Note: Descriptions are shown in the official language in which they were submitted.
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TRAC~C SKIPPE PPAR~TUS FOR VIDEO DISC PLAYER
This invention pertains to an apparatus utilized
in the playback of a video disc record, and more particularly,
5 to an apparatus for selectively repositioning a player stylus
from one convolution to another of a signal-encoded spiral
track disposed on the record surface.
In U. S. Patent No. 3,842,194, issued on October 15,
1974 to Jon K. Clemens, in general video disc playback
10 systems of a variable capacitance form are disclosed. In
an illustrative arrangement therein disclosed, an information
track incorporates geometric variations in the bottom of a
spiral groove in a disc, the surface of which comprises
conductive material covered with a thin coating of dielectric
15 material. Variations in the capacitance presented between a
conductive electrode on a tracking stylus and the conductive
material of the disc occur as the disc is rotated by a
supporting turntable. The capacitance variations are sensed
to recover the recorded information. Capacitive video disc
20 systems may also advantageously employ conductive (or
semiconductive) discs as compared to the coated discs.
In certain applications of a video disc system of
the Clemens type, it may be desirable to provide repeat play
of the displayed image. That is, to repetitively provide
26 output signals of basically the same displayed image on an
associated television monitor. Such image repeat play may
be desirable for allowing a viewer to observe a particular
image for relatively long lengths of time.
A further desirable feature for incorporation with
30 a video disc player is the ability to provide rapid forward
motion or reverse motion of the displayed image. A rapid
forward function is particularly useful for quickly scanning
information recorded on the video disc. A reverse motion
function may also be utilized for aiding in data retrieval,
35and is particularly useful as a teaching aid for reviewing
an instructional picture sequence recorded on the disc.
Moreover, in the playback of the disc records of
the above-mentioned type, conditions are occasionally
encountered when the presence of some form of defect in the
40 disc groove,or information track,causes the player stylus
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1 -2- RCA 73,437
to skip across grooves rather than follow the successive
convolutions of the spiral groove in a regular progression
toward one extremity thereof. For example, as the defect
5 is encountered, the stylus may be deflected toward the
outer disc convolutions thereby causing repeat traversal
of one or more previously traversed convolutions. In some
instances, the outward deflection of the stylus is repeated
for a substantial number of successive encounters with the
10 defect. This condition is herein referred to as a "locked
groove" condition, producing undesired repetitive replay
of the same recorded information, with annoying effects on
picture display and accompanying sound reproductions.
To provide special effect features (e.g., repeat
15 play, fast forward, reverse, trick plays, etc.) and to
correct locked groove conditions, it is desirable to
provide a selectively actuated apparatus for repositioning
the pickup stylus from one convolution to another of the
record spiral track.
U. S. Patent No. 3,963,861, issued on June 15,
1976, to H. N. Crooks, and U. S. Patent No. 3,993,863, issued
on November 23, 1976 to Leedom, et al., described illustrative
groove skipping systems. In these systems, selectively
actuated piezoelectric bimorph elements cause lateral
25 shifting of the stylus-carrying end of the stylus arm.
According to the invention described in U. S.
Patent 4,183,059, issued on January 18, 1980 to R.C. Palmer,
entitled "Track Skipper for Video Disc Player," selective
radial repositioning of the playback stylus is achieved by
30 twisting the stylus arm about its longitudinal axis, and
the offset of the stylus tip from the rotational axis results
in consequent radial motion of the stylus tip across track
convolutions of the disc record. In accordance with a
further feature of the Palmer invention, the stylus-carrying
35 end of the stylus arm is substantially immobilized in the
lateral direction while the stylus arm is rotated to assure
that the twisting of the stylus arm results in rotation of
the stylus about the axis of the stylus arm, rather than
rotation of the stylus arm about the stylus tip.
