U.S. patent number 3,792,194 [Application Number 05/259,625] was granted by the patent office on 1974-02-12 for scan conversion apparatus.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Paul G. Kennedy, William F. Parrish, Kenneth E. Wood.
United States Patent |
3,792,194 |
Wood , et al. |
February 12, 1974 |
SCAN CONVERSION APPARATUS
Abstract
A video magnetic disk is utilized in the conversion of side
looking sonar or slow scan TV data into a form suitable for
displaying as a flicker-free picture on a conventional TV monitor.
In the side looking sonar mode of operation, provision is made for
displaying the sonar information as a moving window display.
Inventors: |
Wood; Kenneth E. (Annapolis,
MD), Parrish; William F. (Baltimore, MD), Kennedy; Paul
G. (Monroeville, PA) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
22985690 |
Appl.
No.: |
05/259,625 |
Filed: |
June 5, 1972 |
Current U.S.
Class: |
348/22; 367/88;
367/11; 348/163; 379/93.17 |
Current CPC
Class: |
G01S
7/533 (20130101); G01S 7/531 (20130101) |
Current International
Class: |
G01S
7/533 (20060101); G01S 7/523 (20060101); G01S
7/531 (20060101); H04n 005/02 (); H04n 005/78 ();
H04n 007/18 () |
Field of
Search: |
;178/6.8,6.6DD,DIG.3,DIG.20,DIG.24,6.6FS ;179/2TV |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Britton; Howard W.
Attorney, Agent or Firm: Schron; D.
Claims
We claim as our invention:
1. Scan conversion apparatus comprising
A. display means for displaying multiple lines of information on a
display area;
B. system means for providing multiple sequential signals
indicative of a condition to be displayed on said display
means;
C. conversion means for converting said multiple sequential signals
to respective display signals each of a time duration for
displaying as a line on said display means;
D. storage means;
E. means for storing said display signals in said storage means;
and
F. circuit means for reading out said stored display signals and
providing same to said display means to be displayed as respective
lines thereon.
2. Apparatus according to claim 1 which additionally includes:
A. means for relatively moving the displayed picture relative to
the display area.
3. Apparatus according to claim 1 wherein:
A. said storage means is a rotating magnetic medium; and
B. said display signals are stored and read out as said magnetic
medium rotates.
4. Apparatus according to claim 3 which includes:
A. drive means for said rotating magnetic medium; and
B. means responsive to a comparison of the occurrence of said
multiple sequential signals and the rotational speed of said medium
for modifying said drive means.
5. Apparatus according to claim 1 wherein:
A. said display means is a TV display.
6. Apparatus according to claim 5 wherein:
A. said time duration is approximately equal to the unblanked
portion of a TV line.
7. A system for displaying multiple sonar return signals,
comprising:
A. a TV monitor;
B. means for time compressing said signals;
C. a rotating storage means;
D. means for placing said time compressed signals into storage
locations of said storage means as it rotates;
E. means for reading said time compressed signals out of said
storage locations of said storage means as it rotates;
F. means for providing synchronizing and blanking signals for use
by said TV monitor; and
G. means for providing said read out time compressed signals to
said TV monitor for displaying as respective TV lines.
8. Apparatus according to claim 7 wherein said time compression
means includes:
A. means for sampling and storing said signals at a first rate;
B. means for extracting said stored signals at a second rate
greater than said first;
C. said second rate being of a value that an extracted stored
signal is of a time duration substantially equal to a displayed TV
line.
9. Apparatus according to claim 7 which includes:
A. means for relatively moving the displayed information on the TV
screen.
10. Apparatus according to claim 7 which includes:
A. means for storing only predetermined ones of said return
signals.
11. Apparatus according to claim 7 which includes:
A. means for prematurely advancing the vertical sweep of said TV
monitor so that TV lines previously in the vertical blanking period
will be displayed.
12. Apparatus according to claim 11 which includes:
A. means for prematurely advancing said sweep after a predetermined
number of sonar return signals have been received.
13. A system for displaying slow scan TV signals on a conventional
TV monitor comprising:
A. means for time compressing said signals;
B. a rotating storage medium having a plurality of storage
tracks;
C. a plurality of writing heads disposed relative to said storage
tracks for writing information into said storage medium as it
rotates;
D. means for sequentially activating said writing heads for writing
sequential time compressed signals into said plurality of storage
tracks; and
E. means for reading out the information stored in said plurality
of storage tracks and presenting it to said TV monitor for
display.
14. A system for transmitting information comprising:
A. a transmitter station at a first location;
B. a receiver station at a second location;
C. relatively low bandwidth transmission means connecting said
stations;
D. said transmitter station including;
i. means for scanning said information to obtain multiple line
signals each compatible for transmission over said low bandwidth
transmission means;
E. said receiver station including;
i. means for time compressing received transmitted line
signals,
ii. means for storing compressed line signals,
iii. display means for displaying input signals on a line by line
basis,
iv. means for reading out said stored signals and presenting them
to said display means for display.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention in general relates to scan conversion apparatus, and
particularly to such apparatus which utilizes a rotating storage
medium such as a magnetic disk.
