JPH0454471Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a pulse reflection type ultrasonic sensor that uses ultrasonic pulse signals to measure the presence of an object and the distance to the object.

[Background technology] Conventionally, as ultrasonic sensors that can be used outdoors, there have been products such as vehicle back sonar that detects obstacles behind the vehicle using a waterproof ultrasonic sensor with a piezoelectric element attached to the inside of a metal case. has been made into For example, when a large amount of snow and ice adheres to the case in winter, the transmitting and receiving sensitivities are significantly reduced, making it impossible to transmit and receive ultrasonic waves, resulting in a loss of detection ability. Ta.

[Purpose of the invention] The present invention has been provided in view of the above-mentioned points, and is a method for detecting an abnormality when a foreign object adheres to the vibrating part of an ultrasonic transducer and it is no longer able to operate normally. The present invention provides an ultrasonic sensor for the purpose of notifying abnormalities.

[Disclosure of the invention] (Structure) The present invention is a pulse reflection type ultrasonic sensor that transmits ultrasonic waves by driving a piezoelectric ultrasonic transducer with a tone bust wave. A gate circuit that passes the received signal for a period corresponding to the reverberant signal component of the received signal in synchronization with the transmitting period, a period measuring circuit that measures the period of the reverberant signal that has passed through this gate circuit, and this period. By providing an abnormality detection circuit consisting of a comparison circuit that compares the measured value of the measurement circuit with a predetermined set value and outputs an abnormality detection signal if the measured value is less than the set value,
The abnormality detection circuit is characterized in that an abnormality is notified when a foreign object adheres to the vibrating part of the piezoelectric ultrasonic transducer and the piezoelectric ultrasonic transducer is no longer able to operate normally.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
FIG. 2 is a sectional view showing an example of a drip-proof ultrasonic transducer A, in which a piezoelectric element 2 such as a piezoelectric ceramic transducer is bonded to the inside of the bottom of a cylindrical case 1 with a bottom. It is configured to vibrate the bottom surface of 1 and output ultrasonic pulses. Case 1
The resonance ring 3 disposed on the inner peripheral surface of the case 1
It has the function of suppressing changes in the basic performance of the ultrasonic transducer A even if external pressure is applied to the side surface of the ultrasonic transducer A. On the opening side of the case 1 are terminals 6a,
A terminal plate 5 having the terminal plate 6b penetrated and fixed is hermetically fixed, and a buffer material 7 is provided between the terminal plate 5 and the resonance ring 3. One terminal 6a fixed to the terminal plate 5 is connected to the piezoelectric element 2 via a lead wire 4a.
The other terminal 6b is connected to the lead wire 4.
It is connected to case 1 via b.

Figure 3 shows the frequency characteristics of the impedance of this ultrasonic transducer A. As shown in this characteristic diagram, the frequency fr where the impedance Z is the minimum is the resonance frequency, and the frequency a where the impedance Z is the maximum is the resonance frequency. It is defined as the anti-resonant frequency. Here, the resonant frequency r is about 40kHz and the anti-resonant frequency
a is approximately 40.6kHz. FIG. 5 shows a transmitted wave application signal of a pulse type ultrasonic sensor using an ultrasonic transducer A having such frequency characteristics and a voltage waveform at both ends of the ultrasonic transducer A. FIG. 5a shows the transmission signal waveform of the tone burst wave applied to the piezoelectric element 2. When the piezoelectric element 2 is driven by the tone burst wave of width t ₁ (s), the piezoelectric element 2, that is, the ultrasonic vibrator In the waveforms at both ends of A, as shown in FIG. 5b, a reverberation signal is generated after the transmission signal ends. This reverberation signal is generated at its own resonant frequency, not the frequency of the transmitted signal.
It vibrates at r (period t ₂ ).

By the way, since the ultrasonic transducer A is drip-proof, it is often used outdoors, and is applied, for example, to a vehicle rear obstacle sensor. When used in such an environment, it is conceivable that foreign matter 8 such as mud, snow, or ice may adhere to the vibration surface of the ultrasonic transducer A as shown in FIG. If a large amount of these foreign substances 8 adhere to the vibrating surface, the vibration of the ultrasonic transducer A is hindered, the sensitivity of transmitting and receiving ultrasonic signals is significantly reduced, and the sensor function is no longer achieved.

As mentioned above, when the foreign matter 8 adheres to the vibration surface of the ultrasonic transducer A, the impedance/frequency characteristics of the ultrasonic transducer A change as shown in Fig. 3, and the resonance frequency r increases. significantly reduced. Therefore, the frequency of the reverberation signal in this case becomes r' (period t ₃ ) as shown in FIGS. 3 and 5c. Therefore, it can be seen that by examining the frequency components of the reverberation signal, it is possible to determine whether or not the foreign matter 8 is attached to the vibration surface of the ultrasonic transducer A. In other words, by outputting a sensor abnormality signal when the reverberation frequency falls outside the set range, it is possible to notify the user of the abnormality when foreign matter 8 adheres to the ultrasonic sensor.

