Note: Descriptions are shown in the official language in which they were submitted.
34~2
SURV~ILLANCE S~ST~ 5
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BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a surveillance
system and, more particularly, to a surveillance system
utilizing radiation such as ultrasonic waves.
(2) Prior Art of the Invention
In recent years, radiation such as ultrasonic waves
has been utilized in a surveillance system which generates an
alarm signal when an unauthorized person enters into an area
under surveillance.
One conventional surveillance system utilizes
Doppler effect. According to this system, ultrasonic waves
having a predetermined frequency are continuously launched into
an area under surveillance which may be in a room, and when
frequency components different from said predetermined frequency
are detected in reflections by objects in the area under
surveillance, the presence of an unauthorized person in the area
under surveillance is detected so that an alarm such as a
buzzer is energized. That is, such a system utilizes Doppler
effect in which the frequency of reflections by an object which
approaches an ultrasonic wave emitter increases, while the
frequency of reflections by an object which moves away from
the ultrasonic wave emitter decreases.
However, in the above-mentioned conventional
system, when the air, in the area under Surveillance
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changes due to the presence of a draft, the operation of an
air conditioner or the like, an object, such as a curtain,
is swayed, the alarm may be activated. Therefore, in order
to prevent the alarm from being erroneously operated,
special circuits which are complex and costly are required.
In addition, the detection sensibility of a receiver must
be adjusted in accordance with the conditions of an area
under surveillance. Furthermore, it is difficult for an
area under surveillance to be established out in the open
in which there may be many various kinds of noises.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to
provide a surveillance system capable of being reliably
operated even when the air in the area under surveilance
changes.
It is another object of the present invention to
provide a surveillance system which requires no adjustment
of the detection sensibility in accordance with the
conditions of an area under surveillance.
It is still another object of the present invention to
provide a surveillance system which can be used in an area
under surveillance established out in the open.
According to the present invention, there is provided
a surveillance system for detecting an unauthorized object
or person in an area under surveillance, comprising: means
for transmitting a radiation energy signal, intermittently,
to the area under surveillance; means or receiving
reflections from the area under surveillance and converting
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analog signals of the reflections lnto digital signals;
means, connected to the receiving means, for storing the
digital signals for a predetermined time; means, connected
to the storin~ means, for forming a reference pattern from
si,~ ntl 1~
the digital ~ stored in the storing means; and means,
connected to the receiving means and the reference pattern
forming means, for comparing a pattern o~ reflections from
the receiving means with the reference pattern of the
reference pattern forming means and for activating an alarm
when the pattern of reflections and the reference pattern
are different.
The present invention will be more clearly understood
from the description as set forth below with reference to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block circuit diagram illustrating an
embodiment of the surveillance system according to the
present invention, and
Figs. 2A through 2D are timing diagrams of the signals
appearing in the circuit of Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Fig. 1, which illustrates an embodiment
of the surveillance system according to the present
invention, the transmitting operation of an ultrasonic
emitter-receiver (hereinafter referred to as an ultrasonic
element) 1 is controlled by a transmitter circuit 2.
Ultrasonic waves emitted from the ultrasonic element 1 are
reflected by desks, shelves and walls in an area under
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surveillance, and are again received by the ultrasonic
element 1. The reflections which are received by the
element 1 are converted into digital signals by a receiver
circuit 3, and are transmitted to an operation processiny
circuit 4. In the operation processing circui-t 4, a
reference pattern i5 prepared in advance based on patterns
of reflections collected by the receiver circuit 3, and
when an area is under surveillance, a pattern of reflec-
tions responsive to the conditions in the area under
surveillance is compared statistically with the reference
pattern. When the two patterns are statistically differentJ
the operation processing circuit 4 energizes an alarm 5
such as a buzzer.
Figs. 2A through 2D are timing diagrams of the signals
appearing in the circuit of Fig. 1. Referring to Figs. 2A
throuyh 2D, the circuit of Fig. 1 will now be explained in
more detail.
In the transmitter circuit 2, an oscillator 21
generates a signal "a" the frequency of which is, for
example, 25 through 50 kH~, as illustrated in Fig. 2A, and
a pulse oscillator 22 generates a pulse-shaped signal "b"
haviny a re~etition period T of the order of, for example,
100 milliseconds and a duration time T of the order of, for
example, several milliseconds, as illustrated in Fig~ 2B.
Therefore, a modulator 23 transmits a signal "c", as
illustrated in Fig. 2C, to the ultrasonic element 1, so
that the ultrasonic element 1 emits ultrasonic waves
intermittently, that is, pulse-shaped ultrasonic waves,
~3~2
towards the area under survei:Llance. The ultrasonic waves are
reflected by desks, shelves and walls in the area under
surveillance. A large number of reflectlons are superposed and
are again received by the element 1 which, in turn, generates
an electrical signal "d".
In the receiver circuit 3, the signal "d" is amplified
by an amplifier 31 and, after that, is rectified by a rectifier
32 for amplitude-modulated detection. In addition, an output
signal of the rectifier 32 is smoothed by a smoothing circuit
33 to form a signal "dl" of which is converted into a digital
- signal "e" by an analog/digital converter 34. In the analog/
digital converter 34, the analog signal "dl" is sampled by
using clock pulses generated from a clock oscillator 35.
The operation processing circuit 4 comprises a buffer
memory 42 for storing the digital signals "e", an address
generator 43 for indicating an address location of the buffer
memory 42. In addition, the circuit 4 comprises a mean value
calculator circuit 44 for calculating mean values of data stored
in the buffer memory 42 at each sampling point and a memory 45
for storing the calculated results by the circuit 44, which
results form a mean value pattern as a reference pattern.
