Note: Descriptions are shown in the official language in which they were submitted.
10~661S
This invention relates to an improvement in a plan position
indication (PPI) system, and more particularly to a device for indicating a
tilt marker and a distance marker on the display screen of the PPI system.
This invention is useful among other things, for application to a sonar
system having a display screen scanned circularly.
~n the sonar system, an ultrasonic wave pulse is emitted from the
transmitter at a specific tilt angle with respect to the horizontal plane to
the whole azimuth at the same time and the pulse reflected by an object is
received by the receiver having a sharp directivity controlled at the same
lo tilt angle and varying the azimuth at a specific frequency. The electron
beam of a cathode ray tube is modulated with the received pulse, thereby indi-
cating the position of the object on the display screen of the cathode ray
tube. According to such prior system, the straight distance and the azimuth
of the object can be observed and obtained directly on the screen, but its
horizontal distance and vertical depth can not be obtained directly unless
j they are calculated from the straight distance and the tilt angle.Accordingly, an object of this invention is to provide a novel
device for indicating a tilt marker and a distance marker on the display
screen of the PPI system, from which the horizontal and vertical components
of the straight distance can be easily observed and obtained.
According to this invention, the device comprises display means
having a display screen scanned with a number of concentric circular arcs,
means for indicating a selected one of said scanning circular arcs as a
bright circle, and means for indicating a radius on said display screen as a
~ bright line, said radius having a tilt angle corresponding to that of the
-~ transmitter and the receiver.
Now, the invention will be described in more detail hereinunder in
cor~junction with a preferred embodiment of the invention with reference to
; the accompanying drawings.
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In the drawings:
Figure 1 is a schematic block diagram representing ~n embodiment of
the device of this invention, applied to a sonar system;
Figure 2 is a diagram illustrative of the scanning mode of the dis-
play screen of the device; and
Figure 3 is a diagram illustrative of a display pattern on the screen
given by the device of Figure 1.
Referring to figure 1, the device includes a cathode ray tube 1
having a circular display screen 2~ vertical and horizontal deflection
electrodes 3 and 4 and an electron beam modulating electrode 5. The ver~ical
and horizontal deflection electrodes 3 and 4 are connected respectively to the
outputs of a sine wave generator circuit 11 and a cosin wave generator cir-
cuit 12 having first inputs connected in common to the count output of a
first counter circuit 13 and second inputs connected in common to the count
output of a second counter circuit 14. The input of the first counter circuit
13 is connected to the output of a reference pulse oscillator 15 which
produces a train of references clock pulses.
The first counter circuit 13 is arranged to count the cloGk pulses
from the pulse oscillator 15 and produce the count output in a coded form~
More specifically, circuit 13 produces a pulse at a first pulse output 16
upon the completion of each predetermined reference count and a pulse at a
second pulse output 17 for each half of said reference count. The reference
count may be determined arbitrarily but is preferably selected as 360 as
described later. The second counter circuit 14 counts the pulses from the
first pulse output 16 of the first counter circuit 13 and produces the
count output in a coded form. The sine and cosine wave generator circuits 11
and 12 are arranged to produce sine and cosine wave signals having a common
period corresponding to the above reference count of the first counter circuit
13 and a common amplitude proportional to the count of the second counter
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circuit 14. It will be understood from the above arrangement by those skilled
in the art that a circular scan, having a cycle corresponding to the above-
mentioned reference count and wherein the diameter increases step by step
upon the completion of each cycle, is carried out on the display screen 2 of
the cathode ray tube 1. It should be noted that this scan cycle is precisely
synchronized with the azimuth rotation of the sonar receiver, as well as with
the ultrasonic wave pulses emitted from the transmitter, by means not shown,
since a further description has not been deemed necessary as it has not
direct connection to the invention and, moreover, it is well known in this
field.
The count output of the second counter circuit 14 is also connected
to a first input of a coincidence gate 18 having a second input which is
supplied from a distance setting unit 19 in a coded form. The coincidence ~-
output of the coincidence gate 18 is connected to one input of an OR gate 20
having an output connected to the beam modulating electrode 5 of the cathode-
ray tube 1.
