Note: Descriptions are shown in the official language in which they were submitted.
1~24391
1 I This application is a divlsional application of
I the Canadian Patent Application No. 275.672 filed on
¦ 6th April, 1977.
I
, B~.C~GRO~ID OF T~E I~VENTI~N
,~
The present invention gen~rally relat~s to reproduci~g
i styluses for information slgnal recording mediums, and m~re
partlcu7arly to a reproducing stylus ~hich scans over trac~s
in a recordinq medi~ on which information si~nal~ are
~ recorded as varlations of geometrlcal configuration, to
reproduce the recorded information signals a3 ~ariations in
electrostatic capacitance, and has a config~ration which
: ¦ enables the reproducing stylus to have a lon~ e.
¦ As one exa~ple of a syste~ which per~or~s high-density
~ recording and r~productlon.of lnfor,matlon slgnals such as a
vldeo andfor an audio si~nal to and from a recording medlum
such a rotary recording medium~ there is a system which
records and reproduce~ the lnformation signals as variatlons
I in ~lectrostatic capacitance~ A rotary recordin~ medium
¦ reproducea b~ this system has ~ spiral gulde groove formed
thereon~ for quiding a tracing ~tylus used for reproduclng a
slgnal. Along the bottom part of thl~ guide groo~e, there
is ~ormed a track o~ an information slgnal which ls recorded
-¦ as a variation of a geometrlaal configuratlon. The tracing
¦ ~tylus ls quided by this guide groo~e while tracin~ the
¦ ~ottom thereof, and thus reproduces the recorded informat~o
I ~ignal. .
¦ On the other hand, the present lnventors haYe made
. ¦ it po~sible to r~cord an~ reproduce ~i~nals ln a syste~ whl~h
¦ doe~ not have a guid~ ~roove, by pxovidln~ a system w~lch
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1 can perform tracking control of the tracing stylus so that
the stylus will trace accurately and positively over the
recorded track. In this system, the information signal is
1 recorded on a rotary recording medium as a variation of a
~ geometrical configuration.
However, in the above described system and the
system developed by the present inventors, the recording
medium must be rotated at a high speed to obtain a high
~ relative linear velocity between the recording medium and the
10 ¦ reproducing stylus, in order to perform reproduction with
a large signal-to-noise (S/N) ratio. Hence, the reproducing
stylus which makes contact with and slides over the recording
medium, is easily worn out due to friction. Accordingly,
l from the practical point of view~ a reproducing stylus which
¦ does not wear out due to friction even when the stylus is
! used for a long time, is desired. Further, it is desirable
that the reproducing function of the reproducing stylus is
not deteriorated even when the stylus is slightly worn out,
¦ and that the reproducing stylus does not damage the recording
¦ medium.
~:
: ¦ SUMMARY OF THE INVENTION
¦ Accordingly~ a general object of the present
1 invention is to provide a novel and useful reproducing stylus .
¦ for an information signal recording medium in which the
l above described requirements have been satisfied.
: ¦ Another and more specific object of the present
invention is to provide a reproducing stylus for an information
¦ signal recording medium, having an electrode surface divided
by a pair of side surfaces in the vicinity of the tip end
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1 part of the reproducing stylus. According to the reproducing
stylus of the present invention, -the width of the electrode
~ surface does not rapidly increase even when the tip of the
¦ reproducing stylus slightly wears out, and fine reproducing
¦ function is maintained.
¦ Still another object of the present invention is to
¦ provide a reproducing stylus for an information signal
¦ recording medium, in which the length of a surface of the
¦ reproducing stylus at the tip end thereof which slides
against the recording medium, along the relative sliding
direction, is larger than the width of the surface of the
reproducing stylus along a direction perpendicular to the
sliding direction. According to the reproducing stylus of the
present invention, the wear of the reproducing stylus due to
¦ friction is small and the stylus can be used for a long time,
since the area of the sliding surface of the reproducing
l stylus which slides against the recording medium can be
¦ made large.
