Optical information recording and reproducing apparatus having a function of preventing overwrite recording

An optical information recording apparatus for at least recording information by irradiating an optical information recording medium having a plurality of information tracks with at least one light beam. The apparatus includes a recorder for recording information on the recording medium with an information recording light beam and a plurality of detecting elements for detecting reflected light from the recording medium. Also provided is a high-frequency component detector for detecting a high-frequency component of a signal corresponding to an output signal from at least one of the plurality of detecting elements. Also provided is a controller for stopping recording of information by the recorder when the high-frequency component detector detects the high-frequency component during recording of information by the recorder.

BACKGROUND OF THE INVENTION 
1.Field of the Invention 
This invention relates to an apparatus for optically recording or 
reproducing information and, more particularly, to an optical information 
recording and reproducing apparatus for preventing overwrite recording, 
i.e., preventing new information from being recorded over information 
already recorded. 
2. Description of the Related Art 
As conventional information recording systems for recording information in 
the form of digital signals, magnetic recording systems, optical recording 
systems and magneto-optical recording systems are known. Optical recording 
systems will be described below by way of example. Various types of 
recording media in the form of a disk, a card, a tape and the like are 
known as a medium on which information is optically recorded or from which 
information is read out. It is believed that a card-like recording medium 
(hereinafter referred to as an "optical card") will be extensively used 
because it can be manufactured easily and has good portability and 
accessibility. 
Various optical information recording and reproducing apparatuses have been 
proposed for use with such an optical card. In each such apparatus 
heretofore proposed, information is recorded or reproduced while automatic 
tracking control and automatic focusing control are being continuously 
performed. Information is recorded on a recording medium in this kind of 
apparatus by scanning information tracks with a light beam modulated in 
accordance with the recorded information and condensed to form a very 
small light spot. Information is recorded as information bit strings which 
can be optically detected. Information is reproduced from the recording 
medium by scanning information bit strings in the information tracks with 
a light beam spot of a certain power such that no signal is recorded on 
the recording medium, and by detecting reflected light or transmitted 
light from the medium. 
As typical examples of an optical system for optically recording and 
reproducing information in this manner, a single light source system and a 
multiple light source system are known. Examples of such light source 
systems will be described. A single light source system will first be 
described with reference to FIG. 1. Referring to FIG. 1, a beam of light 
emitted from a semiconductor laser device 101 is made parallel by a 
collimator lens 102 and is thereafter split into a plural light beams by a 
diffraction grating 103. The split light beams travel through a polarized 
beam splitter 104, a 1/4 wavelength plate 105 and an objective lens 106 to 
be condensed on the surface of an optical card 107. Reflected light from 
the optical card 107 travels through the objective lens 106, the 1/4 
wavelength plate and the polarized beam splitter 108 and a toric lens 108 
to be incident upon a light detecting device 109. Recording, reproduction 
and automatic focusing control (hereinafter referred to as "AF") are 
performed by using 0-order diffracted light in the light beams split by 
the diffraction grating 103, while automatic tracking control (hereinafter 
referred to as "AT") is performed by using .+-.1-order diffracted light. 
An astigmatism method is adopted to perform AF, while a three-beam method 
is adopted to perform AT. 
FIG. 2(a) is a schematic plan view of the optical card 107 used in the 
above-described information recording and reproducing apparatus. A 
multiplicity of information tracks for recording and reproducing 
information are formed on the optical card 107 so as to extend parallel to 
each other. Only tracks T1, T2, and T3 among them are illustrated. These 
information tracks are separated by tracking tracks tt1 to tt4, which are 
formed by grooves in the card or by a material having a reflectivity 
different from that of the material of the tracks T1 to T3, and which are 
used as guides for obtaining a tracking signal. In FIG. 2(a), an example 
of recording of information in the track T3 or reproduction of information 
from this track is illustrated. A light spot 110 of .+-.0-order diffracted 
light for recording, reproduction and AF irradiates the track T3 while 
light spots 111 and 112 of .+-.1-order diffracted light irradiate to the 
tracking tracks tt3 and tt4. 
A later-mentioned tracking error signal is obtained from reflected light 
from the light spots 111 and 112, and tracking control is performed on the 
basis of the tracking error signal so that the light spot 110 scans 
correctly along the track T3. The light spots 110, 111, and 112 are moved 
by an unillustrated mechanism so as to scan horizontally as viewed in FIG. 
2(a) while being maintained in the same positional relationship, thereby 
recording or reproducing information. This scanning is accomplished by a 
method of moving the optical system or a method of moving the optical 
card. In either case, the optical system and the optical card make a 
relative reciprocating motion and, therefore, they are not moved at a 
constant speed near opposite ends of the optical card. FIG. 2(b) shows the 
speed of this relative motion. The abscissa of FIG. 2(b) represents the 
distance in the horizontal direction of the optical card while the 
ordinate represents the scanning speed. Ordinarily, a constant speed area 
at the center of the optical card 107 is used as a recording area. Thus, 
FIG. 2(b) shows a central recording section-constant speed area, and two 
reversing areas at both ends of the card where the light spots reverse 
their direction of travel by decelerating and then accelerating. 
Therefore, the reversing areas comprise acceleration/deceleration areas. 
FIG. 3 is an enlarged illustration of a portion of the information track T3 
and portions of the adjacent tracks shown in FIG. 2(a). The light spot 110 
of 0-order diffracted light for AF is positioned at the center of track T3 
between the .+-.1-order diffracted light for AT and scans the center line 
of the track T3. Hatched areas 113a, 113b, and 113c represent digital 
information recorded by a 0-order diffracted light spot 110a shown in FIG. 
4. Such areas are generally called information pits. The information pits 
113a, 113b, and 113c have a reflectivity different from that of the track 
portion surrounding them. Therefore, when the information pits are again 
scanned with the light spot 110 at a lower intensity than that at which 
they were recorded, reflected light of the light spot 110 is modulated at 
the pits 113a, 113b, and 113c to obtain a reproduction signal in 
accordance with recorded information. 
FIG. 4 is a schematic diagram showing details of the light detecting device 
109 shown in FIG. 1 and a signal processing circuit for processing output 
signals from the light detecting device 109 to form a reproduction signal 
and a servo error signal. The light detecting device 109 is constituted by 
six photosensors, i.e., 4-split photosensors 114 and photosensors 115 and 
116. Light spots 110a, 111a, and 112a are formed by reflected light of the 
light spots 110, 111, and 112 projected onto sensing surfaces of these 
sensors. The light spot 110a is condensed on the 4-split photosensors, 
while the light spots 111a and 112a are condensed on the photosensors 115 
and 116, respectively. Two sets of sensor outputs in diagonal directions 
of the 4-split photosensors 114 are respectively added by addition 
circuits 117 and 118, and addition outputs from these addition circuits 
are further added by an addition circuit 121 to output an information 
reproduction signal RF. That is, the information reproduction signal RF is 
a signal representing the total sum of detection signals obtained as 
detection output fragments from the 4-split photosensors 114. The outputs 
from the addition circuits 117 and 118 are subtracted from each other by a 
differential circuit 120 to output a focusing error signal Af. That is, 
the focusing error signal Af is a signal representing the difference 
between the sums in the diagonal directions of the 4-split photosensors 
114. This astigmatism method will not be described because it is described 
in detail in published documents and because it is not directly related to 
the present invention. Outputs from the photosensors 115 and 116 are 
subtracted from each other by a differential circuit 119 to output a 
tracking error signal A.sub.ts. Ordinarily, tracking control is performed 
in order to prevent deviation of the light spots from the information 
track by controlling the tracking system so that the tracking error signal 
A.sub.ts. becomes zero. 
That is, when the portions of the light spots 111 and 112 located on the 
tracking tracks tt3 and tt4 have the same area, the quantities of 
reflected light of these light spots received by the photosensors 115 and 
116 are equal to each other. Accordingly, if the apparatus is controlled 
so that the tracking error signal A.sub.ts representing the difference 
between the outputs from the photosensors 115 and 116 becomes zero, then 
the light spot 110 of 0-order diffracted light scans the center of the 
information track T3, thus normally performing tracking control. In FIG. 
4, a block 122 represents an addition circuit which adds the output 
signals from the photosensors 115 and 116 to output a tracking sum signal 
A.sub.ta, as described below in detail. T.sub.s1 denotes a received light 
signal from the photosensor 115, while T.sub.s2 denotes a received light 
signal from the photosensor 116. 
