JPS60203879A - Reflection type substance detector - Google Patents

Abstract

PURPOSE:To adjust sensitivity in stages with a simple constitution by adjusting a signal for exciting ultrasonic wave oscillators. CONSTITUTION:Ultrasonic wave oscillators 20a, 30a are connected to the output terminals of driving circuits 50, 70 respectively, discriminating circuits 60, 80 are connected to the output terminals of ultrasonic wave detectors 20b, 30b respectively and the driving circuits 50, 70 and the discriminating circuits 60, 80 are connected to a microcomputer 90. The microcomputer 90 measures time data from the projection of an ultrasonic wave to its detection to discriminate the existence of the substance and a distance and adjusts a binary signal for controlling the excitation of the oscillators 20a, 30a to adjust the detecting sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a reflection-type object detection device that detects an object using ultrasonic waves, and particularly relates to sensitivity adjustment.

For example, in a vehicle, as a device for guiding the driver by detecting obstacles located outside the driver's field of vision,
Object detection devices are known. This type of object detection device generally uses ultrasonic waves. In this type of device, an ultrasonic transmitter emits ultrasonic waves of a predetermined intensity in a predetermined direction, an ultrasonic receiver (one device is faced in the same direction, the ultrasonic wave is emitted, and then the ultrasonic wave The transmission time of the reflected ultrasonic wave, that is, the distance between the detection device and the obstacle, is measured by the time it takes for the signal received by the receiver to exceed a predetermined threshold level.

By the way, the level of reflected waves obtained by hitting any object depends on the distance between the object and the detection device, the shape of the object's surface,
It varies greatly depending on the inclination of the object with respect to the device, the material of the object, etc. Therefore, in order to be able to detect objects under various conditions, it is necessary to set the sensitivity of the detection device to be high so that even objects with small reflected wave levels can be detected.

However, if the sensitivity is made too high, the level of the direct ultrasonic wave emitted from the ultrasonic transmitter, for example, may also exceed the threshold level, and this may be mistaken for a reflected wave. Therefore, in such a case, the sensitivity can be adjusted in multiple stages, for example, the sensitivity can be set gradually higher from the lowest sensitivity, and when the level of the reflected wave exceeds the threshold level for the first time,
Control may be performed to measure the ultrasonic transmission time, that is, the distance to the object, from the time at that time and the time when the ultrasonic wave was emitted.

In order to make the sensitivity variable in this type of detection device,
At least one of the energization level of the ultrasound transmitter, the gain of the amplifier that amplifies the signal from the ultrasound receiver, and the threshold level that determines whether ultrasound is received may be adjusted. In this type of device, the sensitivity needs to be controlled by a control device such as a microcomputer, so when adjusting the gain of an amplifier, for example, conventionally the resistor of a two-resistor voltage divider circuit that determines the amount of feedback of the amplifier was used. The configuration was such that sensitivity could be adjusted by selectively connecting an analog switch. However, this increases the number of components such as analog switches and resistors. Also, this requires many control lines to adjust sensitivity, so for example, a single-chip microcomputer that can be used with a small number of boards.

It was difficult to use it as a control device.

[Objective] It is an object of the present invention to enable sensitivity to be adjusted in multiple stages with a small number of control lines without complicating the device configuration.

[Configuration] To simplify the hardware configuration, a microcomputer or the like may be used so that the sensitivity can be directly adjusted using only software. The wave number 2 of the signal that energizes the ultrasonic transmitter can be adjusted directly with software.
frequency, duty.

There are phases, etc. Therefore, in the present invention, the sensitivity is adjusted using the characteristics of the ultrasonic transmitter and/or the ultrasonic receiver by adjusting the signal that energizes the ultrasonic transmitter.

For example, an ultrasonic transmitter has a mechanical start-up delay, so if the number of pulses to energize it is small,
The level of ultrasound it emits becomes smaller. In other words,
The level of the emitted ultrasound changes depending on the number of pulses that energize the ultrasound transmitter. Therefore, the sensitivity can be adjusted by changing the wave number of the signal that energizes the ultrasonic transmitter. Further, since an ultrasonic transmitter, an ultrasonic receiver, etc. resonate at a specific frequency, the ultrasonic emission level or reception sensitivity decreases for a frequency that deviates from that frequency. Therefore, the sensitivity of the detection device can also be adjusted by adjusting the frequency of the signal that energizes the ultrasound transmitter.