I Another object of the present invention is to
~ provide a reproducing stylus for an information signal
¦ recording medium, in which the tip end part of the surface
I ¦ of the reproducing stylus which slides agains-t the recording
I ¦ medium along the relative scanning direction has an vertex
l of an acute angle. According to the reproducing stylus of
¦ the present invention, fine reproduction can be performed
since the vertex having an acute angle of the reproducing
stylus slides against the reproducing stylus, and dust
l particles, unwanted particles and the like are removed by
¦ the vertex of the above surface of the reproducing stylus
¦ which slides against the recording medium. Moreover,
. .
~439~
1 skipping of the reproducing stylus is hardly introduced.
Still another object of the present invention is
to provide a reproducing stylus for an information signal
¦ recording medium, having a configuration in which an edge part
¦ extends obliquely towards the upward direction from the vertex
of the surface which slides against the recording medium.
According to the reproducing stylus of the present invention,
the process to manufacture the reproducing stylus of the
1 above configuration is facilitated.
~ Further objects and features of the present invention
will be apparent from the following detailed description when
read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
l .
FIG. 1 is a systematic block diagram showing an
example of a recording system far recording information signals
¦ on a recording medium which is reproduced by use of a
reproducing stylus;
¦ FIGS. 2A through 2D are successively enlarged views
¦ respectively showing a portion of an example of a track
; ¦ pattern formed on a rotary recording medium which is
reproduced by a reproducing stylus according to the present
invention;
l FIG. 3 is an enlarged view showing another example
¦ of a track pattern formed on a recording medium which is
reproduced by a reproducing stylus according to the present
invention,
¦ FIGS. 4A and 4B are perspectively:a view showing
¦ one example of reproducing tracing means, and an enlarged
1 perspective view, as viewed from the bottom, showing a tip
~ ~Z4391
1 I end portion of a reproducing stylus according -to the present
¦ invention; and
l FIC. 5 is a systematic block diagram showing an
¦ example of a reproducing system for reproducing a recording
medium.
DETAILED DESCRIPTION
An example of a recording system for recording
information signals on a recording medium is first described
¦ in conjunction with FIG. 1.
¦ Referring to-FIG. 1, a part of a laser beam projected
from a laser light source 11 is reflected, by a half-mirror
12, to a light beam modulator 24. The remaining part of the
l projected laser beam passes through the half-mirror 12 and
¦ is reflected by a reflecting mirror 13 to a light beam -
modulator 16. A recording information signal including a
color video signal and an audio signal is introduced through
l an input terminal 14 and is supplied to a frequency modulator
¦ 15 where it frequency-modulates a carrier. The output
20 ¦ frequency modulated signal is applied to the light beam
¦ modulator 16 where it modulates the laser beam. A first
I modulated light beam, which has been modulated by the frequency
¦ modulated signal at the light beam modulator 16, i9 reflected
¦ by a reflecting mirror 26 to be formed in a light beam of
1 25 ¦ whlch section is elliptic. This light beam passes through
a polarization prism 27. The resulting light beam is
¦ reflected by a reflecting mirror ~8 and projected into an
¦ objective lens 29. The light beam passed through the lens
¦ 29 is focused in such a manner that a focal point of the
lens 29 coincides with a sensitive material 31 coated on an
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l original recording disc 30 made of material such as glass.
Switching pulses are applied to oscillators 20,
21 and 22 through input terminals 17, 13, and 19, respectively.
I The switching pulses cause, for instance, the oscillators 20,
1 21 and 22 to have an output during the interval of positive
l pulse polarity, and to have no output during the interval of
! negative pulse polarity. The o~cillators 20, 21, and 22
oscillate at their original frequencies and generate signals
l having, respectively, single frequencies fp1 ~e.g., 700 KHz),
¦ fp2 ~e.g., 500 KHz), and fp3 ~e.g., 300 KHz).
When every two-frame video signal is to be recorded
on the disc 30 per rotation thereof, for instance, first and
second pulses are used alternatively during every two-frame
I interval. These are input switching pulses which are supplied
I5 ¦ to the input terminals 17 and 18. The pulse width is selected
so that a reference signal for trac~ing control which is
modulated by the above first and second pulses does not
affect a color burst signal. Consequently, the signal fp1 is
l produced for a two-frame interval ~1/15 second) from the
¦ oscillator 20~ in synchronism with the horizontal synchronizing
I signal. Following this, the signal fp2 is produced from the
¦ oscillator 21 for the following two-frame interval, in
¦ synchronism with the horizontal synchronizing signal. The
¦ signals fpl and fp2 are thereafter produced every two-frame
25 ¦ period~ successively and alternately.