2. Description of the Prior Art
In the operation of many sensor systems it would be desirable to
display sensed information on a conventional display such as a TV
monitor. For example, side looking sonar information is produced at
a very low data rate and is generally displayed on a paper
recorder. For displaying the same information on a TV monitor it is
necessary to assemble the return sonar signal on an electronic scan
converter as a one line at a time picture. Due to the relatively
slow speeds of the sonar apparatus through the water, it may take
several minutes to assemble a complete picture and electronic scan
conversion registration becomes a major problem. For broader sonar
coverage a plurality of system may be utilized necessitating the
use of separate electronic tube scan converters.
These electronic tube scan converters are also used for slow scan
TV systems wherein a television picture may be transmitted at a
reduced data rate over a reduced channel bandwidth. This system may
be utilized where a reduced number of transmitted pictures can be
tolerated such as in the transmission of stationary pictures or
slow moving scene information. For example, for a 60 to one time
difference between the slow scan TV picture and the conventional TV
picture, a 60 to one bandwidth compression is achieved, however,
only one scene is transmitted for every 60 scenes of the
conventional TV. The electronic tube scan conversion utilized in
conjunction with this arrangement is complicated and registration
of the recorded and readout signal is a problem because of drifting
of the scan circuits and alignment.
Another method of performing the conversion is to write the slow
scan TV signals on a long persistence phosphor tube. This method is
objectionable however as the picture at the beginning is decaying
in brilliance as the final portion of the picture is being
written.
SUMMARY OF THE INVENTION
A sensor system provides multiple sequential signals indicative of
a condition to be portrayed on a display means which displays
multiple lines of information. The system signals are converted to
respective display signals each having a time duration compatible
with the line time of the display means. The display signals are
stored, preferably on a magnetic disk, and are read out and
provided to the display means at the proper time for
displaying.
In the case where the sensor system is a side looking sonar system,
means are provided for moving the information displayed as movement
through the water of the side looking sonar system takes place.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating, generally, the concept of
scan conversion;
FIG. 2 is a view of one type of side looking sonar apparatus which
may be utilized as the system of FIG. 1;
FIG. 3 is a plan view of the side looking sonar apparatus of FIG. 2
showing the starboard beam only;
FIG. 4 is a block diagram illustrating an embodiment of the present
invention with respect to a sonar system;
FIG. 5 are curves illustrating various signal time occurrences in
the arrangement of FIG. 4;
FIG. 6 illustrates a sonar return signal, and the compression
thereof with respect to time;
FIG. 7 is a block diagram which illustrates one way of obtaining
the sampling pulses illustrated in FIG. 5;
FIG. 8 is a timing diagram illustrating the operation of FIG.
7;
FIG. 9 illustrates a conventional TV display;
FIGS. 10 and 11 illustrate waveforms utilized in obtaining the
display of FIG. 9;
FIG. 12 is a plan view of a magnetic disk with storage locations
thereon;
FIG. 13 is a portion of the disk of FIG. 12 illustrating the
relative storage of a particular signal;
FIGS. 14A, B, and C are charts illustrating the storage of
information in particular address locations of the disk of FIG. 12
in relation to a typical display;
FIG. 15 is a plan view illustrating side looking sonar apparatus as
it proceeds over a target;
FIGS. 16A through G illustrate the appearance on a TV display of
the situation depicted in FIG. 15;
FIG. 17 is a block diagram illustrating in more detail the
arrangement of FIG. 4;
FIGS. 18A, 18B and 18C illustrate the target of FIG. 15 as
presented on the TV display for three different velocity conditions
of the sonar system;
FIG. 19 is a block diagram illustrating a possible correction for
the condition of FIG. 18C;
FIG. 20 is a block diagram illustrating a portion of typical
synchronizing generator which may be utilized herein;
FIG. 21 is a block diagram illustrating a driving arrangement for
the magnetic disk;
FIG. 22 illustrates a magnetic disk having two recording tracks for
the storage of information to be displayed;
FIGS. 23A, 23B, 23C, and 23D serve to illustrate the writing of
information on a magnetic disk such as illustrated in FIG. 22;
FIG. 24 is a block diagram of a slow scan TV system utilized in
conjunction with the magnetic disk of FIG. 22; and
FIG. 25 is a block diagram illustrating a typical use of the
present invention for transmission of information over conventional
telephone lines.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 illustrating the concept of scan conversion utilized
herein, a sensing system 10 provides multiple sequential signals
containing information and which are to be presented on a display
12. The display 12 is of the type which displays multiple lines of
information, with each line being presented on the display in a
certain line time.
In order to insure that the system signals are compatible and can
be displayed in the proper line time of the display 12, there is
provided a signal time conversion means 14 which is responsive to
the system signals and is operable to expand or compress them in
time depending upon whether the particular system signals are of a
shorter or longer time duration than the line time of the display
12. System signals which are converted to respective display
signals are provided to a storage means 16 where they are
maintained and thereafter read out to build up a display
picture.
FIG. 2 illustrates one of many uses of the present invention, the
use being in the side looking sonar field although the invention
may be utilized with various sonar systems. Side looking sonar
transducers mounted on carrier vehicle 20 transmit acoustic energy
pulses in a certain pattern such that the sound energy impinges on
the bottom 22 and scans, or sweeps out elongated narrow insonified
strips such as 24 and 25 produced by starboard and port transducers
respectively. Reflected acoustic energy containing information
relative to the bottom, or targets on the bottom, is picked up by
receiving transducers and then processed and displayed. The carrier
20 is towed by means of a vessel 27 and cable 28, and as it
proceeds along a course line multiple sequential acoustic
transmissions take place such that, as illustrated in the plan view
of FIG. 3, multiple adjacent areas 30, 31, 32 . . . on the bottom
are insonified. Although not illustrated, bottom strips on the port
side of the carrier would also be insonified. Each return signal
contains information and collectively the return signals are
indicative of a sound picture of the target area over which the
apparatus is towed.
