U.S. patent application number 11/510839 was filed with the patent office on 2007-03-01 for transmitting apparatus, sound sensor and autonomous traveling vehicle.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Tatsuya Hirose, Tomoyoshi Tokumaru.
Application Number | 20070046145 11/510839 |
Document ID | / |
Family ID | 35050380 |
Filed Date | 2007-03-01 |
United States Patent
Application |
20070046145 |
Kind Code |
A1 |
Tokumaru; Tomoyoshi ; et
al. |
March 1, 2007 |
Transmitting apparatus, sound sensor and autonomous traveling
vehicle
Abstract
A driving circuit of a transmitting apparatus drives a
piezoelectric element in a frequency band different from a
resonance frequency at which a vibration system including the
piezoelectric element resonates the most strongly. A driving
circuit of a sound sensor drives the piezoelectric element for
transmitting or receiving an acoustic wave in a frequency band
different from a resonance frequency at which a vibration system
including the piezoelectric element resonates the most strongly.
Such a transmitting apparatus is mounted as a transmitting
apparatus of a sound sensor to thereby realize the sound sensor
with a small measurement error. The sound sensor is adopted for
traveling control and steering control of an autonomous traveling
vehicle to thereby enable an autonomous traveling vehicle capable
of stopping in the vicinity of an obstacle to be realized.
Inventors: |
Tokumaru; Tomoyoshi; (Osaka,
JP) ; Hirose; Tatsuya; (Osaka, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
Moriguchi City
JP
|
Family ID: |
35050380 |
Appl. No.: |
11/510839 |
Filed: |
August 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11045144 |
Jan 31, 2005 |
7098579 |
|
|
11510839 |
Aug 28, 2006 |
|
|
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Current U.S.
Class: |
310/317 |
Current CPC
Class: |
G05D 2201/0203 20130101;
B06B 1/0238 20130101; G05D 1/0255 20130101; G01S 15/931
20130101 |
Class at
Publication: |
310/317 |
International
Class: |
H01L 41/09 20070101
H01L041/09 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2004 |
JP |
2004-104391 |
Claims
1. A transmitting apparatus comprising: a piezoelectric element;
and a driving circuit for driving said piezoelectric element to
transmit an acoustic wave; wherein said driving circuit drives said
piezoelectric element in a frequency band different from a
resonance frequency at which a vibration system including said
piezoelectric element resonates the most strongly.
2. A sound sensor comprising: a transmitting apparatus including a
piezoelectric element, and a driving circuit for driving said
piezoelectric element to transmit an acoustic wave; a receiving
apparatus including a receiver for receiving a reflected wave, from
a detection-target object, of an acoustic wave transmitted by said
transmitting apparatus; and a processing circuit for acquiring
information on said detection-target object on the basis of an
elapsed time till the time when said receiver of said receiving
apparatus receives the reflected wave from the time when said
transmitting apparatus transmits an acoustic wave; wherein said
driving circuit drives said piezoelectric element in a frequency
band different from a resonance frequency at which a vibration
system including said piezoelectric element resonates the most
strongly.
3. An autonomous traveling vehicle comprising: a sound sensor, for
detecting a detection-target object, including: a transmitting
apparatus having an piezoelectric element and a driving circuit for
driving said piezoelectric element in a frequency band different
from a resonance frequency at which a vibration system including
said piezoelectric element resonates the most strongly to transmit
an acoustic wave; and a receiving apparatus having a receiver for
receiving a reflected wave from said detection-target object of an
acoustic wave transmitted from said transmitting apparatus; a
processing circuit for acquiring information on said
detection-target object on the basis of an elapsed time tin the
time when said receiver of said receiving apparatus receives the
reflected wave from the time when said transmitting apparatus
transmits an acoustic wave; and a control circuit for performing
traveling control and steering control on the basis of information
on said detection-target object acquired by said processing
circuit.
