JPH0720241A - Ultrasonic sensor - Google Patents

Abstract

PURPOSE:To make the obtaining of a correct distance measured value possible by distinguishing the reflected wave of an ultrasonic wave radiated currently from a multiple reflected wave of the ultrasonic wave radiated previously. CONSTITUTION:When an ultrasonic wave is radiated from a transmission sensor 5 to be reflected on an object, the reflected wave is received with a reception sensor 6 and converted into an electrical signal with a receiving circuit 7 to detect a peak value thereof with a peak detection circuit 13. In one distance measuring cycle, the peak value detected with the peak detection circuit 13 is compared with the peak value stored in a memory 14 with a CPU 1 sequentially and the larger one is stored into the memory 14. At the same time, the CPU 1 works the memory 14 to store time T to the detection of the peak value from the start of the distance measuring cycle as supplied from a timer 15. Then, the CPU 1 performs a computation to measure a distance to the object from the ultrasonic sensor from the time T at which the maximum peak value is detected within a specified time of the distance measuring cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor which emits an ultrasonic wave and detects a reflected wave generated when the ultrasonic wave is reflected by an object.

[0002]

2. Description of the Related Art Conventionally, there is known a mobile robot that autonomously travels according to a built-in map. As a guidance method for such a mobile robot, the guidance is performed while measuring the distance to the wall of the travel route or the work target by an ultrasonic sensor (consisting of a transmitter and a receiver) attached to the mobile robot. What is done is adopted.

FIG. 4 is a block diagram showing a configuration example of an ultrasonic sensor installed in such a mobile robot. In this figure, the CPU 1 outputs a start signal to the ultrasonic wave generation circuit 2 and the counter 3. As a result, the ultrasonic wave generation circuit 2 generates an ultrasonic wave of 45.45 kHz, and at the same time, the counter 3 starts counting. The ultrasonic wave generated by the ultrasonic wave generation circuit 2 is supplied to the wave transmission circuit 4, is resonantly amplified by the wave transmission circuit 4, and is emitted from the wave transmission sensor 5.

Wave transmission sensor 5
The ultrasonic waves radiated by are reflected by the work place of the mobile robot and detected by the wave receiving sensor 6. The detected reflected wave is converted into an electric signal by the wave receiving circuit 7, and signals other than ultrasonic waves are cut by the bandpass filter 8. FIG. 5A shows the detected received waveform. Then, the absolute value circuit 1 is amplified by the amplifier circuit 9.
A 0 folds the negative part. The waveform after this folding back is shown in FIG. Next, the signal is passed through the low-pass filter 11 to extract an envelope as shown in FIG. Then, the level of this envelope is detected by the comparator 12. That is, as shown in FIG. 5D, the detection voltage level V _LEV is set in the comparator 12 in advance.
When the signal level shown in (c) exceeds this detection voltage level V _LEV (see time t _A ), it is determined that the primary reflected wave W ₁ has been detected. When the primary reflected wave is detected, the output signal of the comparator 12 causes the counter 3 to stop counting.

Therefore, the counter 3 measures the time from the emission of the ultrasonic wave to the detection of the reflected wave.
As a result, the distance L (m) from the sensor to the object is obtained by the following formula. L = √ [{(T−T _D ) × v} ² −l _H ² ] / 2−l _D (1) where T is the time [s] measured by the counter 3,
T _D is a delay time of a circuit or the like [s], v is a speed of sound at T ° C. [m / s], l _H is a vertical distance [m] between the transmitting sensor and the receiving sensor, and l _D is the transmitting sensor 5 The distance [m] from the actual sensor to the tip of the horn is shown.