For various operations it would be desirable to portray the return
signals indicative of target information on a conventional TV
monitor. The present invention is capable of performing this
function and to this end reference is made to FIG. 4.
A sonar system 35 provides, on line 36, multiple sequential return
signals indicative of a condition to be displayed on a display
means in the form of a conventional TV display 39. With the system
35 being of the side looking sonar type, the return or echo signals
received from the target area are each to be presented on a
separate line of the TV display, however, their time duration far
exceeds the time it takes to scan one TV line. Accordingly, each
sonar return signal is compressed for displaying as a TV line.
The compression of the signals appearing on line 36 can be
accomplished in a number of ways. FIG. 4 illustrates one such
compression method and includes an analog to digital converter 41,
shift register means 43 and a digital to analog converter 45. With
proper signals from the timing and control circuits 49, the analog
to digital converter 41 including sample and hold circuits will
sample, at a predetermined sampling rate, each sonar signal
presented to it and convert it into digital form. The digital data
is then presented bit by bit to the shift register means 43. For
example, if each sample is converted to a six bit equivalent
digital signal, there could be provided six parallel shift
registers which shift the digital information down at the sampling
rate. The stored signal is then read out, as governed by the timing
and control circuits 49, at a much faster rate than the sampling
rate and chosen such that the resulting signal will be of a time
duration suitable for a one-line display. The signal from the shift
registers 43 is converted back to analog form by means of the
digital to analog converter and is then stored for future display
presentation.
The storage means is preferably in the form of magnetic disk 53,
such disks being well known in the TV industry for the recording of
TV signals for subsequent replay. The basic disk and drive
assemblies have been advanced to a point where signal registration
is mechanically insured and the cost of the apparatus is relatively
inexpensive. In addition, several hundred tracks of information can
be stored on one disk.
The sonar signals, each of a time duration too great for a TV line
display are presented to the analog to digital converter 41 and
emerge from the digital to analog converter 45 as display signals
each of a time duration equal, or substantially equal, to the time
for displaying one TV line.
Prior to storage on the magnetic disk 53, the display signals are
processed in signal conditioning apparatus 56 which may include for
example, such circuitry as preamplifiers, limiters, modulators,
filters, etc.
The recorded signals on the magnetic disk 53 are then presented to
the TV 39 by way of other signal conditioning apparatus 58 which
may include such circuits as preamplifiers, limiters, demodulators,
filters, etc.
Since the display signals are to be presented on the TV 39 there
must be provided certain synchronizing and blanking signals to make
up the complete TV signal. In the embodiment illustrated these
signals are provided by the synchronizing generator 62 and may be
combined with the display signals in the signal conditioning
apparatus 58.
Each time a sonar transmission takes place, this information is
communicated to the timing and control circuitry 49 as a sonar
pulse. In the embodiment of the moving window display, to be
described, the timing and control circuits 49 in response to the
transmissions readjusts the output of the synchronizing generator
62.
By way of example FIG. 5 illustrates a timing diagram for various
events occurring in the operation of FIG. 4. Suppose, by way of
Example, that the pulse repetition frequency (PRF) is 3 hertz (Hz).
FIG. 5 illustrates a first sonar pulse at time equal to zero and
the next pulse 333.33 milliseconds later. At a predictable time
after transmission, a meaningful sonar return is received. Sampling
pulses are continuously provided at a predetermined rate and for
each sampling pulse during the sampling period, the amplitude of
the sonar return is converted to digital form by the analog to
digital converter 41 and provided to the shift registers 43 (See
FIG. 1). Assuming that the disk rotates at a constant 1,800 rpm,
FIG. 5 illustrates that a complete revolution takes place every
33.33 milliseconds and that after 10 revolutions the compressed
signal to be subsequently displayed, is written at a particular
location on the magnetic disk and at a time prior to the next sonar
pulse.
FIG. 6 illustrates the sonar return and the compressed signal in
somewhat more detail. At T.sub.0 an acoustic pulse is transmitted
by the sonar system and at a predictable time later, T.sub.1, the
return signal indicative of target information is initially
received and continues to be received until time T.sub.2, dependent
upon system design. During the time from T.sub.1 to T.sub.2, the
sonar return is sampled at the sampling rate and placed into the
shift registers. At time T.sub.3 the shift registers are read out
at a rate such that the entire sonar signal is presented to the
magnetic disk in the time from T.sub.3 to T.sub.4.
One arrangement for obtaining the sampling pulses is illustrated in
FIG. 7. Let is be assumed for the example that it is desired to
sample each sonar return signal 512 times. The sonar pulse
indication is provided to a delay circuit 66 which provides, after
a predetermined time delay .delta. , an output signal to the S
input of flip-flop 67. Flip-flop 67 provides an output signal when
a signal is presented to the S input, and provides no output signal
when a signal is presented to its R input. The output from the
delay circuit 66 therefore causes the flip-flop 67 to provide an
output signal to start oscillator 69 which then provides the load
pulses. Each pulse output from oscillator 69 is provided to a
counter 71 which provides an output signal when its count reaches
512 at which time the flip-flop 67 is turned off and oscillator 69
ceases to provide pulses. Counter 71 then reverts back to its
initial setting. The timing relationship for this operation is
illustrated in the curves of FIG. 8.
