sub.2 and 
T.sub.3, the periods T.sub.3 and T.sub.4, and so on, which are 
substantially equal to each other, appears, the output pulse Sd is 
generated in the same manner as the case where the period T.sub.2 is 
substantially equal to the period T.sub.2. 
The output pulses Sd thus produced are sent out as the defect detection 
output signal. Each of the output pulses Sd has the leading edge thereof 
antecedent to the leading edge of the pulse Sp corresponding thereto with 
the exception of the last one, and therefore the operation state wherein 
the defect of the optical disc is read is surely represented by each of 
the output pulses Sd without time-lag for every revolution of the optical 
disc during a period of time depending on the size of the defect of the 
optical disc. 
Accordingly, when the defect of the optical disc is read by the light beam 
emitted from the optical head in the disc player, the restraining signals 
St' and Sf' are supplied at an appropriate timing by the switches 30 and 
32, which are controlled by the output pulses Sd derived from the defect 
detecting section 20, to the tracking control signal generating circuit 34 
and the focus control signal generating circuit 36, respectively, in place 
of the tracking error signal St and the focus error signal Sf which would 
have respective extraordinary levels, so that both the tracking 
servo-control and the focus servo-control are kept on being performed 
stably. 
The defect detecting section 20 effecting the defect detection as described 
above is constituted with, for example, a microcomputer and an example of 
the operation program of the microcomputer for such defect detection is 
carried out in accordance with a flow chart shown in FIG. 5. 
In th case of the flow chart shown in FIG. 5, after the start, in the 
initial arrangement in process 101, a mode flag M used for checking 
detection of the period of the pulses Sp, a mode flag F used for checking 
occurrence of the pulses Sp and a count value Cn used for measuring the 
period of the pulses Sp are set to 0, and a count value Cc corresponding 
to a time Tc for determining the pulse width of each of the predictive 
pulses P.sub.1 to P.sub.x-2 is set up. 
Then, in decision 102, it is checked whether the leading edge of the pulse 
Sp occurs or not. In the case where the leading edge of the pulse Sp does 
not occur, the check in the decision 102 is repeated. While, it is 
clarified that the leading edge of the pulse Sp occurs, a count clock 
signal Kc is generated in process 103 and then the count value Cn is 
increased by 1 in response to the count clock signal Kc in process 104. 
Next, in decision 105, it is checked whether the mode flag M is 1 or not. 
If the mode flag M is not 1, it is judged that the period of the pulses Sp 
is being detected and therefore it is checked whether the leading edge of 
the pulse Sp occurs or not in decision 106. If it is clarified that the 
leading edge of the pulse Sp occurs, it is checked whether the count value 
Cn is equal to a count value Cn-1 which has been obtained at the time 
point of the leading edge of the pulse Sp occurring antecedently or not, 
in decision 107. In the case where the count value Cn is not equal to the 
count value Cn-1, a count value Cm used for setting a period of time is 
set up by subtracting a value Ca corresponding to a predetermined short 
time .alpha. from the count value Cn, in process 108. Then, the count 
value Cn-1 is set to have the same value as the count value Cn, and after 
that, the count value Cn is set to 0 in process 109. Thereafter, the step 
is returned to the the process 104, so that the count value Cn is further 
increased by 1 in response to the count clock signal Kc. 
To the contrary, if it is clarified that the leading edge of the pulse Sp 
does not occur in the decision 106, the count value Cm set up in the 
process 108 is decreased by 1 in response to the count clock signal Kc, in 
process 110, and it is checked whether the count value Cm becomes 0 or 
not, in decision 111. If the count value Cm is not 0, the step is returned 
to the process 104. On the other hand, when it is clarified that the count 
value Cm becomes 0, since the period of time corresponding to the count 
value Cm has elapsed from the leading edge of the pulse Sp, one of the 
predictive pulses P.sub.1 to P.sub.x-2 is generated in process 112, and 
thereafter the step is returned to the process 104. 
If it is clarified, as a result of the check in the decision 107, that the 
count value Cn is substantially equal to the count value Cn-1, the leading 
edge of the wide pulse signal Sw rising to the high level is formed and 
the mode flag M is set to 1 in process 113. In addition, the count value 
Cm is set up by subtracting the value Ca from the count value Cn, and 
after that, the count value Cn is set to 0 in process 114, and then the 
step is returned to the process 104. 
