JPH0157313B2 - - Google Patents

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. [Prior Art] For example, in a vehicle, an object detection device is known as a device that detects an obstacle located outside the driver's field of vision and guides the driver. This type of object detection device generally uses ultrasonic waves. In this type of device, an ultrasonic transmitter emits ultrasonic waves with a predetermined intensity in a predetermined direction, an ultrasonic receiver is oriented in the same direction, and the intensity of the signal received by the ultrasonic receiver is The presence of a reflected wave, that is, the presence of an obstacle, is detected from the timing at which the signal is generated. By the way, the intensity of the reflected wave generally decreases as the distance between the object and the detection device increases. Therefore, in order to detect even distant objects, the sensitivity of the device must be increased. However, if the sensitivity is made too high, there is a risk that waves other than reflected waves, such as direct waves emitted from an ultrasonic transmitter, may be mistakenly detected as reflected waves. Therefore, the present applicant has proposed a method in which the distance range to be detected is divided into a plurality of parts, and the sensitivity is set for each range, with the sensitivity being lowered at short distances and higher at long distances. According to this, the sensitivity is low in areas where there is a possibility of receiving direct waves, so false detections are eliminated. However, the intensity of the reflected wave varies greatly depending on the material, shape, inclination, and orientation of the object to be detected with respect to the detection device. Therefore, depending on the conditions of the target object, only a very weak reflected wave may be obtained even at a short distance. In such cases, if the sensitivity is low, the object cannot be detected. However, as described above, in order to prevent false detection, the sensitivity cannot be increased at least at short distances, so in any case objects with weak reflected waves at short distances could not be detected. [Purpose] The present invention distinguishes unnecessary waves such as direct waves emitted from an ultrasonic transmitter and induced noise from target reflected waves, and detects even low-level reflected waves or objects at a short distance that cannot be obtained. The purpose is to [Configuration] Since the distance between the ultrasonic transmitter and the ultrasonic receiver is generally constant, the distance from when the ultrasonic transmitter is energized until the direct ultrasonic wave is received by the ultrasonic receiver is The time is constant, and induced noise and the like usually appear after a predetermined time from the timing of energizing the ultrasonic transmitter. Therefore, the reception output is checked at a predetermined timing when a direct wave etc. may appear, and if a wave is being detected at this timing, the detection of reflected waves is prohibited until it is no longer detected, and the wave is detected. If the detection of the reflected waves is started immediately if the detection is not performed, direct waves and reflected waves can be distinguished. In other words, if the sensitivity is low and the level of unnecessary waves is low, detection of reflected waves will start immediately, so if the sensitivity is controlled to gradually increase, for example, if the object is extremely close to the detector, on the order of several centimeters, Even if the timing at which the unwanted waves appear overlaps with the timing at which the reflected waves appear, as in the case shown in Figure 2, the level of the reflected waves is definitely higher than the unwanted waves, so the object can be detected with low sensitivity. . Also, even if the distance between the object and the detector is relatively small, about 20 cm, and the level of the reflected wave is close to or lower than the level of unnecessary waves, the reflected waves will not be detected until the unnecessary waves are gone. Therefore, if the times at which the unwanted waves and reflected waves appear are even slightly different, the unwanted waves and reflected waves can be distinguished. Moreover, in this way, the time period during which detection is prohibited is automatically set, so there is no need to determine this type of parameter through experiments or the like every time the design of the detection circuit is changed. However, an actual unnecessary wave may have two or more peaks (W1, W2) as shown in FIG. 7d. This is thought to be caused by the superposition of direct waves, induced noise, and the like. In this type of unnecessary waves, the influence of direct waves is much larger than other waves, so the level difference between peaks and troughs is not that large, but the level between multiple peaks and troughs is at a threshold level. If the two match, the unnecessary waves may be detected more than once. In such a case,
If the control is performed in such a way that the presence or absence of waves is determined at a predetermined timing as described above, and once no waves are detected, subsequent waves are considered as reflected waves, the second peak W2 may be mistaken for a reflected wave. . Therefore, in the present invention, the detection sensitivity can be changed in a plurality of steps, and the sensitivity ratio between the steps is set to be higher than the level ratio between peaks and troughs that may appear in the unnecessary waves. When a wave is detected, the sensitivity is changed by at least one step and measurement is performed again to determine whether the previously detected wave is an unnecessary wave. In other words, even if the threshold level falls between the peak and trough of the unwanted wave, if the sensitivity between steps is set as described above, setting the sensitivity one step higher will allow the trough to fall between the unwanted waves. Since the level of the unwanted waves is higher than the level of the previous unwanted wave peaks, the timing when the unwanted wave level falls below the threshold level is after all the unnecessary wave peaks have appeared, and the next wave to appear is a reflected wave. It can be determined that it is from. [Example] Hereinafter, an example of the present invention will be described 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, 30b are attached to both ends of a rear bumper 2 of an automobile 1, respectively. In this embodiment, an ultrasonic transmitter 20a and an ultrasonic receiver 20b, and an ultrasonic transmitter 30a and an ultrasonic receiver 30b are arranged parallel to each other with an interval of 3 cm. Ultrasonic transmitters 20a, 30a and ultrasonic receiver 2 used in this example
0b and 30b are ultrasonic ceramic microphones EFR-OSB40K2 and Matsushita Electric, respectively.
It is EFR-RSB40K2. For example, as shown in FIG. 2, if there is an obstacle 3 behind the automobile 1, 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 resulting reflected wave is received. FIG. 3 shows a block diagram of the electric circuit of the obstacle detection device mounted on the vehicle of FIG. 1. This will be explained with reference to FIG. The ultrasonic transmitters 20a and 30a are driven by drive circuits 50 and 70, respectively.
is connected to the output end of the ultrasonic receiver 20b.
A discriminating circuit 6 is provided at the output terminal of 30b and 30b, respectively.
0 and 80 are connected. Drive circuits 50 and 70 and discrimination circuits 60 and 80 are connected to microcomputer 90, respectively. Microcomputer 90 used in this example
is Intel's 8-bit single-chip microcomputer 8748. 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. The start switch 41 is of a self-reset type and has normally open contacts. The start switch 41 is arranged on the operation panel of the driver's seat. 100 is a buzzer circuit, and a buzzer 102 constituting the buzzer circuit is connected to an output port of a microcomputer 90 via a buzzer drive circuit 101. 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 111 is dynamically driven by a segment drive circuit 112 and a digit drive circuit 113. 120 is a warning circuit. FIG. 4 shows a specific configuration of the drive circuit 50 shown in FIG. 3. In addition, in FIG. 3, the drive circuits 50 and 7
0 have the same configuration, a description of the configuration of the drive circuit 70 will be omitted. Referring to FIG. 4, this circuit includes an inverter 53, a driving transistor, a step-up transformer T, and the like. The input terminal of the inverter 53 is connected to the microcomputer 90.
is connected to a predetermined output port of the A pulse signal Sp that controls the activation 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 the driving transistor. When a pulse signal is applied to the primary side of the transformer T, the secondary side is
A signal with an amplitude of about 100V is generated. This boosted 40KHz signal is applied to the ultrasonic transmitter 20a. 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 ultrasonic wave output from the ultrasonic transmitter changes greatly depending on the number of pulses of the signal Sp (Fig. 7b and 1).
(see table). 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, and thereby the level of the ultrasound output from the ultrasound transmitter is adjusted in two stages. to adjust the detection sensitivity. In this example, the detection sensitivity is the signal
By combining the two-step adjustment by adjusting the number of pulses of Sp and the four-step gain adjustment of the variable gain amplifier 62, which will be described later, adjustment is possible in eight steps.