The second pulse output 17 of the first counter circuit 13 is
connected to the "set" input S of a flip-flop circuit 21 and the first pulse
output 16 is also connected to the ~'reset~ input R thereof. The output of
20 the flip-flop circuit 21 is connected to a reversible counter circuit 22 as
its control input. The output of the reference pulse oscillator 15 is also
connected to the input of the reversible counter circuit 22 and the counter
22 counts the clock pulses from the oscillator 15 under control of the output
of the flip-flop circuit 21 and produces a count output in a coded form.
The flip-flop circuit 21 is arranged to be set in the 'lhigh" state
, ~
by the pulse from the second pulse output 17 of the first counter circuit 13
and produce a high level output~ and to be reset to the "low" stage by the
pulse from the first pulse output 16 of the same counter 13 and produce a low
level output, and the reversible counter circuit 22 is arranged to execute an
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addition operation in response to the low level output of the flip-flop
circuit 21 and a subtraction operation in response to the high level output
thereof. It will be understood from the above arrangement that the reversible
counter circuit 22 executes the addition operation during the first half of
the scan cycle of the display screen 2 and the subtraction operation during
the remaining half thereof.
The count output of the reversible counter circuit 22 is connected
to one input of a second coincidence gate 23, another input of which is
supplied from a subtraction circuit 24. The subtraction circuit 24 has two
inputs, one connected to a tilt control unit 25 and another connected to a
reference angle setting unit 26. The tilt control unit 25 is arranged to
control the tilt angle ~ o~ the directivity of the transducer 27 of the
transmitter and receiver at a predetermined value and produce tilt angle
information in a coded form. The reference angle setting unit 26 is arranged
to produce a coded output corresponding to a predetermined reference angle
which is preset therein. The subtraction circuit 24 is arranged to subtract
the tilt angle supplied by the tilt control unit 25 from the reference angle
supplied by the reference angle setting unit 26 and produce a difference out-
put in a coded form. The coincidence output of the coincidence gate 23 is
; 20 connected to a pulse generator circuit 28 as a control input.
The directivity of the transducer 27 has for practical purposes some
width or deviation as shown by angleJ~, and the pulse generator circuit 28
and a tilt range setting unit 29 are provide~ for indicating this width on
the screen 2. In addition to the input from the coincidence gate 23, the
pulse generator circuit 28 is supplied, as a reference input, with the clock -~
- pulses from the reference pulse oscillator 15. The pulse generator circuit
28 is arranged to produce a pulse having a duration corresponding to the
above angle ~ based upon the reference clock pulses and forward it to another
input of the OR gate 20 under control of the output of the coincidence gate 23.
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The tilt range setting unit 29 has a control input supplied from the second
pulse output 17 of the first counter circuit 13 and is arranged to produce a
coded output corresponding to the preset angle ~and forward it to the
reversible counter 22 under control of the pulse from the counter 13. The
reversible counter 22 is also arranged to subtract this output from its
content when it is supplied.
Now~ the operation of the device of Figure 1 will be described with
reference to Figures 2 and 3. As an aid in understanding, the above-mentioned
reference count is assumed as 360, whereby one degree of scan angle corresponds
to one count of the reference clock pulses. The tilt angle ~ and the tilt
range ~ are also assumed as 30 degrees and 10 degrees. These values are
previously set in the first counter circuit 13, reference angle setting unit
26, pulse generator circuit 28 and tilt range setting unit 29, as described
above.
The train of clock pulses sent out from the reference pulse
oscillator is counted by the first counter circuit 13 and the counter circuit
13 produces an output pulse every 360 counts from its first pulse output 16.
As the sine and cosine wave generators 11 and 12 are arranged to produce sine
and cosine wave signals having periods corresponding to the 360 count of the
first counter circuit 13, the cycle of scan of the cathode ray tube 1 is
repeated every 360 counts and one degree of scan angle corresponds to the
period of the reference clock pulses. As the second counter circuit 14 counts
the pulses from the first counter circuit 13 and the sine and cosine wave
generators 11 and 12 are also arranged to make the amplitude of the sine and
cosine waves proportional to the count of the second counter 14, the diameter
of the scanning circle increases step by step at the end of every scan cycle
and, consequently, the display screen 2 of the cathode ray tube 1 is scanned
by a number of concentric circular arcs as shown in Figure 2
The first coincidence gate 18 compares the count output of the second
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counter circuit 14 with the output of the distance setting unit 1~ and
forwards the output through the OR gate 20 to the beam modulating electrode 5
of the cathode ray tube 1 when coincidence is obtained therebetween. This
results in luminescence of a specific scanning circle which corresponds to the
count output of the counter 14 at that time and which in turn corresponds to
the distance previously se~ in the distance setting unit 19. As shown in
Figure 3, this bright circle 31 can be put on a specific object 32 displayed
on the screen 2 by adjusting the preset value of the distance setting unit 19.
