JPH0656415B2 - Ultrasonic distance detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic distance detecting device used for detecting a distance to an object to be detected using ultrasonic waves.

<Prior Art> Sound waves are radiated from the wave transmitter toward the object to be detected, the reflected wave is captured by the wave receiver, the time from the wave to the wave is measured, and the distance to the object to be detected is measured. Various ultrasonic distance detection devices for measuring have been proposed.

The output waveform from this wave transmitter and the input waveform from the wave receiver are as shown in FIGS. That is, when the wave signal of FIG. 4B is output from the wave transmitter on the basis of the wave transmission signal S _{1 having the} pulse width w (FIG. 4B), the wave signal of FIG. The signal is captured by the wave receiver and is detected as a wave reception signal S ₂ (FIG. 4D) by the detection process. By the way, since the received signal S ₂ is a half-wave signal in which the intensity F of the reflected wave becomes wavy, the receiving time varies depending on which position is the acquisition time.

In this case, it is easiest to take the capture time with the maximum value of the reflected wave intensity F (vertex of the wave), but when there are multiple vertices due to unevenness on the surface of the object to be detected, as shown in FIG. Error is likely to occur.

In order to improve this, there is also a method in which a specific value of the reflected wave intensity F is set as a discriminant value L and the time when the intensity becomes that is set as the capture time by the wave receiver. However, even with such a method, as shown in FIG. 7, the reflected wave intensity F of the measured waveform y may be lower than the normal waveform x due to wind fluctuations and the like.

In this case, the reflected wave intensity F of the discriminant value L appears late as shown in FIG. 8, so that the capture time is delayed and an error ΔT occurs.

Therefore, in order to detect the accurate wave reception time T, it is necessary to subtract the error ΔT from the time (measurement time) T _s until the discrimination value L. That is, it is necessary to calculate the reception time T from the formula T = T _s −ΔT.

And as one of the means, the maximum value of the reflected wave intensity F,
The error ΔT means that the lower the maximum value of the reflected wave intensity F, the more the error ΔT.
Since T has a relationship of increasing, a correction table is created based on the relationship, the maximum value of the reflected wave intensity F is detected, the error ΔT is determined from the correction table, and the measured value Ts is corrected. The method of determining the accurate reception time T can be taken.

<Problems to be Solved by the Invention> However, with such a means, it is necessary to prepare a correction table in advance, formulate it, and input it into the control device, which is troublesome, and the correction table has a limited condition. However, there is a difficulty in being able to cope with changes in the situation, since it is approximately satisfied only in.

It is an object of the present invention to provide an ultrasonic distance detecting device provided with a correcting means, which can eliminate such various conventional defects as much as possible.

<Means for Solving Problems> According to the present invention, a wave transmitter T that is driven by an ultrasonic pulse generator to radiate ultrasonic waves to an object m to be detected, and a reflected wave from the object m to be detected. Wave receiver R and first time function f (t) that increases with time at a certain gradient
And a second time function f ′ that decreases with time at a predetermined gradient.
(t) generating means, while outputting a transmission signal to the ultrasonic pulse generator,
At the same time as the fall of the transmitted signal, the first time function f (t)
Of the reflected wave intensity F set in advance in the transmission control circuit for activating the first generation time function f (t) to start advancing the first time function f (t) and the reception signal S ₂ from the receiver R. High and low discriminant values l ₁ and l ₂
Is applied to determine the arrival time, and the first discriminant value l _{1 of} the reflected wave intensity F becomes low, and at the same time, the first time function f
(t) is stopped and the second time function f ′ (t) is advanced from the stop point to obtain the second discriminant value l ₂ with high reflected wave intensity F, and at the same time the second time function f ′ (t) is reached. The progress of f ′ (t) is stopped, and the stop value of the second time function f ′ (t) is
Index value setting means for setting an index value of the distance between the object to be detected m and the wave transmitter T is provided.