4. The autonomous traveling vehicle as set forth in claim 3, having
a function as a cleaner, wherein said traveling control and
steering control by said control circuit is performed so as to
travel on routes, in parallel with one pair of walls of a
rectangular room facing and in parallel to each other, at
predetermined intervals between adjacent routes in a direction
along the other pair of walls facing and in parallel to each other,
in a zigzag pattern.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No. 2004-104391 filed in
Japan on Mar. 31, 2004, the entire contents of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a transmitting apparatus and a
sound sensor for obtaining information such as the presence/absence
of a detection-target object with an acoustic wave, or a distance
therefrom to the detection-target object, and further relates to an
autonomous traveling vehicle equipped with such a sound sensor.
[0004] 2. Description of Related Art
[0005] Conventionally, there has been known an ultrasonic sensor
that transmits an ultrasonic wave to a detection-target object and,
also, receives a reflected wave from the detection-target object to
thereby measure a distance therefrom to the detection-target object
on the basis of an elapsed time from a transmission start time
point to a reception start time point.
[0006] As a kind of such an ultrasonic sensor, there has been known
an ultrasonic sensor comprising a transmitting apparatus including:
a transmitter which includes a piezoelectric element and transmits
an ultrasonic wave; a driving circuit which drives the
piezoelectric element; and an oscillation circuit which inputs an
oscillation signal in a predetermined frequency band to the driving
circuit, and a receiving apparatus including: a receiver which
includes a piezoelectric element and receives an ultrasonic wave; a
sensing circuit which senses an ultrasonic wave in a predetermined
frequency band on the basis of an electric signal generated as
determined by a vibration of the piezoelectric element caused by
the action of the ultrasonic wave; and a signal processing unit
which performs processing for obtaining information on a
detection-target object on the basis of the electric signal (see,
for example, Japanese Patent Application Laid-Open No. 10-290495
(1998)).
[0007] The transmitter of the ultrasonic sensor described above has
a case in the shape of a hollow cylinder with a bottom working as a
vibration plate, to the inner surface of which a piezoelectric
element is adhered. The driving circuit of the same vibrates the
piezoelectric element at a predetermined resonance frequency band
by applying a voltage to the piezoelectric element on the basis of
an oscillation signal from the oscillation circuit. The resonance
frequency band by which the piezoelectric element is vibrated is
regarded as a resonance frequency at which a vibration system
including the piezoelectric element resonates the most strongly and
in which an ultrasonic wave is transmitted with a large amplitude
of the vibration plate in resonance.
[0008] The ultrasonic wave transmitted from the transmitter is
reflected by a detection-target object and received by the
receiver. The ultrasonic wave received by the receiver is converted
to an electric signal and the electric signal is signal-processed
at the signal processing unit to thereby determine a distance
therefrom to the detection-target object.
[0009] A conventional ultrasonic sensor as mentioned above, as
shown in timing charts of FIG. 1A to FIG. 1C, has a slow rise of
acoustic pressure of a transmitted ultrasonic wave until a
vibration system including the piezoelectric element resonates in a
stable state from the time when a voltage is applied to the
piezoelectric element, for which transition a time T1 elapsed.
[0010] To be concrete, the time T1 elapsed until the vibration
system including the piezoelectric element resonates in a stable
state, as shown in an output waveform of the transmitter of FIG.
1B, from the time when a voltage is applied to the transmitter, as
shown in an output waveform of the driving circuit of FIG. 1A.
[0011] In a case where an ultrasonic wave with such a slow rise of
acoustic pressure is received by the receiver, a time delay arises
until the time when an acoustic pressure of the ultrasonic wave
rises to a predetermined acoustic pressure from the time when the
ultrasonic wave actually reaches the receiver. Since a
configuration is such that determination on whether or not an
ultrasonic wave has been received is performed by whether or not an
electric signal obtained by converting an acoustic pressure of the
received ultrasonic wave exceeds a predetermined threshold value, a
measurement error arises as a time T2, shown in an input waveform
of the receiver on FIG. 1C, elapsed until the input waveform
exceeds a predetermined threshold value from the time when the
ultrasonic wave starts to be received. The conventional sound
sensor has had an unsolved problem that a measurement error, to be
concrete, the time T2 shown in FIG. 1C, indispensably arises due to
such a slow rise of acoustic pressure of an ultrasonic wave.