FIG. 5 is a diagram showing changes in the received light signals T.sub.s1 
and T.sub.s2 from the photosensors 115 and 116 when the light spots 110 to 
112 deviate to the left and right from the information track. The abscissa 
represents the deviation of the light spots from the center of the 
information track along the transverse direction perpendicular to the 
center line of the track, and the ordinate represents the quantity of 
light of the received light signals (light quantities) T.sub.s1 and 
T.sub.s2 from the photosensors 115 and 116. When the light spot 111 or 112 
has no portion located on the tracking track tt3 or tt4, the received 
light signal T.sub.s1 or T.sub.s2 from the photosensor 115 or 116 is at a 
solid reflection level. When the area of the portion located on the 
tracking track is maximized, the received light signal is at a tracking 
track reflection level. 
FIG. 6 is a diagram showing changes in the tracking error signal A.sub.ts 
when the light spots 110 to 112 deviate to the left and right from the 
information track. The abscissa represents the deviation of the light 
spots from the center of the information track along the transverse 
direction perpendicular to the center line of the track, and the ordinate 
represents the amplitude level of the voltage of the tracking error signal 
A.sub.ts. When the light spot 110 is positioned at the center of the 
information track, the light quantities T.sub.s1 and T.sub.s2 are equal to 
each other and the value of the tracking error signal A.sub.ts is zero. 
The amplitude level of the tracking error signal A.sub.ts varies in plus 
and minus directions according to the directions of deviation of the light 
spots to the left and right. If the light spots 110 to 112 deviate in a 
direction perpendicular to the track to such a large extent that the light 
spots 111 and 112 have no portions located on the tracking tracks tt3 and 
tt4, then the signals T.sub.s1 and T.sub.s2 become equal to each other at 
the solid reflection level and the tracking error signal A.sub.ts also 
becomes zero. This state is established when the light spot 111 or 112 is 
at a position X1 or X2 of FIG. 6. 
Referring again to FIG. 3, if the light spot 110 of 0-order diffracted 
light scans along different scanning loci at the times of recording and 
reproduction, that is, if tracking misalignment occurs, the contrast and 
the pit time interval of the information reproduction signal RF may vary 
to such an extent that the information cannot be reproduced. Such a 
situation may take place due to vibration of the apparatus, or dust or a 
scratch on the optical card 107. If different apparatuses are respectively 
used for recording and reproduction, such a situation may also occur due 
to a difference between the characteristics of the apparatuses. In 
particular, in the case of a single light source system such as that 
illustrated in FIG. 1, there is a possibility of information reproduction 
failure even when tracking misalignment between recording and reproduction 
is small, since the size of the light spot is constant during recording 
and reproduction. It can therefore be said that the tracking margin in 
single light source systems is disadvantageously small. Moreover, the 
powers of the light spots 110, 111, and 112 are largely changed during 
recording and non-recording times, and the light spots 110a, 111a, and 
112a are also changed correspondingly to affect the AF control and the AT 
control. 
A dual light source system is known in which the recording-reproducing 
tracking is increased in comparison with that in the single light source 
system to prevent power variation in the light detecting device. Details 
of such a dual light source system will be described. The operation on the 
optical card will first be described below with reference to FIG. 7. In a 
dual light source system, the three light spots of the single light source 
system are not used for recording information; rather a recording light 
spot 225 is separately provided. A light spot 226 for reproduction and AF 
control and light spots 227 and 228 for AT control correspond to the light 
spots 110, 111, and 112 shown in FIG. 3. The light spots 226, 227, and 228 
are equal in size but the light spot 225 is smaller than the light spots 
226, 227, and 228. FIG. 7 illustrates a situation where the track T3 is 
scanned with the light spot 225 in the direction of the arrow to record 
information. The light spot 226 moves ahead of the light spot 225. 
The width of a pit 229a recorded with the light spot 225 as indicated by 
hatching is smaller than that of the reproducing light spot 226. 
Therefore, even if the scanning locus of the light spot 226 is shifted 
from that of the light spot 225 to a small extent, the information 
reproduction signal RF is not considerably influenced by such a shift, in 
contrast with the case of the single light source system shown in FIG. 3. 
The tracking margin becomes larger if the ratio of the sizes of the light 
spot 226 and 225 is increased in this manner. However, a reduction in the 
contrast of the information reproduction signal RF also results and, 
therefore, the increase in the size of the light spot 226 must be limited. 
If the wavelength of the light of the light spot 225 is selected so as to 
be different from that of the light spots 226, 227, and 228, reflected 
light of the light spot 225 can easily be separated by using a dichroic 
mirror to be prevented from mixing in the output from the light detecting 
device to affect the AF and AT controls. 
An example of the construction of such a dual light source system will be 
described with reference to FIG. 8. In the arrangement shown in FIG. 8, an 
astigmatism system is used for AF control and a three-beam system is used 
for AT control. Referring to FIG. 8, a recording semiconductor laser 
device 201 emits a divergent beam of laser light having a wavelength of 
830 nm. The divergent beam is changed into a parallel beam by a collimator 
lens 203. The parallel beam travels through a dichroic prism 207, a 
polarized beam splitter 208 and a 1/4 wavelength plate 209 to be incident 
upon an objective lens 210. The beam is condensed as a small light spot on 
an optical card 211 by the objective lens 210 to record recording pits on 
a recording surface of the optical card 211 in accordance with 
information. The optical card 211 is the same as the optical card 107 
shown in FIG. 1. Reflection light from the optical card 211 travels 
through the objective lens 210 and the 1/4 wavelength plate 209 and is 
reflected by the polarized beam splitter 208 to travel toward a light 
detecting device 213 (same as the device 109 shown in FIG. 1). In this 
case, the reflected light is reflected and absorbed by a toric lens 212 
having a film capable of cutting light having a wavelength of 830 nm which 
is prevented from reaching the light detecting device 213, thereby 
preventing 830 nm light from adversely influencing the information 
reproducing system and the AT/AF control system. 
A divergent light beam from a reproducing semiconductor laser device 202 
having a wavelength of 780 nm is changed into a parallel beam by a 
collimator lens 204, limited by an aperture 205, and split into plural 
beams by a diffraction grating 206. These plural beams are reflected by 
the dichroic prism 207 to irradiate the optical card 211 with a small spot 
by traveling along an optical path which is substantially the same as the 
optical path from the semiconductor laser device 201. Reflected light from 
the optical card 211 travels through the objective lens 210 and the 1/4 
wavelength plate 209, is reflected by the polarized beam splitter 208 and 
is condensed on the light detecting device 213 by the toric lens 212. 
The light beam from the semiconductor laser device 202 forms, on the 
optical card 211, light spots larger than the light spot formed by the 
light from the semiconductor laser device 201, because of the aperture 
control with the aperture 205. The semiconductor laser device 202 is used 
for focusing control and tracking control and is therefore driven by a 
reproducing laser driver 223 so that the quantity of light emitted 
therefrom is constantly set to a small value irrespective of recording and 
reproduction. Information output from a controller 220 having a micro 
processing unit (MPU) is modulated in a modulation circuit 221 to form 
recording codes, and a recording laser driver 222 drives the recording 
semiconductor laser 201 in accordance with the recording codes to record 
the information on the optical card 211. Ordinarily, in actual 
apparatuses, recording information is supplied from an external unit. In 
such a case, the controller 220 includes an interface for connection with 
the external unit, and recording information is transmitted through the 
interface. Reproduced information is also transferred to the external unit 
through the interface. 
The light detecting device 213 is the same as the light detecting device 
109 shown in FIG. 1. More specifically, it includes the same elements as 
photosensors 114 to 116 shown in FIG. 4. A light receiving processing 
circuit 216 has the same components as the addition circuits 117, 118, and 
121 and the differential circuits 119 and 120 shown in FIG. 4, and forms 
information reproduction signal RF, focusing error signal Af and tracking 
error signal A.sub.ts on the basis of signals of light received by the 
light detecting device 213. Focusing error signal Af is used to perform 
focusing control in such a manner that a focusing coil 214 is driven 
through an AF servo circuit 217 to displace the objective lens 210 in a 
focusing direction so that the light spots are focused on the optical card 
211. Similarly, tracking error signal A.sub.ts is used to perform tracking 
control in such a manner that a tracking coil 215 is driven through an AT 
servo circuit 218 to displace the objective lens 210 in a tracking 
direction. The optical card 211 is reciprocatingly moved in the direction 
of the arrows shown in FIG. 8 relative to the light spots by a 
reciprocating movement mechanism (not shown), thereby scanning the 
information tracks of the optical card 211 with the light spots. Also in 
the thus-constructed dual light source system, when light spots deviate in 
a direction perpendicular to the track, received light signals T.sub.s1 
and T.sub.s2 from the tracking control photosensors 115 and 116 of the 
light detecting device 213 change as shown in FIG. 5 and the tracking 
error signal A.sub.ts changes as shown in FIG. 6. 