At time T.sub.0 a sonar transmit pulse occurs. The effect of such
pulse is delayed from time T.sub.0 to time T.sub.1 and from time
T.sub.1 to T.sub.2 loading of the shift registers is accomplished,
the time T.sub.1 to T.sub.2 representing the output signal of
flip-flop 67. For various operations the delay may be modified or
eliminated so that sampling of the sonar return signal takes place
during the deadtime from T.sub.0 to T.sub.1.
Since the display signals are presented to a TV monitor, the
operation of a conventional TV display will be briefly discussed.
For a cathode ray tube TV, the electron beam scans the picture or
display area at repeating intervals giving rise to a series of
single pictures with the repetition rate of successive pictures
detemining the apparent continuity of a moving scene. This rate is
referred to as the frame rate. Most practical TV systems resort to
linear scanning starting at the top of the tube and tracing
successive lines till the bottom of the picture is reached, after
which the beam is returned to the top and the process is repeated.
In order to reduce flicker there is generally utilized an interlace
scanning method wherein two scanning fields are produced for each
complete picture frame. Depending upon the system circuitry and
resolutions desired, any number of scanning lines may be chosen and
by way of example the present invention will be described with a TV
system utilizing 525 lines per frame with 489 of these lines being
actually displayed. The remaining 36 lines are utilized in the
retrace or return of the beam to the top of the screen from the
bottom. With a 2:1 interlace scanning, 18 of the lines are taken up
for each field retrace. With 489 lines being displayed for each
frame, there will be 244 1/2 lines displayed for each field. This
is illustrated in FIG. 9.
If one were to look at the display and consider a single picture,
that is, a single frame, the first line is actually a half line at
the top, the second line is the first full line across the display,
and the lines would continue in numerical order until the last line
490, which is actually half a line. The frame line numbers are
designated under the title Display Line No. The picture, or frame,
however, is made up of two interlaced fields. In FIG. 9 the dotted
lines are the lines of the odd field and the solid lines are the
lines of the even field. The field line numbers are designated
under the title Field Line No. The first line written is the odd
field line number 1. The second line written is the field line
number 2 which in actuality is the third line of the overall
display or frame. After the 245th line in the field is written,
corresponding to the 489th line of the display, the beam is brought
to the top of the screen to begin the display of the even field.
The retrace time takes, for the example illustrated, 18 line
periods so that the first line displayed in the even field is
numbered 264. Again, line No, 264 is actually the second line of
the display. The last line of the even field, line 508 is
equivalent to display line 490 and the remainder of the 525 line
display is taken up in the vertical retrace.
The display of FIG. 9 is accomplished with the provision of the
waveforms of FIGS. 10 and 11. In FIG. 10 the saw tooth horizontal
scanning waveform is presented to the cathode ray deflection plates
or coils and has the effect of scanning the electron beam across
the face of the tube after which it is quickly returned. Thus, for
the portion 74 of the horizontal scanning waveform the cathode ray
beam will scan across the face of the tube in 55 microseconds
(.mu.s), and for the portion 75 will quickly retrace in 8.5 .mu.s.
The horizontal synchronizing pulses serve to initiate each saw
tooth of the scanning waveform and each pulse is illustrated as
occurring coincident with the peak of the saw tooth. During the
portion 74 of the entire 63.5 .mu.s period, information may be
displayed and the horizontal blanking pulses encompass a period
just prior and subsequent to the retrace portion 75. During the
provision of the horizontal blanking pulses the cathode ray beam is
blanked e.g., for 10 .mu.s so that no information is written on the
screen, while the unblanked portion of 53.5 .mu.s is the actual
line display time.
In FIG. 11 there is illustrated the vertical scanning waveform
having a much longer period than the horizontal scanning waveform
and wherein during the portion 78 the scanning beam is moved down
the screen, and during the portion 79 the beam is retraced back to
the top. As was the case with FIG. 10, the vertical synchronizing
pulses occur coincident with the peak of the saw tooth waveform and
the vertical blanking pulses which blank the beam during the
vertical retrace encompass a period prior, and subsequent to the
retrace portion.
If the vertical synchronizing and blanking pulses are made to occur
at a time prior to their normal occurrence, as illustrated by the
dotted line portions of these waveforms, they will have the effect
of starting the vertical scanning waveform at a corresponding
earlier point in time as indicated by the dotted portion of that
waveform. The purpose of this operation will be subsequently
explained with respect to FIGS. 14A, B and C.
In the present invention each sonar signal is compressed to an
equivalent line display time, for example, approximately 53.5 .mu.
s, and is stored on a magnetic disk at a certain address or
location. As the disk rotates the information contained in the
storage locations is read out and displayed on the TV monitor. An
example of a typical disk and the storage locations is illustrated
in FIG. 12.
The disk 90 includes a recording track T for recording display
signals. Each display signal is recorded at a particular location
on the track and these locations are herein termed slots and are
designated by a slot number with the prefix S. Accordingly, for a
525 line TV system, there are 525 slot locations S1 to S525. A
magnetic recording/reading head H is positioned over the track T
and will write in and read out information as the disk 90 rotates
in the direction of the arrow at a constant speed of 1,800 rpm.