<Operation> The ultrasonic wave is emitted to the object m to be detected by the wave transmitter T, and the reflected wave is captured by the wave receiver R. This received signal is shaped as shown in FIG. 4, and it becomes a low discriminant value l ₁ by using discriminant values l ₁ and l ₂ of two reflected wave intensities F of high and low as shown in FIG. At the same time, while stopping the first time function f (t),
At the same time that the second time function f ′ (t) is advanced to a high discriminant value l ₂ , the second time function f ′ (t) is stopped from progressing, and the stop value is set to the detected object m. And an index value of the distance between the transmitter T and the transmitter T.

That is, as shown in FIG. 1, since the rising portion of the normal waveform x has a steep slope, the low discrimination value l ₁ to the high discrimination value l ₂
The time to reach is short. Therefore, the rising value due to the first time function f (t) is small and the falling value due to the second time function f ′ (t) is small. Then, the second time function f ′
The stop value of (t) is used as an index value of the distance between the detected object m and the transmitter T.

On the other hand, when the ultrasonic waves reflected by the same detected object m are fluctuations in the wind or the like and the measurement waveform y having a low reflected wave intensity F is received by the wave receiver R, the detected object m is the same. Therefore, the rising positions are almost equal, and the rising slope is gentle. Therefore, it takes a long time to reach the low discriminant value l ₁ , a large rise value until the stop of the first time function f (t), and a long time to reach the high discriminant value l ₂ , and the second time The falling value of the function f ′ (t) until it stops is also large.
That is, the rise due to the first time function f (t) is canceled by the fall due to the second time function f ′ (t).
Therefore, the stop value of the second time function f '(t) comes close to the stop value of the normal waveform x as shown in FIG.

Therefore, when the rising positions are the same, it is possible to obtain almost the same stop values of the second time function f '(t). Moreover, since the first time function f (t) progresses with the wave transmission, when the rising position is different (distance of the object m to be detected is different), the stop value which is almost proportional to the distance of the rising position is taken out. You will get it.

Therefore, even if the reflected wave intensity F is reduced due to wind fluctuations or the like, it is possible to detect the distance of the detected object m as accurately as possible.

The stop value is determined by the configuration of the time function generating means and is detected as a voltage value, a current value, or the like.

<Embodiment> An ultrasonic distance detecting apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 2 shows an embodiment of the ultrasonic distance detecting apparatus of the present invention.

That is, the wave transmitter T and the wave receiver R are placed in parallel so as to face the object m to be detected. The wave transmitter T and the wave receiver R
A piezoelectric transducer or the like that oscillates by applying an alternating voltage to the piezoelectric element and that receives an ultrasonic wave by the piezoelectric element and can convert the ultrasonic wave into a signal is applied.

The transmitter T is connected to the transmission control circuit 1 and the ultrasonic pulse generator 2 and is based on the transmission signal S ₁ of FIG. Then, an alternating voltage (FIG. 4B) having a predetermined frequency is generated and applied to the piezoelectric element in the transmitter T to radiate ultrasonic waves.

Further, the wave receiver R is connected with an amplifier 4 for amplifying a signal received by a piezoelectric element, a wave detector 5, and a waveform shaper 6, and is connected with a reflected wave intensity correction circuit 7 and a measurement circuit 8. It As shown in FIG. 2, the reflected wave intensity correction circuit 7 and the measurement circuit 8 are also connected to the transmission control circuit 1.

On the other hand, the waveform shaper 6 converts the half-wave signal (FIG. 4D) from the detector 5 into the discriminant values l ₁ and l ₂ of the two reflection intensities F.
To form rectangular pulses P ₁ and P ₂ (FIG. 4E and F) and output command signals d ₁ and d ₂ to the analog switch control circuit 9 of the reflected wave intensity correction circuit 7 at the same time as rising thereof. is there. The waveform shaper 6 constitutes the index value setting means according to the present invention together with the reflected wave intensity correction circuit 7.

As shown in FIG. 3, the reflected wave intensity correction circuit 7 is formed by connecting the analog switch control circuit 9, the capacitor C, the resistor r, and the switches sw ₁ , sw ₂ and sw ₃ to each other. Here, the switches sw ₁ and sw ₂ are connected in parallel to the capacitor C via the resistor r, one end of the switch sw ₁ is connected to the DC power source, and one end of the switch sw ₂ is grounded, and the analog switch control circuit 9 is provided. Command signal d ₁ ,
Opening / closing is controlled by d ₂ . Also, the switch sw ₃ has one end connected to the capacitor C and the other end grounded, so that the opening / closing control is performed at the same time as the rising and falling of the transmission signal S ₁ (FIG. 4B) of the transmission control circuit 1. .