Further, it is clarified that the mode flag M is 1 as a result of the check 
in the decision 105, it is judged that the pulses Sp occur periodically 
and therefore it is checked whether the output pulse Sd is being supplied 
or not, in decision 115. When the output pulse Sd is not being supplied, 
the count value Cm set up in the process 114 or a process 122 described 
later is decreased by 1 in response to the count clock Kc, in process 116, 
and then it is checked whether the count value Cm is 0 or not, in decision 
117. If the count value Cm is not 0, the step is returned to the process 
104. On the other hand, when it is clarified that the count value Cm 
becomes 0, since the period of time corresponding to the count value Cm 
has elapsed from the leading edge of the pulse Sp, one of the predictive 
pulses P.sub.1 to P.sub.x-2 is generated and the time point of the leading 
edge of the output pulse Sd is fixed at the time point of the leading edge 
of that predictive pulse, in process 118. Then, in process 119, the output 
pulse Sd is formed to have the leading edge at the time point fixed in the 
process 118 and to take up a high level, and is supplied to the switches 
30 and 32. After that, the step is returned to the process 104. 
When it is clarified that the output signal Sd is being supplied as a 
result of the check in the decision 115, it is checked whether the leading 
edge of the pulse Sp occurs or not in decision 120. If it is clarified 
that the leading edge of the pulse Sp occurs, the mode flag F is set to 1 
in process 121. Further, the count value Cm is set up by subtracting the 
value Ca from the count value Cn, and after that, the count value Cn is 
set to 0, in process 122, and then the step is returned to the process 
104. 
To the contrary, if it is clarified as a result of the check in the 
decision 120 that the leading edge of the pulse Sp does not occur, it is 
further checked whether the trailing edge of the pulse Sp occurs or not, 
in decision 124. In the case where the trailing edge of the pulse Sp does 
not occur, the count value Cm set up in the process 122 is decreased by 1 
in response to the count clock Kc in process 125 and the count value Cc 
set up in the initial arrangement is decreased by 1 in response to the 
count clock Kc in process 126, and then the step is advanced to decision 
127. 
In the decision 127, it is checked whether the count value Cc is 0 or not. 
If the count value Cc is not 0, the step is returned to the process 104. 
On the other hand, if it is clarified as a result of the check in the 
period of time corresponding to the count value Cc has elapsed from the 
leading edge of the pulse Sp, the count value Cc is reset, in process 128, 
and the time point of the trailing edge of the output pulse Sd is fixed at 
the time point to which the period of time corresponding to the count 
value Cc has elapsed from the leading edge of the pulse Sp and the 
trailing edge of the output pulse Sd is formed at the fixed time point to 
fall down from the high level, so that the supply of the output pulse Sd 
is terminated, in process 129. 
Further, when it is clarified in the decision 124 that the trailing edge of 
the pulse Sp occurs, the step is directly advanced to the process 129, so 
that the time point of the trailing edge of the output pulse Sd is fixed 
at the time point of the trailing edge of the pulse Sp checked in the 
process 124 and the trailing edge of the output pulse Sd is formed at the 
fixed time point. As a result, the supply of the output pulse Sd is 
terminated. 
After that, it is checked whether the mode flag F is 1 or not, in decision 
130. If the mode flag F is 1, the mode flag F is changed to 0 in process 
131 and the step is returned to the process 104. To the contrary, if the 
mode flag F is not 1, it is judged that the last one of the pulses Sp 
having occurred periodically occurs, and therefore the trailing edge of 
the wide pulse signal Sw falling from the high level is formed and the 
mode flag M is set to 0, in process 132. Then, the step is returned to the 
decision 102. 
With such operation of the microcomputer as described above, when the wide 
pulse signal Sw continues to take up the high level, the output pulses Sd 
each having its leading edge at the time point of the leading edge of one 
of the predictive pulses P.sub.1 to P.sub.x-2 and its trailing edge at the 
time point of the trailing edge of the pulse Sp occurring first after the 
time point of the leading edge thereof or the time point of the trailing 
edge of the predictive pulse P.sub.x-2, are generated and derived from the 
defect detecting section 20. 
APPLICABILITY FOR INDUSTRIAL USE 
The device for detecting a defect of a disc-shaped record medium according 
to the present invention is capable of being applied to broadly to disc 
players and is especially suitable to be used with a disc player for 
reproducing an information signal recorded on an optical disc, such as an 
optical digital audio disc player or an optical video disc player. 
Further, the device according to the present invention is also suitable 
for use in various types of disc players for reproducing an information 
signal recorded on a disc other than the optical disc.