BRIEF SUMMARY OF THE INVENTION
[0012] The present inventors conducted researches including
experiments with serious efforts for the purpose of decreasing a
measurement error revealed as a time T2 shown in FIG. 1C mentioned
above. Through the research, the present inventors have found that
a response time of a vibration system including a piezoelectric
element is reduced in a case where a frequency which drives the
piezoelectric element is set to a frequency different from a
frequency at which the vibration system including the piezoelectric
element resonates the most strongly, which is dissimilar to that in
a conventional way, to thereby cause a steep rise of acoustic
pressure of an ultrasonic wave transmitted by the vibration system,
with the result that the time T2 shown in FIG. 1C can be greatly
reduced, that is, the measurement error can be considerably
reduced.
[0013] The invention has been made on the basis of the knowledge
and findings mentioned above, and aims to provide a transmitting
apparatus and a sound sensor capable of realizing a steep rise of
sound pressure of an acoustic wave by adopting a configuration in
which a piezoelectric element is driven in a frequency band
different from a resonance frequency at which a vibration system
including the piezoelectric element resonates the most
strongly.
[0014] The invention also aims to provide a sound sensor having a
small measurement error by adopting a configuration in which a
piezoelectric element is driven in a frequency band different from
a resonance frequency at which a vibration system including the
piezoelectric element commonly used in transmission/reception of an
acoustic wave resonates the most strongly.
[0015] The invention further aims to provide an autonomous
traveling vehicle capable of stopping in the vicinity of, for
example, a detection-target object by comprising the sound
sensor.
[0016] A transmitting apparatus according to a first aspect of the
invention is a transmitting apparatus comprising: a piezoelectric
element; and a driving circuit for driving the piezoelectric
element to transmit an acoustic wave; characterized in that the
driving circuit drives the piezoelectric element in a frequency
band different from a resonance frequency at which a vibration
system including the piezoelectric element resonates the most
strongly.
[0017] In the transmitting apparatus according to the first aspect
of the invention, the driving circuit applies to the piezoelectric
element a voltage that alters in a frequency band different from a
resonance frequency at which a vibration system including the
piezoelectric element resonates the most strongly. Since the
piezoelectric element vibrates by applying a voltage from the
driving circuit, an acoustic wave is transmitted. By driving the
piezoelectric element in a frequency band different from a
resonance frequency at which the vibration system including the
piezoelectric element resonates the most strongly, a response time
of the vibration system becomes shorter and a rise of acoustic
pressure of an acoustic wave becomes steep as compared with a case
where the piezoelectric element is driven in frequency at which the
vibration system including the piezoelectric element resonates the
most strongly.
[0018] A sound sensor according to a second aspect of the invention
is a sound sensor comprising: a transmitting apparatus including a
piezoelectric element, and a driving circuit for driving the
piezoelectric element to transmit an acoustic wave; a receiving
apparatus including a receiver for receiving a reflected wave, from
a detection-target object, of an acoustic wave transmitted by the
transmitting apparatus; and a processing circuit for acquiring
information on the detection-target object on the basis of an
elapsed time till the time when the receiver of the receiving
apparatus receives the reflected wave from the time when the
transmitting apparatus transmits an acoustic wave; characterized in
that the driving circuit drives the piezoelectric element in a
frequency band different from a resonance frequency at which a
vibration system including the piezoelectric element resonates the
most strongly.
[0019] In the sound sensor according to the second aspect of the
invention, the driving circuit of the transmitting apparatus drives
the piezoelectric element in a frequency band different from a
resonance frequency at which the vibration system including the
piezoelectric element resonates the most strongly to thereby
transmit an acoustic wave from the transmitting apparatus. Since an
elapsed time till the vibration system including the piezoelectric
element resonates in a stable state becomes shorter than a case
where the piezoelectric element is driven in a resonance frequency
at which the vibration system including the piezoelectric element
resonates the most strongly, a rise of acoustic pressure of a
transmitted acoustic wave becomes steep. An acoustic wave reflected
by a detection-target object is received by the receiving apparatus
and converted to an electric signal, which is, for example,
processed in order to detect a distance therefrom to the
detection-target object.