The slot numbers correspond to the field line numbers shown in FIG.
9 and into these slot locations will be written the corresponding
display lines, each of which is designated by a number preceded by
the letter L. According to FIG. 9 display line 1 is written into
the first slot location, display line 3 written into the second
slot location... and display line 525 is written into the 263rd
slot location. The very next slot location 264 will contain the
second display line, slot 265 the fourth display line... and slot
525 will contain the 524th display line. In one complete revolution
of the disk 90 with head H in the read out mode, the odd field will
be displayed starting with line 1 and after the vertical blanking
period the even field will be displayed starting with line 2 and
after the second vertical blanking period the process is
repeated.
At the rotational speed designated, a slot location, as illustrated
in FIG. 13, occupies the equivalent of 63.5 .mu.s. Within this slot
location is the display signal 93 recorded in FM form and occupying
an equivalent of approximately 53.5 .mu.s with the remaining 10
.mu.s being for blanking and retrace.
FIG. 14A illustrates, in linear form, the circular slot and line
arrangement on disk 90 of FIG. 12. The line number is the top most
series of numbers designed L and the numbers directly below them
are the slot numbers designated S. As mentioned, one complete
rotation of the disk with the head H in the read out mode will
present a display as in FIG. 9. Thus, in FIG. 14A, the displayed
odd field starts in the middle of line 1 and continues for 244 1/2
lines up to line 491. Vertical blanking takes place for 18 lines
after which the 244 1/2 lines of the even field are displayed
starting with line 2 and ending in the middle of line 490. The even
vertical blanking for 18 lines then brings the system around to its
initial starting point. Waveform 95 illustrates the vertical
scanning in relation to the displayed fields.
As the side looking sonar apparatus proceeds over a target it is
desirable that an observer see a picture on the TV display moving
as if he were facing the direction of motion of the apparatus. In
FIG. 15 there is illustrated a vessel 99 at position P1. FIG. 15
also illustrates an alternate embodiment wherein the side looking
sonar apparatus is carried by the vessel which also includes a TV
display 100. As the vessel 99 proceeds to position P2, the
insonified area 102 proceeds over a target 104. The present
invention provides means for moving displayed information on the
screen as the apparatus proceeds over a target area. Thus, for the
situation depicted in FIG. 15, the TV display 100 will portray the
target 104 as illustrated in A through G of FIG. 16. One way of
accomplishing this moving window display is to slip the sync and
advance the vertical synchronizing pulse by one line time as
described previously with respect to FIG. 11. For example, and with
reference again to FIG. 14A, let it be assumed that no information
has been recorded in any of the slot locations and accordingly, no
meaningful information is presented on the TV display. The first
and second sonar returns converted to display signals are stored
respectively in slots 263 and 525. When the sync is slipped one
line time early, as indicated by arrow 107, the information
contained in the particular slot locations will be displayed as the
respective lines indicated in FIG. 14B. In other words, information
previously stored in unviewed slot 263 will now, in FIG. 14B, be
displayed as line 2 and information stored in slot 525 previously
unviewed will be seen as line 1, more particularly, one half of
line 1. The second and third returns, converted to display signals,
are stored respectively in slots 262 and 524. When the sync is
slipped one line time as indicated by arrow 108, the situation will
be as depicted in FIG. 14C wherein the initial information received
and stored in slot 263 is now displayed as line 4, the second piece
of information in slot 525 now appears as line 3, information in
slot 262 appears as line 2 and the information in slot 524 appears
as line 1. By continuing this process of slipping the sync after
each two returns the display picture will move down the screen as
in FIG. 16.
There are various methods of accomplishing this recording, display
and movement operation and FIG. 17 illustrates one embodiment. In
order to insure synchronism of operation, it is preferable that the
disk contain synchronizing information in the form of synchronizing
pulses. Accordingly, the disk 110 includes a first clock track CT1
which provides an output for each revolution of the disk, a second
clock track CT2 for providing an output signal for each slot
location, and a third clock track CT3 for providing clocking pulses
utilized for reading out the shift registers, in addition to being
utilized in the generation of the synchronizing waveforms. For ease
of understanding, these clock tracks are illustrated as being
individual tracks however, it is to be understood that the
information could be incorporated into a single track with a
certain number of clock pulses being equal to one slot location and
a certain number of slot locations being equal to one
revolution.
The clock tracks are read by respective heads 113, 114, and 115. In
the exemplary embodiment being described, with the occurrence of a
sonar pulse there are 10 disk revolutions until a return is to be
written. (e.g., See FIG. 5). Accordingly, a sonar pulse indication
on line 118 is utilized to reset a counter 120 which receives a
signal from head 113 for each revolution of the disk 110, and
provides an output signal on line 121 when the count of ten is
attained.
Counter 124 is of the type which receives the signals from head 114
and in response thereto provides a unique output signal on output
line 125 indicative of the particular slot count. It is to be noted
that the use of the term line herein is meant to include one or
more signal conducting wires. At the beginning of each disk
revolution, counter 124 is reset by means of the signal on line
127.
The actual slot location is compared with a desired slot location
into which information is to be recorded and if the two are alike,
and if the correct number of revolutions has taken place, then the
writing of the information into the disk at the proper slot
location can take place. For this purpose, there is provided
comparison means 130 which receives the actual slot indication on
line 125 from counter 124, and a desired slot indication on line
133 from encoding means 134 to provide an enabling output signal on
line 136 when the two are identical.
Gating means such as AND gate 139 receives, at one input, the
indication that the two slot locations are identical, and at its
other input, an indication that the correct revolution has been
attained, to provide an enabling output signal on line 140. This
enabling signal may be utilized as a write command to the signal
conditioning apparatus 143 and may be additionally utilized to
enable AND gate 145 to pass the clock pulses being provided to it
from head 115. These pulses passed through OR gate 148 serve to
shift the information out of the shift registers 150, after which a
conversion takes place by the digital to analog converter 153,
which also receives the clock pulses via line 155. Since the signal
conditioning apparatus 143 is receiving a write command, the analog
information will then be written into track T by means of head
157.
Upon the occurrence of the very next slot, the output of counter
124 will no longer be equal to the desired slot indication on line
133 and the enabling signal on line 136 will be removed. With AND
gate 139 disabled, the write command is removed and information is
no longer shifted out of the shift registers 150. The head 157,
however, provides signals indicative of the information stored on
track T to the signal conditioning apparatus 160 which combines the
output from the disk with the synchronizing information, to present
a TV signal to the TV display 163.
When the next sonar return is received it is also fed to the analog
to digital converter 166 on line 167, which also receives the
sampling pulses, from FIG. 7, as does the shift registers 150
through OR gate 148, to load a new return.
Each sonar return is to be written into a different slot location
as predetermined by the encoding means 134. One way of providing
the moving window display, as previously discussed, is to write the
first two returns in slots 263 and 525, respectively, the next two
in slots 262 and 524, etc. This may be accomplished with the
provision of counters 178 and 179 each being responsive to count
input signals to in turn provide, on respective output lines 182
and 183, signals indicative of the number of inputs counted. Both
counters can count up to 525, however, a reset signal on line 185
provided at the start of operations, will set counter 178 to the
number 264 and will set counter 179 to the number 1. The reset
signal also resets flip-flop 189 so that upon the receipt of a
first sonar pulse it will provide an output on line 191 to counter
178, and upon receipt of the next sonar pulse will provide an
output signal on line 192 to counter 179. The output signals are
thereafter alternated between these two lines with subsequent
inputs to flip-flop 189. The first sonar pulse, therefore, will
have the effect of triggering counter 178 to the next count below
264, such that counter 178 provides the number 263 to enable gate
193. The enable gate 193 is enabled by virtue of an enabling signal
on line 191 and OR gate 196 passes this number to the comparison
means 130 as the desired slot location. The sonar return is then
written into that slot location as previously described. The next
sonar return is to be written into slot 525. When the next sonar
pulse is received, line 192 provides the output signal to counter
179 which assumes its next count of 525. This count is passed
through enable gate 198, enabled from line 192, through the OR gate
196, and presented to the comparison means 130 as the desired slot
location. The counters continue to count down until the last number
in sequence is reached, after which the counting sequence will
repeat.
Starting with the first input signal to the counters, the counting
sequence will be as indicated in the following chart:
Counter 178 Counter 179 263 525 262 524 261 523 . . . . . . 3 265 2
264 1 263 525 262 524 261 523 260 . . . . . . 266 3 265 2 264 1
Since the vertical synchronizing will be slipped by one line after
two entries have been made, such indication may be obtained from
line 192 to provide the slip sync signal indicated on line 200.
If the sonar apparatus is proceeding over the target area at a
certain velocity, then the target on the moving window display will
appear geometrically correct, as in FIG. 18A. If the velocity is
relatively slower, with the same pulse repetition frequency, there
will be a greater number of returns for the same area thus giving a
distorted picture, as in FIG. 18B. Similarly, if the relative
velocity is faster, fewer returns will be obtained, information
will be missing, and the target will appear as in FIG. 18C.
Accordingly, the present apparatus includes means for eliminating,
or reducing, these geometric incongruities due to variations in
velocity over the target area.
With reference again to FIG. 17, this can be accomplished with the
provision of the pulse selector means 204 which receives each sonar
pulse on line 206 and will provide an enabling signal on line 207
to the enabling gating means 209 as follows: Let it be assumed for
example that the sonar speed is such that a normal picture as in
FIG. 18A is presented. In such instance the pulse selector 204
provides an output for each pulse input, which is then passed
through the enable 209, and through OR gate 212 to appear as a
sonar signal on line 118.
If the apparatus is proceeding too slowly, certain ones of the
returns are not to be written and displayed. Accordingly, with the
proper setting, the pulse selector 204 will provide an enabling
signal on line 207 only after a predetermined number of pulses has
occurred on line 206 such that the sonar pulses on line 118 will be
the result of one out of every two, one out of every three, seven
out of twelve, or any other desired selection. As indicated, the
pulse selection may be made manually or it may be made
automatically in accordance with the actual velocity of the
apparatus by means of a velocity indication signal on line 217.
