Note: Descriptions are shown in the official language in which they were submitted.
RCA 69,402
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The present invention relates generally to a
video disc record player and more particularly to an
apparatus for relieving the signal pickup from a locked
groove condition, if and when such a condition is
encountered.
In certain video disc systems video information
is recorded by means of geometric variations in the bottom
of a smooth spiral groove on the surface of a disc record.
The disc record surface includes a coating of conductive
material which is preferably covered with a thin deposit
of dielectric material. A signal pickup, supported at
one end of a pickup arm, engages the spiral groove and
includes a conductive electrode which establishes a
capacitance with the conductive coating and the dielectric
deposit of the disc record. When the disc record is
rotated, the pickup/record capacitance varies in response
to the geometric variations in the bottom of the spiral
groove. The capacitance variations are converted to
electrical signal variations by suitable signal processing
circuitry coupled to the pickup electrode. The output
signal of the signal processing circuitry may be coupled
to a conventional television receiver for reproduction.
The other end of the pickup arm is releasably secured to
a support member of a supporting structure of the playback
system. A system of the aforementioned type is described
in detail in U.S. Patent No. 3,842,194, issued to
J. K. Clemens on October 15, 1974, and entitled "INFOR-
MATION RECORDS AND RECORDING/PLAYBACK SYSTEMS THEREFOR". ,
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1 Video disc systems of the aforementioned type
generally utilize disc records having groove densities in
the order of four to eight thousand groove convolutions
per inch. A typical video disc record of this type may
have a groove convolution spacing in the order of 3.5microns. The fragile walls of relatively narrow grooves
of the disc record cannot be dependably relied upon to
pull the weight of the pickup arm assembly, around the
pickup arm pivot support, across the entire recorded
surface of the disc record. Also in video disc systems
utilizing variable capacitor concept, it is desirable for
accurate reproduction of the prerecorded signals that the
signal pickup electrode maintain a substantially constant
attitude in the spiral groove. Therefore, the supporting
structure includes a radial feed drive mechanism for
traversing the supported end of the pickup arm in proper
time relationship with the radial motion of the signal
pickup tip engaged in the spiral groove so as to con-
tinuously maintain the longitudinal axis of the pickup
20 arm substantially tangential to the spiral groove at the
point of engagement. Reference may be made to the
U.S. Patent No. 3,870,835, issued to F. R. Stave, and
entitled "VIDEO DISC PLAYBACK APPARATUS", for an illus-
tration of a suitable radial feed drive mechanism for
, 25 providing the indicated radial motion.
. .
Further, in the above-mentioned type video disc
systems it has been recognized that the relative motion
between the disc record and the signal pickup should be
maintained at a predetermined speed, and within specified
tolerance limits (e.g., 450 rpm, +O.Ol percent), in order
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I to obtain high fidelity of reproduction of the prerecordedsignals. The predetermined speed and the specified
tolerance limits are also necessary to assure that the
horizontal and vertical synchronizing information is
stable and within the lockup range of the deflection
circuits of the television receiver. Moreover, when the
prerecorded information is a color television signal with
chrominance information recorded as a modulated carrier
signal, the recovered signal must be stable and within
the lockup range of the color processing circuits of the
playback system in order to reduce color phase distortion.
The disc record/signal pickup relative speed
may be maintained at the predetermined speed, and within
the specified tolerance limits by rendering the pickup arm
support member subject to cyclical, translatory motion
along the longitudinal axis of the pickup arm in a manner
that opposes deviations of the instantaneous relative
speed from the predetermined speed. Illustratively, the
means for imparting translatory motion to the support ;~
member may be of the type disclosed in the U.S. Patent
No. 3,711,641, issued to R. C. Palmer on January 16, 1973,
and entitled "VELOCITY ADJUSTING SYSTEM".
It may be noted that the disc records having
high groove densities (e.g., 4,000 to 8,000 grooves per
inch) are subject to occasional flaws causing premature
termination of the spiral groove. Such premature
termination (commonly referred to as a "locked groove")
may result in an undesired repetition of a particular
groove convolution during disc record playback. It is
therefore desirable to incorporate in a video disc player
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an apparatus suitable for relieving a signal pickup from a
locked groove condition, when encountered.
