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DESCRIPTION JP2009175007

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DESCRIPTION JP2009175007
To provide an obstacle detection device capable of eliminating the extension of reverberation
time. SOLUTION: Two transmission / reception blocks 7 each having a piezoelectric element 1
and capable of transmitting and receiving ultrasonic waves to a predetermined detection range
by the piezoelectric element 1, and each transmission / reception block 7 are controlled
respectively And a control unit 8 for performing a detection operation of detecting an obstacle
within the detection range. In each transmission / reception block 7, one electrode of the
piezoelectric element 1 is in contact with the vibration case made of a conductive material, and is
connected to the subsequent circuit via the vibration case. The control unit 8 performs a
preliminary operation of driving the piezoelectric element 1 of each transmission / reception
block 7 in advance before performing the detection operation. The extension of the reverberation
time due to the change in the state of electrical connection between the electrode of the
piezoelectric element 1 and the vibration case due to long-term nonuse is prolonged to some
extent by the preliminary operation. [Selected figure] Figure 1
Obstacle detection device
[0001]
The present invention relates to an obstacle detection device.
[0002]
BACKGROUND Conventionally, an obstacle detection device has been provided that detects the
presence of an obstacle by transmitting ultrasonic waves to a detection range and receiving a
reflected wave reflected by the obstacle.
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[0003]
As an obstacle detection device of this type, an ultrasonic transducer having a plurality of wave
receiving piezoelectric elements for receiving reflected waves is used, and by comparing the
output of each of the wave receiving piezoelectric elements Some can also detect the direction.
For example, in the case of an obstacle detection device using two piezoelectric elements 1 as
shown in FIG. 3, one piezoelectric element 1 intermittently transmits ultrasonic pulses toward a
detection range as a transmission piezoelectric element. The two piezoelectric elements 1 receive
the waves reflected by the obstacle T present in the detection range as the receiving piezoelectric
elements.
[0004]
The operation of the obstacle detection device will be described in detail with reference to FIG.
(A) of FIG. 4 shows the input signal waveform to the piezoelectric element for transmission, (b) of
FIG. 4 shows the waveform of the received signal by the output of one piezoelectric element 1,
and (c) of FIG. The waveform of the received wave signal by the output of the other piezoelectric
element 1 is shown. In (b) and (c) of FIG. 4, L1 and L2 are components of reverberation, and E1
and E2 are components of a reflected wave reflected by the obstacle T. The distance L to the
obstacle T can be detected by the time t1 from the transmission of the ultrasonic wave to the
reception of the reflected wave, and the time until the one piezoelectric element 1 receives the
ultrasonic wave and the other The obstacle detection device and the obstacle T are connected to
a plane whose normal line is a straight line along the direction in which the piezoelectric
elements 1 are lined from the difference t2 with the time until the piezoelectric element 1
receives the ultrasonic wave. The angle θ formed by the straight line can be detected. For
example, as shown in FIG. 5, a plurality (two in the figure) of such obstacle detection devices are
attached to the front of the vehicle C, and detect obstacle T in a detection range Z in front of the
vehicle C. Used for Since the direction of the obstacle T can be detected, whether or not the
obstacle T exists on the path of the vehicle can be detected more accurately than an obstacle
detection device that simply detects the distance to the obstacle T. be able to.
[0005]
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As an obstacle detection apparatus provided with the two piezoelectric elements 1 as mentioned
above, there exist some which are shown, for example in FIG. 6 (for example, refer patent
document 1). This obstacle detection device includes a vibration case 2 as a vibrating body made
of a conductive material and in which two storage recesses 21 are juxtaposed, and a piezoelectric
element 1 stored in each storage recess 21.
[0006]
Explaining in detail, the vibration case 2 is made of metal such as aluminum, for example, a flat
plate portion 26 in the form of an oblong flat plate, and two back sides of the flat plate portion
26 arranged in the longitudinal direction and having a gap therebetween. And a tubular portion
24. The piezoelectric element 1 is bonded (adhered) to a portion which is the back surface (the
lower surface in FIG. 6) of the flat plate portion 26 and is surrounded by the cylindrical portion
24 with an adhesive B (see FIG. 7). A storage recess 21 is formed in a portion surrounded by the
cylindrical portion 24, and a partition recess 23 is formed between the two cylindrical portions
24. Further, the surface (upper surface in FIG. 6) of the flat plate portion 26 is an incident /
incidence surface 22 on which the ultrasonic wave is emitted and incident.
