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JPH04125488

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DESCRIPTION JPH04125488
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic sensor used to determine the presence or absence of a detection object by
transmission and reception of ultrasonic waves, and more specifically, the detection object has an
ultra short distance less than a predetermined distance. The present invention relates to an
ultrasonic sensor suitable for detecting the presence or absence of the sensor. [Prior Art] A
single-element reflection type ultrasonic sensor is fixed at a predetermined position, and
ultrasonic waves are repeatedly received and transmitted from an arbitrary detection body from
this position, and ultrasonic waves emitted at the time of transmission are detected It is for
measuring the distance to the detection body by being reflected by the body and detecting it
upon reception, and is used in various applications. The detectable distance of this type of
ultrasonic sensor is one having an ultrasonic transducer with a diameter of 2 cm capable of
measuring a relatively short distance, and is usually 5 cm or more. Although the maximum
detectable distance in the case of this ultrasonic sensor is about 30 cm, the reception time can
also be limited by shortening the time for the ultrasonic wave to reciprocate between the sensor
and the detection body. . [Problems to be Solved by the Invention] As described above, the
conventional ultrasonic sensor can not detect the presence or absence of the detection body if it
is not located at a distance within a predetermined range, and the detection body detects In the
case of being located at a short distance below the minimum (5 cm in the above example) of the
region, the data was unstable even if it was undetectable or detected. This is because, in the
conventional ultrasonic sensor, when the detection body is located in a predetermined detectable
area, as shown in FIG. 3, the transmission signal A (see (a)) is detected as -wide reflected wave
A1. (See (b)). However, when the distance is shorter than that, the reception time is extremely
short (as shown in FIG. 3 (c), the primary reflected wave AI for the transmission signal A is the
waveform of the reverberation signal of the transmission signal A). It is due to the fact that it is
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not possible to distinguish between -Broad Reflected Wave A or Reverberation signal received in
B. In this case, if it is intended to detect the presence or absence of a detection object located at a
short distance below the detectable region, the secondary reflected wave A2 or the tertiary
reflected wave A3 which can be received outside the waveform B of the reverberation signal is
captured and detected. There is a need to. However, the surface shape of the conventional
ultrasonic transducer is formed to be flat or convex, and the transmission wave and the reception
wave have a certain spread. Therefore, when the reception of the high-order reflected wave is
used as described above, there is a problem that the reception becomes unstable due to the
attenuation and the diffusion of the ultrasonic beam at the time of reflection.
Moreover, the temporarily reflected wave reception time TI at the long distance L1 shown in
FIGS. 4 (a) and 5 (a) and at the short distance L2 shown in FIGS. 4 (b) and 5 (b). Since the highorder reflected wave reception time T2 is the same time, it is difficult to specify which distance is
detected and the detection distance. Furthermore, when trying to detect a so-called passing
object in which the detecting body moves, the conventional method also detects an object behind
the passing detecting body due to the above-mentioned transmission wave having a certain
spread, etc. It also had problems such as being subject to usage restrictions. The present
invention has been made to solve the above-described problems, and can stably and reliably
detect only the presence or absence of a detection object located at a short distance, which can
not be detected conventionally or is unstable. An object of the present invention is to provide an
ultrasonic sensor having a novel structure which does not perform detection at a position beyond
the detection area. [Means for Solving the Problems] In order to achieve the above object, the
ultrasonic sensor for short distance detection of the present invention has one ultrasonic
transducer, and the ultrasonic transducer is used to The ultrasonic sensor transmits an acoustic
wave and receives an ultrasonic wave reflected by the detection body to detect the presence or
absence of the detection body, so that the ultrasonic wave can be focused at a predetermined
distance. The surface of the ultrasonic element is formed in a concave shape, and the presence or
absence of the detection body can be detected only when the distance to the detection body is
equal to or less than the distance to the focusing point. [Operation] In such a configuration, the
ultrasound always converges at a predetermined distance. Therefore, it is possible to prevent the
attenuation and diffusion of the ultrasonic wave at the time of reflection by receiving the highorder reflected wave. On the other hand, when the detection body is located at a distance farther
than the focusing point, the ultrasonic wave is diffused at the time of reflection, and the amount
of the received wave received by the ultrasonic sensor becomes small. It can only be measured if
it is located. The ultrasonic sensor according to the present invention will be described in more
detail with reference to the embodiments shown in the drawings. FIG. 1 is a perspective view of
an ultrasonic sensor 1 of the present embodiment. In the figure, reference numeral 2 denotes a
casing, in which an ultrasonic transducer 3 to be described later is incorporated in the front, and
a member (not shown) such as a circuit board is disposed inside. The ultrasonic transducer 3 is
not particularly limited as long as the surface shape, that is, the surface 3a (see FIG. 2) opposed
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to the detection body is formed in a concave shape. In this embodiment, in order to enable
detection in the case where the detection body is located at a short distance of 2 cm or less, it is
formed in a circle with a diameter of 1 cm and the radius of curvature of the surface, that is,
concave surface 3a is 2 cm. The distance X to the focusing point 0 shown in a) was 2 cm.