Further, the circuit 4 comprises a standard de~iation calculator
circuit 46 for calculating standard values of data stored in
the buffer memory 42 at each sampling point and a memory 47 for
storing the calculated results by the circuit 46, which results
form a standard deviation pattern as a reference
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pattern. That is, the reference pattern includes two
patterns, i.e., the mean value pattern and -the standard
deviation pattern. It should be noted tha-t a reference
pattern forming means is comprised of the elements 44
through 47.
Furthermore, the operation processing circuit 4
comprises a comparing means which is comprised of a
difference computing circuit 48 and a discrimination
c~rcuit 49. The diffe~ence computing circuit 48 calculates
a difference between a first digital value of the signal "e"
and a second digital value stored in the memory 45 the
address location of which corresponds to the sampling point
of the first digital value and is indicated by the address
generator 43. The discrimination circuit 49 compares the
value of the difference computing circuit 48 wi-th a third
digital value stored in the memory 47 the address location
of which also corresponds to said sampling point, When the
absolute value of the difference value is larger than the
third digital value, the circuit 49 energizes the alarm 5.
The fonmation of a reference pattern will now be
explained based upon reflections in accordance with the
area under surveillance when there is no person present.
First, a counter 24 of the transmitter circuit 2 is reset
by a reset signal R, so that the counter 24 begins to count
pulses of the signal "b" generated from the pulse oscillator
22. The value of the counter 24 is compared with a
predetermined value N by a comparator 25. In this case,
when the value of the counter 24 is smaller than the
i3~
predetermined value N, the comparator 25 generates a high
potential signal, while, when -the value of the counter 24 is
equal or larger than the predetermined value N, the comparator
25 generates a low potential signal. As a result, in the
operation processing-circuit 4, gates 41-1 and 41-2 are opened
and closed, respec~ively, with regard to the digital signal "e"
from the receiver circuit 3 for a predetermined period of time
after the counter 24 of the transmitter circuit 2 is reset.
Therefore, the data of the digital signal "e" is stored via the
gate 41-1 in the buffer memory 42 at an address location
_ indicated by the address generator 43 which is controlled by the
pulse oscillator of the transmitter circuit 2 and by the clock
oscillator 35 of the receiver circuit 3. Thus, a plurality of
patterns of reflections of a predetermined number of samples
lS are stored in the buffer memory 42. The operation for storing
patterns :is completed when the value of the counter 24 has
reached the predetermined value. Thereafter, mean values of
the data stored in the buffer memory 42 are calculated by a mean
value calculator circuit 44 for each sampling point, and the
calculated results are stored in the memory 45. In addition,
standard deviation values of the data stored in the buffer
memory 42 are calculated by a standard deviation calculator
circuit 46 for each sampling point, and the calculated results
are stored in the memory 47.
It should be noted that the above-mentioned reference
patterns can be renewed at any time when a reset signal R
~L~L5~
is applied to the coul~ter 24 of the transmitter circuit 2.
On the other hand, when an area is under surveillance,
the gates 41-1 and 41-2 are closed and opened, respectively,
for the digital siynal "e", since the comparator 25 generates
a high potential signal. Therefore, the digital signal "e"
is supplied to an input of the difference computing circuit 48
via the gate 41-2, while another input of the circuit 48 is
supplied with a mean value stored at a corresponding address
location of the memory 45 which is indicated by the address
generator 43. The difference between the two values is compared
_ with a standard deviation value stored at a corresponding
address location of the memory 47 which is also indicated by the
address generator 43. When the difference is equal or larger
than the standard deviation value, the discrimination circuit
49 energizes the alarm 5. Thus, when the pattern of reflection
is statistically different from the reference pattexn, the
alarm 5 is energized. For example, as illustrated in Fig. 2D
in which a solid line represents the reference pattern (mean
value pattern), the alarm 5 is energized when a portion
lndicated by an arrow X or Y is present in the pattern of
reflections due to the presence of an unauthorized person who
enters in the area under surveillance. ~;~
In the above-mentioned embodiment, ultrasonic waves
are used. However, it should be noted that other radiation
energy signals such as sonic waves or electromagnetic waves
including ligh~ can be used. For example, in case of sonic
waves, a phone generator and a phone receiver can be used
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3~
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instead of the ultrasonic emitter-receiver 1. In addition,
in case of light, photodiodes or phototransistors can be
used ïnstead of the ultrasonic emitter-receiver 1.
Further, in the above-mentioned embodiment, a
reference pattern is unchangeable unless a reset signal R
is supplied to the counter 24. However, the reference
pe~ ~"~`r ,~
pattern can be ~5R~ ~Ls~}~ renewed based on a pre-
determined number of new patterns. In this case, the
counter 24, the comparator 25 the gates 41-1 and 41-2 are
omitted so that the data s-tored in the buffer memory 42 are
per,;o~, c~
also s~a437~sT~y renewed.
The surveillance system according to the present
invention has such advantages, as compared with the
conventional system, that the system can be reliably
operated even when the air in the area under surveillance
fluctuates; adjustment of the detection sensibility is
unnecessary; and the system can be reliably operated even
out in the open air. This is because a reference pattern
including a mean value pattern and a standard deviation
pattern is formed in accordance with the conditions in an
area under surveillance. For example, when the fluctuation
of the air in the area under surveillance is large or the
area under surveillance is established in the open air,
standard deviation values in the re~erence pattern are
relatively large.