[0007]
The piezoelectric element 1 is formed in a disk shape, and has electrodes 11 and 12 made of a
conductive material such as metal on both surfaces of the main body 10 made of piezoelectric
ceramic as shown in FIG. One electrode 11 of the piezoelectric element 1 is brought into contact
with the bottom of the housing recess 21 of the vibration case 2 so as to be drawn out through
the vibration case 2 and the lead wire 6, and the other electrode 12 is drawn out through the
lead wire 6 Each is connected to an external circuit for analyzing the output of the piezoelectric
element 1 and is used for ultrasonic wave reception. That is, in the vibration case 2, the bottoms
of the storage recesses 21 are the diaphragms in the claims. Although the adhesive B having no
conductivity is interposed between the vibration case 2 and the piezoelectric element 1, since the
fine unevenness is present in the vibration case 2, the electrode 11 of the piezoelectric element 1
vibrates. Contact conduction is made to the convex part of the fine unevenness of case 2. Here,
one piezoelectric element 1 is also connected to a drive circuit for generating an ultrasonic wave,
and is used to transmit the ultrasonic wave. That is, each piezoelectric element 1 is a receiving
piezoelectric element, and the piezoelectric element 1 connected to the drive circuit also serves
as a transmitting piezoelectric element. That is, one piezoelectric element 1 connected to the
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drive circuit and driven at the time of detection of an obstacle is the first piezoelectric element in
the claims, and the other piezoelectric element 1 is the second piezoelectric element in the
claims. In addition, on the surface opposite to the light incident surface 22, the partition recess
23 is provided between the storage recess 21 in which the transmission piezoelectric element is
stored and the storage recess 21 in which the reception piezoelectric element is stored. become.
Furthermore, each storage recess 21 is filled with a buffer filler 3 for suppressing reverberation.
[0008]
The vibration case 2 is accommodated in the housing 4 in such a manner as to expose the
incident / incidence surface 22 from the opening of the housing 4.
[0009]
Further, between the housing 4 and the vibration case 2, there is a holding body 5 made of an
elastic material such as synthetic rubber, for example, having a higher sound absorption
coefficient to the ultrasonic wave generated by the transmitting piezoelectric element than the
material of the vibration case 2. It is provided.
In the holder 5, two holding recesses 51 are provided side by side. The dimension of the outer
periphery of the holder 5 is formed to be the same as the inner periphery of the housing 4, and
the dimension of the inner periphery of the holding recess 51 is formed to be the same as the
dimension of the outer periphery of the cylindrical portion 24 of the vibration case 2. The
cylindrical case 24 of the vibration case 2 is press-fit into the holding recess 51, and the holding
body 5 is press-fitted into the housing 4, whereby the vibration case 2 is held by the housing 4.
Further, a sound absorbing portion 52 housed in the dividing recess 23 and absorbing the
reverberation between the piezoelectric elements 1 is provided at a portion of the holding body 5
which divides the two holding recesses 51. JP 2004-253911 A
[0010]
In the obstacle detection device as described above, when the period in which the piezoelectric
element 1 is not driven is long, for example, several years, the duration of the reverberation
component shown by L1 and L2 in FIG. Call it "Reverberation time". May have been longer than
at the time of manufacture. Thus, when the reverberation time is extended, the components of
the reflected wave shown by E1 and E2 in FIG. 4 (b) (c) are embedded in the component of the
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reverberation and the distinction between the component of the reflected wave and the
component of the reverberation There is a high possibility of false positive or false negative due
to failure to
[0011]
The present invention has been made in view of the above, and an object thereof is to provide an
obstacle detection device capable of eliminating the extension of the reverberation time.
[0012]
The invention according to claim 1 is an obstacle detection device for detecting an obstacle
within a predetermined detection range by transmission and reception of ultrasonic waves, which
is made of a conductive material and directed to the detection range to emit and enter ultrasonic
waves. Two diaphragms having an incidence / incidence surface, and electrodes provided on both
sides in the thickness direction, and one electrode is in contact with one surface of the diaphragm
opposite to the incidence / incidence surface. And driving the first piezoelectric element to
generate an ultrasonic wave, and each of the diaphragms receives the reflected wave that is
reflected in the detection range by the ultrasonic wave. Control unit configured to detect an
obstacle based on the electric signal generated in each piezoelectric element respectively, and the
control unit is configured to drive at least the second piezoelectric element before performing the
detection operation. It is characterized by doing.
[0013]
According to the present invention, extension of reverberation time due to long-term nonuse is
eliminated to some extent by the preparatory operation.
[0014]
According to a second aspect of the present invention, in the first aspect, each of the piezoelectric
elements is provided with an input / output section which amplifies the electric signal by being
interposed between each of the piezoelectric elements and the control section to configure a
transmission / reception block with the piezoelectric element The control unit is characterized by
detecting an abnormality of each transmission / reception block based on an output of each
piezoelectric element input through the input / output unit at the time of the preliminary
operation.
[0015]
According to the present invention, the preparatory movement can be effectively utilized for
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detecting an abnormality.
[0016]
According to the invention of claim 1, since the control unit performs the preliminary operation
of driving at least the second piezoelectric element before performing the detection operation,
extension of the reverberation time due to long-term nonuse is achieved by the preliminary
operation. It is eliminated to some extent.
[0017]
According to the invention of claim 2, since the control unit detects an abnormality of each
transmission / reception block based on the output of each piezoelectric element input through
the input / output unit during the preliminary operation, the preliminary operation is performed.
It can be effectively used to detect abnormalities.
[0018]
Hereinafter, the best mode for carrying out the present invention will be described with
reference to the drawings.
[0019]
The basic configuration of the present embodiment is the same as that of the conventional
example, and therefore, the same reference numerals are given to the common parts, the
description will be omitted, and only different parts will be described.
[0020]
The present embodiment is an obstacle detection device mounted on a vehicle, and as shown in
FIG. 1, ultrasonic waves with respect to a predetermined detection range Z (see FIG. 5) by the
piezoelectric element 1 each having the piezoelectric element 1 It comprises two transmission /
reception blocks 7 capable of transmission and reception, and a control unit 8 for controlling
each transmission / reception block 7 respectively.
The power supply of each part is supplied from a battery (not shown) mounted on the vehicle.
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[0021]
Each transmission / reception block 7 amplifies the transmission signal which is an electric
signal output from the control unit 8 to drive the piezoelectric element 1 and the piezoelectric
element 1 to transmit ultrasonic waves. A circuit 71, a receiving side amplifier circuit 72 for
amplifying a receiving signal which is an electric signal generated in the piezoelectric element 1
in response to vibration due to reverberation or a reflected wave, and a receiving signal amplified
by the receiving side amplifier circuit 72 And a detection circuit 73 for generating a signal to be
input to the control unit 8.
That is, each piezoelectric element 1 shown in FIG. 6 is included in different transmission /
reception blocks 7, and in each transmission / reception block 7, the transmission side
amplification circuit 71 and the reception side amplification circuit 72 are shown in FIG. The two
electrodes of the piezoelectric element 1 are electrically connected to each other through the pair
of lead wires 6 shown.
As shown in FIG. 2, the detection circuit 73 compares the amplitude of the received signal input
from the receiving amplifier circuit 72 with a predetermined discrimination threshold, and
during a period in which the amplitude of the received signal is equal to or greater than the
discrimination threshold. The output is at the H level, and the output is at the L level during a
period in which the amplitude of the reception signal is less than the discrimination threshold.
Although the reverberation component L1 in one transmission / reception block 7 is taken as an
example in FIG. 2, the operation for the components E1 and E2 of the reflected wave and the
operation in the other transmission / reception block 7 are the same.
The control unit 8 determines the times t1 and t2 used in the operation described in FIG. 4 as the
timing when the reflected wave is received, which is the rise timing at which the output of the
detection circuit 73 can be determined to correspond to the reflected wave. .
That is, the transmission side amplification circuit 71, the reception side amplification circuit 72,
and the detection circuit 73 constitute an input / output unit in the claims.