¦ In correspondence to the time point when the signals
fpl and fp2 switch, a third reference signal fp3 is sent
¦ out from osclllator 22. This signalfp3 is an indëx puIse atthe
¦ time of reproduction.
The lnvention may be used to carry out a special
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l reproduction such as still-motion or slow-motion. It is
particularly useful if the information signal is principally
a video signal. A kick-back control is required for shifting
~ or forcibly transferring a reproducing tracing means tracing
~ one track, to another track within a vertical blanking period
~abbreviated as V.BLK hereinafter). For this kick-back control
operation, the signal fp3 is recorded at the V.BLK part of
l the video signal. The pulses may be recorded as the signal fp3
¦ during two or three H periods at the initial horizontal
0 ¦ synchronizing pulse part following equalizing pulses, projecting
toward the white side. However~ when the tracing stylus is
actually kicked back by the signal fp3, at the time of still-
motion reproduction or slow motion reproduction, the tracing
1 stylus is not stabilized on a predetermined track immediately
5 ¦ after jumption. Rather, the tracing stylus hunts to some
extent. Interrelatedly with a response characteristic of the
¦ mechanism for moving the tracing stylus, some noise may
I appear on the upper part of the picture responsive to the
¦ kick-back operation.
0 ¦ Therefore, in order to kick back completely within
the V.BLK interval, the switching operation is carried out
¦ at the time of signal recording and reproduction either just
¦ before or just after of the respective ends of the video
l signal intervals.
5 ¦ The signals fp1, fp2, and fp3 are composed at the
adder 23, and applied as a modulation signal, to the light
¦ beam modulator 2g. The second modulated output light beam
¦ from the light beam modulator 24 is attenuated by a light
l filter 25. The brightness (beam light quantity) is adjusted
0 ¦ to be attenuated appropriately in comparison with the quantity
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1 of light of the first modulated light beam. The attenuated
, second modulated light beam thereafter advances to a
¦ polarization prism 27, where the polarization plane of the
¦ light beam is deviated by 90 with respect to the polarization
1 plane of the first modulated light beam.
¦ The second modulated light beam which has passed
through the polarization prism 27, together with the first
modulated light beam, is reflected by the reflecting mirror
l 28 and passes through the objective lens 24. Then the beams
¦ irradiate the sensitive material 31 on the rotating recording
disc 30. The polarization prism 27 adjusts the incident
light path of the second modulated light beam toward the
objective lens 29, with respect to the first modulated light
~ beam.
¦ The exposure of the light beams by the above
described optical system on the sensitive material of the
rotating recording disc 30 is performed in the radial direction
thereof by a predetermined pitch. After this exposure,
l developing process is pérformed, whereby the spiral track, for
¦ instance, is formed as a change of the geometrical
¦ configuration such as pits in accordance with the exposure.
Pits are not formed directly by only exposure of the light
beam on the light sensitive material 31. As a result of the
l above described adjustment, the second modulated light beam
records and forms a sub-track, which is separated by
¦ approximately a l/2 track pitch from a main track formed by
¦ the first modulated light beam. Herer the track pitch refers
to a distance between two tracing center lines of adjacent
l tracks.
¦ Moreover~ it may not be appropriate to divide the
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I beam into two beams by the half-mirror 12. For example, the
beam power of the laser light source 11 may be too low. If
so, another laser light source 32 (indicated by a dotted line
~ in FIG. 1) may be additionally provided. In this case, the
1 light beam intensity, the modulation index and the like, of
the beam projected from the laser light source 32 are
appropriately adjusted with respect to the first modulated
light beam.
l The light beam projected from the laser light source
¦ 32 is reflected by a reflecting mirror 33 and is then supplied
¦ to the light beam modulator 24. Moreover, interrelatedly
l with the provision of the laser light source 32, the half-
¦ mirror 12 is omitted and the light beam projected from the
¦ laser light source 11 is supplied to only the light beam
¦ modulator 16.