If a tracking control error occurs during information recording, the light 
spots may move to an adjacent or other track to destroy information 
already recorded in this track by doubly recording new information on the 
already-recorded information. To prevent information from being destroyed 
in this manner, a destruction prevention means for preventing information 
destruction by detecting a tracking control disturbance is adopted in each 
of the single and dual light source systems. In general, a tracking 
control error is detected through the level of the tracking error signal. 
That is, as explained above with reference to FIG. 8, the level of the 
tracking error signal is zero when the light spot 110 is positioned at the 
center of the information track. If the light spot 110 deviates in a 
direction perpendicular to the tracking direction from this state, the 
tracking error signal level changes in the plus or minus direction 
according to the direction of the deviation. A method is therefore adopted 
in which, when this level exceeds a predetermined positive or negative 
level, the occurrence of a tracking control error stops the information 
recording operation and prevents information from being destroyed by 
overwrite recording. 
Such a prevention method, however, entails a problem described below. If 
the light spots 111 and 112 deviate from the tracking tracks tt3 and tt4 
so that no portions thereof are located on the tracking tracks, then the 
tracking error signal becomes zero, as described above with reference to 
FIG. 6. This state cannot be discriminated from the normal state of 
tracking control. Thus, there is a possibility of failure to detect a 
tracking control error. This problem will be explained with reference to 
FIG. 9. FIG. 9 illustrates a situation where light spots 110 to 112 of the 
single light source system or light spots 225 to 228 of the dual light 
source system are scanning the information track T2 in the direction of 
the arrow to record information, and where a defect 224, such as a medium 
defect, an foreign particle attached to the card or a scratch, exists in 
an intermediate portion of the information track T2. 
In the situation illustrated in FIG. 9, tracking control is normally made 
before a point O is reached. When the spots thereafter pass over the 
defect 224, the tracking error signal cannot be formed normally and 
tracking control is disturbed, so that the light spots move toward the 
adjacent information track T3. When the light spots pass the defect 224 
and reach a point X such that no portions of the tracking control light 
spots 111 and 112 or 227 and 228 are located on the tracking tracks tt3 
and tt4, the tracking error signal becomes zero, the tracking state is 
recognized as normal and this tracking control error cannot be detected. 
Thus, if such defect 224 exists on the information track, there is a 
possibility that the light spots moves to the adjacent information track 
T3 while the detection systems fails to perform tracking control, and new 
information is recorded over already-recorded information to destroy the 
same. 
SUMMARY OF THE INVENTION 
In view of the above-described problems, an object of the present invention 
is to provide an optical information recording and reproducing apparatus 
in which a high-frequency pit signal component which appears in a 
detection signal from a light detecting device for detecting reflected 
light from a recording medium is detected to detect a tracking control 
error and a recorded signal component, and which is therefore capable of 
reliably preventing already-recorded information from being destroyed by 
overwrite recording. 
According to one aspect, the present invention which achieves these 
objectives relates to an optical information recording apparatus for at 
least recording information by irradiating an optical information 
recording medium having a plurality of information tracks with at least 
one light beam. The apparatus includes means for recording information on 
the recording medium with an information recording light beam. The 
apparatus also includes a plurality of detecting elements for detecting 
reflected light from the recording medium. In addition, high frequency 
component detection means detects a high frequency component of a signal 
corresponding to an output signal from at least one of the plurality of 
detecting elements. Control means stops the recording of information by 
the recording means when the high-frequency component detection means 
detects the high-frequency component during recording of information by 
the recording means. 
In one embodiment, the recording means projects at least three light beams 
onto the recording medium. Two of the at least three light beams area used 
for tracking control for the third of the at least three light beams. The 
high-frequency component detection means detects the high-frequency 
component from an output signal from at least one of the plurality of 
detecting elements detecting reflected light from the two of the at least 
three light beams for tracking control. The third of the at least three 
light beams can be the information recording light beam and the apparatus 
can further comprise tracking control means for performing tracking 
control of the information recording light beam using the two of the at 
least three beams for tracking control. 
In another embodiment, the apparatus further comprises a single light 
source producing a single light beam and a beam splitter for splitting 
this single light beam into a plurality of light beams, one of which is 
the information recording light beam used by the recording means for 
recording information on the recording medium. Alternatively, the 
apparatus can comprise a first light source for emitting the two of the at 
least three light beams for tracking control and a second light source for 
emitting the third of the at least three light beams, the third of the at 
least three light beams being the information recording light beam. 
The apparatus can further comprise adjustment means for adjusting a change 
in the amplitude of the signal detected by the high-frequency component 
detection means according to the intensity modulation of the information 
light recording beam. 
In another embodiment, the apparatus further comprises means for generating 
at least three light beams one of which is the information recording light 
beam which the recording means projects onto the recording medium for 
recording information thereon. The other two light beams are used for 
tracking control of the information recording light beam. This embodiment 
also includes means for generating a tracking error signal on the basis of 
an output signal from at least one of the detecting elements detecting 
reflected light from the light beams for tracking control. In this 
embodiment, the high-frequency component detection means detects the 
high-frequency component of the tracking error signal. 
In an alternative embodiment, the apparatus comprises means for generating 
an additional signal of output signals from at least two of the detecting 
elements detecting reflected light of the light beams for tracking 
control. The high-frequency component detection means detects the 
high-frequency component of the addition signal. 
The apparatus can further comprise means for reproducing information from 
the recording medium with the information reproducing light beams. When 
such means is included, the high-frequency component detection means can 
detect the high-frequency component from a signal corresponding to an 
output signal from at least one of the detecting elements detecting the 
reflected light of the information reproducing light beam. In addition, a 
single light source can be provided for emitting a single light beam. In 
this instance, means for splitting the single light beam into the 
information reproducing light beam and the information recording light 
beam can be provided. In this embodiment, means can also be provided for 
sampling a signal corresponding to an output signal from at least one of 
the detecting elements detecting the information reproducing light beam 
according to the intensity modulation of the information recording light 
beam. The high-frequency detection means detects a high-frequency 
component of the sampled signal in this embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention will be described below 
in detail with reference to the accompanying drawings. A first embodiment 
of the present invention will be described. FIG. 10 is a circuit diagram 
of the first embodiment applicable to the above-mentioned dual light 
source system. An amplifier 1 is provided to amplify received light signal 
T.sub.s2 from the photosensor 116 shown in FIG. 4. It is assumed here that 
received light signal T.sub.s2 from the photosensor 116 for detecting 
reflected light of light spot 228 in the dual light source system shown in 
FIG. 7 is input to the amplifier 1. Low-frequency components of the 
received light signal T.sub.s2 are removed by a high-pass filter formed by 
a capacitor C1 and a resistor R1 before the received light signal T.sub.s2 
is input to the amplifier 1. Resistors R2 and R3 are provided to determine 
the amplification factor of the amplifier 1. An output signal TC from the 
amplifier 1 is two-valued to form a two-valued signal TD by being compared 
with a reference value V.sub.r1 by a comparator 2. The two-valued signal 
TD is output from the comparator 2 to a condition detection circuit 3. The 
condition detection circuit 3 detects a disturbance in the tracking 
control by determining the condition of the tracking control from the 
output signal TD from the comparator 2. When the condition detection 
circuit 3 detects a tracking control disturbance, it outputs a signal CD 
to a micro processing unit (MPU) 4. The MPU 4 is a processing circuit for 
controlling the components of the apparatus and for performing control to 
stop the information recording operation if a tracking control disturbance 
is detected. 
The operation of the above-described embodiment will be described with 
reference to FIG. 11. The waveform shown in FIG. 11(a) represents the 
behavior over time of the received light signal T.sub.s2 from the 
photosensor 116 which detects reflected light of tracking control light 
spot 228 in the dual light source system as described above. The received 
light signal T.sub.s2 shown in FIG. 11(a) is obtained from the photosensor 
116 when light spots 225 to 228 of the dual light source system move in 
the vicinity of a point Y shown in FIG. 9. In this example, there is a 
defect 224 on the information track T2 when information is recorded by 
scanning the information track T2 with the light spots 225 to 228, as 
shown in FIG. 9. In this situation, tracking control is disturbed when the 
light spots pass the defect 224, so that the light spots deviates from the 
information track T2 and move to the adjacent track T3, as described 
above. The received light signal T.sub.s2 shown in FIG. 11(a) is detected 
by the photosensor 116 in the vicinity of the point Y, and components of 
the pit signal along the locus of movement of the light spot 228 appear as 
high-frequency components in the received light signal T.sub.s2. These 
high-frequency components are not observed during normal recording, but 
appear in the received light signal T.sub.s2 when tracking control is 
disturbed. The frequency of such high-frequency components is much higher 
than the frequency changes in the tracking error signal caused by 
vibration or the like or changes in the tracking error signal and the 
information reproduction signal due to a non-uniformity of the recording 
medium or foreign particles. Also, such pit signal components appear in a 
known regular arrangement, and the low-frequency component of the received 
light signal T.sub.s2 shown in FIG. 11(a) is due to low-frequency 
fluctuations caused by vibration or a medium non-uniformity. 