Next, with reference to FIG. 1 showing a specific circuit diagram of the ultrasonic sensor, the function of the sensor function and the function of notifying an abnormality when foreign matter adheres to the ultrasonic sensor will be explained. The pulse reflection type ultrasonic sensor that can be used for both transmitting and receiving waves uses a periodic oscillation circuit 11 to
A trigger pulse is created at a constant or arbitrary period, and a time width signal to be transmitted is created in synchronization with the trigger pulse by the transmission width creation circuit 12, and the oscillation circuit 1
3, a signal of the ultrasonic signal frequency is output only during the transmission width created by the transmission width creation circuit 12. This signal is amplified by the transmitting amplifier circuit 14 and drives the ultrasonic transducer A via the transmitting/receiving switching circuit 15 to output an ultrasonic signal. When the transmission is completed, the transmission/reception switching circuit 15 guides the signal of the ultrasonic transducer A to the reception amplification circuit 17, where it is amplified to a level that can be processed at the next stage. After this signal is detected by the detection circuit 18, it is converted into a high-level and low-level digital signal at a certain threshold level.

Next, a detection gate signal having a time width corresponding to the detection distance range is synchronized with the trigger pulse output of the periodic oscillation circuit 11 to the detection gate signal generation circuit 1.
This detection gate signal is applied to the gate circuit 20, and the gate circuit 20 allows the signal of the detection circuit 18 to pass only within a set time width. The detection output signal generation circuit 21 generates an output signal from the output circuit 2 by the signal output of the gate circuit 20 every wave transmission period.
If there is a received signal within the detection gate, the output circuit 22 is turned on, and if there is no received signal within the detection gate, the output circuit 22 is turned off.

Next, the gist of the present invention will be explained. The gist of the present invention is that an abnormality detection circuit B is added to the above circuit configuration, and has the following configuration.
First, the output of the receiving amplification circuit 17 is directly converted into a digital signal by the waveform shaping circuit 23, and in synchronization with the trigger pulse of the periodic oscillation circuit 11, a reverberation detection gate signal is created in order to extract a part of the reverberation signal. A gate signal is created in the circuit 24, and a gate signal is generated in the gate circuit 25.
The reverberation signal is extracted by the period measurement circuit 26.
The period of the reverberation signal is measured at , and the comparison and determination circuit 27 compares and determines whether the period is equal to or less than a preset value such as the resonance frequency r. The comparison judgment circuit 27 makes a judgment, and if the value is less than the set value, the display output circuit 28 indicates that there is an abnormality.
It is displayed by. Therefore, it can be seen from the display by the display output circuit 28 that foreign matter is attached to the currently used ultrasonic sensor.

[Effect of idea]

The present invention provides a pulse reflection type ultrasonic sensor that is driven by a tone bust wave and transmits ultrasonic waves as described above. A gate circuit that passes the received signal for a period corresponding to the reverberant signal component of It is equipped with an abnormality detection circuit consisting of a comparison circuit that outputs an abnormality detection signal if the measured value is less than the set value. By detecting the frequency component of the reverberation signal and outputting an abnormal signal when the frequency of the reverberation signal falls outside a preset range, it is possible to detect whether the ultrasonic transducer is operating normally. When foreign matter adheres to the vibrating surface of the sonic vibrator and it no longer functions as a sensor, it becomes possible to notify the abnormality, and the user can easily deal with the problem.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an ultrasonic sensor according to an embodiment of the present invention, Fig. 2 is a sectional view of the ultrasonic transducer of the same as above, Fig. 3 is a characteristic diagram showing the relationship between impedance and frequency of the same as above, and Fig. 4 The figure is an explanatory diagram of the same as above, No. 5
The figure is an operation waveform diagram same as above. A is an ultrasonic transducer, and B is an abnormality detection circuit.

Claims (1)

[Scope of utility model registration request] In a pulse reflection type ultrasonic sensor that transmits ultrasonic waves by driving a piezoelectric ultrasonic transducer with a tone bust wave, the received signal is A gate circuit that passes the received signal for a period corresponding to the reverberant signal component in the gate circuit, a period measuring circuit that measures the period of the reverberant signal that has passed through this gate circuit, and a measured value of this period measuring circuit and a predetermined setting value. An ultrasonic sensor comprising an abnormality detection circuit comprising a comparison circuit that compares the measured values and outputs an abnormality detection signal if the measured value is less than a set value.