When the sensitivity is adjusted by adjusting the number of energizing pulses, the energizing frequency, etc., there is no need to provide a special control line for sensitivity adjustment, and there is no need to use a special amplifier or the like. If the sensitivity cannot be adjusted by a predetermined number of steps only by adjusting the signal that energizes the ultrasonic transmitter, it may be used in combination with conventional sensitivity adjustment.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the appearance of an automobile equipped with an obstacle detection device. Referring to FIG. 1, in this embodiment, ultrasonic transmitters 20a, 30a and ultrasonic receivers 20b, 30 are installed at both ends of the rear bumper 2 of an automobile l.
b is attached.

In this embodiment, an ultrasonic transmitter 20a and an ultrasonic receiver 2
0b, an ultrasonic transmitter 30a, and an ultrasonic receiver 30b are arranged parallel to each other with an interval of 3cI11. Ultrasonic transmitters 20a and 30 used in this example
a and an ultrasound receiver 20b.

30b are ultrasonic ceramic microphones EFR-O8840 and EFR-R8B manufactured by Kensho Denki, respectively.
It is 2 in 40.

For example, as shown in FIG. 2, if there is an obstacle 3 behind the automobile I, the ultrasonic waves emitted from the ultrasonic transmitter are reflected by the obstacle 3, and the reflected waves reach the ultrasonic receiver. Therefore, the distance between the detection device and the obstacle 3 can be measured by measuring the time from when the ultrasonic wave is emitted until the reflected wave obtained by the ultrasonic wave is received.

FIG. 3 shows a block diagram of the electric circuit of the obstacle detection device mounted on the vehicle shown in FIG. 1. The temperature will be explained with reference to FIG. The ultrasonic transmitters 2Qa and 30a are connected to the output ends of drive circuits 50 and 70, respectively, and the discrimination circuits 60 and 80 are connected to the output ends of the ultrasonic receivers 20b and 30b, respectively. . Drive circuits 50 and 70 and discrimination circuits 60 and 80 are connected to microcomputer 90, respectively. The microcomputer 90 used in this embodiment is an 8-bit single-chip microcomputer 8 manufactured by Intel Corporation.
It is 748. 90a is a crystal oscillator for generating clock pulses which are the basis of the operation of the microcomputer. Reference numeral 40 denotes a starting circuit, which is composed of a starting switch 41 and a waveform shaping circuit 42. Start switch 4
1 is a self-resetting type with normally open contacts. The start switch 41 is arranged on the operation panel of the driver's seat. Reference numeral 100 denotes a buzzer circuit, and a buzzer 102 constituting the buzzer circuit is connected to the output port of the microcomputer 90 via a buzzer drive circuit wIlO1. 110 is a distance display circuit that displays the distance between the vehicle body and an obstacle. The distance display circuit 110 includes a 7-segment display 111 with three digits. The display device itt is driven for dynamic display by a segment drive port [112 and a phase drive circuit 113. 120 is a warning circuit.

FIG. 4 shows a specific configuration of the drive circuit 50 shown in FIG. 3.

Incidentally, in FIG. 3, the drive circuits 50 and 70 have the same configuration, so a description of the configuration of the drive circuit 70 will be omitted. Referring to FIG. 4, this circuit includes an inverter 53.
1-transistor for driving.

It is equipped with a step-up transformer T, etc. The input terminal of the inverter 53 is connected to a predetermined output port of the microcomputer 90.
It is connected to 1. A pulse signal Sp that controls the energization of the ultrasonic transmitter 20a is applied to this signal line. This pulse signal Sp is applied to the primary side of the step-up transformer T via a driving transistor. 1- When a pulse signal is applied to the primary side of the lance 'r, a signal with an amplitude of about 100V is generated on the secondary side. This boosted 4 0 K +17. Our belief is that the ultrasonic transmitter 20a
is applied to

As will be described later, the pulse signal Sp is generated by the microcomputer 90 using software.