¦ If the main recording information signal is a
color video signal, the reference signals may be obtained by
¦ frequency dividing a chrominance sub-carrier of the color
¦ video signal.
¦ Further, instead of recording with a light beam,
¦ the recording is by a double electron beam.
I ; ¦ Accordingly, a track pattern recorded on the disc
¦ by the system in FIG. 1 is as indicated in FIG~ 2A through
¦ FIG. 2D, for instance. The signals fpl, fp2, and fp3 are
¦ recorded in alignment in the radial direction of the disc
¦ 50. FIG. 2B schematically shows an example of a track pattern
which circles the diac indicated in FIG. 2A, for convenience
¦ of description. A track pattern indicated in FIG. 2C is a
¦ magnification of part of the track pattern in FIG. 2B. In
FIG. 2B, numerals ~1), (2), (3), .... respectively indicate
I
,.
. . . .
l parts where the first, the second, the third .... horizontal
synchronizing signals of the first frame of the video
signal are recorded Numerals (521)', (522)', ... (525)'
l respectively indicate parts where the 521st, the 522nd,
... the 525th horizontal synchronizing signals of the
second frame of the video signal are recorded. That is,
in the present example, two frames of the video signal
having 525 horizontal scanning lines per one frame are
recorded for every rotation of the disc.
l In FIG. 2c, reference marks t1, t2, t3,
respectively designate the first, the second, the third
... main tracks which are recorded and formed, one track
during every rotation of the disc 50. The recording is
~ made by forming a number of intermittent pits 50. The
¦ reference signals fp1 and fp2 are recorded alternately
with a period of one rotation between them. The reference
signals are formed by intermittent pits located between
l the adjacent main tracks. The pits are shallow in comparison
¦ with the depth of the pits of the main track. Further,
¦ although the illustration is omitted in FIG. 2B for the
; ¦ sake of simplification, the reference signal fp3 is
recorded as timing pulse at a position 52 where the
recording of the signal fp1 and fp2 i5 switched as indicated
l by a broken line in FIG. 2c. The switched position
corresponds to a position ~525)' in FIG. 2B.
I ¦ If the main information signal comprises at
¦ least the video signal, a recording of the reference
signals is effected similar to the recording in the
l preceding description. That is, in order to prevent the
¦ beat disturbance of cross modulation between the reference
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~L~24391
l signals and the video signal, the signals fp1 and fp2
are recorded within a H.sLK interval, as indicated by
the numeral 53 in FIG. 2c. The signal fp3 is recorded
at a V.BLK part 52. Therefore, none of the signals
1 fp1, fp2, and fp3 is recorded in the video information
period 54.
Further, to record and reproduce the signals
fp1 and fp2 with higher sensitivity, the present embodiment
~ is arranged so that the positions of the signals fp1 and
0 ¦ fp2 are respectively alternately recorded separately
along every track. These signals are located at positions
in the H . BLK period with a period of 2H interval.
Furthermore, the recording of the signals fp1 and fp2
~ is such that the recording positions of the signals fp1
5 1 and fp2 are located within the H.B1K period at positions
which are separated or deviated by every 1H interval
alternately with respect to the adjacent tracks.
According to this arrangement, the signals fp1 and fp2
are recorded without affecting the main information
0 ¦ signal. Further, the reference signals can be recorded
¦ with a wider dimension even when the main information
signal is recorded with very small track pitch, i.e.,
¦ with high density. The reference signals can be
l reproduced in a stable manner, thereby stabilizing the
l tracking control operation. However, the signals fp1
¦ and fp2 may be recorded at positions corresponding to
every H.BLK of the video signal. Further~ by using a
¦ single low frequency, the reference signal can be
¦ reproduced in a stable manner. This low frequency has
I a longer wavelength as compared to the reference signals
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1 described hereinbefore.
FIG. 2D indicates a part of ~he track pattern
indicated in FIG. 2s, with further enlargement. The
l track pattern is formed by recording a main track with
track pitch 58 (e.g., 2.8 ~m), pit width 55 (e.g., 2.6 ~m),
and a sub-track with pit width 56 (e.g., 1.2 ~m) at an
intermediate position between the adjacent main tracks,
with overlap on the main track at parts 57, 57'.