If the apparatus is proceeding too rapidly, then information will
have to be added to the picture to prevent the distortion shown in
FIG. 18C. This information, to a good approximation, can be
obtained from previously written information and in such mode of
operation, the pulse selector 204 will provide a plurality of
pulses on line 218 for each input pulse received on line 206. These
plurality of pulses then appear on line 118 as the sonar pulses as
though they emanated directly from line 206. In order to rewrite
previously received target information, the pulse on line 218 is
additionally utilized to recirculate the shift registers as
indicated in FIG. 19. FIG. 19 shows the analog to digital
converter, the shift registers, and the digital to analog converter
shown at the lower portion of FIG. 17. If it is desired to have the
capabilities to rewrite information, then gating means can be added
to take the information as it comes out of the shift register and
put it back in. For example, the output of the shift registers is
provided through an AND gate 220 the output of which is fed to OR
gate 221. For normal operation the Recirculate Shift Registers
signal to the AND gate is not provided and the apparatus operates
as previously described. When an output signal is provided on line
218 of FIG. 17, the AND gate 220 will be enabled and the
information will not only be provided to the digital to analog
converter for subsequent recording on the disk but will
additionally be provided to the input of the shift registers and
will be read out again when all the conditions for writing are
met.
The synchronizing generator 62 illustrated in FIG. 4 may be of the
well known variety which utilizes a series of counters for
providing the synchronizing and blanking waveforms. FIG. 20
illustrates a portion of the generator and includes counter
circuitry 224 which is normally responsive to pulse input signals
on line 225 to in turn provide output signals to the vertical
synchronizing and blanking circuits 227 and 228. Similar circuits
can be provided for the horizontal synchronizing and blanking
waveforms. To insure synchronism with the information on the
rotating disk, the input pulses to the counter circuitry 224
preferably are derived from a clock track on the disk. The slip
sync circuit 230 is provided to add a count to the counter
circuitry 224 at the precise time to achieve the advanced condition
described in FIG. 11. This pulse, which may be adjusted with
respect to time, is added in response to the slip sync signal (FIG.
17), coupled with information relative to revolution and slot
count. For displaying port sonar information similar apparatus may
be utilized with a reversal of scanning of the TV horizontal
sweep.
Although it is possible to provide a track on the disk to trigger
the sonar system, it is preferable that the sonar pulse repetition
rate be the controlling factor in driving the disk. FIG. 21 shows
an arrangement wherein the sonar pulse repetition frequency is
compared with the disk rotation frequency and any error is utilized
to correct the disk speed. A phase comparison means 233 receives as
one input each sonar pulse from the sonar system 234. Another input
is provided by the division circuit 236 which provides an output
signal after a certain number of disk rotations. In the present
example, there are 10 disk revolutions for each sonar pulse. If the
sonar pulse occurs at the same instant of time as the tenth
revolution then no corrective output signal is provided to the
amplifier 238 to correct the speed of the motor 240 driving the
disk 242. Should the rotational speed vary from the desired speed,
the resultant out of phase signals applied to the phase comparison
means 233 will provide an error signal to the amplifier 238 to
correct the condition.
FIG. 12 illustrated a disk containing a single information storage
track for the TV display and rotatable at 1,800 rpm. Various other
track arrangements and rotational speeds are possible, one such
other arrangement being illustrated in FIG. 22.
Disk 248 is rotatable at 3,600 rpm and contains two information
tracks T1 and T2 for the recording of the display signals. All of
the even field lines may be recorded in slot locations on track T1
and all of the odd field lines may be recorded in slot locations on
track T2. A few of the even field lines are illustrated around head
250, and a few of the odd lines are illustrated around head 252,
and since there are an odd number of lines, 525, half of line L1 is
in track T1 and half in T2. This arrangement may be utilized not
only in conjunction with sonar systems but may be utilized with
other information generating systems. For example, in the
arrangement of FIG. 2, the carrier vehicle 20 in addition to the
sonar apparatus may also carry television viewing equipment. In
order to transmit television pictures up the cable 28 to the vessel
27 to be processed, it is necessary to utilize a cable 28 of a
particular design capable of handling the bandwidth requirements
for such signal. In instances where the cable 28 is extremely long,
its cost becomes excessive. A slow scan TV system, however, can be
utilized in conjunction with the normal towing cable, although the
information rate is slower. A typical slow scan TV camera will not
have the scanning interlace and will produce approximately 4 camera
scan lines in a time that disk 248 of FIG. 22 makes one revolution.
Accordingly, 4 writing heads are provided as in FIG. 23A with heads
1 and 3 being for writing on track T1 and heads 2 and 4, positioned
at 90.degree. from the other two heads, being for writing on track
T2. When all of the necessary information for display has been
recorded in the slot locations or during the recording process,
heads 1 and 5 are operable for alternately reading out their
respective tracks.
In FIG. 23A head 1 is dark indicating that it is writing into a
particular slot location. Arrow 254 is utilized as a reference mark
for comparison with the subsequent FIG. 23B where head 2, shown
dark, is writing into the next slot location on the opposite track
one quarter of a revolution plus one half a slot distance later.
The next information is written by head 3, FIG. 23C, wherein the
reference mark 254 has rotated through another 90.degree. plus one
half a slot. In FIG. 23D head 4 is writing and the reference mark
254 has rotated another 90.degree. plus another half slot distance.
With reference back to FIG. 22 suppose that head 250, equivalent to
head 1 of FIG. 23A, proceeds to write line 2 information in its
correct slot location. After the information has been written, the
beginning of the line 2 slot location will have proceeded
90.degree. in the direction of the arrow and one half slot later
line 3 will be written by head 2, and so on.
An arrangement for a slow scan TV system is illustrated in FIG. 24.