The received light signal T.sub.s2 is input to the high-pass filter formed 
by the capacitor C1 and the resistor R1 to cut low-frequency components 
and to extract only high-frequency components. The high-frequency 
components extracted by the high-pass filter are amplified by the 
amplifier 1, as shown in FIG. 11(b). The output signal TC from the 
amplifier 1 is compared with the reference voltage V.sub.r1 by the 
comparator 2, as shown in FIG. 11(c). The comparator 2 outputs a signal TD 
at a low level when the output signal TC of the amplifier 1 is higher than 
the reference voltage V.sub.r1, and outputs the signal TD at a high level 
when the output signal TC is not higher than the reference voltage 
V.sub.r1. The output signal TD from the comparator 2 is output to the 
condition detection circuit 3, and the condition detection circuit 3, the 
configuration and the operation of which will be described below in 
detail, detects a tracking control error on the basis of the output signal 
TD. The condition of light spot tracking control is discriminated on the 
basis of the output signal TD from the comparator 2. If circuit 3 
determines that a tracking control error has occurred, the condition 
detection circuit 3 outputs a high-level signal CD representing a tracking 
control error as shown in FIG. 11(d). The MPU 4 monitors the output signal 
CD from the condition detection circuit 3 and performs control of the 
apparatus to stop the information recording operation by setting an 
information recording permission signal WE to low level if a tracking 
control error is determined to have occurred, as shown in FIG. 11(e). That 
is, the output signal WE from the MPU 4 is output to the recording laser 
driver 222 shown in FIG. 8, and the recording laser driver 222 is 
controlled so as to be allowed to record information when the signal WE is 
high level and inhibited from recording information when the signal WE is 
at a low level. However, when there is a tracking control error, the 
signal WE is set to a low level, as mentioned above, to stop the recording 
operation of the recording driver 222. 
FIG. 12 is a circuit diagram showing an example of the condition detection 
circuit 3. In this example, the circuit is arranged to prevent a defect 
from being erroneously detected as a pit signal component, since recording 
media such as optical cards generally have many defects. Each of blocks 5 
and 6 in FIG. 12 represents a retriggerable monostable multivibrator 
("MMV", hereinafter). Each of MMVs 5 and 6 is a device which, if a trigger 
is again input within a set time period, continues an output during the 
set time period from the moment at which the trigger is input. This device 
may be selected from various articles on the market, e.g., SN74123 
(commercial name of a product from Texas Instruments Inc.) and TC74HC4538 
(commercial name of a product from Toshiba Corp.) 
A clear bar input terminal (inverting input terminal) C1 of MMV 5 is 
maintained at a high level, and the output signal TD from the comparator 
shown in FIG. 10, i.e., a signal obtained by causing the output signal 
from the amplifier 1 to take one of two values by comparing it with the 
reference voltage V.sub.r1, is input to a trigger input terminal TR1. 
Accordingly, the output signal TD is input as a trigger to MMV 5, and an 
output Q1 from MMV 5 is set to high level by a rising edge of the trigger 
when the trigger is input. The output Q1 is thereafter maintained at high 
level for a set time period T.sub.w1. The output Q1 from MMV 5 is input to 
a clear bar input terminal (inverting input terminal) of MMV 6 at the next 
stage. The output signal TD from the comparator 2 is also input to a 
trigger terminal TR2 of MMV 6. Accordingly, an output Q2 from MMV 6 is set 
to high level by a rising edge of the output signal TD only when the 
output Q1 of MMV 5 is high level. The output Q2 is thereafter maintained 
at high level for a set time period T.sub.w2. 
The operation of the above-described condition detection circuit 3 will be 
described with reference to FIGS. 13(a)-13(d). Hatched areas in FIG. 13(a) 
represent information pits optically recorded in an information track of 
the optical card shown in FIG. 2, and defects such as scratches or foreign 
particles existing on the information track, i.e., information pits P1 to 
P10 and defects D1 and D2. As an information recording method, a pit 
length recording method is adopted in which information is recorded as pit 
sizes and distances between pits. The same method is also used in the 
other embodiments of the invention. The waveform shown in FIG. 13(b) 
represents the output signal TD obtained by the comparator 2 when the 
light spot 228 scans the information pit array shown in FIG. 13(a). The 
output signal TD assumes a high level when the light spot 228 scans the 
information pits and assumes a low level when the light spot 228 scans 
between the information pits. The output signal TD also assumes a high 
level when light spot 228 scans a defect. 
The output Q1 of MMV 5 assumes a high level when light spot 228 scans the 
leading end of the first defect D1, as shown in FIG. 13(c), since the 
signal TD rises to a high level at the leading end of the defect D1. The 
output Q1 is thereafter maintained at a high level for the time period 
T.sub.w1. That is, the defect D1 is so long that the signal TD is not 
changed during the predetermined time period T.sub.w1. Accordingly, the 
output Q1 of MMV 5 is maintained at a high level for the predetermined 
time period T.sub.w1 and is inverted to a low level at the end of this 
time period. The output Q1 of MMV 5 and the signal TD are respectively 
input to the clear bar input terminal C2 and the trigger input terminal 
TR2 of MMV 6 to drive MMV 6. In this case, the output Q1 of MMV 5 rises to 
a high level with a time lag from the moment at which the signal TD 
changes from low level to high level. For this reason, the output Q1 of 
MMV 5 is at a low level and MMV 6 is not operated at the moment when the 
signal TD input to the trigger input terminal C2 of MMV 6 rises to high 
level when light spot 228 scans the leading end of the defect D1. The 
output Q2 (CD) of MMV 6 is therefore maintained at low level, as shown in 
FIG. 13(d). 
Consequently, during passage of the light spot 228 over the defect D1, the 
output Q2 of MMV 6 is maintained at low level and the signal CD is not 
output. 
Next, when the signal TD rises to high level when the light spot 228 scans 
the leading end of information pit P1, the output Q1 of MMV 5 is 
correspondingly inverted to high level, as shown in FIG. 13(c). The signal 
TD also assumes a high level when the light spot 228 scans the leading end 
of the next information pit P2 to again trigger MMV 5, so that the output 
Q1 of MMV 5 is further maintained at a high level. That is, because the 
time period T.sub.pm during which the light spot 228 scans from the 
leading end of information pit P1 to the leading end of information pit P2 
is shorter than the set time period T.sub.w1 of MMV 5, MMV 5 is triggered 
when the light spot 228 scans the leading end of information pit P2 to be 
maintained at high level. Since the time period T.sub.w1 is set so as to 
be longer than the time period T.sub.pm taken to scan the maximum pit 
pitch of the information pit array, the output Q1 of MMV 5 is maintained 
at high level as long as information pits are spaced so they can be 
scanned within time period T.sub.pm. 
The output Q1 of MMV 5 rises to a high level when the light spot 228 scans 
the leading end of information pit P1 and this high level signal is 
thereafter supplied to the clear bar input terminal C2 of MMV 6. 
Therefore, the output Q2 of MMV 6 is inverted to a high level when the 
signal TD assumes a high level when the light spot 228 scans the leading 
end of information pit P2, as shown in FIG. 13(d). The signal CD is 
thereby output and the MPU 4 performs control of the apparatus in response 
to the signal CD to stop the information recording operation. To 
continuously output the signal CD, it is necessary that the set time 
period T.sub.w2 of MMV 5 is longer than T.sub.pm, as in the case of 
T.sub.w1. In this case, T.sub.w2 is set so as to be longer than T.sub.w1. 
There is also defect D2 in the information pit array, as shown in FIG. 
13(a), and the output Q1 of MMV 5 is inverted to a low level at the end of 
the time period T.sub.w1 starting from the moment the light spot 228 scans 
the leading end of the defect D2, as shown in FIG. 13(c). Accordingly, the 
output Q2 from MMV 6 is simultaneously inverted to a low level, so that 
the signal CD is interrupted at an intermediate position on the 
information pit array. A modification in signal processing provided to 
solve this problem will next be described. 