~ FIG. 3 is an enlarged plan view showing a
~ part of a track pattern of a second embodiment. The
track pattern is formed by recording the main track with
a track pitch 58 of 2.8 ~m, which is the same as that
of the main tracks in FIG. 4D. The track pitch coincides
l with the pit width 59 without any vacant space between
¦ the adjacent main tracks. Also the sub-track is
recorded with a pit width 60 of 1.0 ~m, for instance,
l at the intermediate part between the center lines of
; I adjacent main tracks so as to entirely overlap on the
¦ main track. The track pattern set forth is more
¦ effective for increasing or improving the signal
reproducing sensitivity and the recording density of
the information track.
Furthermore, the signals fp1 and fp2 may be
l recorded with pits of a size which will not overlap
25 ¦ with respect to the main information pit pattern.
However, as shown in FICS. 2B, 2C, 2D, it is desirable
¦ for the information pits of the main information
¦ signal and the pits of the signals fpl and fp2 to be
¦ formed at the intermediate parts of the main information
30 ¦ signal pits. Moreover, the pits of fp1 and fp2 partially
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~24~91
1 overlap parts with respect to the pits on both of their
sides. Even ~hen recording is carried out in this
manner, the above mentioned reference signal has no
electerious effect whatsoever on the main information
l signal, particularly as long as the reference is within
the horizontal blanking period~
In this case, since the reference signal
recording track has a greater width, the stabilization
l of the tracking control operation becomes better.
0 ¦ However, for accomplishing an excellent reproduction
of the main information signal, it is desirable that
only one of the signals fp1 and fp2 be recorded in the
corresponding parts of the horizontal blanking period
~ of the main information signal recording track. This
5 ¦ can be done by recording the signals fp1 and fp2
intermittently with periods 2H, 3H, ... etc., for example.
As is known, if the main information signal is
an audio signal, there is no periodic signal such as a
¦ horizontal synchronizing pulse in the audio signal.
0 ¦ ~owever, by recording the reference signals fpl and fp2
with different phases, respectively front and rear, in the
rotational direction at the opposite lateral side parts
of the audio signal track, tracking control can be
l accomplished even more advantageously than in the above
¦ described case. The reference signal recording position
l is limited to the part corresponding to the horizontal
¦ blanking period.
As is also known in this connection, the horizontal
l scanning frequency of a television video signal of the NTSC
¦ system is 15.75 KHz. Since the rotational speed of the disc
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~1~4391
1 50 in this example is 900 rpm, the fundamental error period
at the time of disc eccentricity is merely 15 Hz. This
period is ample to provide the information tracking control.
l Moreover, instead of using the signal fp3, the
ll deficient part is detected and discriminated from the
other recording part. The reproduced signals fp1 and fp2
pass through an integration circuit at the time of the
reproducing mode, without recording the signals fp1 and fp2
l during the 2H through 3H intervals within the V.BLK period.
1 FIG. 4A shows one example of a reproducing tracing
means which can be applied to a reproducing stylus according
to the present invention.
l A disc-shaped recording medium (disc) 71 has on
I ¦ its surface a thin metal film coating. On this disc surface,
¦ pits of the main information signal and reference signals
¦ fp1 and fp2 are respectively recorded on opposite lateral
¦ sides~ as shown in FIGS. 2 and 3. The disc 71 is positioned
1 on and rotates with a turntable 73 rotated synchronously by
I ¦ a disc motor (not shown) at, for example, 900 rpm. Turning
¦ is in the arrow direction 72 at the time of reproducing.
~ ¦ A tracing stylus 74, which is an embodiment of a reproducing
¦~ ¦ stylus according to the present invention, is positioned to
¦ contact and slide over the disc 71. For example, a signal
¦ pickup may be an electrostatic capacitance type. A video
¦ signal of two frames is reproduced on every rotation of the
¦ disc 71.