The straight or true distance of the object 32 can be obtained from the
intersection of this circle 31 and the orthogonal reference axis X or Y
having a calibrated distance graduation
As described previously, the reversible counter circuit 22 executes
addition and subtraction operations alternatingly every half cycle of scan,
that is, every 180 counts of the reference clock pulses. As the counter
circuit 22 also counts the s~me clock pulses from the clock pulse oscillator
15, the count output of the counter 22 increases from zero to 180 and then
decreases from 180 to zero during one cycle of scan. It will be understood
that the count of the counter circuit 22 corresponds to the circumferential
angle measured upwardly from the radius OY which corresponds to the zero
count of the counter 22.
However, the tilt angle ~ of this embodiment is measured downwardly ;~
from the horizontal plane and is preferably indicated on the screen 2 with
reference to the horizontal axis X. The subtraction circuit 24 is provided -
for this purpose to produce a complementary angle of the tilt angle-~. In
` order to obtain a desired result, the angle to be set in the reference angle
` setting unit 26 is selected as 90 - ~ , where the angle ~ is the abovementioned
- tilt width or tilt range. ~n this example, 90 - 10/2 = ~5 is previously
~ set in the unit 26 which in turn produces a corresponding coded output. As
;~- the tilt control unit 25 produces an output corresponding to the preselected ~
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tilt angle, 30 , in this example, the 9ubtraction circuit 24 execute an
operation of 85 - 30 = 55 . As the angle of 55 corresponds to the count
of 55 pulses in the reversible counter circuit 22, the coincidence gate 23
produces its coincidence output at a radius 33, which makes an a~gle of 55
with respect to the reference line oY as shown in Figure 3, on every scan
line, during the first half of the scan cycle.
At the beginning of the remaining half of the scan cycle, however,
the first counter circuit 13 forwards a pulse from its second pulse output ;~
17 to the tilt range setting unit 29 and the unit 29 feeds its output, the
preset angle ~ = 10 , to the reversible counter circuit 22 in response to
this pulse. The counter circuit 22 subtracts this angle from its content,
180, and initiates its reverse counting action from 170. Accordingly, the
count of 55 is reached earlier by 10 pulses at a radius 34~ which makes an
angle of 65 with respect to the reference line OY', as shown in Figure 3.
Thus, the coincidence gate 23 produces its coincidence output at the radius
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34" on every scan line during the remaining half of the scan cycle.
The pulse generator circuit 28, which is arranged to produce a
pulse having a duration corresponding to the tilt range, ~ = 10 , in response
to the output f-rom the coincidence gate 23, supplies its output continuously
through the OR gate 20 to the beam modulating electrode 5 of the cathode ray
tube 1 during the time interrals from the radius 33 to 34 and from the radius
, 34' to 33' of e~ery scan cycle. This results in 11~;nous indication of two
9 symmetric sectorial domains between these radii as shown by the shadowed areas
in the drawing.
As readily understood from the above description, two symmetric
radii 35 and 35~ which represent the tilt angle ~ can be luminously indicated
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j on the screen 2 by setting zero as the tilt range ~ in the units 26, 28, and
29, and that the requested horizontal distance and vertical depth of the
object can be obtained visibly as the X and Y ~o-ordinates s and d,
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respectively, of the intersection of the luminous circle 31 and the radius 35
as shown by the drawing. In the case of indicating the tilt range 0, the
errors of the values s and d are also obtainable from the circle 31 and the
radii 33 and 34.
It is also understood that, when the device has no need for the
tilt range indication, it can be simplified by omitting the units 28 and 29
and connecting the output of the coincidence gate 23 directly to the OR gate
20 and, moreover, when the tilt control unit 25 is arranged to produce the
complement of the tilt angle, the units 24 and 26 are also omittable.
Although the above description was made in conjunction with an
embodiment in sonar system, it should be noted that this invention is
. applicable also to various systems other than the sonar system provided that
these systems utilize circular scanning as shown in Figure 2.
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