In the example shown in FIGS. 13(a)-13(d), even if a defect exists on the 
information track and even if the size of the defect is excessively large, 
there is no possibility of outputting the signal CD by erroneously 
recognizing the defect as an information pit because the signal TD does 
not change continuously within the set time period T.sub.w1. It is 
therefore possible to reliably prevent erroneous detection of a defect as 
a pit signal. Therefore, even if the optical card has many defects, the 
recording operation of the apparatus is not frequently stopped and the 
recording operation is stopped only when the tracking control is 
disturbed. With respect to detection of information pits, one information 
pit cannot be detected separately but two or more information pits can 
reliably be detected as long as they are scanned successively. Thus, it is 
possible to reliably prevent erroneous detection of a defect as well as to 
detect pit signal components with high detection sensitivity of two 
information pits. 
Another example of the condition detection circuit 3 will next be 
described. In the example shown in FIG. 12, there is a possibility of the 
signal CD being interrupted if there is a defect at an intermediate 
position on an information pit array, as described above. That is, even 
through information pits P6 and P7 are recorded, they are masked with the 
defect D2 located on them, as shown in FIG. 13(a). In such a situation, 
the signal TD is not changed, as shown in FIG. 13(b), the output Q1 of MMV 
5 is inverted to a low level at the intermediate position, and the signal 
CD is also inverted to a low level. When information pit P8 and subsequent 
information pits are successively scanned after the defect D2, the signal 
CD is output again and is interrupted at an intermediate position on the 
information pit array. Such a phenomenon is not a problem if the operation 
is intended to detect only the initial pit. In general, however, error 
correction codes are added to recorded information to enable an error 
destroying a part of recorded information to be corrected. If the 
recording operation is stopped when the signal CD is output for a set 
error-correctable time period, the probability of stoppage of the 
recording operation caused by erroneous detection due to a medium defect 
can be reduced. However, if the signal CD is interrupted, such a control 
cannot be performed. 
The example of the condition detection circuit shown in FIG. 14 is arranged 
to solve the problem of such an interruption of the signal CD. Blocks 5 
and 6 also represent the same MMVs as those shown in FIG. 12. The output 
Q2 of MMV 6 and the signal TD are input into an AND gate 8, and an output 
from the AND gate 8 is input to a trigger input terminal TR4 of an MMV 7, 
which is a retriggerable monostable multivibrator similar to MMVs 5 and 6. 
A clear bar input terminal (inverting input terminal of MMV 7 is always 
maintained at high level and an output Q4 from MMV 7 is output as signal 
CD. 
The operation of the condition detection circuit 3 shown in FIG. 14 will be 
described with reference to FIGS. 15(a)-15(f). Information pits are 
recorded in an information track, as shown in FIG. 15(a). Information pits 
P11 to P17 form one information pit array and information pits P18 to 20 
form another information pit array. That is, information pits P11 to P17 
form a pit array of one track number or recorded sector, while information 
pits P18 to P20 form a pit array of another track number or recorded 
sector. A defect D3 exists over information pits P14 and P15 so as to mask 
these pits. The waveform shown in FIG. 15(b) represents the output signal 
TD obtained by the comparator 2 when the information track shown in FIG. 
15(a) is scanned with the light spot 228. The output Q1 from MMV 5 rises 
to a high level when the light spot 228 scans the leading end of 
information pit P11, as shown in FIG. 15(c). Since as in the case of the 
example shown in FIG. 12, the set time period T.sub.w1 of MMV 5 is set so 
as to be longer than the time period T.sub.pm taken to scan the maximum 
pit pitch with the light spot 228, the high level of output Q1 is 
maintained as long as information pits appear successively. However, since 
the defect D3 exists at an intermediate position on the information pit 
array, the output Q1 from MMV 5 is inverted to low level after a time 
period T.sub.w1 starting from the moment when the light spot 228 scans the 
leading end of the defect D3. 
On the other hand, the output Q2 from MMV 6 rises to a high level when 
light spot 228 scans the leading end of information pit P12, as shown in 
FIG. 15(d), and becomes inverted to assume a low level after a time period 
T.sub.w1 starting from the moment when the light spot 228 scans the 
leading end of the defect D3, as in the case of the output Q1 of MMV 5. 
The signal TD is gated by the AND gate 8 with the output Q2 of MMV 6 to 
input a trigger signal such as that shown in FIG. 15(e) to the trigger 
input terminal TR4 of MMV 7. As a result, the output Q4 from MMV 7 rises 
to a high level when the light spot 228 scans the leading end of 
information pit P12 to be output as signal CD, as shown in FIG. 15(f). 
Actually, it is possible that the signal CD is delayed slightly according 
to a time lag of the circuit. Such a delay, however, is negligible in 
comparison with the pit scanning time. 
If the time period taken to scan from the leading end of the defect D3 to 
the leading end of the rearmost information pin P17 of the pit array is 
T.sub.d, the set time period T.sub.w4 of MMV 7 is set so as to be longer 
than the time period T.sub.d (T.sub.w4 &gt;T.sub.d). Therefore, even when the 
outputs Q1 and Q2 of MMVs 5 and 6 assume a low level after a time period 
T.sub.w1 starting from the moment when the light spot 228 scans the 
leading end of the defect D3, the output Q4 of MMV 7 is maintained at a 
high level to continuously output the signal CD, as shown in FIG. 15(f). 
The outputs Q1 and Q2 of MMVs 5 and 6 are respectively inverted to assume 
a low level after a time period T.sub.w1 starting from the moment the 
light spot 228 scans the leading end of the rearmost information pit P17 
of the pit array, as shown in FIGS. 15(c) and 15(d). Since MMV 7 is 
triggered when the light spot 228 scans the leading end of information pit 
P17, the output Q4 from MMV 7 is inverted to a low level after a time 
period T.sub.w4 from when MMV 7 has been triggered, as shown in FIG. 
15(f). Consequently, the signal CD is output from the moment when the 
light spot 228 scans the leading end of the second information pit P12 of 
the pit array to time T.sub.w4 after the moment when the light spot 228 
scans the leading end of the rearmost information pit P17 of the pit 
array. Pit signals are detected with respect to one pit array in the 
above-described manner, and pit signal detection is also performed in the 
same manner with respect to the pit array starting from the next 
information pit P18. The time intervals between the pit arrays is Ts, as 
shown in FIG. 15(a). To set the signal CD to a low level between the pit 
arrays, it is necessary that T.sub.W4 &lt;T.sub.S. It is also necessary to 
select as T.sub.S the shortest interval with respect to various sector 
patterns to be recorded. 
As described above, in the example shown in FIG. 14, the signal CD can be 
continuously output without being interrupted even if a defect exists in 
the information pit array. In this example, however, it is possible to 
prevent interruption of the signal CD with respect to defects having 
lengths not larger than the minimum sector interval. Accordingly, the MPU 
4 stops the recording operation when the signal CD is output during a 
predetermined error-correctable time period, thereby reducing the 
probability of recording operation stoppage caused by erroneous detection 
due to a defect. 
Still another example of the condition detection circuit will next be 
described. Small defects exist on the recording medium as well as large 
ones, and the probability of the existence of small defects within the 
maximum pit pitch is not negligibly small. Therefore, there is a 
possibility of the occurrence of erroneous CD detection due to such a 
small defect in the case of the examples shown in FIGS. 12 and 14. FIG. 16 
shows an improved condition detection circuit to solve the problem due to 
such a small defect. Blocks 5 and 6 in FIG. 16 represent the same MMVs as 
those shown in FIG. 12, and a block 13 represents an MMV connected as a 
stage subsequent to MMV 6. MMV 13 is a retriggerable monostable 
multivibrator similar to MMVs 5 and 6. The output Q2 from MMV 6 and the 
signal TD are respectively input to a clear bar input terminal (inverting 
input terminal) C3 and a trigger input terminal TR3 of MMV 13, and an 
output Q3 from MMV 13 is output as signal CD. 
The operation of the condition detection circuit shown in FIG. 16 will be 
described with reference to FIGS. 17(a)-17(e), which illustrate defects on 
an information track and an information pit array in the track. Hatched 
areas D4 to D6 represent defects while hatched areas P1 to P6 represent 
information pits. A time period T.sub.dp1 during which the pitch between 
defects D4 and D5 is scanned is shorter than the set time period of 
T.sub.w1 of MMV 5 (T.sub.dp1 &lt;T.sub.w1) Thus, a small defect exists within 
the maximum pit pitch. The set time period T.sub.w1 of MMV 5 is set so as 
to be longer than the time period taken to scan the maximum pit pitch, as 
in the case of the examples shown in FIGS. 12 and 14. The time interval 
needed to scan defects D5 and D6 is longer than T.sub.w1, and information 
pits P1 to P6 are recorded after defect D6. 