[0006]

By the way, in the above-mentioned conventional ultrasonic sensor, multiple reflected waves are detected in addition to the primary reflected wave W ₁ of the emitted ultrasonic waves. Then, this multiple reflected wave is detected by the comparator at the detected voltage level V
_May be detected as exceeding _LEV . For example, as shown in FIG. 5 (d), after the primary reflected wave W ₁ 2
It is assumed that the next reflected wave W ₂ is detected as exceeding the detection voltage level V _LEV . When the distance measurement is performed only once, there is no problem because the primary reflected wave W ₁ is detected earlier than the multiple reflected waves after the secondary reflected wave W ₂ . However, in general, distance measurement is continuously performed at predetermined intervals according to the traveling speed of the mobile robot and the like. For example, when the distance measurement is continuously performed at a cycle of 25 msec, as shown in FIG.
_The previous multiple reflection wave W ₂ 'exceeding _LEV may be detected as a distance measurement waveform before the current primary reflection wave W ₁ which should be detected originally (see time t _B ). Therefore,
When continuous distance measurement is performed at a constant cycle, there is a problem that the original reflected wave and the previous multiple reflected waves cannot be distinguished and a correct distance measurement value cannot be obtained.

The present invention has been made under such a background, and corrects the distance measurement by distinguishing the reflected wave of the ultrasonic wave emitted this time from the multiple reflected wave of the ultrasonic wave emitted previously. An object is to provide an ultrasonic sensor capable of obtaining a value.

[0008]

An ultrasonic sensor according to the present invention radiates ultrasonic waves at regular intervals and detects a reflected wave generated when the ultrasonic waves are reflected by an object to detect the distance to the object. In the ultrasonic sensor for measuring, a peak detection means for detecting a peak value of the reflected wave, and a control means for making a maximum one of the peak values the primary reflected wave of the ultrasonic wave are provided. I am trying.

[0009]

According to the above construction, when the ultrasonic wave is radiated at regular intervals and reflected by the object, the peak value of this reflected wave is detected by the peak detecting means. The control means detects the maximum peak value among the peak values detected by the peak detection means as the primary reflected wave.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an ultrasonic sensor according to an embodiment of the present invention. In this figure, parts corresponding to those in FIG. 4 are assigned the same reference numerals and explanations thereof are omitted. In FIG. 1, 13 is a peak detection circuit, which detects the peak value of the waveform signal supplied from the absolute value circuit 10 and supplies a signal (hereinafter, detection signal) to the CPU 1 to inform that the peak value has been detected. . 1
Reference numeral 4 denotes a memory, which is used by the CPU 1 to detect the peak detection circuit 1
The peak value detected by 3 is stored. Also, 15
Is a timer, which supplies a clock signal to the CPU 1 at predetermined time intervals. CPU1 is the peak detection circuit 1
When the detection signal is supplied from 3, the peak value detected at that time is stored in the memory 14. Further, the CPU 1 counts the clock signal supplied from the timer 15 to measure the time T (hereinafter, detection time) from the start of the distance measuring cycle to the detection of each peak value. At the same time, the detection time T of the peak value is stored in the memory 14.

Next, the operation of this embodiment will be described with reference to the time chart shown in FIG. Hereinafter, a case will be described where the distance measurement with a constant distance measurement period is continuously performed. First,
At time t ₁ , the CPU 1 outputs a start signal for the nth distance measurement cycle to the ultrasonic wave generation circuit 2, and the ultrasonic wave generation circuit 2 generates ultrasonic waves. At the same time, CPU1
Starts counting the clock signal supplied from the timer 15. The ultrasonic wave is supplied to the wave transmission circuit 4, is resonantly amplified, and is emitted from the wave transmission sensor 5. Here, when the reflected wave is detected by the wave receiving sensor 6, the reflected wave is converted into an electric signal by the wave receiving circuit 7 as in the conventional case,
It is input to the peak detection circuit 13 via the bandpass filter 8, the amplification circuit 9, and the absolute value circuit 10.