An advantageous configuration for selectively
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changing the convolution which is tracked by the stylus is
herein described. In accordance with the apparatus pursuant
to this invention, a playback stylus is mounted on the
5 stylus arm near its free end. The other end of the stylus
arm is pivotally secured to a carriage, which is radially
translated during playback in synchronism with the motion
of the stylus toward the center of disc record. A permanent
magnet is mounted on the stylus arm near its free end. A
10 pair of spaced coils having non-magnetic cores are mounted
on the carriage such that the permanent magnet is disposed
therebetween. A circuit is provided for selectively ener-
gizing the coils to cause a shift in the radial location of
the stylus.
15 IN THE DRAWINGS
FIGURE l is a block diagram representation of a
video disc player incorporating the track skipper apparatus
of this invention;
FIGURE 2 illustrates a pickup cartridge suitable
20for use in the video disc player of FIGURE l;
FIGURE 3 shows an enlarged view of a portion of
the pickup cartridge of FIGURE 2;
FIGURE 4 depicts a carriage having a compartment
for receiving the pickup cartridge of FIGURES 2 and 3;
FIGURE 5 is an enlarged view of a portion of the
carriage of FIGURE 4;
FIGURE 6 shows a pair of bumpers mounted in the
carriage for limiting side-to-side motion of the stylus; and
FIGURES 7 and 8 diagrammatically illustrate the
30relative disposition of certain elements of the track skipper
apparatus of FIGURE 1.
Referring now to FIGURE 1, a video disc playback
system incorporating a locked groove detection and correction
- system is shown. The circuit shown in FIGURE 1 for detecting
35the occurrence of a locked groove condition is of the type
described in detail in U.S. Patent 4,198,658 issued on
April 15, 1980, to R. C. Palmer and entitled
"Recording/Playback Apparatus Facilitating Track Skip
Detection." A track skipper apparatus pursuant to this
40invention, and suitable for use with a locked groove
,
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detection circuit, such as that disclosed in the Palmer
application, is hereinbelow described. The locked groove
detection circuit will be described first in conjunction with
5 FI~RE 1.
As shown in FIGURE 1, a video disc player 10 has
a turntable 12 for rotatably supportlng a video disc 14
ha~ing a spiral information track containing picture signal
information inclusive of synchronizing components and a
10 pilot signal. The frequencies of the synchronizing components
and the pilot signal are such that an integral number of
synchronizing components and a non-integral number of pilot
signal cycles occupy each convolution of the spiral track.
The player 10 further includes a carriage 16 subject to
15translation in synchronism with the radial motion of the
player stylus during playback. The carriage 16 has a
compartment for removably receiving a pickup cartridge 18
which houses the signal pickup assembly.
A pickup circuit 20, responsive to the output of
20 the signal pickup, develops at its output terminal a pulse
train representative of the recorded information. The
pickup circuit 20 is illustratively of the type described
in the U.S. Patent No. 4,080,625, issued on March 21, 1978
to Kawamoto, et al. The output of the pickup circuit 20 is
25delivered to a pair of bandpass filters 22 and 24. The
picture carrier bandpass filter 22 has a relatively wide
passband encompassing the deviation range of the high
frequency picture carrier (e.g., 4.3 to 6.3 MHz) as well as
the requisite adjacent sideband regions, and selectively
30passes the picture carrier component of the recorded signal
to the relative exclusion of the sound carrier component
thereof.
The sound carrier bandpass filter 24 has a
relatively narrow passband encompassing the deviation range
35Of the low frequency sound carrier (e.g., 716 KHz + 55 KHz)
as well as the requisite adjacent sideband regions, and
selectively passes the sound carrier component of the recorded
signal to the relative exclusion of the picture carrier
component thereof.
The outputs of the respective bandpass filters 22
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l -5- RCA 73,437
and 24 are passed to respective demodulators 26 and 28. The
picture demodulator 26 develops at its output terminal the
recorded picture signal information inclusive cf synchronizing
5 components, and the sound demodulator 28 develops at its
output the recorded audio signal information and the pilot
si.gnal.