When the light spot 228 scans the information track shown in FIG. 17(a), 
the signal TD is output from the comparator 2, as shown in FIG. 17(b). As 
shown in FIG. 17(c), the output Q1 from MMV 5 rises to a high level when 
the light spot 228 scans the leading end of defect D4, MMV 5 is triggered 
when the light spot 228 scans the leading end of defect 5, and the output 
Q1 is inverted to a low level at a time T.sub.w1 after the moment at which 
MMV 5 is triggered. As shown in FIG. 17(d), the output Q2 of MMV 6 rises 
to a high level when the light spot 228 scans the leading end of defect D5 
and becomes inverted to assume a low level simultaneously with the output 
Q1 of MMV 5 assuming a low level. The output Q3 of MMV 13 is maintained at 
a low level and the signal CD is not output, as shown in FIG. 17(e). In 
the examples shown in FIGS. 12 and 14, a sequence of small defects D4 and 
D5 such as that shown in FIG. 17(a) causes erroneous detection, since the 
output Q2 of MMV 6 is output as signal CD. In this example, the signal CD 
is not output in such a situation and there is no possibility of erroneous 
detection of small defects, because MMV 13 is connected subsequently to 
MMV 6. A single defect D6 after defect D5 cannot not cause the CD signal 
to be output. 
When information pits P1 to P6 are scanned, the output Q3 from MMV 13 rises 
to a high level when the light spot 228 scans the leading end of 
information pit P3, and the signal CD is output when the light spot 228 
scans the third information pit from the head pit P1 of the information 
pit array, as shown in FIG. 17(e). That is, since the circuit is arranged 
so that the signal CD is not output even if two small defects are 
successively scanned, information pits cannot be detected unless the 
number of successive information pits is three or more. In other words, 
the information pit detection sensitivity in terms of the number of 
information pits is reduced to three pits, because the probability of 
erroneous detection of small defects is reduced. Accordingly, if a 
recording medium in which many small defects appear successively with a 
pitch smaller than T.sub.w1, a certain number of retriggerable monostable 
multivibrators according to the number of successive defects may be 
connected subsequently to MMV 13 to correspondingly reduce the probability 
of erroneous detection due to the defects. However, the information 
detection sensitivity is also reduced correspondingly. 
Thus, in the example shown in FIG. 17, the possibility that small defects 
existing successively with a pitch smaller than the maximum pit pitch are 
erroneously detected as information pits is reduced and the reliability of 
pit signal detection is improved. It has been stated with respect to this 
example that it is possible to prevent erroneous detection due to defects 
by connecting a suitable number of MMVs. However, a recording medium 
having many small defects existing successively with a pitch smaller than 
T.sub.w1 is regarded as useless considering the ordinary function of 
recording media. Therefore, the arrangement in which three MMVs are 
connected as shown in FIG. 16 will suffice for ordinary use. If MMV 7 is 
connected subsequently to MMV 13 through AND gate 8 as shown in FIG. 14, 
it is possible to prevent interruption of the CD signal due to a defect in 
the pit array. 
FIG. 18 is a circuit diagram of the second embodiment of the present 
invention. The same reference numerals and letters as those used in FIG. 
10 designate the same elements. This embodiment is applicable to an 
apparatus using the single light source system shown in FIG. 1. In the 
single light source system, when information is recorded, the recording 
light spot 110 shown in FIG. 3 is intensity-modulated in accordance with a 
recording pulse, and the tracking control spots 111 and 112 are also 
modulated simultaneously. Therefore, if the circuit shown in FIG. 10 is 
used, a signal synchronized with recording pulses appears in the output 
signal TD from the comparator 2 and the CD signal is output from the 
condition detection circuit 3 even under normal recording conditions. This 
embodiment is arranged to be applied to the single light source system by 
removing the undesirable influence of such recording pulse modulation. 
Referring to FIG. 18, a series combination of a resistor R4 and a switching 
device SW1 is connected in parallel with a resistor R3 forming a feedback 
circuit of an amplifier 1. The switching device SW1 is turned on by a 
recording pulse WP. When the switching device SW1 is turned on and the 
switch SW1 is closed, the feedback resistance of the amplifier 1 is set to 
the resistance value of a parallel combination of the resistors of R3 and 
R4, thereby reducing the gain of the amplifier 1. In this embodiment, the 
ratio of the resistance value of the resistor 3 and the resistance value 
of the parallel combination of the resistors R3 and R4 is set to be equal 
to the ratio of light intensity modulation with recording pulses, thereby 
ensuring that even if the tracking control light spots are 
intensity-modulated, the output from the amplifier 1 is not influenced by 
this modulation. Except for these points, the configuration of this 
embodiment is the same as that of the embodiment shown in FIG. 10, and 
control of the apparatus is performed so that the information recording 
operation is stopped if tracking control is disturbed so that a pit signal 
high-frequency component is detected from the received light signal 
T.sub.s2. Thus, in this embodiment, the influence of intensity modulation 
of the light spots on recording pulses can be eliminated to detect a 
tracking control disturbance in the single light source system as 
effectively as the embodiment of FIG. 10, thereby preventing the 
occurrence of overwriting of recorded information. 
FIG. 19 is a circuit diagram of the third embodiment of the present 
invention. The same reference numerals and letters as those used in FIG. 
10 designate the same elements. In this embodiment, a tracking control 
disturbance is detected from the tracking error signal A.sub.ts, while in 
the first and second embodiments a tracking control disturbance is 
detected from the received light signal T.sub.s2. That is, the 
above-described embodiments are arranged to detect a pit signal component 
appearing in the received light signal T.sub.s2 from the photosensor 116 
shown in FIG. 4. However, such a pit signal component also appears in the 
tracking error signal A.sub.ts. Also, the tracking error signal A.sub.ts 
becomes positive and negative according to the directions of deviation of 
the light spots, as shown in FIG. 5. Therefore, this embodiment is 
arranged to detect a tracking control disturbance by detecting a pit 
signal component in the tracking error signal, thereby preventing 
overwriting of recorded information. The embodiment shown in FIG. 19 can 
be used in common in the single and dual light source systems, because the 
intensity modulation of the recording light beam does not influence the 
tracking error signal. 
Referring to FIG. 19, low-frequency components of the tracking error signal 
A.sub.ts are removed by a high-pass filter formed by a capacitor C1 and a 
resistor R1, and only high-frequency components are input to an amplifier 
1. A signal output from the amplifier 1 is compared with a negative 
reference value V.sub.r1 by a comparator 2 and with a positive reference 
value V.sub.r2 by a comparator 9 to be converted into a two-value signal. 
That is, the tracking error signal A.sub.ts. changes in plus and minus 
directions according to the direction of deviation and is therefore 
compared with the negative reference value V.sub.r1 by the comparator 2 
when a negative pit signal component appears therein and is compared with 
the positive reference value V.sub.r2 by the comparator 9 when a positive 
pit signal component appears. Output signals from the comparators 2 and 9 
are input into an OR circuit 10 and the result of a logical OR operation 
is output to a condition detection circuit 3. Except for these points, the 
configuration of this embodiment is the same as that of the embodiment 
shown in FIG. 10. 
In the circuit shown in FIG. 19, in a case where tracking control is 
disturbed so that the light spots are shifted toward the information track 
T3, a negative pit signal component appears in the tracking error signal 
A.sub.ts. In this case, high-frequency components appearing in the output 
from the amplifier 1 are two-valued by being compared with the reference 
value V.sub.r1 in the comparator 2, and the two value signal thereby 
obtained is output to the condition detection circuit 3 through the OR 
circuit 10. The condition detection circuit 3 detects a tracking control 
disturbance on the basis of the two-valued signal, as in the case of the 
embodiment shown in FIG. 1, and the MPU 4 performs control of the 
apparatus to stop the information recording operation. On the other hand, 
in a case where information has already been recorded in the information 
track T1 and where tracking control is disturbed during scanning of the 
light spots on the information track T2 so that the light spots are 
shifted toward the information track T1, a positive pit signal component 
appears in the tracking error signal A.sub.ts. Accordingly, in this case, 
the output from the amplifier 1 is two-valued by being compared with the 
reference value V.sub.r2 in the comparator 9, and the condition detection 
circuit 3 detects a tracking control disturbance on the basis of the 
two-valued signal. If a tracking control disturbance is detected, the MPU 
4 performs control of the apparatus to stop the information recording 
operation. 
Thus, in this embodiment, a tracking control disturbance is detected from a 
pit signal component appearing in the tracking error signal. A tracking 
control disturbance can therefore be detected if the light spots are 
shifted to the left or right from the information track. Thus, tracking 
control disturbances can be detected regardless of the direction in which 
the light spots move, and it is therefore possible to prevent overwrite 
recording on information tracks to the left and right of a scanned 
information track with one circuit. 