[0020] An autonomous traveling vehicle according to a third aspect
of the invention is an autonomous traveling vehicle characterized
by comprising: a sound sensor, for detecting a detection-target
object, including: a transmitting apparatus having an piezoelectric
element and a driving circuit for driving the piezoelectric element
in a frequency band different from a resonance frequency at which a
vibration system including the piezoelectric element resonates the
most strongly to transmit an acoustic wave; and a receiving
apparatus having a receiver for receiving a reflected wave from the
detection-target object of an acoustic wave transmitted from the
transmitting apparatus; a processing circuit for acquiring
information on the detection-target object on the basis of an
elapsed time till the time when the receiver of the receiving
apparatus receives the reflected wave from the time when the
transmitting apparatus transmits an acoustic wave; and a control
circuit for performing traveling control and steering control on
the basis of information on the detection-target object acquired by
the processing circuit.
[0021] In the autonomous traveling vehicle according to the third
aspect of the invention, the autonomous traveling vehicle transmits
an acoustic wave from the transmitting apparatus and receives the
acoustic wave reflected by a detection-target object with the
receiving apparatus. The received acoustic wave is converted to an
electric signal and then processed, for example, to measure a
distance therefrom to the detection-target object. The distance to
the measured detection-target object is processed as one of control
information for controlling autonomous traveling.
[0022] An autonomous traveling vehicle according to a fourth aspect
of the invention is, in the third aspect, characterized by having a
function as a cleaner, and characterized in that the traveling
control and steering control by the control circuit is performed so
as to travel on routes, in parallel with one pair of walls of a
rectangular room facing and in parallel to each other, at
predetermined intervals between adjacent routes in a direction
along the other pair of walls facing and in parallel to each other,
in a zigzag pattern.
[0023] In the autonomous traveling vehicle according to the fourth
aspect of the invention, since the autonomous traveling vehicle
according to the third aspect of the invention has a function as a
cleaner, the autonomous traveling vehicle travels on routes along
one pair of walls of a rectangular room facing and in parallel to
each other, so as to travel forward on one route and then backward
on the next route to thereby perform cleaning.
[0024] According to the transmitting apparatus of the first aspect
of the invention, a response time becomes shorter, a rise of
acoustic pressure of an acoustic wave becomes steep, so that a
measurement error generated in an input waveform of the receiver
becomes smaller as compared with a case where the piezoelectric
element is driven in a resonance frequency at which the vibration
system including the piezoelectric element resonates the most
strongly.
[0025] According to the sound sensor of the second aspect of the
invention, since an elapsed time until an acoustic pressure of an
acoustic wave received by the receiving apparatus takes a
predetermined value from the time when the acoustic wave reaches
the receiving apparatus becomes shorter, an elapsed time until the
acoustic wave actually exceeds a threshold value for use in
determination of having detected from the time when the acoustic
wave actually reaches the receiving apparatus becomes shorter,
which makes a measurement error smaller.
[0026] According to the autonomous traveling vehicle of the third
aspect of the invention, since a measurement error of the sound
sensor becomes smaller to thereby enable a distance therefrom to
the detection-target object with a high accuracy, an event in which
the vehicle collides with the detection-target object because of a
delay in control for stoppage is prevented from occurring.
[0027] According to the autonomous traveling vehicle of the fourth
aspect of the invention, since the autonomous traveling vehicle of
the third aspect of the invention, in a case where being configured
as a cleaner, can perform cleaning a rectangular room while
traveling routes along one pair of walls of the rectangular room
facing and in parallel to each other, so as to travel forward on
one route and then backward on the next route, the floor surface of
the room is cleaned at every part thereof to thereby enable
portions near walls where dust is easy to be gathered in the room
to be cleaned with certainty.