The transmission side amplification circuit 71 and the reception side amplification circuit 72 may
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include a filter circuit for removing noise.
Further, when the piezoelectric element 1 and the control unit 8 are disposed at positions
separated from each other, a plurality of transmission side amplifying circuits 71 and receiving
side amplifying circuits 72 may be provided.
[0022]
The control unit 8 performs detection (detection operation) of an obstacle by each transmission /
reception block 7 in accordance with a control signal input from the outside.
The contents of the detection operation are as described with reference to FIGS. 3 and 4. The
appropriate piezoelectric element 1 of the transmission / reception block 7 is a transmission
piezoelectric element, and the control unit 8 is for transmission. By inputting a rectangular wave
of, for example, 72 kHz as a transmission signal to the piezoelectric element 1 as a piezoelectric
element via the transmission side amplification circuit 71, the piezoelectric element 1 is driven
by the separately excited method. Further, the control signal indicates, for example, the operating
state of the engine, the state of a detection switch that is turned on and off by a manual operation
to instruct ON / OFF of the detection operation, the traveling direction and speed of the vehicle,
and the power supply voltage. In the control unit 8, the engine is operating, the detection switch
is turned on, the traveling direction of the vehicle is in the direction of the detection range Z, and
the vehicle speed is less than a predetermined operating speed (for example, 10 km per hour)
Furthermore, detection is periodically performed only during a period in which the power supply
voltage of the battery is higher than a predetermined operating voltage required for the detection
operation (for example, 7 V when the rated voltage of the obstacle detection device is 9-15 V). Do
the action. If an obstacle is detected as a result of the detection operation, a notification signal
indicating the direction of the detected obstacle and the distance to the obstacle is output. The
notification signal is used, for example, to control a load (not shown) for notifying a user, such as
a liquid crystal display or a warning buzzer.
[0023]
Further, the present embodiment is characterized in that the control unit 8 performs a
preliminary operation of driving the piezoelectric element 1 of each transmission / reception
block 7 after the start (power on) and before the detection operation. Specifically, the control unit
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8 performs a preparatory operation when at least one of the information indicated by the control
signal changes from a state where the detection operation should not be performed to a state
where the detection operation should be performed. . That is, as the timing at which the control
unit 8 performs the preparatory operation, the timing when the engine is started, the timing
when the detection switch is turned on, the timing when the vehicle starts moving in the
direction of the detection range Z, the detection range Z The timing at which the moving speed of
the vehicle in the direction changes from a higher state to a lower state than a predetermined
preliminary speed set slightly higher than the operating speed (for example, the operating speed
is 10 km per hour as described above) Alternatively, timing when the power supply voltage
changes from lower to higher than the operating voltage may be considered. The detection
operation is performed when the above conditions such as the engine operation, the detection
switch, the moving direction and speed of the vehicle, and the power supply voltage are all
satisfied, and other conditions are satisfied after the engine is started. By the time, since it is
almost impossible for the time to extend the reverberation time (that is, for many years), the
control unit 8 may perform the preparatory operation only when the engine is started. The
frequency of the rectangular wave output by the control unit 8 to drive the piezoelectric element
1 during the preliminary operation is, for example, 72 kHz as in the detection operation, and the
driving of the piezoelectric element 1 in the preliminary operation is Each 250 μs is performed
5 times every 5 ms.
[0024]
According to the inventor's experiment, the above-mentioned preparatory movement makes the
reverberation time lengthened by long-term nonuse as described in the section of the subject
short (that is, the prolongation of the reverberation time is eliminated to some extent) To be
done) has been confirmed. The inventor of the present invention changes the state of the contact
surface between the electrode 11 of the piezoelectric element 1 and the vibration case 2 along
with the vibration due to the driving of the piezoelectric element 1 as described above for
shortening the reverberation time. It is believed that this is because the electrical connection
between the vibration case 11 and the vibration case 2 has changed.
[0025]
Here, in the preparatory operation, it is not necessary to drive both of the piezoelectric elements
1, but in the case where one of the piezoelectric elements 1 (first piezoelectric element in claims)
is always used as a transmitting piezoelectric element, the other piezoelectric element 1 In the
element 1 (second piezoelectric element in the claims), since the reverberation time tends to be
long, it is necessary to drive at least the other piezoelectric element 1 in the preliminary
operation.
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[0026]
Furthermore, in the present embodiment, detection of abnormality in each transmission /
reception block 7 is also performed in the preliminary operation.
Specifically, the control unit 8 detects an output due to reverberation associated with the drive of
the piezoelectric element 1 in the preliminary operation from each transmission / reception
block 7, and drives the piezoelectric element 1 for all five times of the drive in the preliminary
operation. If the output of the detection circuit 73 is L level in the period of 600 μs to 800 μs
after the start of the reception, the reception part of the transmission / reception block 7
including the detection circuit 73 (ie, the piezoelectric element 1 or the reception side amplifier
circuit 72 or It is determined that there is an abnormality in the detection circuit 73 or the
electrical connection between them. However, when it is determined that there is an abnormality
in the reception part of all the transmission / reception blocks 7 with respect to the driving of the
piezoelectric element 1 of one transmission / reception block 7, the control unit 8 receives the
transmission / reception blocks 7. It is determined that there is an abnormality in the
transmission part of the transmission / reception block 7 including the driven piezoelectric
element 1 (that is, the piezoelectric element 1 or the transmission amplification circuit 71 or the
electrical connection therebetween), not the wave part. When it is determined that there is some
abnormality, the control unit 8 outputs a notification signal indicating information of the portion
determined to have the abnormality to the outside. Further, in a state where it is determined that
there is an abnormality, for example, when the preliminary operation is performed at the time of
starting the engine or when the detection switch is turned on, the drive of the piezoelectric
element 1 is started for all five driving in the preliminary operation. After that, if the output of
the detection circuit 73 is at the H level in a period of 600 μs to 800 μs, the control unit 8
determines that the abnormality is recovered and outputs a notification signal indicating the
recovery from the abnormality. As described above, the notification signal output during the
preliminary operation is used to control a notification load (not shown) such as a liquid crystal
display, similarly to the notification signal output at the time of obstacle detection.
[0027]
Furthermore, in a system using a plurality of obstacle detection devices, the notification signal
indicating the abnormality is used as a control signal in another obstacle detection device, and
any obstacle detection device constituting the system detects the abnormality. The detection
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operation may be performed only when it is not. In this case, when a control signal (notification
signal) indicating recovery is input from an obstacle detection apparatus in which only an
abnormality is detected in the system (that is, an obstacle detection apparatus in which an
abnormality is detected is in the system). The control unit 8 may perform the preparatory
operation when the state is changed from the existing state to the non-existing state).
[0028]
As shown in FIG. 6, the piezoelectric elements 1 of the transmission / reception blocks 7 are fixed
to the common vibration case 2 (in other words, each vibration plate in the claims is configured
as one vibration case 2). The vibration case 2 may be fixed (that is, each diaphragm in the claims
may be configured as a separate vibration case 2). Even in this case, for example, each vibration
case 2 is held by the common holder 5 so that the reverberation due to the vibration of one
piezoelectric element 1 can be detected by the other piezoelectric elements 1 as well. For
example, determination of abnormality by the above-mentioned preliminary operation is possible.
[0029]
1 is a block diagram illustrating an embodiment of the present invention. It is explanatory
drawing which shows operation | movement of a detection circuit same as the above. It is an
explanatory view showing an example of operation of an obstacle detection device. It is
explanatory drawing which shows an example of operation | movement of an obstacle detection
apparatus, (a) is an input signal waveform to the piezoelectric element for transmission, (b) is an
output signal waveform of one piezoelectric element, (c) is the other piezoelectric. The output
signal waveform of an element is shown. It is an explanatory view showing an example of usage
of an obstacle detection device. It is sectional drawing which shows the principal part of an
example of an obstruction detection apparatus. It is explanatory drawing which shows the
connection state of a piezoelectric element and a vibration case.
Explanation of sign
[0030]
REFERENCE SIGNS LIST 1 piezoelectric element 2 vibration case 7 transmission / reception block
8 control unit 11, 12 electrode 22 incident surface 71 transmission side amplification circuit 72
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reception side amplification circuit 73 detection circuit
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