In the embodiment shown in FIG. 19, a tracking control disturbance is 
detected from the tracking error signal. However, it is also possible to 
detect a tracking control disturbance from the tracking sum signal in the 
same manner. That is, high-frequency components of the pit signal appear 
in the received light signals T.sub.s1 and T.sub.s2 from the photosensors 
115 and 116 shown in FIG. 4, and, naturally, a pit signal component 
appears in a signal obtained by adding these light signals. The received 
light signals from the photosensors 115 and 116 shown in FIG. 4 are added 
to each other in the addition circuit 122 to form the tracking sum signal 
A.sub.ta and a tracking control disturbance can be detected on the basis 
of this signal. A fourth embodiment of the present invention will be 
described as an example of this method. However, when the light spots 
deviate to the left or right, the tracking sum signal A.sub.ta is at the 
tracking reflection level, as shown in FIG. 5, and does not change in the 
plus and minus directions according to the direction of deviation of the 
light spots as in the case of the tracking error signal. 
More specifically, to detect a tracking control disturbance from the 
tracking sum signal in the dual light source system, the system may be 
arranged so that the tracking sum signal A.sub.ta is input to the circuit 
of the embodiment shown in FIG. 10 instead of the received light signal 
T.sub.s2. If the tracking sum signal is input to the circuit of the 
embodiment shown in FIG. 10, a pit signal component appears in either case 
of shifting the light spots to the left or right. Therefore, it is 
possible to detect a tracking control disturbance regardless of the 
direction in which the light spots are shifted, as in the case of the 
embodiment shown in FIG. 19. If a tracking control disturbance is detected 
from the tracking sum signal, it is not necessary to use two comparators 
as in the arrangement shown in FIG. 19; rather, only one comparator may 
suffice. It is therefore possible to detect a tracking control disturbance 
with a simplest arrangement to prevent overwrite recording on information 
tracks other than the target track. With respect to the single light 
source system, the arrangement may be such that the tracking sum signal is 
input to the circuit of the embodiment shown in FIG. 18. 
A fifth embodiment of the present invention will next be described. In the 
embodiment shown in FIG. 10, high-frequency components are detected from 
the received light signal from one of the two tracking control 
photosensors. If the positions of tracks in which information has been 
recorded and a track in which information is to be newly recorded are 
known, high-frequency components may be detected from one of the two 
received light signals as in the arrangement shown in FIG. 10. That is, 
referring to FIG. 9, in a case where information is recorded first on 
track T3, then on track T2, and then on track T1, a pit signal component 
appears first in the received light signal of reflected light of the light 
spot 228 (or 112) when the light spots are shifted toward the upper 
information track (track T3) in FIG. 9, and high-frequency components of 
the received light signal T.sub.s2 of the corresponding photosensor may be 
detected. Conversely, in a case where information is recorded first on 
track T1, then on track T2, and then on track T3, high-frequency 
components of the received light signal T.sub.s1 of the photosensor 
corresponding to the light spot 111 (or 227) may be detected. Further, the 
arrangement may be such that high-frequency components of both the 
received light signals T.sub.s1 and T.sub.s2 are detected and the 
recording operation is stopped when a high-frequency component appears in 
one of the two received light signals. 
In such a case, a pair of circuits each consisting of the components from 
the high-pass filter to the condition detection circuit 3 in the 
arrangement shown in FIG. 10 may be provided and the MPU 4 may immediately 
stop the recording operation when a pit signal component is detected in 
one of the condition detection circuits 3. Thus, even if it is not known 
on which tracks information has been recorded or on which information is 
to be newly recorded, it is possible to reliably prevent overwrite 
recording by detecting high-frequency components of the two received light 
signals T.sub.s1 and T.sub.s2 and by stopping the recording operation if a 
pit signal component is detected from one of the received light signals. 
In this example, however, such a pair of circuits is required and the 
circuit configuration is complicated. A sixth embodiment of the present 
invention, modified to use only the single circuit, will now be described 
with reference to circuit diagram of FIG. 20. The same reference numerals 
and letters as those used in FIG. 10 designate the same elements. The 
received light signals T.sub.s1 and T.sub.s2 from the photosensors 115 and 
116 shown in FIG. 4 are input to a capacitor C1 of a high-pass filter, 
comprising capacitor C1 and resistor R1, through a switching device SW2. 
The switching device SW2 is switched between light signals T.sub.s1 and 
T.sub.s2 under the control of an MPU 4. By this switching, the received 
light signals T.sub.s1 and T.sub.s2 are alternatively input to the 
high-pass filter. Except for these points, the configuration is the same 
as that of the embodiment shown in FIG. 10. However, the example shown in 
FIG. 20 is adapted to the dual light source system. The timing of the 
switching of the switching device SW2 may be such that the switching 
device SW2 is switched at intervals of a scanning time corresponding to 
several pits to about 10 pits. Considering the speed at which tracking 
control is disturbed, it is suitable to use such changeover timing for the 
effect of preventing overwrite recording. Consequently, it is possible to 
reliably prevent overwrite recording by using a simple arrangement if the 
received light signals are changed by such predetermined timing. Needless 
to say, in the case of the single light source system, the arrangement may 
be such that a pair of circuits, each circuit consisting of the circuit 
shown in FIG. 18 are provided and the two received light signals are input 
by being changed in a time division manner by a switching device. 
A seventh embodiment of the present invention will next be described. In 
the above-described embodiments, to prevent overwrite recording, a 
tracking control disturbance is detected by detecting some pit signal 
high-frequency components appearing in the received light signals T.sub.s1 
and T.sub.s2 from the tracking control photosensors 115 and 116, the 
tracking error signal A.sub.ts and the tracking sum signal A.sub.ts. 
However, it is possible to fail to detect a tracking control disturbance 
by detection of these signals. For example, if the defect 224 on the 
information track T2 in FIG. 9 is so large as to extend even to the point 
X or Y, tracking control is largely disturbed when the light spots scan 
the defect 224, and the light spots move to a point Z when they passed the 
defect 224. In such a case, no pit signals appear in the above-mentioned 
three signals, and there is a possibility of the occurrence of overwrite 
recording immediately after the passage of the light spots over the defect 
224. 
Also, in a situation where one track is divided into plural sectors, where 
information has already been recorded in some of these sectors and where 
information is to be recorded in some sector in the same track other than 
the sectors containing already-recorded information, there is a 
possibility of overwrite recording when the light spots pass the sectors 
containing already-recorded information. Needless to say, such a case is 
not due to a tracking control disturbance, and overwrite recording is not 
prevented because no pit signal components appear in the above three 
signals. To solve this problem, overwrite recording may be prevented by 
detecting a pit signal component from the information reproduction signal 
RF shown in FIG. 4. More specifically, in the case of the dual light 
source system, the arrangement may be such that the information 
reproduction signal RF is input to the circuit of the embodiment shown in 
FIG. 10 instead of the received light signal T.sub.s2, and control of the 
apparatus is performed so that the MPU 4 immediately stops the recording 
operation when the condition detection circuit 3 detects a pit signal 
component from the information reproduction signal RF. When a pit signal 
component appears in the information reproduction signal RF, overwrite 
recording has already been started. However, some data destroyed can be 
restored since error correction codes are included in ordinary information 
recording to enable an error to be corrected. 
In the case of the single light source system, it is necessary to separate 
the recording operation with respect to recording and reproduction since 
recording is performed by using the same light spot as that for obtaining 
the information reproduction signal RF. FIG. 21 is a circuit diagram of an 
eighth embodiment of the present invention applicable to the single light 
source system. The same reference numerals and letters as those used in 
FIG. 10 designate the same elements. In this embodiment, a sample and hold 
circuit for sampling and holding the information reproduction signal 
during time periods other than the periods of recording pulses WP is 
provided between an amplifier 1 and a comparator 2. The information 
reproduction signal RF is input to a capacitor C1 forming a high-pass 
filter with resistor R1. Except for these points, the configuration is the 
same as that of the embodiment shown in FIG. 10. The sample and hold 
circuit is formed by a switching device SW3 connected between the 
amplifier 1 and the comparator 2, a drive circuit for driving the 
switching device SW3 including an inverter 11 and an AND circuit 12, and a 
capacitor C4 for holding the output signal from the amplifier 1 when the 
switching device SW3 is turned on. The driving circuit also includes a 
delay circuit formed by a resistor R5 and a capacitor C5, the output of 
which is input into AND circuit 12. 