In particular, in this example, the software adjusts the number of pulses per measurement of the pulse signal Sp that energizes the ultrasonic transmitter in accordance with the set sensitivity. In other words, when the number of pulses is small, the amplitude of the ultrasound output from the ultrasound transmitter is
It changes greatly depending on the number of pulses of the signal Sp (see FIG. 7b and Table 1). Therefore, in this embodiment,
The number of pulses of the signal Sp is changed depending on whether the sensitivity data is an even number or an odd number, thereby adjusting the level of the ultrasonic waves output from the ultrasonic transmitter in two stages, thereby adjusting the detection sensitivity. In this example, the detection sensitivity is adjusted in two stages by adjusting the number of pulses of the signal Sp, and by variable gain amplification 1i162, which will be described later.
In combination with the four-stage gain adjustment, it is possible to adjust the gain in eight stages.

Table 1 FIG. 5 shows a specific configuration of the discrimination circuit 60 shown in FIG. 3. Note that since the discrimination circuits 60 and 80 have the same configuration, a description of the discrimination circuit 80 will be omitted. This will be explained with reference to FIG. The ultrasonic receiver 20b includes the amplifier circuit 6 of the discrimination circuit 60.
Connected to 1.

The amplifier circuit 61 includes three stages of cascade-connected narrowband amplifiers AI, A2, and A3. Each of the amplifiers AI, A2, and A3 is an inverting amplifier composed of an operational amplifier, and each feedback path has a
A parallel resonant circuit consisting of a capacitor resonating at KHz and an electric coil is connected.

62 is a variable gain amplifier. This variable gain amplifier 62 is composed of an operational amplifier 62a, an analog switch (analog multiplexer) AS, and a large number of resistors. To briefly describe the variable gain amplifier 62, this circuit consists of a microcomputer 90 applied to the 2-bit control inputs CO and C1 of the analog switch As.
The resistor selected according to the signal from the operational amplifier 6
2a as a feedback resistor, and amplifies the signal with an amplification degree determined by the resistor and the input resistor rin. In other words,
The amplification degree G of this circuit 62 is determined by the combined resistance of the feedback resistors connected between the inverting input terminal and the output terminal of the operational amplifier 62a.
If t, it is expressed by the following formula.

G=-r t/rin T T Fung fist + Italy (1
) Analog switch As has its ports XO, XI.

Select one of X2 and X3 with a 2-bit gain setting signal applied to control inputs CO and C1,
The port is electrically connected to the common boat YO. For example, if the data of the gain setting signal is
In the case of "0", which is L and L, respectively, po1-XO is selected and the combined resistance rt becomes rO, so the gain G becomes -rO/rin. Similarly, when the data of the gain setting signal is "lJ", "2" and "3", ports Xi, X2 and X3 are selected respectively, and the combined resistance rt becomes rO+rl and rO+, respectively.
rl+r2 and ro+rl+r2+r3. Therefore, the gain G of the variable gain amplifier 62 can be set in four stages by the gain setting signal. In this embodiment, C is set such that the maximum gain when the gain setting signal data is "3" is approximately 128 times the minimum gain when the gain setting signal data is "0".

63 is a signal processing circuit that determines the presence or absence of an AC analog electric signal and applies a binary signal according to the result to a predetermined input port of the microcomputer 90.

The signal waveforms of each part of the circuit are as shown in FIG. 7a. That is, the operational amplifier OPl is a normal amplifier, and when an ultrasonic wave is received, an electric signal v1 of a frequency of 4.0 KHz corresponding to the ultrasonic waveform appears at the output terminal of OPl.

The operational amplifier OP 2 is an analog comparator and the signal Vl
The level of is compared with a predetermined threshold level, and a binary signal V2 corresponding to the magnitude thereof is output.

This binary I number is smoothed by a rectifier/smoothing circuit including a diode, a capacitor, and a resistor connected to the output terminal of the operational amplifier OP2. The signal v obtained by this
3 is compared with a predetermined threshold value by an analog comparator consisting of an operational amplifier OP3, and a binary signal v4 corresponding to the magnitude thereof is outputted from OF2. A circuit connected to the output terminal of the operational amplifier OP3 is an interface circuit provided to match the level of the signal V4 with the input level of the microcomputer 90.

The operation of the microcomputer 90 is shown in FIGS. 6a, 6b, 6c, and 6d. First, the general operation will be explained with reference to FIG. 6a. When the power is turned on, the output boat is set to a predetermined initial level (unenergized level),
Clear memory.

Check the status of the input boat and wait for the start switch 41 to be turned on. When the start switch 41 is turned on,
Execute the obstacle detection subroutine.

