JPH10268035A - Ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect even a closest object accurately by providing a filter for passing a difference frequency between a resonance frequency and an oscillation frequency and extracting a reflection wave in reverberation vibration. SOLUTION: When the resonance frequency of a transducer is set to fr, an oscillation circuit performs a pulse oscillation output with a frequency f1 that is different from the resonance frequency fr. A filter for passing a frequency of |fr-f1| is used. Reverberation vibration after a transducer sends the ultrasonic signal with a frequency of f1 is generated by a resonance frequency of fr. Therefore, when a reflection wave R from an object overlaps with the reverberation vibration, a beat with a frequency of |fr-f1| is generated by the reverberation vibration of the reflection wave R with a frequency of f1 and a resonance frequency of fr. The filter can pass the frequency |fr-f1|. Therefore, when there is the reflection wave R that overlaps with the reverberation vibration, an output with a frequency of |fr-f1| appears in the filter, thus calculating a distance to the object by a processing circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor for detecting presence of an object and calculating a distance to the object by detecting a reflected wave of the ultrasonic signal from the object.

[0002]

2. Description of the Related Art An ultrasonic sensor outputs an ultrasonic signal from a transducer and receives a reflected wave from an object by the transducer to detect the presence of the object or to detect a reflected wave from the transmission time of the ultrasonic signal. It detects the distance to the object from the time until the reception time, and in many cases, the transmission of the ultrasonic signal and the reception of the reflected wave are performed by a single transducer.

[0003]

In this case, when the oscillation output shown in FIG. 5 is applied to the transducer to transmit an ultrasonic signal, the transducer is still affected by the reverberation vibration E even after the oscillation output stops. In the detection of the reflected wave R from the object, the object cannot be detected if the distance to the object is short and the reflected wave R is buried in the reverberation vibration. Even in the case where the transmission of the ultrasonic signal and the reception of the reflected wave are performed by different transducers, there is almost the same problem because the transmitted ultrasonic signal goes around the receiving transducer.

Japanese Unexamined Patent Publication No. 6-76199 discloses an apparatus capable of switching between a short-distance mode and a long-distance mode by switching the output time of an ultrasonic wave.
Also in this case, the reflected wave R from the object has reverberation vibration E
In such a case, object detection cannot be performed. The present invention has been made in view of such a point,
It is an object of the present invention to provide an ultrasonic sensor capable of detecting an object without causing a malfunction due to reverberation vibration even when the object is very close.

[0005]

According to the present invention, there is provided an ultrasonic sensor for transmitting an ultrasonic signal and receiving a reflected wave of the ultrasonic signal from an object by a transducer.
A frequency f different from the resonance frequency fr of the transducer
An oscillation circuit for applying the pulse oscillation output of 1 to the transducer, and connected to the reception output of the transducer |
It is characterized by including a filter that passes the frequency of fr-f1 | and a processing circuit that processes the output of the filter. Even if the reflected wave is buried in the reverberation vibration, the existence of the reflected wave can be extracted.

At this time, the transmission time Tt of the pulse oscillation output at the frequency f1 of the oscillation circuit is set so that | fr-f1 |> 1 / Tt with respect to the frequency of | fr-f1 | Since the filter output appears as a waveform having one or more wavelengths, the presence of the reflected wave can be more reliably detected.

[0007] In addition, an oscillator circuit for applying a pulse oscillation output having a frequency f2 substantially equal to the resonance frequency fr to the transducer and a filter connected to the reception output of the transducer and passing the frequency f2 are provided. It is also possible to detect when there is an object at a distance, and the resonance frequency fr is higher than the frequency f1.
If a combination of an oscillation circuit for applying a pulse oscillation output of a frequency f3 distant from the transducer to the transducer and a filter connected to the reception output of the transducer and passing the frequency | fr-f3 | The reflected wave from can be detected.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of the present invention will be described. In FIG. 2, an intermittent pulse oscillation output from an oscillation circuit 12 at a timing determined by a periodic oscillation circuit 11 is output by an amplifier 13. After being amplified, it is applied to a transducer 1, which emits an ultrasonic signal. The reflected wave from the object is captured by the transducer 1, and the output of the transducer 1 passes through the filter 2,
And to the processing circuit 17 through the comparator 16 and
The processing circuit 17 calculates the distance to the object, and the display circuit 18 displays the presence of the object and the distance to the object.

Here, the transducer 1
When the resonance frequency is fr, the oscillation circuit 12 performs pulse oscillation output at a frequency f1 different from the resonance frequency fr. And the above filter 2 has | fr-f1
The one passing the frequency of | is used. Since the reverberation vibration after the transducer 1 transmits the ultrasonic signal of the frequency f1 occurs at the resonance frequency fr, when the reflected wave R from the object overlaps the reverberation vibration, the frequency f1
The reflected wave R and the reverberation vibration of the resonance frequency fr cause a groan of a frequency of | fr-f1 |. Filter 2
Is to pass this frequency | fr-f1 |, so that if there is a reflected wave R overlapping the reverberation vibration, an output of the frequency | fr-f1 | appears in the filter 2. For this purpose, as shown in FIG. 1, the processing to calculate the distance to the object from the time Δt from the oscillation time to the time when the waveform-shaped output by the comparator 16 appears appears in the processing circuit 17.
Can be performed.