[0028] The above and further objects and features of the invention
will more fully be apparent from the following detailed description
with accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0029] FIG. 1A, FIG. 1B and FIG. 1C are timing charts for
illustrating operations of a conventional ultrasonic sensor;
[0030] FIG. 2 is a block diagram showing a schematic configuration
of a first embodiment of an ultrasonic sensor according to the
invention;
[0031] FIG. 3 is a graph showing a relationship between an acoustic
pressure and a frequency of an acoustic wave transmitted from a
transmitter;
[0032] FIG. 4A, FIG. 4B and FIG. 4C are timing charts for
illustrating operations of an ultrasonic sensor according to the
invention;
[0033] FIG. 5 is a block diagram showing a schematic configuration
of an ultrasonic sensor of a second embodiment;
[0034] FIG. 6 is a block diagram schematically showing a functional
configuration of an autonomous traveling cleaner as one embodiment
of the autonomous traveling vehicle according to the invention
equipped with the ultrasonic sensor according to the invention;
and
[0035] FIG. 7A, FIG. 7B and FIG. 7C are descriptive illustrations
showing traveling loci of an autonomous traveling vehicle according
to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Detailed description will be given of the invention below on
the basis of the accompanying drawings showing preferred
embodiments thereof. FIG. 2 is a block diagram showing a schematic
configuration of a first embodiment of an ultrasonic sensor
according to the invention.
[0037] An ultrasonic sensor according to the invention, as shown in
FIG. 2, is, roughly speaking, constituted of a transmitting
apparatus 1 according to the invention and a receiving apparatus 2
and further includes a signal processing unit 30. Such a ultrasonic
sensor according to the invention is basically configured so that
an acoustic wave is transmitted from the transmitting apparatus 1,
the acoustic wave reflected by a detection-target object is
received by the receiving apparatus 2, whereby a distance therefrom
to the detection-target object is detected on the basis of an
elapsed time until a reception time point from a transmission time
point of the acoustic wave.
[0038] The transmitting apparatus 1 comprises a timing circuit 10,
a driving circuit 11, a boosting circuit 12 and a transmitter 13.
The timing circuit 10 outputs a trigger signal to the driving
circuit 11 at predetermined intervals. The driving circuit 11
includes a built-in oscillator 11a, and outputs an oscillation
signal of a frequency "f", which is outputted by the oscillator
11a, in synchronism with the trigger signal given from the timing
circuit 10 to the boosting circuit 12 only for a predetermined time
width. The boosting circuit 12 boosts a voltage of the oscillation
signal given from the driving circuit 11 and outputs to the
transmitter 13. The transmitter 13 applies the voltage boosted by
the boosting circuit 12 to a built-in piezoelectric element 13a.
The piezoelectric element 13a vibrates corresponding to the
frequency "f" of the applied voltage and transmits an acoustic
wave.
[0039] Note that in the first embodiment, the transmitter 13 in use
was a piezoelectric buzzer (MR-18) manufactured by NIHON CERATEC
CO., LTD. FIG. 3 is a graph showing a relationship between an
acoustic pressure and a frequency of an acoustic wave transmitted
by the transmitter 13.
[0040] The transmitter 13 is, as shown in FIG. 3, configured so as
to enable an acoustic wave of a frequency in the range from near
100 Hz to near 100 kHz to be transmitted. In the conventional
technology, a transmitter for driving a piezoelectric element in a
resonance frequency band is configured so as to have a sharp
frequency characteristic such that an acoustic pressure is
attenuated by 20 dB or more in frequency bands outside a range
.+-.5 kHz of a resonance frequency at which an acoustic pressure is
maximized. In the first embodiment of the invention, however, the
transmitter 13 has, as shown in FIG. 3, frequency bands smaller in
acoustic pressure by 10 and a few dB outside a range .+-.5 kHz of a
resonance frequency (4.4 kHz) at which an acoustic pressure is
maximized by the strongest resonance of a vibration system
including the piezoelectric element 13a. The transmitter 13, as
shown in FIG. 3, further has frequency bands in each of which an
acoustic pressure becomes larger at about 17 kHz, about 32 kHz and
about 50 kHz. The magnitudes of each acoustic pressure are only to
be larger by 10 and a few dB than the surrounding frequency bands;
therefore, the transmitter 13 of the invention is configured so as
to have a more gently-sloping frequency characteristic, as compared
with a transmitter in the conventional technology in which a
piezoelectric element is driven in a resonance frequency band.
[0041] A value of a frequency "f" of an oscillation signal
outputted from the oscillator 11a is set to a frequency different
from a resonance frequency at which the vibration system including
the piezoelectric element 13a resonates the most strongly and, to
be concrete, set to a frequency in the vicinity of 50 kHz.