As described above, the waveform shaper 6 provides the received signal S ₂ from the wave receiver R with the two discriminant values l ₁ and l ₂ having different reflected wave intensities F, and The reflected wave intensity correction circuit 7 stops the first time function f (t) at the same time when the reflected wave intensity F becomes the _first discriminant value l _1, and the second time function f ′ (t ), The second discriminant value l ₂ having a high reflected wave intensity F is reached, and at the same time, the second time function f ′ (t) is stopped from progressing. And the reflected wave intensity correction circuit 7 constitute the index value setting means according to the present invention.

Next, the operation of this embodiment will be described.

First, by the operation of the transmission control circuit 1 and the ultrasonic pulse generator 2, the ultrasonic wave signal S ₁ (FIG. 4A) is controlled, and the ultrasonic wave signal of a predetermined frequency is transmitted from the wave transmitter T (FIG. 4B). Oscillates. At the same time when the transmission signal S ₁ rises, the transmission control circuit 1 closes the switch sw ₃ and switches the switch sw _3.
1 , ₁ and sw ₂ are separated (FIG. 5D), the capacitor C discharges via the conductive path 10 and zeroes out. Next, at the same time as the fall of the transmission signal S ₁ , the switch sw ₃ is opened and the switch sw ₁ is closed, and the charging of the capacitor C from the conductive path 11 is started.

As a result, the capacitor C has a potential V according to the first primary time function f (t) having a predetermined slope as shown in FIG.
Rises.

Next, the ultrasonic wave from the wave transmitter T is reflected by the object m to be detected and is captured by the wave receiver R, the signal of FIG. 4C is received, and the half wave is detected by the wave detector 5. The wave-shaped received signal S ₂ is detected. Here, in the waveform shaper 6, the discriminant values l ₁ and l _{2 of the} two predetermined high and low reflected wave intensities F are preset, and the waveform of the received signal S ₂ is shaped. That is, the low discrimination value l ₁ forms the rectangular pulse P ₁ , and the high discrimination value l ₂ forms the rectangular pulse P ₂ .

Then, along with the rise of the rectangular pulse P ₁ , the waveform shaper 6 sends a command signal d ₁ to the analog switch control circuit 9, and the command signal d ₁ causes the analog switch control circuit 9 to open the switch sw _1. Switch sw ₂
Is closed (Fig. 5B). As a result, the charging of the capacitor C is stopped and the discharging is started via the conductive path 12. That is, the potential V of the capacitor C decreases with the lapse of time based on the second primary time function f ′ (t) having a predetermined gradient.

Next, the command signal d ₂ is sent from the waveform shaper 6 to the analog switch control circuit 9 along with the rise of the rectangular pulse P ₂ , and the control circuit 9 opens the switch sw ₂ by this command signal d _2. (Fig. 5 c). Thus, the discharge of the capacitor C is stopped, and the measuring circuit 8 detects the potential V _p (stop value).

Then, again, the switch sw ₃ is closed (FIG. 5D) under the control of the transmission control circuit 1 with the rise of the transmission signal S ₁ , and the capacitor C is discharged again and returns to zero.

In this process, the potential V _p output from the measuring circuit 8 is
It serves as an index value of the distance between the detected object m and the transmitter T. That is, since the first primary time function f (t) proceeds with the fall of the transmitting signals S _1, the potential V _p being determined by the discriminating value l _1, l ₂ is received wave from transmitting signals S ₁ It is almost proportional to the time of the rising position of the signal S ₂ . Therefore, the potential V _p can be an index value of the distance between the detected object m and the wave transmitter T. Therefore, it is possible to detect the distance from the wave transmitter T and the wave receiver R to the detected object m based on the value of the potential V _p .