In the United States Patents of Marvin A. Leedom
No. 3,993,863, issued November 23, 1976, entitled
5 ' "DISC RECORD GROOVE SKIPPER", and of H. N. Crooks,
No. 3,963,861, issued June 15, 1976, entitled
"DISC RECORD GROOVE SKIPPER APPARATUS",
arrangements for repositioning a
signal pickup from one convolution to another of a spirally
gxooved disc record are described. The above-said
arrangements employ a bimorph type element for producing
special effects (e.g., stop action, fast forward, slow
motion, etc.) and for relieving the signal pickup from
the locked groove. The present invention is concerned
S simply with an apparatus for relieving a signal pickup
from a locked groove condition, if and when such condition
is encountered.
In a system for playing back prerecorded
information from a spirally grooved disc record by a
groove-engaging signal pickup secured to a pickup arm
when relative speed is established therebetween, a locked
groove escape apparatus is provided. Transducer means varies
the position of the signal pickup in relation to the groove
in a manner that opposes deviations of the relative speed
from a predetermined speed. A carriage housing the pickup
arm is mounted on the player base for movement between a
playback mode and a standby mode. The carriage is driven
radially inward in synchronization with rotation of the
disc record during playback independent of radial motion of
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RCA 69 ,402
1 the signal pickup due to the spiral groove. Locked groove
detector means coupled to the transducer means generates
a locked groove recognition pulse when the signal pickup
encounters a locked groove. A guide member is secured to
the carriage adjacent the free end of the pickup arm such
that when the transducer means drives the pickup arm in
response to the locked groove recognition pulse against
the guide member, a radially inward movement of the pickup
arm is effected, thereby relieving the signal pickup from
the locked groove condition.
In another embodiment of the present invention,
a steering member is secured to the carriage adjacent the
pickup arm such that the steering member and the disc record
center are on the opposite sides of the pickup arm. When
the signal pickup encounters a locked groove, the advancing
steering member engages the pickup arm in order to effect
radially inward movement thereof, whereby the signal pickup
is relieved from the locked groove condition.
Other objects, features, and advantages of the
present invention wi]l be more fully understood from the
following detailed description of the preferred embodiment,
the appended claims, and the accompanying drawings in which:
FIGURE 1 illustrates a partially cut-away
perspective view of a portion of a video disc player;
FIGURE 2 is an exaggerated top view of a video
disc player similar to that shown in FIGURE 1, diagram-
matically illustrating a first embodiment of the locked
groove escape apparatus pursuant to the principles of the
present invention;
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1 FIGURE 3 illustrates, via a block diagram ~`
representation, the video disc player of FIGURE 2 incor-
porating translatory motion imparting means for maintaining
the pickup/record relative motion at a predetermined speed;
FIGURE 4 is a perspective view of the first
embodiment of the locked groove escape apparatus of
FIGURES 2 and 3;
FIGURE 5 is a perspective view of another version
of the first embodiment of the locked groove escape
apparatus of FIGURES 2, 3, and 4;
FIGURE 6 is an exaggerated top view of the video
disc player of FIGURE l, schematically illustrating a
second embodiment of the locked groove escape apparatus
pursuant to the principles of the present invention;
FIGURE 7 schematically illustrates the self
adjustment of the clearance between a pickup arm and a
: steering member of the second embodiment of the locked
groove escape apparatus due to the eccentricity of the
disc record; FIGURE 8, located on sheet 4 . .
the drawing, illustrates diagrammatically an
arrangement of a pickup arm lifting/lowering bracket and
the steering member of the second embodiment of the locked
groove escape apparatus; and FIGURE 9, located on sheet 4
of the drawinq, schematically illustrates initial upward
2S shifting of a pickup arm carrying a signal picku~) as the
locked groove escape apparatus of FIGURES 1-7 attempts to
; effect radially inward movement of the pickup arm about its
pivot support.
FIGURES l and 2 illustrate a video disc player
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1063520 RCA 63,402
1 having a base 10. The player is suitable for use in a video
disc system such as disclosed in the aforementioned Clemens
patent. A turntable 11 is rotatably mounted on the base 10.
The upper surface of the turntable 11 is adapted to support
a video disc record 12. Video information is recorded by
means of geometrical variations in the bottom of a smooth
spiral groove 13 on the substrate of the disc record 12.