[0042] The receiving apparatus 2 includes a receiver 20, an
amplifier 21, a band pass filter (BPF) 22, a detection circuit 23
and a comparator 24. An acoustic wave transmitted from the
transmitter 13 of the transmitting apparatus 1 is reflected by the
detection-target object and the reflected acoustic wave is received
by the receiver 20 of the receiving apparatus 2. In the first
embodiment, the receiver 20 in use was a condenser microphone
(KUB4223) manufactured by Hoshiden Corporation.
[0043] The receiver 20 can receive an acoustic wave including from
the audible region on to the ultrasonic wave region (in the
vicinity of 100 kHz) to convert the acoustic wave into an electric
signal. Therefore, the receiver 20 is configured so as to receive
an acoustic wave transmitted from the transmitter 13 and reflected
by the detection-target object and to convert the received acoustic
wave into an electric signal.
[0044] The amplifier 21 is connected to the receiver 20. An
electric signal, from the receiver 20, amplified by the amplifier
21 is inputted to the detection circuit 23 after passing through
the BPF 22 through which a signal of a frequency in the vicinity of
50 kHz passes. An output from the detection circuit 23 is inputted
to the comparator 24. The comparator 24 is configured so as to
compare the electric signal inputted from the detection circuit 23
with a predetermined threshold value and to output a pulse signal
as a timing stop signal to the signal processing unit 30 when the
electric signal exceeds the predetermined threshold value.
[0045] The signal processing unit 30 is equipped with a timer 30a,
and a trigger signal outputted by the timing circuit 10 is inputted
as a timing start signal thereto. The signal processing unit 30
measures an elapsed time till the pulse signal outputted as the
timing stop signal by the comparator 24 is inputted thereto from
the time when the timing start signal (the trigger signal) is
inputted thereto. The signal processing circuit 30 multiplies a
time as a result of the measurement by a propagation velocity of an
acoustic wave in a propagation medium to thereby calculate a
distance to the detection-target object and output the calculated
distance.
[0046] As described above, in the transmitting apparatus 1
according to the invention, the driving circuit 11 is configured so
as to drive the piezoelectric element 13a in a frequency band (in
the vicinity of 50 kHz) different from a resonance frequency (in
the vicinity of 4.4 kHz) at which the vibration system including
the piezoelectric element 13a resonates the most strongly. Hence,
the time T3 until the vibration system including the piezoelectric
element 13a resonates in a stable state, as shown in timing charts
of FIG. 4A and FIG. 4B, becomes shorter and a rise of acoustic
pressure of a transmitted acoustic wave becomes steep, compared
with a case where the piezoelectric element 13a is driven in a
frequency (in the vicinity of 4.4 kHz) at which the vibration
system including the piezoelectric element 13a resonates the most
strongly.
[0047] To be concrete, the time T3 elapsed until the vibration
system including the piezoelectric element 13a resonates in a
stable state as shown in an output waveform of the transmitter 13
of FIG. 4B from the time when a voltage is applied to the
transmitter 13 as shown in an output waveform of the driving
circuit 11 of FIG. 4A is very much shorter, as compared with the
time T1 in the conventional technology shown in FIG. 1B.
[0048] In an ultrasonic sensor according to the invention, since an
acoustic wave whose acoustic pressure rises steeply as mentioned
above is transmitted and received by the receiver 20, a time T4
elapsed until the electric signal converted in the receiver 20, as
shown in FIG. 1C, exceeds a predetermined threshold value is very
much shorter as compared with a case of the conventional
technology; therefore, an error in measurement of a distance of the
detection-target object becomes smaller.
[0049] Note that while in the above first embodiment, a value of a
frequency "f" of an oscillation signal outputted from the
oscillator 11a is set to a value in the vicinity of 50 kHz, no
limitation is required to be placed on the frequency "f". A value
of the frequency "f" of an oscillation signal outputted from the
oscillator 11a has only to be set in a frequency band different
from a resonance frequency at which the vibration system including
the piezoelectric element 13a resonates the most strongly.