¦ The tracing stylus 74 has a tip shape as shown in
¦ FIG. 4B. The tracing stylus proper is made of a material
¦ such as diamond or sapphire. The entering or leading part
¦ 88 of this tracing stylus 74 is formed by the acute vertex
I
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1 of the sliding surface 89. An electrode 86 made of a metal
such as titanium is secured to a back surface 91 of the
stylus which becomes the electrode surface, by a sputtering
process. The width 87 of the electrode corresponds
substantially to the pit width, being approximately 2 ~m
in the present embodiment. For preserving the serviceable
life oE the stylus over a long period, the area of the
contacting and sliding surface 89 of the stylus tip end
~ should be made large. For this purpose, the dimensions of
¦ the contact at least in the longitudinal direction is made
large. The width and area of stylus contact with the disc
surface should be large relative to the information pit.
l Accordingly, the sliding surface 89 makes simultaneous contact
I ~ with a plurality of pits at the time of contact. The
1 electrode width 87 corresponds to the information width of
a single pit. Therefore, while the contact area is amply
~ large, pit information can be picked up in the form of
; ¦ variations of electrostatic capacitance. There is a high
sensitivity from the electrode part 86.
¦ The width of the back surface 91 provided on the
1 electrode 86, in the vicinity of the tip end part of the
¦ back surface 91, 1S restricted by a pair of right and left
¦ side surfaces 92. Accordingly, even when the part of the
1 tracing stylus 74 in the vicinity of the tip end thereof,
¦ begins to slightly wear out from the sliding surface 89
due to friction, the width 87 of the electrode 86 does not
exceed the width of a single pit. Hence, the life of the
¦ tracing stylus is lengthened.
I In addition, the leading part 88 which forms the
¦ tip end of the tracing stylus 74 in the relative tracing
~ I
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1 direction with respect to the disc 71, is formed as a vertex
having an acute angle as described above. Therefore, dust
particles on the disc 71 is swept away on both sides with
~ respect to the tracing stylus 74, by the leading part 88.
1 Accordingly, the dust particles are prevented from entering
between the sliding surface 89 and the disc 71, and the
signal-to-noise ~S/N) ratio does not deteriorate. Thus,
fine reproduction can be performed in which the skipping
l of the tracing stylus 74 is not introduced.
¦ Further, the sliding surface 89 is of a pentagon
shape, as shown in FIG. ~B ! As clearly shown in FIG. ~B,
the length Q of the sliding surface 89 in a direction
perpendicular to the width direction of a maximum width part
~ 90, is larger than the width~87 of the electrode. Hence,
5 ~ the area of the sliding surface can be made large, by not
particularly enlarging the width of the sliding surface 89,
to reduce the pressure of the stylus per unit area.
Accordingly~ the wear of the tip end of the stylus due to
l friction can be made small. Thus, the life of the tracing
0 ¦ stylus is also lengthened from this point of view~
¦ Since and edge 93 is formed obliquely in the
upward direction from the vertex of the leading part 88, the
size of the main stylus body at the base end side of the
l stylus can be made large compared to the size of the stylus
¦ at the tip end thereof. Therefore, the process to manufacture
¦ the tip end of the stylus is facilitated. Moreover, it is
¦ easy to mount the stylus onto the cantilever.
¦ The tracing stylus 74 is secured to a moving
¦ shaft 78 of a moving coil mechanism 80 by way of a thin leaf
spring 75, a shock-absorbing member 76, and a bracket 77.
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~l12~39~ 1
1 j The spring 75 and the shock-absorbing mem~er 76 enable a
stable contact between the sliding tip of the tracing
, stylus 74 and the information surface on the disc 71, with
~ a light pressing force of approximately 30 mg. Furthermore,
1 the light up-and-down pressing force of the tracing stylus
74 is imparted to a signal pickup part 79, which is so
constructed that it does not move in the left-and-right
direction. The moving coil mechanism 80 is constructed
l similar to a loudspeaker and comprises a permanent magnet,
10 l a driving coil, and a yoke none shown). The part is axially
~ supported by a damper and is provided with the moving shaft
¦ 78. This moving shaft 78 is displaced in its radial direction,
that is, in an arrow direction 81, which is the disc radial
l direction. Shaft 78 is displaced in response to the
¦ direction and magnitude of the electric current supplied to
the above mentioned driving coil.