The potential V _p is above the locus lowered accordance with a second time function f inverted by discriminating value l ₁ from the first primary time function f (t) '(t) , to stop the discrimination value l ₂ It is taking the value that stopped. Therefore, even if the inversion wave intensity F is low, a substantially constant potential corresponding to the position of the object m to be detected.
V _p can be detected.

That is, when the waveform of the received signal S _{2 has} a low reflected wave intensity F due to the fluctuation of the wind, the rising gradient thereof is gentle.
Therefore, since the time to reach the low discriminant value l ₁ is long, the increase value to reach the stop of the first primary time function f (t) is large, and the time to reach the high discriminant value l ₂ is long. The descending value until the stop of the primary time function f ′ (t) is also large. Thus, if the rise is based on the first primary time function f (t), it will be canceled by the fall based on the second primary time function f '(t). Therefore, even if the reflected wave intensity F is high or low, the stop value V _{p of} the second primary time function f ′ (t) is
Is almost constant, and it is possible to detect a substantially constant wave reception time corresponding to the position of the object m to be detected.

In the present embodiment, the time functions f (t) and f '(t) are generated by the charging / discharging time of the capacitor to be a linear function, but the first time function f (t) has a predetermined gradient and the transmitter It suffices that the conditions that the oscillation progresses from T and that increases with time are satisfied, and that the second time function f ′ (t) progresses at the same time as the stop of the first time function f (t). , A quadratic function may be used as long as it satisfies the condition that the gradient decreases with time. Further, the index value setting means can also be configured by a central controller.

<Effects of the Invention> As described above, the present invention can detect the predetermined wave receiving time corresponding to the position of the object m to be detected even if the reflected wave intensity F is reduced due to the fluctuation of the wind or the like. Therefore, there is an excellent effect that the distance can be detected as accurately as possible.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing a correction means of the present invention, FIG. 2 is a detection circuit diagram of an embodiment, FIG. 3 is a detailed diagram of a reflected wave intensity correction circuit 7, and FIGS. Fig. 5
D is a circuit diagram showing the operation of the reflected wave intensity correction circuit 7,
FIG. 7 is a waveform diagram showing an example of the received signal, and FIG. 8 is a waveform diagram showing a conventional correction means. 1; transmission control circuit, 2; ultrasonic pulse generator, 6; waveform shaper, 7; reflected wave intensity correction circuit, 8; measurement circuit, 9;
Analog switch control circuit, sw ₁ , sw ₂ , sw ₃ ;
Switch, T: Wave transmitter, R: Wave receiver

Claims (2)

[Claims] 1. A wave transmitter T which is driven by an ultrasonic pulse generator and radiates ultrasonic waves to an object m to be detected, a wave receiver R which receives a reflected wave from the object m to be detected, and a predetermined wave. First time function f (t) that increases with time in the gradient
And a second time function f ′ that decreases with time at a predetermined gradient.
(t) generating means, while outputting a transmission signal to the ultrasonic pulse generator,
At the same time as the fall of the transmitted signal, the first time function f (t)
Of the reflected wave intensity F set in advance in the transmission control circuit for activating the first generation time function f (t) to start advancing the first time function f (t) and the reception signal S ₂ from the receiver R. High and low discriminant values l ₁ and l ₂
Is applied to determine the arrival time, and at the same time when the first discriminant value l _{1 of} the reflected wave intensity F is low, the first time function f (t) is stopped, and The second time function f ′ (t) is advanced to reach the second discriminant value l ₂ with high reflected wave intensity F, and at the same time, the second time function f ′ (t) is stopped and the second time function f ′ (t) is stopped. An ultrasonic distance detecting apparatus, comprising: an index value setting means for setting a stop value of the second time function f '(t) as an index value of a distance between the object to be detected m and the transmitter T. 2. The means for generating the first time function f (t) is started to be charged at the same time as the falling edge of the wave transmission signal from the wave transmitter T, and a predetermined gradient is obtained depending on the relationship between the charging time and the potential V. At the first time function f (t) which increases with time, the means for generating the second time function f ′ (t) is used to stop the first time function f (t). A capacitor C for generating a second time function f '(t) which starts discharging at the same time and decreases with time according to a relationship between the discharging time and a potential V with a predetermined gradient. The ultrasonic distance detection device according to item 1.