[0050] In the first embodiment, a condenser microphone is used as
the receiver 20, on which no specific limitation is placed. For
example, a configuration is also possible in which, for example, a
piezoelectric element is used instead of the condenser microphone
and an electric signal is generated according to a vibration of the
piezoelectric element by the action of the received acoustic
wave.
[0051] Another configuration may also be allowed in which a horn is
mounted to the transmitter 13 to thereby enable a directional
characteristic of an acoustic wave transmitted from the transmitter
13 to be adjusted.
[0052] FIG. 5 is a block diagram showing a schematic configuration
of a second embodiment of a ultrasonic sensor according to the
invention.
[0053] In FIG. 5, numeral 40 denotes a transmitter/receiver, which
is equipped with a piezoelectric element 40a. The piezoelectric
element 40a is applied with a voltage outputted from a boosting
circuit 12 according to an oscillation signal of a frequency "f"
outputted from an oscillator 11a of a driving circuit 11. The
piezoelectric element 40a vibrates according to the frequency "f"
of the applied voltage given from the boosting circuit 12 and
transmits an acoustic wave.
[0054] The transmitter/receiver 40 receives an acoustic wave
reflected by a detection-target object to generate an electric
signal according to the vibration of the piezoelectric element 40a
by the action of the received acoustic wave. The generated electric
signal is inputted to the detection circuit 23 through an amplifier
21 and a BPF 22 in a similar way to that in the case of the above
mentioned first embodiment.
[0055] Since the other configuration and operations are similar to
those in the first embodiment, the same reference symbols are
attached to the corresponding elements, of which descriptions are
omitted.
[0056] Note that while the ultrasonic sensors of the first and
second embodiments each are configured such that a distance of a
detection-target object is measured, needless to say that another
configuration may also be adopted in which a distance of the
detection-target object is not measured but the presence/absence
thereof is detected.
[0057] A practical application of the ultrasonic sensor according
to the invention as mentioned above can be mounted, for example, on
an autonomous traveling vehicle which travels autonomously. FIG. 6
is a block diagram schematically showing functional configuration
of an autonomous traveling cleaner as one embodiment of the
autonomous traveling vehicle according to the invention equipped
with the ultrasonic sensor according to the invention.
[0058] In FIG. 6, numeral 5 denotes a vehicle body having a
rectangular parallelepiped shape. Wheels 6R and 6L are freely
rotatably arranged on both side surfaces extending in the
longitudinal direction (a forward to backward direction) of the
vehicle 5 and facing each other. One end of longitudinal direction
of the vehicle body 5 is determined as the front side. Accordingly,
the vehicle body 5 is configured so as to travel (moves forward)
toward one side of the longitudinal direction by rotating the both
wheels 6R and 6L together in the positive direction, while to
travel (moves backward) toward the another side of the same by
rotating the both wheels 6R and 6L together in the reverse
direction. In addition, a dust-suction port 50 for sucking dust is
provided under the vehicle body 5.
[0059] The wheels 6R and 6L are coupled with rotary shafts of
respective two motors 60R and 60L disposed within the vehicle body
5. Hence, in a case where the left wheel 6L rotates in the positive
direction, while the right wheel 6R rotates in the reverse
direction at the same speed of the left wheel 6L, the vehicle body
5 makes a so-called spin turn in a clockwise direction at a
position prior to the spin turn without moving either forward or
backward, and to the contrary, in a case where the left wheel 6L
rotates in the reverse direction, while the right wheel 6R rotates
in the positive direction at the same speed of the left wheel 6L,
the vehicle body 5 makes a so-called spin turn in a
counterclockwise direction at a position prior to the spin turn
without moving either forward or backward.
[0060] The motors 60R and 60L are connected to a control unit 7,
respectively, and by being driving-controlled of them mentioned
above, traveling control and steering control are performed by the
control unit 7. The timing circuit 10 and the comparator 24 of the
ultrasonic sensor according to the invention are connected to the
control unit 7. Hence, a trigger signal as a timing start signal is
inputted to the control unit 7 from the timing circuit 10 and,
also, a pulse signal as a timing stop signal is inputted to the
control unit 7 from the comparator 24. The control unit 7 is
equipped with a timer 70 by which an elapsed time till the time
when the timing stop signal is inputted from the time when the
timing start signal is inputted is measured and in which a distance
therefrom to a detection-target object is detected by multiplying
the measured time by a propagation velocity of an acoustic wave in
air, both of which are similar to those in the ultrasonic sensor
according to the invention.