The two track 3,600 rpm disk is not illustrated, however, it would
include clock tracks as described with respect to the disk in FIG.
17. Clock pulses from a clock pulse track will appear on line 260,
pulses indicative of each half slot rotation appear on line 261 and
pulses indicative of each revolution of the disk appear on line
262.
The slow scan TV signal is presented on line 264 and is fed via
line 265 to the analog to digital converter 267, the digital output
signal of which is placed into the shift registers 269 at a rate
determined by the output of oscillator 271.
The stored signal is compressed by the increased read out rate
determined by the clock pulses and after conversion to analog form
in the digital to analog converter 273 and after passage through
the signal conditioning apparatus 275 (where it is combined with
synchronizing and blanking information from generator 277,) is
presented to respective power amplifiers of heads 1 through 4.
These power amplifiers are enabled in sequential order as described
in FIGS. 23A through D by means of an enabling signal from AND
gates 283 to 286. These AND gates are enabled in sequence by the
output of ring counter 289, which, in response to each new slow
scan TV line will provide an enabling signal on a different one of
its output lines 292 through 295, in sequence.
Since the slow scan TV signal on line 264 contains synchronizing
signals, information relative to the occurrence of each line may be
obtained by separating the synchronizing signal by means of the
sync separator 298 which will provide a signal H on line 300 at the
start of each new line and will provide a signal V on line 302 at
the start of each new field. In the slow scan TV case each slow
scan TV line can be stored in the exact same slot location, for
each new picture. The mechanization for designating the slot
location includes counter 305, encoding means 307 and comparator
means 309. The V signal on line 302 is utilized to reset the
counter 305, encoder 307 and ring counter 289. Each new slow scan
TV line is designated by the H signal on line 300 and counter 305
counts these signals to provide an indication thereof to the
encoder 307 operable to supply a unique slot location designation
to the comparator 309. The other input to the comparator is an
indication of the actual slot location, to a half slot accuracy,
provided by counter 112 which is resettable by the output of OR
gate 113 each time that the disk makes a revolution or each time
that a new V signal is supplied.
When the actual location is equal to the desired location, the
comparator 309 provides an output signal on line 316 to enable the
AND gates 283 to 286 and signals via line 318, the generator 277 to
supply the necessary signals to the signal conditioning apparatus
275.
The generator 277 provides these signals in response to the H and V
information of the slow scan TV sync signals and the disk
revolution, so that there is stored at a particular slot location
for read out not only the desired information signal but also the
desired synchronizing signals.
When the heads aren't enabled for writing, they are operable for
reading information. However, in the embodiment illustrated, only
two of the heads, head 1 and head 5 will do the reading function.
The output signal from head 1 is fed to a read preamplifier 322 and
the output of head 5 is fed to read preamplifier 323. Since one
field is stored on one track and the other field is stored on the
other track, the first track can be read out in its entirety for a
revolution and thereafter the second track can be read out in its
entirety for a revolution. The alternate selection of head 1 and
head 5 is accomplished by select gating means 225 which alternately
passes the signal from read preamplifier 322 and 323 to its output
327, in response to each revolution of the disk as indicated on
line 262. The signal to be displayed is processed by the signal
conditioning apparatus 330 and presented to the TV display 332.
As an added feature, it would be desirable, for many operations, to
be able to look at a past picture. For this purpose there is
included a storage system 335 which receives the TV signals and
stores them whereby they may be recalled by a select circuit 337
under control of an operator. The storage system 335 may if desired
include another magnetic disk arrangement or the signals may be
stored on unused tracks of the same disk.
The present invention additionally allows the transmission of high
quality pictures over reduced bandwidth channels. FIG. 25
illustrates an arrangement whereby slow moving scene information or
pictures may be transmitted over conventional telephone lines.
Although pictures can be transmitted over telephone lines by means
of facsimile apparatus the resolution of the pictures received
nowhere would approach the resolution utilizing the present
invention which makes it particularly useful in the medical field
for example for diagnosing transmitted X-rays or in the industrial
field for transmitting precise picture information.
At the transmitting end a conventional television camera 350 views
the information to be transmitted but provides video signals which
cannot be accommodated over conventional telephone lines. The video
signals therefore are expanded in time to be equal to, for example,
a slow scan TV signal, in the down conversion apparatus 352. The
down conversion apparatus can be similar to the apparatus described
herein in that each video line signal can be recorded in a separate
slot location on a magnetic disk and thereafter each slot may be
read out into an analog to digital converter where the signal may
then be stored in a plurality of shift registers and read out at a
slow rate for telephone transmission. The signal conditioning
apparatus 355 conditions the signal for transmission and presents
it to an acoustic coupler 357. Such couplers are well known and are
sometimes called modems, short for modulator-demodulator. The
transmitting telephone apparatus 360 sends the signal via the
telephone exchange to a receiving telephone apparatus 362 where the
signal is converted by acoustic coupler 364 and is provided to the
signal conditioning apparatus 366. The remainder of the apparatus
at the receiving end is the same as that illustrated in FIG. 1 and
includes a signal time conversion means 368 for compressing the
received signal to place it into storage 370, such as a magnetic
disk, whereby it can be presented to display 372, preferably a
conventional television monitor.
In the instance where a slow scan TV camera 374 is utilized at the
transmitting end, its output signals may be fed directly to the
signal conditioning apparatus 355 since there is no requirement for
the down conversion.
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