The disc record 12 surface includes a conductive coating
which is preferably covered with a thin deposit of dielectric
material. A signal pickup 14, coupled 20 to, and supported
by a conductive
/pickup arm lS, engages the spiral groove 13 and includes a
conductive electrode tnot shown) which, together with the
conductive coating and the dielectric deposit, form a
capacitor, When relative motion is established between
the signal pickup 14 and the disc record 12, an edge of
the electrode included in the signal pickup, while riding
in the smooth spiral groove 13, serves as an electrode of a
capacitor varying due to the geometric variations in the
bottom of the spiral groove passing underneath. The
other end of the pickup arm 15 is releasably secured to
a support member 16 carried by a pickup arm supporting
structure 17, in the manner to be also described sub-
sequently.
The pickup arm supporting structure 17 comprises
a radial feed drive mechanism 18 and a translatory motion
imparting means 19. As indicated before, the radial feed
drive mechanism 18 traverses the pickup arm support 16
during playback independent of the motion of the signal
pickup 14 due to the spiral groove 13, and in proper time
relationship with the radial motion of the signal pickup
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RCA 69,402
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1 tip engaged in the spiral groove so as to steadily
maintain the longitudinal axis of the pickup arm sub-
stantially tangential to the spiral groove at the point of
engagement, Reference may be made to the aforementioned
U.S. Patent No. 3,870,835 for an illustration
of a suitable mechanism for providing the indicated
radial motion.
Reference is now made to FIGURE 3 illustrating,
via a block diagram representation, the general arrangement
10 of a translatory motion imparting system for maintaining .
the pickup/record relative speed at a predetermined value.
The spirally grooved video disc record 12 rests upon the
turntable 11 which is rotated by a suitable rotational
drive mechanism 21 at the desired predetermined speed
(e.g., 450 rpm). A pickup circuit 22 is electrically
coupled to the electrode (not shown) incorporated in the
signal pickup 14, and serves to translate the pickup/record
variations to electrical signal variations representative
of the prerecorded signal. Illustratively, the pickup circuit
may be of the advantageous form shown in the
U.S. Patent of D. J. Carlson et al., No. 3,872,240
issued March 18,1975, and entitled "PICKUP APPARATUS FOR
VIDEO DISC PLAYERS".
The composite video signals appearing at the output
of the pickup circuit 22 is supplied to a video signal pro-
cessing circuit 24, via a demodulator 23. The video signalprocessing circuit 24 serves to process the demodulator 23
output to a form suitable for application to a conventional
television receiver 25 for image display. Where the
prerecorded composite video signal is representative of
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1 color pictures and incorporates a chrominance component of
a "buried subcarrier" form, the video signal processing
circuit 24 may be of the desirable form shown in the
U.S. Patent 3,938,179, of J. G. Amery, issued
February 10, 1976, and entitled "COMB FILTER FOR
VIDEO PROCESSING".
A sync separator 26, coupled to the output
terminal of the video signal processing circuit 24, serves
to separate the deflection synchronizing components from
recovered composite prerecorded signal and develops a pulse
train at its output corresponding to the horizontal
synchronizing component of the prerecorded signal.
A velocity error detector 27, coupled to the
sync separator 26, develops a direct voltage speed error
correction signal at its output terminal having an amplitude
which varies in response to the shifting frequency of the
sync pulses (e.g., the detected horizontal sync pulse
frequency vis-a-vis the standard frequency of 15.734 KHz)
appearing at the output terminal of the sync separator 26.
Illustratively, the velocity error detector 27 may be
of the preferred form shown in the U.S. Patent No. 3,711,641,
issued to R. C. Palmer, on January 16, 1973, and entitled
"VELOCITY ADJUSTING SYSTEM".
An electro-mechanical transducer 28 (also known
as "armstretcher") mechanically coupled to the pickup arm 15
carrying the signal pickup 14 varies the position of the
signal pickup in relation to the disc record groove in
response to the speed error correction signal developed by
the velocity error detector 27 in a manner that opposes
deviations of the pickup/record relative speed from the pre-
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1 determined speed (e.g., 450 rpm). Illustratively, theelectro-mechanical transducer may be of the recommended
form shown in U.S. Patent 3,983,318, issued Sept. 28, 1976,
for M. E. Miller et al., and entitled
"VELOCITY CORRECTION SYSTEM WITH DAMPING".
The support member 16 rigidly transmits the
cyclical translatory motion of the electro-mechanical
transducer 28 of the translatory motion imparting means 19
to the signal pickup 14, while accommodating vertical and
lateral motion of the signal pickup in the spiral groove 13
due to the vertical and lateral runout (eccentricity) of
the disc record 12. Reference may be made to the
U,S. Patent 3,917,903 of B. K. Taylor et al., issued Nov. 4,
1975, and entitled "PICKUP ARM MAGNETIC COUPLER", for
an illustration of a releasable coupling between the pickup
arm 15 and the electro-mechanical transducer 28 of an
advantageous form.
A box-like, conductive carriage 30 (shown in
FIGURES 1 and 2 with its lid removed for clarity) is mounted
to the supporting structure 17 for enclosing the conductive
pickup arm 15. During playback, the pickup arm 15 is
lowered through an opening 31 in the bottom wall 32 of the
carriage 30 for permitting the signal pickup 14 to ride in
the spiral groove 13 by a pivotally mounted lifting/lowering
bracket 33. The bracket 33 lifts the free end of the
pickup arm 15 to disengage the signal pickup 14 from the
spiral groove 13, when the player is inoperative.
In the first embodiment (FIGURES 2, 4, and 5),
a locked groove detector 29 is coupled to the electrQ-
mechanical transducer 28, as illustrated in FIGURE 3, of
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1 the translat~ry motion imparting means 19. Illustratively,the locked groove detector 29 may be of the advantageous
form shown in the U.S. Patent 3,963,860
T. W. surrus, issued June 15, 1976,
and entitled "LOCKED GROOVE DETECTION AND CORRECTION IN
VIDEO DISC PLAYBACK APPARATUS". Pursuant to the Burrus'
system, when a locked groove condition is encountered in
the playback of a video disc having sync signal recording
locations non-radially aligned in successive groove
convolutions, each initiation of a repeat reading of the
same groove convolution results in a timing disturbance
of the recovered sync signals. The disturbance is detected
by an arrangement employing a phase locked loop responsive
to the horizontal sync component of the prerecorded signal.
A filtered voltage output of the phase locked loop is
applied to a voltage comparator to effect discrimination
against noise and minor, transitory timing disturbances. A
stairstep voltage generator, responsive to the voltage
comparator output, provides an output sufficient to trigger
generation of a locked groove recognition pulse, when the
voltage comparator threshold is exceeded a sufficient number
of times within a selected time interval to verify an
occurrence of a sustained locked groove behavior. To avoid
a false generation of a locked groove recognition pulse
under certain transient conditions (e.g., signal pickup
set-down, signal pickup jump due to player jarring, et al.),
a retriggerable one-shot multivibrator circuit is interposed
between the voltage comparator and the stairstep voltage
generator and provided with parameters aiding discrimination
against the relatively high frequency repetitions of sync
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1 pulse timing disturbances that are associated with such
transient conditions. A suitable locked groove escape
apparatus, such as the electro-mechanical transducer 28,
is activated to advance the signal pickup radially inward
upon generation of a locked groove recognition pulse.
The first embodiment of the locked groove escape
apparatus will now be described with reference to FIGURES 2
and 4. A guide member 34 is secured to the carriage 30
adjacent the free end of the pickup arm 15 such that when
the electro-mechanical transducer 28 drives the pickup arm
in response to the locked groove recognition pulse against
the guide member, a radially inward movement of the pickup
arm is effected whereby the signal pickup 14 is relieved
from the locked groove condition. In order to prevent the
engagement of the pickup arm 15 with the guide member 34
during normal operation of the transducer 28 in response to
the speed error correction signal developed by the velocity
error detector 27, the following arrangement may be made.
- First, the amplitude of the speed error correction signal
may be limited within a given range. Second, the location
of the guide member 34 in relation to the free end of the
pickup arm 15 may be made such that the guide member/pickup
arm engagement does not take place when the speed error
correction signal causes a maximum displacement of the
pickup arm.
FIGURE 5 is a perspective view of another version
of the first embodiment of the locked groove escape
apparatus of FIGURES 2 and 4. In the arrangement of FIGURE
5, the guide member 34 is mounted inside the carriage 30
3 for engagement with an extension member 35 attached to the
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1 pickup arm 15 in order to completely conceal the locked
groove escape apparatus within the carriage.
The second embodiment of the locked groove escape
apparatus will now be described with reference to FIGURE 6.
A steering member 36 is secured to the carriage 30 adjacent
to the pickup arm 15 such that the steering member and
the center of the disc record 12 are on the opposite
sides of
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1 the pickup arm. When the signal pickup 14 encounters a
locked groove, the steering member 36 advancing with the
carriage 30 engages the pickup arm 15 in order to effect
radially inward movement thereof, whereby the signal pickup
is relieved from the locked groove condition.