The operation of this embodiment will be described below. A signal obtained 
by inverting recording pulses WP by the inverter 11 and a signal obtained 
by delaying recording pulses WP by the delay circuit formed by the 
resistor R5 and the capacitor C5 are input into the AND circuit 12 to form 
an output to the switching device SW3. The output signal from the AND 
circuit 12 is formed of a pulse signal having a width corresponding to a 
delay time of the delay circuit from the trailing end of each recording 
pulse WP, i.e., a time period other than the periods of recording pulses 
WP. The switching device SW3 is driven so as to be turned on to connect 
amplifier 1 to the comparator 2 during the period of this pulse signal. 
Accordingly, the output signal from the amplifier 1 is held by the 
capacitor C4 during time periods other than the periods of the recording 
pulses, i.e., when the intensity of the light spot is at a reproducing 
power level, thereby sampling and holding the information reproduction 
signal RF during the time periods other than the periods of the recording 
pulses WP. The signal held by the capacitor C4 is caused to be two-valued 
by the comparator 2 and pit signal high-frequency components are detected 
from the two-valued signal in a condition detection circuit 3, as in the 
case of the embodiment shown in FIG. 10. When a pit signal component is 
detected, an MPU performs control of the apparatus so as to stop the 
information recording operation. 
As described above, the information reproduction signal RF is sampled and 
held when the recording pulses are supplied at the reproducing power 
level, thus making it possible to detect a pit signal component from the 
information reproduction signal RF even in the single light source system. 
It is therefore possible to prevent overwrite recording on tracks other 
than a target track or on sectors containing already-recorded information 
in a track containing a target sector in the single light source system in 
a case where there is a very large defect as described above. In this 
embodiment, no pit signal component can be detected if information newly 
recorded and information already recorded are entirely equal to each 
other. However, this is a rare case and it is usually possible to 
sufficiently detect components of the recorded pit signal from the 
information reproduction signal RF only by sampling and holding the 
information reproduction signal RF during the time periods other than the 
periods of the recording pulses WP. 
As is apparent from the above description, for prevention of overwrite 
recording, it is necessary to detect pit signal components from a 
plurality of signals among the received light signals T.sub.s1 and 
T.sub.s2 from the photosensors 115 and 116, the tracking error signal 
A.sub.ts, the tracking sum signal A.sub.ta and the information 
reproduction signal RF instead of detecting pit signal components from 
only one of these signals. For the desired effect, there are three 
possible combinations of these signals: 
(1) a combination of received light signal T.sub.s2 (or T.sub.s1) and 
information reproduction signal RF, or a combination of received light 
signals T.sub.s1 and T.sub.s2 and information reproduction signal RF; 
(2) a combination of tracking error signal A.sub.ts and information 
reproduction signal RF; and 
(3) a combination of tracking sum signal A.sub.ta and information 
reproduction signal RF. 
With respect to the combination (1), in the case of the dual light source 
system, a pair of circuits each consisting of the components from the 
high-pass filter to the condition detection circuit 3 of the embodiment 
shown in FIG. 10 are provided, and received light signal T.sub.s2 (or 
T.sub.s1) and information reproduction signal RF are input to each 
circuit. If high-frequency components are detected from both received 
light signals T.sub.s1 and T.sub.s2, the same three circuits may be 
provided. The control of the apparatus may be such that the MPU 4 stops 
the recording operation if a pit signal component is detected in one of 
these circuits. The arrangement may alternatively be such that a single 
circuit formed of the embodiment shown in FIG. 10 is provided and received 
light signal T.sub.s2 (or T.sub.s1) or both T.sub.s2 and T.sub.s1 and 
information reproduction signal RF are input to this circuit by being 
switched in a time division manner by a switching device, an analog 
multiplexer or the like. 
In the case of the single light source system, the arrangement may be such 
that a single unit or a pair of units of the circuit shown in FIG. 18 or a 
single unit of the circuit shown in FIG. 21 is provided and the recording 
operation is stopped if a pit signal component is detected in one of these 
circuits. If high-frequency components are detected from both received 
light signals T.sub.s1 and T.sub.s2, the arrangement may be such that a 
single unit of the circuit shown in FIG. 18 is provided and received light 
signals T.sub.s1 and T.sub.s2 are input by being switched in a time 
division manner. 
With respect to the combination (2), in the case of the dual light source 
system, tracking error signal A.sub.ts is input to the circuit shown in 
FIG. 19 while the information reproduction signal is input to the circuit 
shown in FIG. 10. In the case of the single light source system, however, 
information reproduction signal RF is input to the circuit shown in FIG. 
21. The recording operation is stopped if a pit signal component is 
detected in one of these circuits. 
With respect to the combination (3), in the case of the dual light source 
system, a pair of circuits from the high-pass filter and the detection 
circuit 3 are provided and tracking sum signal A.sub.ta and information 
reproduction signal RF are input to each circuit. The arrangement may 
alternatively be such that a single unit of the circuit shown in FIG. 10 
is provided and the tracking sum signal and the reproduction information 
signals are input by being switched in a time division manner. In the case 
of the single light source system, the tracking sum signal and the 
information reproduction signal RF may be input to the circuit shown in 
FIG. 10 and the circuit shown in FIG. 21, respectively. In each of the 
single and dual light source systems, the recording operation is stopped 
if a pit signal component is detected in one of these circuits. 
Examples of the circuits with respect to these combinations have been 
described. In the case of any one of these combinations, it is possible to 
discriminate a pit signal component and a signal due to a medium defect 
from each other according to the conditions under which the signal CD 
appears. For example, in the case of the combination (1) in the dual light 
source system, if three units of the circuit shown in FIG. 10 are provided 
to input received light signal T.sub.s1 or T.sub.s2 and information 
reproduction signal RF, and if the signal CD are simultaneously output 
from both received light signal T.sub.s1 or T.sub.s2 and information 
reproduction signal RF, then it can be determined that these outputs are 
not obtained by detecting a pit signal component. Also, it is not actually 
possible that the CD signals are obtained simultaneously from both 
received light signals T.sub.s1 and T.sub.s2. If outputs are obtained in 
this manner, it can be determined that the result is not due to detection 
of a pit signal but due to a defect. In such a case, therefore, the MPU 4 
may continue the recording operation by determining that the output 
condition is due to a medium defect. 
As mentioned above, error correction codes are ordinarily added to recorded 
information and it is therefore possible to correct and restore a 
destroyed part of data. The circuit shown in FIG. 14 has been described as 
an example of means for preventing interruption of the signal CD. Such a 
means may be used in each of the above-described embodiments to perform a 
control of the apparatus in such a manner that the recording operation is 
stopped when the signal CD from the detection circuit 3 is sustained 
through a predetermined period of a correctable error length, thereby 
reducing the probability of an operation failure of the apparatus due to 
erroneous detection of medium defects. In the above-described embodiments, 
a pit signal component is detected during information recording to prevent 
overwrite recording. However, it is also possible to discriminate tracks 
containing recorded information by inputting information reproduction 
signal RF to the circuit shown in FIG. 10 or FIG. 12 at the time of 
information reproduction. 
The embodiments of the present invention have been described as an 
apparatus using a three-beam system as a tracking control system. The 
present invention, however, can also be applied to apparatuses having 
other types of tracking systems. For example, there is a one-beam system 
in which one light spot irradiates one of tracking tracks tt1 to tt4 of 
the optical card shown in FIG. 2(a) and an image of the tracking track is 
obtained by one or two photosensors. In this one-beam system, signal 
components of recorded pits also appear in the received light signals from 
the photosensors, if tracking control is disturbed. Therefore, the present 
invention can also be applied to such a one-beam system as well as to the 
three-beam system. There is also another tracking control system in which 
one elongated light spot irradiates and extends from a center of a track 
to portions of adjacent tracking tracks. In this system, photosensors are 
also disposed at positions corresponding to the track center and the 
tracking tracks. Therefore, the present invention can also be applied to 
an apparatus using such a system as well as to three-beam type and 
one-beam type apparatuses. 
In the apparatuses of the above-described embodiments, an optical card is 
used as an information recording medium. However, the present invention 
can also be applied to apparatuses using any medium other than the optical 
card, for example, an optical disk. In the described embodiment, a pit 
length recording method has been described as an example of the 
information recording method. Needless to say, the present invention is 
not limited to this recording method and can also be applied to 
apparatuses using any other recording method, e.g., a pit position 
recording method. 
While the present invention has been described with respect to what is 
presently considered to be the preferred embodiments, it is to be 
understood that the invention is not limited to the disclosed embodiments. 
The present invention is intended to cover the various modifications and 
equivalent arrangements included within the spirit and scope of the 
appended claims.