When this subroutine is executed, if an obstacle exists, the measured distance data is stored in the register RB, so if there is distance data, the data is displayed on the display 110. Additionally, the buzzer 102 and lamp 121 are energized as necessary.

Next, the obstacle detection subroutine will be explained. Roughly speaking, first, set the sensitivity G to the lowest, emit ultrasonic waves, and
It waits until the determination circuit 60 or 80 determines that "ultrasonic waves are being received." When "ultrasonic waves are being received", the time data from when the ultrasound was emitted is read.

The ultrasonic wave is emitted by executing the ultrasonic wave emitting subroutine shown in FIG. 5, 6d. The ultrasonic emission subroutine will be explained. Sensitivity data G is stored in register RC. In this example, the sensitivity can be adjusted in eight steps, so the sensitivity data G takes values in the range of 0 to 7. Shift the data in register RC by 1 bit toward the lower bit. In other words, divide the data value by 2.

When this is done, the data of the least significant bit is set to the carry flag. If the sensitivity data G is an even number, the carry flag will be 0, but if it is an odd number, the carry flag will be II.
l It will be 11. If the carry flag is On, that is, an even number, a value N (the number of pulses of Sp) is set in the register RD, and if the carry flag is II II II, that is, an odd number, a value N+γ is set in the register RD.

The data of the register RC (1/2 of the sensitivity data) is set to the output port, and the gain data is set to the analog switch As of the variable gain amplifier 62. For example, if the sensitivity data is 6, the value 3 (signal lines CO and C1 are both prLn) is applied to the variable gain amplifier 62, and the gain of the amplifier 62 becomes maximum.

Next, set the signal line (S p) to high level H, and
After waiting for 2.5 μsec, the signal line (
Sp) is set to a low level L, and after waiting for 12.5 μsec, the contents of register RD are changed to -IL, and this process is repeated until the contents of RD become 0. 1, a pulse signal with a period of 25 μsec and a duty of 50% is output for the number of waves corresponding to the value stored in the register RD.

Therefore, when the sensitivity data G is an odd number, more pulses Sp are output in one ultrasonic emission process than when it is an even number. As mentioned above, the level of the ultrasound output from the ultrasound transmitter changes depending on the number of pulses of the signal SP, so when the sensitivity data G is an odd number, the sensitivity is higher than when it is an even number. becomes higher.

In this example, the gain ratio between each step of the variable gain amplifier 62 is kept constant, and the sensitivity ratio K between the case where the number of pulse signals SP is N and the case where the number of pulse signals SP is N+γ is the same at each step of the DJ variable gain amplifier 62. The gain ratio is set to the l/2 power of the gain ratio between the two. In other words, if the sensitivity of the entire device when the sensitivity data G is 0 is Go, then the sensitivity data G is 1.2, 3
, 4, 5.6 and 7, the sensitivity of the entire device is Go·K, respectively.

Go・K', Go-K 3. Go'ni' +Go・K
5. Qo.K' and Go.K7 double each other.

Hyper? After emitting the S wave, first set the interval timer to Sera 1 and count the elapsed time since the ultrasonic wave was emitted.

When an ultrasonic wave is emitted, a relatively low-level noise wave appears at a predetermined timing at the output terminal of the variable gain amplifier 62 due to a direct wave or the like that is not caused by reflection. Furthermore, when an object is located at a predetermined position, ultrasonic waves reflected by the object cause reflected waves to appear at a timing corresponding to the distance between the object and the detection device.

The level of reflected waves varies greatly depending on the distance, material, shape, etc. of the object. If the level of the reflected wave is clearly higher than the noise wave such as a direct wave, the level of the reflected wave with low sensitivity will reach the threshold level Vth (one of ○P2) before the noise wave appears IL. voltage applied to the side input terminal)
Therefore, the distance to the object can be determined from the time when a wave that exceeds the threshold level vth first appears. However, for example, if the level of the reflected wave is lower than the noise wave as shown in Figure 7C, the noise wave is There is a possibility of false detection.

Therefore, in this embodiment, the timing TKL at which the noise wave appears is determined in advance, and when this timing is reached,
It is checked whether there is a wave that exceeds the threshold level Vth, and if it does, it is checked until it no longer exceeds the threshold level (point P
1) Wait. Also, in this embodiment, the gain (sensitivity) G
When is greater than or equal to the predetermined value Gc, TKII (slightly larger than TKU) is used instead of timing TKL.