Of course, these numerical values can be set arbitrarily according to the detection distance. A
coaxial cord 4 is used to connect the ultrasonic sensor 1 of the present embodiment to an
external power supply. Reference numeral 5 denotes a plate, which is disposed to fix the
ultrasonic sensor 1 of the present embodiment to an arbitrary fixed part. The ultrasonic sensor l
of this embodiment operates as follows. This will be described based on FIG. The broken line in
FIG. 2 indicates the propagation of ultrasonic waves. First, as shown in FIG. 2 (b), when the
detection object k is located at a focusing point 0 or less and at a distance of 1/2 or more of the
distance between the brown sensor 1 and the focusing point 0. The ultrasound reflected by the
body is focused by the time it is received by the ultrasound transducer 3. Therefore, the primary
reflected wave can be stably detected without diffusion of the ultrasonic wave at the time of
reflection on the detection body. When the detection body k is located at a distance shorter than
a half of the distance to the focusing point 0, as shown in FIG. 2 (c), the high-order reflected wave
is received and the detection operation is performed. In this case, the ultrasonic wave does not
diffuse even when it is reflected on the surface 3a of the ultrasonic transducer 3. Therefore, the
short-distance detection can be stably performed without the ultrasonic wave being attenuated
even by the reflection of several orders. Can. On the other hand, when the detection body k is
located at a distance farther than the position of the focusing point 0, as shown in FIG. 2 (d), the
ultrasonic wave reflected by the detection body is diffused and the ultrasonic transducer is It is
propagated to 3 (the received wave becomes weak. Therefore, even if this signal is present as the
primary reflected wave within the high-order reflected wave reception time, the ultrasonic sensor
1 does not perform the detection operation, so that the detection distance can be easily specified.
According to the ultrasonic sensor of the present invention, short distance detection can be
performed easily and stably. In addition, even if the primary reflected wave from a long distance
enters in the high-order reflected wave reception time, the received wave is weak and it is easy to
specify the detection distance. Therefore, stable detection can be performed without the
influence of background. In addition, since it has become possible to detect near distances that
were not possible with conventional ultrasonic sensors, general proximity switches (those with a
detection distance of 1 to several + mm) can not be used and there are many dusts and vapors
etc. Under adverse circumstances, these proximity switches can be used instead.
[0002]
Brief description of the drawings
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[0003]
FIG. 1 is a perspective view showing an embodiment of the ultrasonic sensor of the present
invention, FIG. 2 is a schematic side view for explaining the operation of the ultrasonic
transducer used in the embodiment, and FIG. Explanatory drawing which shows the relationship
of the transmission signal of an ultrasonic sensor, and a received signal, FIG. 4 and FIG. 5 receive
waveform at the time of measuring a different detection distance using the conventional
ultrasonic sensor, ultrasonic sensor, and detection It is a schematic diagram which shows the
positional relationship with a body.
i --- Ultrasonic sensor 2 · · · · · · · Casing 3 · · · · · · · Ultrasonic transducer patent applicant: Japan
Automation Co., Ltd.
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