A picture siqnal processor 30, coupled to the
picture demodulator, effects the separation of the chrominance
10 information from the liminance information. A composite video
signal generator 32 recombines the chrominance and the
luminance information in accordance with, for example, the
NTSC format. A transmitter 34 processes the sound, luminance
and the chrominance information to form a signal suitable for
15 delivery to a color TV receiver 36, wherein color image
displays may be developed in accordance with the rec~rded
information. Illustratively, where signal delivery to the
antenna terminals of a color TV receiver is desired, the
circuits include means for combining the separated components
20 to form a new composite signal, which composite signal
modulates a suitable RF carrier. U.S. Patent No. 4,097,899,
issued to J.P. Yu, describes an illustrative transmitter
apparatus.
A pilot signal bandpass filter 38 having a
25 relatively narrow passband (e.g., 21.18 KHz + 1.5 KHz) passes
the recovered pilot signal to the exclusion of other recorded
information. A phase locked loop 40, responsive to the
deviations in the phase of the recovered pilot signal due to
a disruption in the regular progression of the player stylus
30 along the spiral track by a sudden radial shift in the location
of the stylus, developes an error signal having an amplitude
and a polarity indicative of the magnitude and sense of the
disruption in the regular progression. A groove skipper
driver circuit 42 responsive to the development of an error
35 signal of a given sense and an amplitude exceeding a given
threshold develops a standard correction pulse. A suitable
groove skipper mechanism responsive to the correction pulse
effects a radial shift in the location of the player stylus
in a manner that offsets the disruption in the regular pro-
40 gression of the player stylus. One type of groove skipper
.
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mechanism is described in detail in U.S. Patent 4,183,059,
issued on January 8, 1980, to R.C. Palmer and
entitled "TRACK SKIPPER FOR A VIDEO DISC PLAYER".
A track skipper apparatus in accordance with the
instant invention will now be described in detail with
reference to FIGURES 2-8. Shown in FIGURE 2 is the pickup
cartridge 18. The cartridge comprises a stylus arm 50 which
carries at the free end thereof a stylus holder 52. A
10 pickup stylus 54 is secured to the stylus holder 52. An
extension 56, disposed on the stylus holder 52, is inter-
posed between a pair of non-magnetic, plastic bumpers 58 and
60 (FIGURES 4-6) mounted on the carriage 16. The bumpers
58 and 60 serve to limit side-to-side excursion of the stylus
15 54.
The other end of the stylus arm 50 is secured to a
connector plate 62 via a compliant coupler 64. A flexible
diaphragm 66 secures the connector plate 62 to the cartridge
body 68. A U-shaped spring 70 serves to retain the stylus
20 assembly within the confines of the cartridge during storage
~nd handling. A conductive leaf spring 72 connects an
electrode (not shown) incorporated in the stylus 54 to a
terminal (not shown) disposed on the cartridge 18.
The cartridge 1~ is removably received in a
25compartment 80 provided in the carriage 16 (FIGURE 4). As
previously indicated, the carriage 16 is subject to trans-
lation toward the record center in correlation with the
radial motion of the stylus during playback.
Mounted in the carriage 16 are a stylus arm lifting/
30lowering mechanism 82 and an armstretcher apparatus 84. The
stylus arm lifting/lowering mechanism may be of the type
described in U.S. Patent No. 4,053,161 issued to J.C. Bleazey,
et al. on October 11, 1977. The lifting/lowering mechanism
82 serves to gently lower the pickup stylus 54 on the video
35disc for playback. The mechanism 82 also serves to lift the
stylus away from the record, for example, for allowing the
stylus to clear the peripheral bead of the record as the
carriage 16 is translated from the off-record, rest position
to the on-record, play position, or for example, when the
40player is in the pause mode.
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The armstretcher apparatus 84 is provided with a
support 86. When the cartridge 18 is installed in the
compartment 80 and the lid 88 of the carriage is closed, a
5 mechanism 90, responsive to the lid movement, effects
engagement between the connector plate 62 of the cartridge 18
ancl the support 86 of the armstretcher 84. The mechanism 90
also serves to effect engagement between the cartridge
terminal and another terminal 92 disposed on the carriage
10 for electrically connecting the stylus electrode to the rest
of the player circuitry. The support 86 of the armstretcher
apparatus imparts translatory motion to the stylus arm in a
manner that opposes cyclical deviations in the stylus/record
relative velocity during playback. The cs7clical deviations
15 in the stylus/record relative velocity result from a number
of sources, for example, eccentricity, warp, etc. U.S. Patent
No. 3,983,318 (Miller) describes an illustrative armstretcher
apparatus.
The bottom wall of the carriage has an opening 94
20 for permitting the playback stylus to protrude therethrough
during playback to effect stylus/record engagement when the
stylus arm is lowered by the stylus arm lifting/lowering
mechanism 82.
A lever (not shown) disposed on the lid 88 serves
25to defeat the U-shaped, stylus arm retaining spring allowing
the stylus arm to rest on an arm 96 of the lifting/lowering
mechanism 82 when the lid is closed after installing the
cartridge in the carriage compartment.
Secured to the back side of the extension 56 is a
30 small, light-weight permanent magnet 100 (e.g., made from
material such as samarium cobalt. The magnet 100 is secured
to the extension 56 such that the north-south axis is in the
vertical direction with the north pole above the south pole.
Illustratively, the dimensions of the permanent magnet are
350.015 x 0.015 x 0.100 inches. A pair of large diameter,
air-core coils 102 and 104 are disposed about the non-magnetic,
plastic bumpers 58 and 60 as illustrated in FIGURES 4, 5 and
7. An error signal, indicative of a groove skip, is applied
to the coils in such manner that they generate aiding
40magnetic fields (i.e., when one inner face is magnetically
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1 -8- RCA 73,437
north, the other face has a magnetically south polarity).
Illustratively, each coil comprises 126 turns (e.g., 7 layers
wlth 18 turns per layer) of #38 gauge wire. Other
5 illustrative coil parameters are: coil diameter: 0.125
inches; coil resistance: 5.7 ohms; drive current: 0.44
arnperes; and pulse duration: 0.5 milliseconds. Generally,
it is desirable that the coils 102 and 104 are disposed in a
Helmholtz configuration (that is, the coll diameter is equal
10 to twice the coil separation). This configuration gives
nearly uniform field strength in the region between the ends
of the two coils. This arrangement minimizes variations in
skip sensitivity when record surface waviness and eccentricity
cause the stylus to move around laterally and vertically
15between the coils. However, the actual coil construction
may deviate from an exact Helmholtz configuration without
substantially affecting the performance of the skipper (for
example, a coil separation of 0.235 inches may be used).
If desired, the coils 102 and 104 may be inter-
20connected in a way such that the application of a singleerror signal will set up aiding magnetic fields as described
above. That is, when coils 102 and 104 are interconnected
they form a two terminal device to receive an error signal
which causes one inner face to be magnetically north and the
25opposing inner face to be magnetically south.
As can be seen from FIGURE 8, only one pole of the
magnet 100 (e.g., the north pole) is directly located between
the driving coils 102 and 104 when the stylus arm 50 is
disposed in the lowered position. Thus, although the two
30poles of the magnet 100 may exDerience opposing forces when a
current pulse is applied to the coils, the upper end receives
a much larger force, and thus a net force difference is
generated which then moves the stylus 54. ~ecause the
distances moved are quite small (e.g., 0.001 inch), a 0.5
35millisecond electrical pulse is adequate to disPlace the
stylus 54, and movement to overcome a locked groove condition
can, therefore, be accomplished with minimal picture
disturbance.
When an error signal is applied to the coils 102
40and 104, a magnetic field is set up in the vicinity of the
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1 ~9- RCA 73,437
upper pole of magnet lO0 and the magnetic forces thus
generated cause a twisting motion of stylus arm 50 as well
as lateral motion. It is belleved that this complex form
5 of motion occurs because the upper pole of magnec 100 is
well above the plane in which the arm 50 lies during playback.
That is, the offset position of magnet 100 on extension 56
generates the twisting motion about the longitudinal axis
of the arm 50.
It will be noted that while the description herein
is in the context of grooved discs, it is e~ually applicable
to flat discs. Various defects on flat discs can cause the
player stylus to retrace the same track again and again. The
system described herein can be advantageously employed to
15 clear such a condition in the playback of a flat disc in
accordance with the principles of the present invention.