By this construction, the signal pickup structure
79 includes the tracing stylus 74 mounted on the moving
¦ shaft 78. The tracing stylus 74 is capable of high-speed
¦ control driving the tracing stylus 74 in the direction
~ ¦ perpendicular to the signal track traced on the disc 71.
I ¦ Furthermore~ the signal pickup structure 79 and the moving
coil mechanism 80 are mounted on a traversing mechanism
~ (not shown). They travel in a straight line and at a low
¦ speed synchronized with the rotational speed of the disc 71.
I ¦ Travel is in the radial direction 82 of the disc 71 at the
¦ time of signal recording or reproduction.
¦ Next, an example of a reproducing system will be
l described in conjunction with FIG, 5.
I In the system shown in FIG. 5, a reproduced signal
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1 picked up as ~ minute variation of electrostatic capacitance
, by the tracing stylus 74 Erom the disc 71 is supplied to a
preamp]ifier 95 having a resonant circuit. The resonant
frequency varies in response to this variation in electrostatic
1 capacitance and is formed into a signal of a desired level.
The resulting output of the preamplifier 95, is demodulated
into the original information signal by a demodulator 96
and is sent out as an output through an output terminal 97.
The output signal of the preamplifier 95, is
supplied respectively to amplifiers 98, 99, and 100. Here,
each of the amplifiers 98 and 99 is a kind of band-pass
amplifier. The amplifier 98 is designed to have a steep
passing frequency characteristic at only the frequency fp1.
The amplifier 99 is designed to have a steep passing frequency
characteristic at only the frequency fp2. As a result, the
signal of frequency fp1 and the signal of frequency fp2 are
obtained separately from the amplifiers 98 and 99,
respectively. These signals respectively pass through level
adjustors 101 and 102, where their levels are adjusted.
~ 20 The resulting signals are then supplied to a gate switching
;~ circuit 103. These reproduced signals fp1 and fp2 are pulse
trains respectively having periods corresponding to 2H (2
horizontal scanning periods). Moreover, they have a
coinclding phase in the horizontal blanking period of the
reproduced video signal. When this horizontal blanking
period is approximately 11 microseconds, for example, and
the frequencies fp1 and fp2 are set at 500 KHz and 300 KHz,
respectively, the signals fp1 and fp2 become cyclic waveforms
of approximately 5 cycles and 3 cycles, respectively.
A switching pulse generated in the position
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243~1
l designated by reference numeral 52 in FIG. 2C, and is supplied
throuyh an input terminal 104 to the gate switching circuit
103. (This position is the V.BLK part if the recorded main
l information signal is the video signal.) This switching
S I pulse is which switches the signals fp1 and fp2 every
revolution period of the disc 71. The disc rotational speed
¦ in the present example is 900 rpm. as mentioned hereinbefore.
Therefore, two frames of the video signal are recorded for
~ each revolution of the disc 71. The switching pulse applied
¦ to the input terminal 104 has inverting polarities which
change every two frames (1/15 second). As a result, the
gate switching circuit 103 supplies the signals fp1 and fp2
to detecting circuits 105 and 106, respectively, for a period
l of two frames. In the following two frame period, the signals
lS ¦ fp2 and fpl are respectively supplied to the detecting circuits
105 and 106.
The band-pass amplifier 100 is designed to have a
band-pass filter characteristic by which is separately
I filters only the signal of frequency fp3. The signal fp3
¦ which has been separated and amplified in this band-pass
; ¦ amplifier 100, is supplied to an integration circuit 107.
¦ There, its wave is shoped so that it is not affected by
noise and other influences. The wave-shaped signal is
l then applied to trigger a flip-flop 108. The resulting
¦ output of this flip-flop 108 is sent out through an output
terminal 109 and applied to the aforementioned input terminal
1 104.
¦ Means are provided to suppress the effects of
¦ interruption, dropouts, noise, etc., in the signal derived
¦ from the tracing stylus 74. To obtain an even more stable
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and accurate switching pulse from the terminal 109, it is
desirable to use, before directly triggering the flip-flop
108 with the signal fp3, a means such as a flywheel
oscillator, which is a free running oscillator at 15 Hz or
I an AFC circuit that is capable of accomplishing the same
function.