[0061] The transmitter 13 of the transmitting apparatus 1 and the
receiver 20 of the receiving apparatus 2 are arranged almost on the
front of the vehicle body 5 and an acoustic wave transmitted from
the transmitter 13 is reflected by the detection-target object
located in a direction in which the vehicle body 5 travels forward
and received by the receiver 20.
[0062] With a configuration described above adopted, the autonomous
traveling cleaner autonomously travels about in a rectangular room
80 surrounded by walls 8a, 8b, 8c and 8d as shown in FIG. 7A, FIG.
7B and FIG. 7C. Detailed description will be given below.
[0063] The autonomous traveling cleaner, as shown in FIG. 7A,
travels straight from one corner of the room 80 (in the bottom
left-hand corner in FIG. 7A) along one wall 8a to temporarily stop
at a position 2 cm inwardly apart from the wall 8b present in the
forward direction thereof. A distance between the autonomous
traveling cleaner and the wall 8b in this case is detected by the
ultrasonic sensor according to the invention mounted on the
autonomous traveling cleaner.
[0064] The autonomous traveling cleaner that has temporarily
stopped as described above makes a spin turn by 90 degrees in a
clockwise direction, as shown in FIG. 7B, at the position where the
cleaner temporarily stopped, travels straight (forward) along the
wall 8b by a length equal to the width of the vehicle body 5 and
thereafter, again stops there. The autonomous traveling cleaner
that has again stopped makes a spin turn in a clockwise direction
by 90 degrees at the position where the cleaner temporarily stopped
again and further travels straight (forward) in parallel to the
wall 8a toward the wall 8c facing the wall 8b.
[0065] Then, the autonomous traveling cleaner, as shown in FIG. 7C,
temporarily stops again at a position in a predetermined length,
for example, 2 cm inwardly apart from the wall 8c present in the
forward direction thereof, makes a spin turn in a counterclockwise
direction by 90 degrees at the position where the cleaner has
temporarily stopped. The autonomous traveling cleaner travels
straight (forward) along the wall 8c by a length equal to the width
of the vehicle body 5, thereafter, again stops there, makes a spin
turn in a counterclockwise direction by 90 degrees at the position
where the cleaner has again stopped and further travels straight
(forward) in parallel to the wall 8a toward the wall 8b facing the
wall 8c.
[0066] The autonomous traveling cleaner cleans all the floor
surface of the room 80 at every part thereof by traveling along and
in parallel to the wall 8d in a zigzag pattern in such a way and
continuing such traveling to a position where a distance becomes a
predetermined distance, for example 2 cm, inwardly apart from the
wall 8b or 8c.
[0067] Since the autonomous traveling vehicle according to the
invention is equipped with the ultrasonic sensor according to the
invention and can measure a distance from the walls 8b and 8c while
approaching them with high accuracy, the vehicle body 5 can be
stopped at a position very close to the walls 8b and 8c. Hence,
cleaning can be certainly conducted in portions close to the walls
8a, 8b, 8c and 8d where dust is easily gathered in the room without
collision of the vehicle body 5 with the walls 8b and 8c.
[0068] While description has been given of the transmitting
apparatus 1, the sound sensor and the autonomous traveling vehicle
according to the invention above on the basis of the configurations
shown in the embodiments, configurations of the transmitting
apparatus, the sound sensor and the autonomous traveling vehicle
according to the invention are not limited to the configurations
shown in the embodiments, and any addition, modification or
deletion can also be made within the spirit and scope of the
invention.
[0069] As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
embodiments are therefore illustrative and not restrictive, since
the scope of the invention is defined by the appended claims rather
than by the description preceding them, and all changes that fall
within metes and bounds of the claims, or equivalence of such metes
and bounds thereof are therefore intended to be embraced by the
claims.
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