The transmission time Tt of the pulse oscillation output of the frequency f1 by the oscillation circuit 12 is set to satisfy the relationship of | fr-f1 |> 1 / Tt with respect to the frequency of | fr-f1 |. . Therefore, when a signal having a frequency of | fr-f1 | appears at the output of the filter 2 due to the presence of the reflected wave R, this signal always appears as a waveform having one or more wavelengths, so that a reliable detection operation can be performed. is there.

However, in the above-described apparatus, the object can be detected only when there is an object at a short distance where the reflected wave R overlaps with the reverberation vibration. Therefore, as shown in FIGS.
As the control circuit 3 also serving as the oscillation circuit 12, one capable of switching and outputting the pulse oscillation of the frequency f1 and the pulse oscillation of the frequency f2 substantially equal to the resonance frequency fr of the transducer 1 is used. Is provided with a filter 2 that passes the frequency of | fr-f1 | and a filter 2a that passes the frequency f2, as shown in FIG. It is possible to detect an object (and a distance to the object) at a distance at which the reflected wave R is to be received, and to detect an object at a short distance (and a distance to the object) at the time of pulse oscillation at the frequency f1. Detection can be performed.

The pulse oscillation of the frequency f1 and the pulse oscillation of the frequency f2 are alternately performed. In addition, although only the pulse oscillation of the frequency f2 is normally performed, the change in the distance to the object calculated by the control circuit 3 is not affected. The pulse oscillation of the frequency f2 and the pulse oscillation of the frequency f1 may be automatically switched accordingly. In addition, the oscillation circuit 12 can output a pulse oscillation output at a frequency f3 that is farther from the resonance frequency fr than the frequency f1, and | fr
−f3 |
The detection of an object at a very short distance may be performed, or the pulse oscillation frequency of the oscillation circuit 12 may be automatically switched between f1, f2, and f3 according to the detected distance.

[0013]

As described above, according to the present invention, an oscillation circuit for applying a pulse oscillation output having a frequency f1 different from the resonance frequency fr of the transducer to the transducer, and | fr connected to the reception output of the transducer
It is characterized by including a filter that passes the frequency of −f1 | and a processing circuit that processes the output of the filter. Even if the reflected wave of the frequency f1 overlaps with the reverberation vibration of the resonance frequency fr, an output indicating the presence of the reflected wave at the frequency of | fr-f1 | appears in the output of the filter connected to the reception output of the transducer. Therefore, it is possible to detect the presence of an object at a short distance or the distance to the object without any problem.

By setting the transmission time Tt of the pulse oscillation output of the oscillation circuit at the frequency f1 to | fr-f1 |> 1 / Tt with respect to the frequency of | fr-f1 |, the filter output for the reflected wave is obtained. Will appear as a waveform of one or more wavelengths, which makes it possible to more reliably detect the presence of a reflected wave.

[0015] Further, if the oscillation circuit for applying the pulse oscillation output of the frequency f2 substantially equal to the resonance frequency fr to the transducer and the filter connected to the reception output of the transducer and passing the frequency f2 are combined, the distance between the oscillation circuit and the filter is long. It can also detect when there is an object,
A frequency f3 farther from the resonance frequency fr than the frequency f1
And a filter that is connected to the receiving output of the transducer and passes a frequency | fr-f3 |, also detects a reflected wave from an object at a short distance. Is what you can do.

[Brief description of the drawings]

FIG. 1 is an operation explanatory diagram of an example of an embodiment of the present invention.

FIG. 2 is a block circuit diagram of the same.

FIG. 3 is a block circuit diagram of another example.

FIG. 4 is an operation explanatory view of the above.

FIG. 5 is an operation explanatory diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transducer 2 Filter 12 Oscillation circuit

Claims (4)

[Claims] An ultrasonic sensor for transmitting an ultrasonic signal and receiving a reflected wave of the ultrasonic signal from an object by a transducer, wherein the resonance frequency f of the transducer is
an oscillation circuit for applying a pulse oscillation output having a frequency f1 different from r to the transducer, a filter connected to a reception output of the transducer and passing a frequency of | fr-f1 |, and a processing circuit for processing the filter output. An ultrasonic sensor, comprising: 2. The transmission time Tt of a pulse oscillation output of a frequency f1 of an oscillation circuit is | fr-f1 |> 1 / Tt with respect to the frequency of | fr-f1 |. The ultrasonic sensor as described. 3. A frequency f2 substantially equal to the resonance frequency fr.
3. The ultrasonic sensor according to claim 1, further comprising an oscillation circuit for applying the pulse oscillation output to the transducer and a filter connected to the reception output of the transducer and passing the frequency f2. 4. An oscillation circuit for applying a pulse oscillation output of a frequency f3 farther from the resonance frequency fr than the frequency f1 to the transducer, and a filter connected to a reception output of the transducer and passing the frequency | fr-f3 | The ultrasonic sensor according to claim 1, wherein the ultrasonic sensor further comprises: