JPS63235879A - Ultrasonic obstacle detector - Google Patents

Abstract

PURPOSE:To achieve a higher distance measuring accuracy with the correction of errors due to wind direction or the like, by averaging propagation times for continuous even frequencies arithmetically as extracted each time connection is switched between a transmitting element and a receiving element to calculate distance to an obstacle. CONSTITUTION:A switching circuit 6 is provided to reconnect a transmitting element 1, connected to a transmission circuit 4, to a reception circuit 5 while a receiving element 2 connected to the reception circuit 5 is reconnected to the transmission circuit 4. Then, a signal is sent to the switching circuit 6 from a control section 10 comprising a microcomputer to which the connection. A measuring circuit 3 averages propagation times for continuous even frequencies arithmetically as extracted each time the connection is switched to calculate distance to an obstacle. Thus, the measuring circuit 3 calculates distance to the obstacle allowed for a base line distance between the elements 1 and 2 to correct errors due to wind direction with the switching circuit 6, the control section 10 and the measuring circuit 3 thereby achieving a higher distance measuring accuracy.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention detects the presence or absence of an obstacle at a predetermined distance based on the round-trip propagation time for an ultrasonic pulse emitted into the air until it is reflected by an obstacle and returns. The present invention relates to an ultrasonic obstacle detection device that detects by contact and is particularly suitable as a proximity recognition device for a self-propelled robot that cleans a room while avoiding obstacles.

[Conventional technology]

Research and development of devices that measure the distance to obstacles and determine the presence or absence of obstacles by measuring the propagation time of ultrasonic pulses propagating through the air has been actively conducted for about 10 years. There is.

Many applications have been put into practical use, including autofocus in cameras, object detection behind cars, intrusion alarms in homes, and level measurement in storage rooms.

Of these, for autofocus, for example, National Technical Revo), '1101. 28°No,
2.19B2, April, P., 317-330, "Autofocus System for 2-Deo Camera".

Regarding level measurement, for example, sensor technology, Vo
l, 5. No. 6. May 1985 Special Issue (Sensor Circuit Design Book) P, 258-259゜P, 262-265 "Ultrasonic Level Meter Receiving Circuit",
Examples include those described in "Configuration and circuit of ultrasonic level meter", and these are relatively long distances (50 am or more).
This makes it possible to measure distances accurately and reliably.

In particular, in the above-mentioned known example, STC (Sensitivity) is used as a device to accurately detect propagation time.
)FTime Control) is adopted. Here, STC will be briefly explained.

The longer the measurement distance from the transmitting/receiving element to the obstacle, the more
That is, the longer the propagation time, the smaller the amplitude of the reflected wave of the ultrasonic pulse from the obstacle.

For this reason, an amplitude-dependent time detection error appears, but the error is corrected using a reference signal (STC signal) that changes depending on time. STC is a method that attempts to remove self-generated noise (direct waves) that are not reflected waves from @.

Specifically, there are the following two methods.

(1) A method in which the gain of the preamplifier that amplifies the received signal is kept low during transmission, and increased over time after transmission.

(2) A method in which the received signal after envelope linear detection is waveform-shaped using a threshold value that is high during transmission and becomes lower as time passes after transmission.

Note that a charging/discharging voltage generated by a resistor and a capacitor is generally used as the reference signal.

Now, acoustic noise and wind are major error factors for ultrasonic signals in the air. Acoustic noise can be roughly divided into three types: direct waves, reverberation, and external noise.

A direct wave leaks directly from a transmitting element to a receiving element, and one of its media is a structure that supports the transmitting and receiving element.

Therefore, since the spacing between the elements is short and the speed of sound in a solid is an order of magnitude higher than in air, the direct wave is detected by the receiving element almost at the same time as the transmission starts.

This direct wave is prevented from becoming a problem even in the conventional example by the above-mentioned STC.

Reverberation occurs when ultrasonic waves emitted by a transmitting element undergo multiple reflections between multiple obstacles, scattering and reverberating before reaching the receiving element. After the detection of the main reflected wave, a similar reflected wave (however, its envelope The frequency component is low and the amplitude is small), which is repeatedly detected by the receiving element.

Note that even if there is no multiple reflection, if there is an obstacle with a large reflective ability far behind the obstacle to be measured, significant noise will be generated.

Conventionally, this type of noise has been dealt with by making the transmission interval of ultrasonic pulses sufficiently long.The setting of the interval depends on the designer's experience, and it varies and is sometimes insufficient. It may malfunction with incorrect settings.

This is because appropriate setting values differ depending on conditions such as the place where the device is used. In this respect, the above-mentioned level meter has limited conditions and is relatively easy to set appropriately. Incidentally, if the transmission interval becomes long, a problem naturally arises in response time.

External noises include telephones, clock bells, buzzers, and the sound of coins colliding, which contain ultrasonic components.In addition to these being edicted by the WA as a cause of malfunction, there are now ultrasonic noises from televisions, air conditioners, etc. The pulse emitted by the sonic remote controller is a major factor.

Furthermore, motors are used in self-propelled cleaning robots.

Measures also need to be taken to deal with the steady noise generated by the cleaner system.

In the autofocus system of the above-mentioned camera, these external noises are dealt with mainly by the software of the micro combinator (hereinafter referred to as microcomputer).
The method is to select data with similar numerical values from among the data detected several times, and consider the average value of the selected data to be the true value. This method is considered effective against impulse noise.

However, considering the influence of the periodic ultrasonic pulses emitted by the remote controller and the influence of time detection data shifted by stationary noise (long-period errors in the hardware stage), it is difficult to avoid obstacles. However, it cannot be applied to self-propelled robots that clean rooms.

Next, the influence of wind will be explained. When the air, which is the propagation path, is disturbed by wind, the sound pressure amplitude of the received ultrasonic wave,
It is known that both phases vary greatly, which can cause malfunctions.

Here, considering the influence on the speed of sound, the speed of sound and the wind speed influence each other in a one-to-one correspondence, as shown in the principle of an ultrasonic flowmeter. In other words, assuming that the sound speed in still air is C1 and the wind speed is V, when the propagation direction of the ultrasonic wave is the same as the wind direction, the sound propagation speed is (C+v), and when it is in the opposite direction to the wind direction, it is ( C
-v).

The speed of sound C in air is about 544 m/s, and the normal wind speed V is several m/s, so it can be said that C > ) v, but since the wind speed V during strong winds is about 10 o1/8, This cannot be ignored from the point of view of accuracy.

Only when the propagation direction of the ultrasonic wave and the wind direction are in the same axial direction, changes in the sound speed of the emitted wave and the sound speed of the reflected wave cancel each other out and pose no problem. However, if the two directions overlap, an error will occur that varies depending on the angle they form.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, no consideration was given to errors caused by wind direction, and there were problems in terms of accuracy and malfunction when applied to self-propelled robots and the like.

Regarding the distance calculation method, the conventional technology simply applies a basic method in which the distance is 1/2 of the product of the propagation time and the speed of sound in all cases, and adopts a transmitting and receiving only type as the system configuration. However, errors due to the spacing between the transmitting and receiving elements were ignored.

An object of the present invention is to provide an ultrasonic obstacle detection device that eliminates errors caused by wind direction and the distance between a transmitting element and a receiving element, has good distance measurement accuracy, and detects the presence or absence of an obstacle in a non-contact manner. purpose.

[Means for solving problems]

Obstacle detection using reflection of ultrasonic pulses is basically the same as ultrasonic distance measurement, and the distance measurement principle in the present invention will be explained here.

First, in an ultrasonic obstacle detection device that measures a relatively short distance (50 cm or less), a transmitting/receiving type that uses separate electroacoustic transducers is suitable for the configuration of the transmitting element and receiving element.

The reason for this is that in a transmitter/receiver type that uses a transmitting element and a receiving element in common, it is not possible to receive while transmitting, and it is difficult to receive immediately after transmitting due to the transient response characteristics of the converter (piezoelectric ceramic, etc.).

FIG. 2 is a conceptual diagram of a transmission/reception type ultrasonic distance measurement according to the present invention, and the distance measurement principle of the present invention will be explained below using this diagram.

In the figure, a radiation wave (ultrasonic pulse) emitted from a transmitting element is reflected by an obstacle in front, and this reflected wave reaches the receiving element at a time Tx after being radiated. The reflected sound pressure PO from an obstacle at the position of this receiving element is determined by the distance from the transmitting element to the index point (between the obstacle and The distance to the arbitrarily determined position is X+, the sound pressure on the transmitting element side at the index point is PI, the absorption coefficient is α1, the reflection ability is Rp
Then, it can be expressed by the following formula.

p, = p, e 1(X t ”
r − represent Further, when applied to the case of a transmitting/receiving only type, the reflection power RP can be expressed as follows.

・・・・・・・・・(2) Here, if there is no scattering attenuation factor in the propagation path, the incident sound pressure Ptr is as follows:
This is nothing but the reflected sound pressure P at the position of the receiving element.

Note that the reach distance 1 of ultrasonic waves in the air is simply expressed by the following formula.

1 = xt 10Xr = 4.5 X 1 010 / f2 (m)...
(6) Here, f is the frequency of the ultrasonic wave. Equation (5) shows that when the frequencies are separated, the attenuation increases and the reach distance becomes 1 or shorter.

However, the reach distance l naturally changes depending on the transmission power, reflection power Rp, noise level, etc., and equation (3) indicates a generally good value as a general guide.

By the way, the reflected sound pressure P in equation (1) is converted into the received voltage Vx by the altruism element. Furthermore, if the transmission voltage Vt applied to the transmission element is at a small signal level, the sound pressure P at the index point is proportional to the transmission voltage Vt. Further, within a range where the sound speed C can be considered to be approximately constant, km (xt+xr) is proportional to the time TX. Therefore, once the detection target is determined, the following approximate equation holds true, with the attenuation constant being Ω.

■R=vTΩe−αTx/TX...song...
...Song...Song...Equation (4) (4) shows that the faster the obstacle is, the longer the propagation time is, and the level of the received voltage Vi is e-
”It shows that it decreases according to TX/Tx.

Now, if the baseline distance, which is the interval between the transmitting and receiving elements, is D, and the measured distance between the transmitting and receiving elements and the obstacle is X, then the propagation distance of the ultrasonic wave (xt+x,) is x+b-i.

On the other hand, the sound speed C of the ultrasonic wave is c=s, where t is the temperature in degrees Celsius.
s1.45+0.6o7t, (m/S)−・−・−−
---It is approximated as in (5). Furthermore, the temperature coefficient θ
is θ=0.607/331.45X100=0.183
(%/℃) ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・(6).

Here, the time Tx is expressed as (xt+xr)/C, and since (xt+xr) is X + D2 + X2, the measured distance X can be expressed as in the following equation.

I D2 x = (TX c Tx C> ・・・・・・・・・
...... River... (7) It is clear from equation (7) that there is a time Tn during which distance measurement is invalid after the ultrasonic wave is radiated. In other words, the time Tx at which X=0
is Tn and is expressed by the following formula.

Tn=D/C・・・・・・・・・・・・ Song・
...beat, song, river... (8) The above is...
This is the distance measurement principle related to the present invention, and the measurement distance @X is calculated based on equation (7).

Therefore, the objects of the present invention described above are as follows (1) to (
9) can be achieved by adopting technical means.

(1) STC is employed to exclude direct waves, and its reference signal (STC signal) is set to a function of e-αTx/Tx. In other words, the time Txtl-e-αTX/TX
Converts the STC signal into the signal generator section.

(2) In order to exclude the influence of reverberation, the transmission interval To is set to 4
, 5X1 o10/(f2 C) or more and less than twice that. Note that here, f is the frequency and C is the speed of sound.

(3) As an air temperature correction unit that corrects the temperature characteristics of the sound speed C,
An amplifier with a thermistor inserted in the negative feedback loop is provided.

In other words, the gain of this amplifier has the temperature coefficient of θ in equation (6).

(4) In order to eliminate malfunctions due to impulse noise, etc., there is a pulse width setting section that accurately sets the width of the ultrasonic pulse, a pulse width reading section that detects the pulse width of the reflected wave, and this pulse width reading section. A determining unit is provided to determine whether the output data is valid or invalid, and a measuring circuit is provided to extract (calculate) the distance from the propagation time when the determining unit considers the output data to be valid.

(5) A floating threshold generator is provided to eliminate errors caused by stationary noise and the like. This floating threshold generation section integrates the received signal and generates a floating threshold. The floating threshold increases as the presence of stationary noise increases, and also increases slightly to cope with the tendency for signals with larger amplitudes to have wider widths relative to normal received signals. Then, an adder is provided to add this floating threshold to the STC reference signal. This eliminates stationary noise added to the normal received signal.

(6) A measurement circuit is provided that calculates the distance X from the detected propagation time Tx using equation (7).

(7) A measurement circuit is provided that displays that distance measurement is uncertain when the detected propagation time Tx is within the distance measurement invalid time Tn of equation (8).

(8) Modulating the ultrasonic pulse, which is a radiation wave, to improve the S/N ratio of the received signal (PSK modulation and amplitude modulation)
A phase modulation section and an oscillation modulation section are provided.

(9) In order to correct errors based on wind direction, a switching circuit is provided to connect the transmitting element to the receiving circuit and the receiving element to the transmitting circuit at the same time. A measurement circuit is provided that calculates the distance to the obstacle based on the arithmetic average of the propagation times Tx obtained by successive switching times. In other words, ultrasonic pulses are propagated from the forward direction and the reverse direction through one propagation path, and the shape of the wind direction is removed by arithmetic averaging.The basic principle is similar to that of a flowmeter using the synchronous sing-around method. , such a flowmeter extracts the flow velocity (V) by taking the difference rather than taking the arithmetic mean.

[Effect]

The effects of the above technical means (1) to (9) will be summarized in correspondence with their respective numbers.

(1) s with the function of e-αTx/+I+x as the reference signal
The 'rc signal generator corrects the above-mentioned amplitude-dependent time detection error more than ever before.

(2-pin transmission 1laTo 4.5 x 1010/(
The control unit that sets f2 G) or more and twice that or less generates an ultrasonic pulse when the reverberation is sufficiently attenuated, so S
/N ratio is improved.

(3) Since the temperature correction section corrects the temperature characteristics of the sound speed C,
Improve measurement accuracy of propagation time.

(4) The pulse width setting unit, pulse width control unit, determination unit, and measurement circuit exclude impulse noise, eliminating malfunctions.

(5) The floating threshold generator and the adder remove stationary noise, improving the S/N ratio.

(6) The measurement circuit calculates the distance to the obstacle using equation (7), taking into account the baseline distance between the transmitting and receiving elements, improving accuracy.

(7) Since the measuring circuit displays the measurement indeterminate based on the equation (8), the user can judge whether the usage conditions are acceptable or not.

(8) The phase modulation section and the amplitude modulation section improve the S/N ratio of the received signal by modulating the ultrasonic pulse.

(9) The switching circuit, control unit, and measurement circuit correct errors based on wind direction, improving distance measurement accuracy.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the ultrasonic obstacle detection device according to the present invention, in which 1 is a transmitting element in FIG. 2, 2 is a receiving element in FIG. 2, 6 is a measuring circuit, and 4 is a receiving element in FIG. 5 is a transmitting circuit, 5 is a receiving circuit, and 6 is a switching circuit.

In the same figure, both transmitting element 1 and receiving element 2 are 70KH.
Ultrasonic element for z (1 for Ei FR-TF'B70)
It is connected to the transmitting circuit 4 and the receiving circuit 5 via the switching circuit 6.

In addition, the switching circuit 6 is an analog switch (CD40558
E), an inverter (CD40698Pi), etc., and is controlled by control signals G, , G, of the measurement circuit 3.
The transmitting signal from the transmitting circuit 4 is supplied to the transmitting element 1 or the receiving element 2 (separately excited system), and the receiving signal from the transmitting element 1 or the receiving element 2 is supplied to the receiving circuit 5. In addition, signal G
Depending on the settings of , , and G, the transmitting element 1 may operate as a transmitting/receiving type.

This is done when detecting an obstacle relatively far away (50 cm to 3 m).

The measurement circuit 6 has the following blocks. That is, a control section 10 consisting of a microcomputer, etc., a basic oscillation section 11 consisting of a ceramic oscillator (CSB400A) etc. that supplies a driving clock to the control section 1, and two JKs that divide the clock of the basic oscillation section 11 by three. Flip 70 Tsubu (CD4D27
A frequency dividing section 12 consisting of a frequency dividing section 12 such as BE), a time measuring section 16 consisting of a counter (CD40408E) etc. that counts the clock of this frequency dividing section 12 via an OR section (CD4000BE) 15, and a digital calculation of the counted value of the time measuring section 16 D/A converter 17, D/A, which consists of a converter (CD4000BE) that converts data into analog, an R-2R ladder, a resistor circuit network, etc.
The temperature correction section 18 is composed of an operational amplifier (HA17904PS) with a thermistor connected to a feedback loop that amplifies the output of the conversion section 17, and the output of the temperature correction section 18 is sent to the control section 10.
An A/D conversion unit 19 consisting of an R-2R ladder, a resistor network, a comparator (1 (A17903PS), etc.), and a control unit which converts the analog signal into a 1-bit digital signal based on the signal from the R-2R ladder and supplies it to the control unit 10. The start pulse to be supplied to the transmission circuit 4 is predetermined based on the data calculated by 1o based on equation (7), the display unit 14 that displays the presence or absence of an object within a predetermined distance, and the transmission interval T preset by the control unit 10. A level shifter 13 converts the amplitude into an amplitude of , and an input/output section (not shown) connected to the control section 10.

Note that this input/output section sets the distance range XI for detecting the presence or absence of obstacles, and also sets the base line distance 1 between the transmitting and receiving elements.
[D (=10 cm), its square value, and a representative sound velocity C (=344 m/S) value are set, and furthermore, the square value of the ultrasonic frequency f (=67 KHz) is set. Note that the control unit 10 supplies distance measurement data to the host computer via an input/output unit, but a description thereof will be omitted.

Next, the transmitting circuit 4 has the following blocks.

That is, a JK flip-flop (CD4027BB
) etc. The start pulse supplied from the frequency divider 20 and the level shifter 13 is made into a predetermined pulse width by counting the clock from the frequency divider 20, and is sent to the counting circuit 3 and the receiving circuit 5. Supply JK flip-flop (CD4027BK) and counter (CD4024BEl)
), etc. 2. The tank section 21 consists of a current source that converts the clock from the frequency dividing section 20 into a sine wave, a parallel resonant circuit, etc., and the signal supplied from the pulse width setting section 22 is differentiated. , by this differential signal, the tank section 21
An analog switch ( A burst generating section 24 consisting of a CD4053BE), etc., and an analog switch (
CD40518B), etc., and two operational amplifiers (LF'353N), etc., and are normally connected with a common negative feedback loop configured for the purpose of improving the common mode rejection ratio (CMMR), that is, differential This is an input/output type two-phase output amplification section 25.

This two-phase output amplification section 25 amplifies the signal supplied from the phase modulation section 7, converts it into a signal whose phase relationship is shifted by 180 degrees, and supplies it to the transmitting element 1 or the receiving element 2 via the switching circuit 6. It is.

Note that the phase modulation section 7 achieves PSK modulation by switching the supply of the burst signal from one of the two input terminals of the two-phase output amplification section 25 of the differential input/output type to the other.

The receiving circuit 5 has the following blocks.

That is, a single-peak filter section 26 consisting of a parallel resonant circuit removes noise from the signal received by the receiving element 2 (or transmitting element 1) supplied via the switching circuit 6, and the output signal of this filter section 26 is amplified. preamplifier (μPC57
7H), etc., supplied from the amplification section 27.
Diode (IS2076) that rectifies the signal
and two operational amplifiers (LP353N), etc., and a low-pass operational amplifier (HA1790) that powers and amplifies the received signal supplied from the absolute value circuit 28.
ηe-αTx/T from the floating threshold generation unit 9 consisting of 4PS) and the count value Tx of the time measurement unit 16 of the measurement circuit 3.
The standard (STC) is a function of x (where η is a set constant)
) An STC signal generating section 8 is composed of a redundant memory (hereinafter referred to as ROM), an R-2R ladder, a resistor circuit network, etc., which generates a signal.

Here, the count value Tx of the time measuring section 16 is supplied to the address input of the ROM, and the ROM is 1e-α according to the address.
A digital signal corresponding to Tx/Tx is supplied to the R-2R ladder-resistance network as a data output. R-
The 2R ladder-resistor network converts this digital signal into an analog signal and outputs it.

The receiving circuit 5 further includes the following blocks.

An adder 29 that adds the reference signal supplied to the STC signal generator 8 and the output signal of the floating threshold generator 9; a comparison that compares the output signal of the adder 29 with the received signal that is the output of the absolute value circuit 28; part (HA/7903ps) so, an inverter and a diode (I
S2076) and capacitor, resistor and RS flip 70
Detection section 3 consisting of a tube (CD4023'l/BE) etc.
1. A counter (
A decoder (CD4028BE) that outputs a good judgment signal when the pulse width read by the width reading section 32 is almost the same as the output signal of the pulse width setting section 22, an OR circuit, etc. When the outputs of the determining unit 36 and determining unit 53 are good, a good signal is latched at the rising edge of the negative logic pulse of the detecting unit 31 (at the end of the pulse), and the R87 lip 70 of the detecting unit 31 is latched.
Set the knob to stop the detection operation, and then set the OR part 1.
This is a latch unit (CD4013BEf) 54 that supplies a signal to 5 to stop the counting operation of the time measurement unit 16.

Note that the latch section 34 and the time measurement section 16 are reset by a pulse of a predetermined width from the pulse width setting section 22. That is, these are conflicts that are reset when the ultrasound pulse is being emitted.

In addition, the topmost pin of the output terminal of the time measurement unit 16) (MS
The signal B) is supplied to the OR section 15 to prevent the time measurement section 16 from overflowing.

Furthermore, the filter section 26 and the amplification section 27 are physically provided near the switching circuit 6 and are electrically shielded.

Now, the present invention will be explained in detail using FIG.

Now, when the system is powered on, the basic oscillation section 11 starts oscillating and the control section 10 starts operating.

Further, the division section 12 divides the 400 KHz clock of the basic oscillation section to 1/3 to generate a 133 KHz clock, and the 2 frequency divider section 20 further divides this to 1/2 and generates a 133 KHz clock.
Generates a 67 KHz clock of 0%.

Further, the tank section 21 converts the clock of the frequency divider 20 into a sine wave and outputs the sine wave.

On the other hand, the control unit 10 receives from a preset input/output unit (not shown) the distance range X1 for detecting the presence or absence of an obstacle, the baseline distance between the transmitting and receiving elements jllD, and its square value DZ.

Six values such as the representative value of the sound speed C and the square value f2 of the set frequency f of the ultrasonic pulse are read and stored.

Further, the control unit 10 transmits the control signals (Gl, G,) to (1°1
) and output. With this setting, the switching circuit 6 connects the transmitting element 1 to the transmitting circuit 4, and at the same time connects the receiving element 2 to the transmitting element 1.
is connected to the receiving circuit 5.

Furthermore, when a detection start signal is supplied from the host combinator or user through an input/output unit (not shown),
The control section 10 supplies a start pulse (pulse width 100 μs) to the pulse width setting section 22 via the level shift section 15.

, - The Hals width setting unit 22 starts counting the clock of the frequency divider 20 from the time it receives the start pulse, and generates pulses to output a signal for transmission until a predetermined count value is reached. This time is approximately 0 from the time the start pulse is received.
．． It is 48m5. The time measuring section 16 and the latch section 64 are reset by this 0.4E1 mS pulse.

Further, the width modulation section 23 amplitude modulates the output signal (sine wave 47 KHz) of the tank section 21, and the burst generation section 24
The output signal of the tank section 21 is supplied to the phase modulation section 7 for a pulse time of 0.48 m5 including this amplitude modulated period.

Then, the phase modulation section 7 modulates the phase of the supplied burst signal of 0.48 m5 every approximately 0.12 m5 and sends it to the two-phase output amplification section 25.

The two-phase output amplification section 25 amplifies the supplied signal, and
The switching circuit 6 generates two transmission signals with a phase shift of 80 degrees.
It is supplied between the electrodes of the transmitting element 1 via. This results in
The transmitting element 1 emits 67 KHz ultrasonic pulses.

When the emission of this ultrasonic pulse ends, the reset of the time measuring section 16 and the latch section 34 is released.

Therefore, the time measuring section 16 starts counting the 133 KHz clock output from the frequency dividing section 12 via the OR section 15.

Further, the latch section 34 outputs a signal so that the detection section 31 performs a detection operation.

Further, the D/A conversion section 17 supplies a voltage that gradually increases linearly to the temperature correction section 1 day according to the count value of the time measurement section 16.

The temperature correction unit 1B calculates the temperature coefficient ('(+0.183%/℃)
The change in the sound speed C due to temperature is canceled out by the temperature correction section 18.

The output signal of this temperature correction section 18 is supplied to an A/D conversion section 19.

Further, a reference signal that decreases from a predetermined voltage at ηe-αTX/IIIX is supplied to the adder 29 in accordance with the count value of the STC signal generator 8 measurement unit 16.

Eventually, the ultrasonic pulse emitted from the transmitting element 1 is reflected by an obstacle, and when this reflected wave reaches the receiving element 2, this received signal is supplied to the amplifying section 27 via the switching circuit 6 and the filter section 26. Ru.

The amplification section 27 amplifies this and sends it to the absolute value circuit 28, which further rectifies the aftermath and sends it to the floating threshold generation section 9 and the comparison section 50.

The floating threshold generating section 9 generates a floating threshold and sends it to the adding section 29 , and the adding section 29 adds the STC (reference) signal and the floating threshold and sends it to the comparing section 30 .

The comparator 60 shapes the waveform of only the output signal of the absolute value circuit 28, which is equal to or higher than this threshold value, and outputs the waveform-shaped signal.

The detection section 51 performs envelope detection on the output signal of the comparison section 30, the pulse width reading section 52 reads the pulse width of this detected signal using the clock of the frequency divider 20, and the determination section 33 determines that the pulse width is 0. It is determined whether the value is close to 48+nS, and if it is good, a good signal is supplied to the latch section 34.

The latch section 34 latches this to stop the counting operation of the time measurement section 16 and also stops the operation of the detection section 31.

After further time has elapsed, control 8I510 indicates 4.5×1
When detecting that the time calculated by o10/(f2G) has arrived, the control section 10 sends a signal to the A/D conversion section 19, reads the data, and determines the propagation time Tx from this data. Then, this Tx is Tn expressed by equation (8)
If it is below, this fact is displayed on the display unit 14. Otherwise, store this Tx as Txl. Then, the control signals (Gl, G2) are set to (1°0) and output.

With this setting, the switching circuit 6 switches the receiving element 2 from the transmitting circuit 4.
At the same time, the transmitting element 1 is connected to the receiving circuit 5, and a start pulse is generated again to cause the system to perform the same operation as described above.

The propagation time Tx obtained from this result is stored as Txz,
The control unit 10 further performs (TXI + '['X2) /
2 to find T'x, and using this T'x as Tx in equation (7), calculate equation (7) to calculate the distance X of the obstacle.

Then, compared with the preset distance box gXt,
When the condition of X≦X1 is met, it is displayed on the display unit 14 and a signal is sent to the host computer via an input/output unit (not shown).

Note that after the control signals (Gl, G2) are set to (o, 1) (for example, 1 m5 after transmission) + (0, O), the transmitting element 1 operates as a transmitting/receiving type.