FIG. 3 shows an example of the waveform signal input to the peak detection circuit 13. As shown in this figure, in the peak detection circuit 13, each peak value P, P, ...
_{P w2 ', ..., P w1} , ..., P is detected. A detection signal is supplied from the peak detection circuit 13 to the CPU 1 every time the peak values P, P, ..., P _{w2 ′} , ..., P _w1 , ..., P are detected. When the CPU 1 receives this detection signal,
The detection time T of the peak value P, which is the count value of the clock signal from the timer 15, is stored in the memory 14 together with the peak value P detected by the peak detection circuit 13. The CPU 1 sequentially performs this process at the time T _s until the time t ₄ shown in FIG.

When the time T _s elapses, the CPU 1 reads out all the peak values P, P, ..., P _{w2 ′} , ..., P _w1 , ..., P stored in the memory 14 from time t ₁ to time t _4. , By performing the comparison calculation, the peak value P of the distance measurement cycle,
The maximum of P, ..., P _{w2 ′} , ..., P _w1 ,. This value becomes the peak value of the primary reflected wave in this distance measurement. For example, as shown in FIG. 3, at time t ₂ , the peak value P of the multiple reflection wave by the n-1th distance measurement is obtained.
_{It is assumed} that _{w2 ′} is detected, and at time t ₃ , the peak value P _w1 of the primary reflected wave in the nth distance measurement cycle is detected. In this case, the peak value P _w1 is obtained as the maximum value at the time T _s . Therefore, the CPU ₁ reads out the time T _w1 from the time t ₁ to the time t _3, and uses this time T _w1 to perform the calculation of the distance measurement by the above-mentioned formula (1). Then, at time t ₅ , the (n + 1) th distance measurement is started. The above time t
The time T _c from ₄ to the time t ₅ is the time for calculating the distance measurement, and therefore the time T _s is set shorter than the distance measurement cycle.

As described above, according to this embodiment, even if the (n-1) th multiple reflection wave W _2'is input before the nth distance measurement primary reflection wave W ₁ , Since the multiple reflected wave due to the ultrasonic wave radiated the second time is attenuated, the peak value P _{w2 ′} of the multiple reflected wave W _{2 ′} is smaller than the peak value P _w1 of the primary reflected wave W ₁ . Therefore, by comparing the peak values, the primary reflected wave of the distance measurement can be distinguished from the multiple reflected wave of the previous distance measurement, and the correct distance measurement value can be obtained.

[0015]

As described above, according to the present invention, the peak detecting means for detecting the peak value of the reflected wave and the control means for making the maximum peak value the primary reflected wave are provided. Therefore, the reflected wave of the ultrasonic wave radiated this time and the multiple reflected wave of the ultrasonic wave radiated last time can be discriminated, and the correct distance measurement value can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an ultrasonic sensor according to an embodiment of the present invention.

FIG. 2 is a time chart explaining the operation of the ultrasonic sensor according to the embodiment.

FIG. 3 is a diagram showing an example of an input waveform of a peak detection circuit 13 in the same embodiment.

FIG. 4 is a block diagram showing a configuration of a conventional ultrasonic sensor.

5A is an output waveform of the wave receiving circuit 7, FIG. 5B is a waveform after passing through the absolute value circuit 10, and FIG. 5C is a low-pass filter 1.
The waveform after one passage, and (d) are diagrams showing the waveform for explaining the level detection of the waveform signal.

FIG. 6 is a diagram illustrating a problem of level detection in a conventional ultrasonic sensor.

[Explanation of symbols]

 1 CPU 5 Wave Sending Sensor 6 Wave Receiving Sensor 13 Peak Detection Circuit 14 Memory 15 Timer

Claims (1)

[Claims] 1. An ultrasonic sensor for radiating an ultrasonic wave at regular intervals and detecting a reflected wave generated when the ultrasonic wave is reflected by an object to measure a distance to the object. An ultrasonic sensor comprising: a peak detection unit that detects a peak value; and a control unit that sets a maximum one of the peak values as a primary reflected wave of the ultrasonic wave.