FIGURE 7 schematically illustrates the self
adjustment of the clearance between the pickup arm 15 and
the steering member 36 of the second embodiment of the
locked groove escape apparatus due to the eccentricity of
the disc record 12. The disc record eccentricity (illus-
tratively, in the range of 0.01 to 0.06 inches) results
due to several reasons: For example, (1) disc record
manufacturing variations, (2) disc record warpage, and
(3) turntable and drive mechanism mounting eccentricity,
etc., to name a few. The disc record groove eccentricity
may be lateral and/or vertical. The lateral and vertical
disc record groove eccentricities cause the pickup arm 15
to oscillate back and forth, as illustrated in FIGURE 7,
when the pickup arm is lowered to effect the engagement of
the signal pickup 14 in the disc record groove 13 for
playback. If the guide member 36 were absent, the pickup
arm 15 would have traversed an arc 37 as shown by the
dotted lines in FIGURE 7 due to the disc record groove
eccentricity. However, because of the steering member 36,
the pickup arm 15 is shifted radially inward (i.e., the
signal pickup is displaced into an inner groove convolution),
and the pickup arm now traverses an arc 38. In this
position the pickup arm 15 barely touches the steering
member 36 during its outward swing, whereby a minimum
clearance is established between the pickup arm and the
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1 steering member. The minimum clearance for a given
eccentricity of the disc record is the smallest spacing
between the pickup arm 15 and the steering member 36 which
would permit the pickup arm to oscillate back and fourth
without hindrance from the steering member and yet assure
an early relief of the signal pickup 14 from the loc~ed
groove condition. Thé chronology of the events is as
follows: When the signal pickup 14 encounters a locked
groove, the pickup arm 15 repetitively bumps into the
steering member 36 during its outward swings as the steering
member advances into the path of the arc traversed by the
pickup arm. As the steering member 36 advances further
and further into the path of the pickup arm 15, the force
exerted by the steering member on the pickup arm gradually
increases. When this force exceeds a certain value
determined by the mass, damping, and the stiffness of the
pickup arm assembly, the pickup arm 15 is shifted radially
inward, and the signal pickup 14 is thereby relieved from
the locked groove condition.
It is important to note that the minimum clearance
is a function of the disc record eccentricity and, there-
fore, varies for each record. The locked groove escape
apparatus, pursuant to the principles of the present
invention, automatically develops the minimum clearance
between the steering member 36 and the pickup arm 15 when
the pickup arm is initially lowered to effect the engagement
of the signal pickup 14 with the disc record groove 13 for ~-
playback.
In order to obtain the mlnimum clearance between
3 the steering member 36 and the pickup arm 15, it is
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1 necessary that the initial spacing between the steering
member and the pickup arm is such that the pickup arm will
at least barely engage the steering member during its
outward swing when the pickup arm is lowered for playback.
The aforesaid requirement may be met by proper positioning
of the pickup arm pivot support 16 with respect to the
steering member 36. Other arrangements for fulfilling the
aforesaid requirement are as follows: First, the pickup
arm 15 can be lightly biased toward the steering member 36.
Second, the pickup arm lifting/lowering bracket 33 can be
slanted as shown in FIGURE 8 toward the steering member 36 to
assure initial contact between the steering member and
the pickup arm 15.
FIGURE 9 schematically illustrates initial upward
shifting of the pickup arm 15 carrying the signal pickup 14
prior to radially inward displacement of the pickup arm
as the locked groove escape apparatus of FIGURES 1-7
attempts to effect radially inward movement of the pickup
arm about its pivot support 16. The surface 39 of the
guide member 34 and the steering member 36 engaging the
pickup arm 15 when the signal pickup 14 encounters a locked
groove are slanted in a manner that reduces the signal
pickup/record frictional forces as the respective members
effect radially inward movement of the pickup arm, whereby
the disc record life is extended. In FIGURE 9, (1) W is
the weight of the pickup arm assembly, (2) N is the normal
reaction of the member surface 39, (3) G is the radially
outward force lnitially exerted by the groove 13 on the
pickup arm 15 via the signal pickup 14, and (4) F is the
frictional force between the pickup arm and the member
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1 surface. The upward component of the normal reaction N
reduces the tracking force between the signal pickup 14
and the groove 13, and thereby enhances the disc record 12
life.
Thus, it may be seen that the locked groove
escape apparatus of the present invention relieves the
signal pickup from a locked groove condition, if and when
such a condition is encountered.
.
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