¦ The detecting circuits 105 and 106 detect the
envelopes of their respective input reference signals and
¦ convert the envelopes into DC voltages. These voltages
¦ are then supplied to the input terminals of differential
amplifiers (not shown) within a tracking servo circuit 110.
I This tracking servo circuit 110 compares the output signals
¦ of the two detecting circuits 105 and 106 which vary in
l response to the reproduced levels of the signals fp1 and fp2.
¦ This generates an output tracking error signal which indicates
the tracking error direction and the error quantity. This
error signal is further amplified to a specific level by
known circuitry. Then, it is applied through an output
terminal 111 to the moving coil mechanism 80 of the tracing
¦ stylus 74. Thus, the tracking of the tracing stylus 74 is
stably controlled by the resulting closed loop.
¦ In operation, the reproduction of the track t2 is
to start, continuing from the recording position 52 of the
l signal fp3, upon completion of the reproduction of the track
l tl of the tracing stylus 74, in FIG. 2B. In the instant
¦ embodiment of the invention the reference pulse signal fp3
¦ is extracted from the signal reproduced from the track t1.
¦ With this signal fp3 as reference, the polarities of the
¦ signals fp1 and fp2 are inverted upon reproduction of the
track t2. The control direciton by the signals fp1 and fp2
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l is inverted from that at the time of reproduction of the
track tl, to control the moving coil mechanism 80.
The reason for this is that the reference pulse
¦ signals fp1 and fp2 are recorded along the sides of the
1 information track. The reference pulse signals are
alternatively switched to opposite sides of each adjacent
track, as is apparent from the explanation of the track
pattern used in the recording system. For example, in the
~ direction which the stylus traces along the track, the
signal fp1 is formed on the right side of the track tl,
while the signal fp2 is formed on the left side of the track
t1; the signal fp1 is formed on the left side of the track
t2, while the signal fp2 is formed on the right side of
l the track t2.
¦ For this reason, at the time of reproduction of
the track t2~ the tracing stylus is controlled and moved
toward the outer periphery of the disc 71 responsive to
1 reproduction of the signal fp1, and then moved toward the
¦ center of the disc by the reproduction of the signal fp2.
20 ¦ Therefore, this time, it is possible to trace accurately and
positively in succession over the track t2. ~
The track t3 is reproduced upon completion of the
tracing of the track t2, per revolution. By the lnversion
¦ again of the polarities of the signals fp1 and fp2 at the
¦ recording position 52 of the signal fp3, tracing and tracking of
the track t~ is-~imilàrly carr.ied out. Similarly thereafter,the
signal pickup structure 79 shown in FIG. 4A accurately and
¦ positively traces and reproduces the successive track paths,
l following one after another. The pickup successively movies,
¦ with a specific pitch, in the radial direction of the disc
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l 71, for example, from the outer periphery -toward the center
of the disc. Thus, a normal reproduced picture is obtained.
The present invention reproduces a still motion
~ picture by continuous reproduction of the same track and
1 reproduces slow-motion pictures by repeated reproduction of
each track. For example, upon completion of the first time
reproduction of the track t1, a pulse is obtained responsive
to the pulse signal fp3 which is detected from the signal
i recording position 52. This pulse signal has a compulsory
¦ power, with respect to the tracking servo circuit 110, and
is applied from outside. A signal is applied from a
tracking servo amplifier (not shown) to the moving coil
l mechanism 80. The tracing stylus is caused to jump or
¦ kick back at the position 52. In this manner, a continuous
¦ tracing of only the track t1 can be effected.
Furthermore, it is also possible by reducing to
1/3 the traversing speed of the signal pickup structure 79
in the disc radial direction. The above described operation
¦ is repeated three times for reproducing each of the
succeeding tracks in a desired reproduced picture, for example.
Interrelatedly with this, the switching pulses of the signals
fp1 and fp2 are processed so that the same track will be
reproduced three times each, and a 3:1 slow-motion picture
l is obtained. In addition, various operations such as
¦ high-speed searching, determination of the starting point of
¦ reproducing and forward-reverse reproduction can be carried
¦ out as desired.
¦ Further, this invention is not limited to these
l embodiments. Variations and modifications may be made without
departing from the scope and spirit of the invention.
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