Further, a plurality of peaks (Wl, W2) often appear in the noise wave as shown in FIG. 7d due to the superposition of a plurality of waves. In this case, when the threshold level vth falls between the two peak levels and the valley level between them, the peak W2 of the second noise wave appears after the wave that appeared at timing TKL disappears as described above. This may be detected at the timing of point P2.

Therefore, in this embodiment, the sensitivity ratio K between each sensitivity step is set to the level V of the maximum peak that can occur in the noise wave.
The noise wave and the reflected wave are discriminated by setting the value to be larger than the ratio (VH/VL) between H and the lowest valley level VL and performing time measurements multiple times with different sensitivities.

In other words, even if the peaks and troughs of the noise wave cross the threshold level vth, as shown by the solid line in Fig. 7d, if the sensitivity is increased by one level, the sensitivity will be as shown by the dashed-dotted line. The level of the trough of the noise wave is the threshold level vth
Therefore, if the cursed noise wave falls below the threshold level at timing TKL, the second and subsequent peaks of the noise wave will no longer be detected. Therefore,
If we compare these resulting time data, we get
It is possible to determine whether the data is valid or not based on their magnitude and the difference between them.

Furthermore, the time data is detected as the time from when the interval timer is started until the level of the reflected wave W3 (see Figure 7e) exceeds the threshold level vth.
As shown in FIG. 7e, when the level of the reflected wave W3 is different, the rise time (tt-to or t2-tO
) are different, so as shown by the solid line in Figure 7e, the time data obtained when the reflected wave level slightly exceeds the threshold level vth and the time data obtained when the reflected wave level is sufficiently larger than the threshold level With the time data obtained in
The measurement results will vary greatly, and this will result in a distance measurement error.

Therefore, in this embodiment, even if a reflected wave is detected, the sensitivity is updated and measurements are performed multiple times, and if it is determined that the result is a reflected wave reflected by the same object, selects the data obtained when the sensitivity is high and calculates the distance from that data. In other words, when the sensitivity is high, the time required for rise is short, so by always selecting data when the sensitivity is high, the difference between the rise times included in each time data, that is, the distance measurement error, becomes small.

The specific operation of the obstacle detection subroutine will be described with reference to FIGS. 6b and 6c, but before that, the functions of typical registers used in this routine will be explained.

CNI...Noise wave detection timing (Ti, TKll
) is a counter CN2 that counts the number of times a wave is detected.
・Counter Tgmax that counts the number of times a wave is detected at times other than the noise wave detection timing...Object measurement period RA...Register RB that holds valid time data...R separation data (measurement results) Holding register Tw...Waiting time α to avoid the effects of noise, ripples, etc. included in the signal...Reference time data to determine whether the waves are reflected from the same object or not and is set according to the value of CN2. This value is smaller than the maximum value of the rise time, ie, the time required from when the wave first reaches the receiver until its level reaches the threshold level when the maximum amplitude of the reflected wave is just around the threshold level. Now compare the difference between tn and tn-1.

β...Reference time data tn for distinguishing between noise waves such as direct waves and reflected waves...Time data tn- obtained by this measurement
+...Time data Gmax obtained from the previous measurement
... Maximum value of sensitivity data (7) CN 2max ...
After setting the maximum value interval timer of CN 2,
Wait until the timer value reaches TKL. When TKL is reached, the output level of the signal processing circuit 63 is referred to and it is checked whether the received level of the ultrasonic wave exceeds the threshold level Vth. If it exceeds ■Lh,
The value of the counter CNI is incremented by 1 and the process waits until the ultrasonic reception level falls below the threshold level vth.

If the reception level is lower than vtb at timing TKL, the process immediately proceeds to the next process.

The value obtained by adding the waiting time ゛rW to the timer value is stored in register T.
Wait until the value of the timer exceeds the value of Tmax. Next, referring to the output level of the signal processing circuit 63, it is checked whether ultrasonic waves and waves have been received (whether or not the reception level exceeds the threshold level vth). If not received, this check is repeated until the timer value reaches Tgmax. If the timer value reaches Tgmax before ultrasonic waves are received, the gain data G is increased by one step to increase the sensitivity, and the processing after ultrasonic emission is executed again.

When the ultrasonic wave is received, the contents of the counter CN2 are checked. The first time, the contents of counters CN and 2 are cleared to 0, so the value of the timer at that time is stored in register RA.
Store in. Since ultrasonic waves were detected, counter CN2
Add 1 to the content of The value of counter CN2 is CN2IIIl
If it is not larger than ax, wait until the timer value reaches Tgmax, update the gain G by one step to increase the sensitivity, and execute the process after ultrasonic emission again.

When the ultrasonic wave is received in step S42, the counter CN
If the content of 2 is 1 or more, the value α of the memory table is read according to the content of CN and 2. In addition, counter CN2
The values α1゜α2... stored in the memory table associated with the values 1, 2.3..., n. α3...αn is
It is set to satisfy the following relationship.

α1〉α2〉α3〉...〉αn In other words, the reflected wave level is the first threshold level Vt, h
There is a possibility that there will be a relatively large difference between the time data of 04 that exceeds 04 and the time data measured at the next gain.
1 is made relatively large, and as the directivity of CN2 becomes large, the difference in time data becomes small, so the reference value is also made small.

The time data tn-+ obtained in the previous measurement (when the sensitivity was lower than the current state) and the time data tn obtained this time are compared.

t tI< t n-+, and tn+α>tn-+
For example, if the time data tl shown in FIG. 7e is tn
As can be understood by associating t2 with -1 and t2 with tr+, it can be determined that the time data is the result of receiving a wave reflected by the same object. If this condition A is satisfied, the current data has a shorter rise time, so the contents of the register RA are updated to the current time data.

Moreover, if the content of counter CN2 is 2, then the following condition B
Determine whether it satisfies. In other words, if the value of counter CN2 is 2, the previously measured time data tn-1(R
The content of A) is, for example, the unnecessary wave W2 shown by the solid line in Fig. 7d.
There is a possibility that this is time data that should be invalidated and corresponds to the detected point P2. Therefore, if the content of CN2 is 2, it is determined whether tn-β)tn-+ (condition B) is satisfied. If the time data to-+ corresponds to the point P2, the time data tn measured this time corresponds to the point P3 and should be larger than tn-1 by a predetermined value or more. This predetermined value is the reference value β.

If condition B is satisfied, the contents of register RA are updated to the current time data (timer value).

Also, if -5 conditions A and B are not satisfied and the current time data is smaller than the previous time, then 1. For example, there is an object relatively far away that produces a high-level reflected wave, and there is a smaller object nearby. Since there may be an object that only generates reflected waves, in this case, in this embodiment, the current time data is not valid, the counter CN2 is cleared, and the contents of the register RA are updated to the current time data. Continue measurement. However, if the value of counter C1'jl is 1
In this case, there is a possibility that the current time data tn corresponds to, for example, point P2 shown in FIG. 7d, so this condition is ignored.

If none of the conditions A, B and t n < t n-1 are satisfied, if the value of counter CN2 exceeds its maximum value, and if gain G exceeds its maximum value and there is no valid value in register RA, If data exists, calculate the distance of the object from the time data stored in register RA,
The result is stored in register RB.

In the above embodiment, the sensitivity can be adjusted in multiple stages by combining the gain adjustment of the receiver amplifier and the transmission level adjustment of the ultrasonic transmitter. You can adjust the sensitivity. In that case, fine transmission level adjustment is required, but only adjusting the number of pulses as described above provides a relatively low degree of freedom in sensitivity adjustment. In such a case, for example, an ultrasonic oscillator, an ultrasonic receiver 1B.

Fine sensitivity adjustments can be made using the frequency characteristics of the amplifier, etc.
: f no uru. That is, as shown in FIGS. 8a and 8b, the output level of the ultrasonic transmitter and the sensitivity of the ultrasonic receiver vary greatly depending on the frequency of the signal.

Therefore, by adjusting the frequency of the signal that energizes the ultrasonic transmitter, the transmission level or sensitivity can be adjusted.

To implement this, for example, the ultrasonic emission subroutine of the above embodiment may be modified as shown in FIG. 8C. Note that in the subroutine shown in FIG. 8C, the ultrasonic transmission level is adjusted in only two stages, similar to the embodiment described above. Referring to FIG. 8C, a value (pulse width data) corresponding to the frequency is stored in the register RE, and the time corresponding to this value becomes the high level period and the low level period of the control pulse Sp. In this example, the numerical value N is set to match the center frequency of the ultrasonic transmitter, and the numerical value N + γ is set to match a frequency that deviates from the center frequency by a predetermined amount. The sound wave emission level is low,
When the number is odd, the ultrasonic emission level is set to be high.

In the above embodiment, the ultrasonic emission level is adjusted by adjusting the number of consecutive pulses, but it is also possible to remove a part of the central part from a predetermined number of consecutive pulses, or change the pulse interval.
The ultrasonic emission level can be similarly adjusted by adjusting the duty between the high level period and the low level period. Further, the adjustment may be made by combining these means, for example, pulse number adjustment and frequency adjustment.

[Effect] As described above, according to the present invention, the sensitivity is adjusted by controlling the wave number, two frequencies, etc. of the binary signal that energizes and controls the JL ultrasonic receiver. For example, by using a microcomputer as a control device, The device configuration can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an automobile equipped with an object detection device according to an embodiment, viewed from the rear. 2 is a plan view showing the rear part of the automobile shown in FIG. 1. FIG. FIG. 3 is a block diagram showing a schematic configuration of the object detection device. FIG. 4 is an electrical circuit diagram showing the configuration of the drive circuit 50 shown in FIG. 3. FIG. 5 is an electrical circuit diagram showing the configuration of the discrimination circuit 60 shown in FIG. 3. Figures 6a, 6b, 6c and 6d are the third
2 is a flowchart showing a schematic operation of the microcomputer 90 shown in the figure. Fig. 7a is a waveform diagram showing the signal waveforms of each part of the electric circuit shown in Fig. 5, Fig. 7b is a waveform diagram showing the correlation between the number of pulses of the energizing pulse Sp and the reflected wave level, Figs. 7c and 7d. FIG. 7E and FIG. 7E are timing charts showing examples of changes in the reception level of ultrasonic waves. FIGS. 8a and 8b are graphs showing examples of frequency characteristics of an ultrasonic transmitter and an ultrasonic receiver, respectively, and FIG. 8c is a brochure 1- of an ultrasonic emission subroutine in another embodiment. 1: Car 2: Rear bumper 3: Obstacles 20a, 30a: Ultrasonic transmitter (ultrasonic generator) 20
b, 30b: Ultrasonic receiver (ultrasonic receiving means) 40: Starting circuit 50, 70: Drive circuit 60.80: Discrimination circuit 6]: Narrow range amplifier (amplifying means) 62: Variable gain amplifier 63: Ia second processing circuit 90: Microcomputer (electronic control means) 111:
Display device patent applicant Aisin Seiki Co., Ltd. and 1 other person A 1 ■ Taku 2 What 7 a What 7 b ■ 7 c Haruma 8 a ■ 8 b How many cycles Temperature (kHz) 8 ゜ ■ Departure JlηγW-chin〉 1 Tree G Down A and 1; Direction 1゛ 7) ('/2T turn) ~, YES (even 11) 1 U 7) 17 (odd 1i) l: 1E-N+γ E -N - RC tail and 7' switch 1 and ttnos exchange and beg, D = O? 'vEs Shin also line S, (; crystallization he]shi l) f -> HE Korikito Ginma 5 SPl = 13-cho Haruma 1 from the outside? I'5] To--8:RD-1

Claims (2)

[Claims] (1) Ultrasonic generating means for generating ultrasonic waves; energizing means for energizing the ultrasonic generating means; ultrasonic receiving means for receiving ultrasonic waves; amplifying means for amplifying the signal from the ultrasonic receiving means; When an object detection instruction is given, the ultrasonic generator is energized, and the time data from ultrasonic emission to reception is measured to determine the presence or absence of an object and the distance, and the energization of the ultrasonic generator is controlled. A reflective object detection device comprising: electronic control means for adjusting detection sensitivity by adjusting a binary signal of the object. (2) The electronic control means adjusts the sensitivity by adjusting the number of pulses output for one measurement of the binary signal that controls the energization of the ultrasonic energizing means. )
Reflective object detection device as described in Section 1. (a) Bud 2 4 mountains 11a... 壬RRULEL 10 Uki khA+
The reflective object detection device according to claim 1, wherein the sensitivity is adjusted by adjusting the frequency of the binary signal to be controlled.