Next, FIG. 3 shows the interelectrode voltage waveform (a) when a transmission signal is supplied to the transmission element 1 of FIG. 1, and the output signal generation of the absolute value circuit 28, which is the received signal in case 6). (b) and the floating threshold value which is the output signal of the adder 29
The waveform (d) of the C signal is shown. Further, (c) shows the received signal waveform when no modulation is applied to the transmitted signal.

Note that (b) and (0) in the figure have the same scale on the vertical axis (swing axis) and horizontal axis (time), but (d) has the scale of the vertical axis expanded, and (a) The scale is expanded on both the vertical and horizontal axes.

The pulse width of the interelectrode voltage in (a) is about 0.48 m5, and is phase (PSK) modulated every 0.12 m5. Also, the amplitude is large in the first half of about 0.24 m5, and the amplitude is small in the second half. Note that the time of 0.12 m5 is approximately the rise time of the ultrasonic element used.

Also, some damped vibration is observed after 0.48 m5, which is due to the inertia of the element.

The upper part of (b) is the same transmission signal as in (a), and the lower part is the output signal of the absolute value circuit 28 in the receiving circuit 5 of FIG.
In other words, it shows the received signal.

(Q) represents the amplitude modulation section 23 and phase modulation section 7 in the transmitting circuit 4.
The transmitted and received signals are obtained when . is removed, and the measurement position is the same as in (b).

Comparing (b) and (C), it can be seen that the S/N ratio of the received signal is improved by modulating the transmitted signal.

Note that phase modulation increases the amplitude of the received signal,
Amplitude modulation tends to reduce the amplitude of noise.

Further, even though the transmitted signal is phase (PSK) modulated, the reason why this modulation does not appear in the received signal is because the ultrasonic element has a narrow band and the filter 26 is provided.

In (d), the school on the vertical axis is expanded to show the S'I'C (reference) signal obtained by adding the received signal in (b) and the floating threshold.

The two signals are compared by the comparator 50, and the high-level portion of the received signal is waveform-shaped and output from the comparator 30. Stationary noise can be removed by introducing a floating threshold method.

〔Effect of the invention〕

As invented above, according to the present invention, the switching circuit connects the transmitting element to the receiving circuit and the receiving element to the transmitting circuit at the same time, the control unit controls the switching operation of this switching circuit, and the switching circuit continuously connects the transmitting element to the receiving circuit. Since we have installed a measurement circuit that calculates the distance to the obstacle based on the arithmetic average of the individual propagation times when switching only an even number of times, errors based on wind direction can be corrected, and this improves the distance measurement accuracy. It is possible to provide an ultrasonic 14 harmful object detection device which has excellent functions except for the drawbacks of the above-mentioned prior art.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an ultrasonic obstacle detection device according to the present invention, FIG. 2 is a schematic diagram of a transmitting/receiving type ultrasonic ranging according to the present invention, and FIGS. d) is a diagram showing a signal waveform at a specific location in FIG. 1; DESCRIPTION OF SYMBOLS 1... Transmitting element, 2... Receiving element, 3... Measuring circuit, 4... Transmitting circuit, 5... Receiving circuit, 6... Switching circuit, 7... Phase modulation section, 8... STC signal signal generation part... floating threshold generation part, 10... control part (microcomputer), 16... time measurement part, 18... temperature correction part, 22... pulse width Setting section, 23...amplitude modulation section,
62...Pulse width reading section.

Claims (1)

[Claims] 1. The transmitting element and the receiving element are configured separately, and the ultrasonic pulse emitted by the transmitting element into the air is transmitted from the transmitting element to the receiving element depending on the propagation time until it is reflected by an obstacle and reaches the receiving element. In an ultrasonic obstacle detection device that measures the distance to an obstacle and detects the presence or absence of an obstacle within a predetermined distance, the transmitting element connected to the transmitting circuit is reconnected to the receiving circuit, and the transmitting element connected to the transmitting circuit is reconnected to the receiving circuit. A switching circuit is provided to reconnect the connected receiving element to the transmitting circuit, and a control section is provided to send a control signal to this switching circuit to switch the connection. An ultrasonic obstacle detection device characterized by comprising a measurement circuit that calculates the distance to the obstacle based on the arithmetic average value, and corrects an error based on wind direction. .