【table】

[Table] 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. Ultrasonic receiver 20b
is connected to the amplifier circuit 61 of the discrimination circuit 60. The amplifier circuit 61 includes three stages of cascade-connected narrowband amplifiers A1, A2, and A3. Each of the amplifiers A1, A2, and A3 is an inverting amplifier composed of an operational amplifier, and a parallel resonant circuit composed of a capacitor and an electric coil resonating at 40 KHz is connected to each feedback path. 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. variable gain amplifier 6
2, this circuit connects the 2-bit control inputs C0 and C of the analog switch AS.
The resistor selected according to the signal from the microcomputer 90 applied to 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.
That is, the amplification degree G of this circuit 62 is expressed by the following equation, where rt is the combined resistance of the feedback resistors connected between the inverting input terminal and the output terminal of the operational amplifier 62a. G=-rt/rin...(1) Analog switch AS has its ports X0,
1, X2 and X3 is selected by a 2-bit gain setting signal applied to control input terminals C0 and C1, and the selected port and common port Y0 are electrically connected. For example, if the data of the gain setting signal is "0" which becomes L and L for input terminals C0 and C1, respectively, port X0 is selected and the combined resistance rt becomes r0, so the gain G is - It becomes r0/rin. Similarly, when the data of the gain setting signal is "1", "2" and "3", ports X1, X2 and X3 are selected respectively, and the combined resistances rt are r0+r1 and r0+
They become r1+r2 and r0+r1+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, the maximum gain when the gain setting signal data is "3" is set to about 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. In other words, operational amplifier
OP1 is a normal amplifier, and when it receives ultrasonic waves, the output terminal of OP1 has a signal corresponding to the ultrasonic waveform.
An electrical signal V1 with a frequency of 40KHz appears. The operational amplifier OP2 is an analog comparator, and compares the level of the signal V1 with a predetermined threshold level, and outputs a binary signal V2 according to the magnitude thereof. This binary signal 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 V3 thus obtained 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 OP3. 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 port is set to a predetermined initial level (non-energized level) and the memory is cleared.
Check the status of the input port and wait for the activation switch 41 to be turned on. When the start switch 41 is turned on, an obstacle detection subroutine is executed. 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, that data is displayed on the display 110. In addition, the buzzer 102 and lamp 12 may be installed as necessary.
1 is energized. Next, the obstacle detection subroutine will be explained. Roughly speaking, first, the sensitivity G is set to the lowest level, ultrasonic waves are emitted, and the process waits until the discrimination 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 waves are emitted by executing the ultrasonic emitting subroutine shown in FIG. 6d. The ultrasonic emission subroutine will be explained. to register RC,
Store sensitivity data G. In this example the sensitivity is 8
Since it can be adjusted in stages, the sensitivity data G takes values in the range of 0 to 7. Shift the data in register RC one bit toward the lower bit. In other words, divide the data value by 2. When this is done, the least significant bit data is set to the carry flag. If the sensitivity data G is an even number, the carry flag becomes "0", but if it is an odd number, the carry flag becomes "1". If the carry flag is "0", that is, an even number, a numerical value N (the number of pulses of Sp) is set in the register RD, and if the carry flag is "1", that is, an odd number, a numerical value N+γ is set in the register RD. Set the data of the register RC (1/2 of the sensitivity data) to the output port, and set the gain data to the analog switch AS of the variable gain amplifier 62. For example, if the sensitivity data is 6, a value of 3 (both signal lines C0 and C1 are "1") is set in the variable gain amplifier 62, and the gain of the amplifier 62 is maximized. Next, set the signal line (Sp) to level H,
After waiting for 12.5 μsec, set the signal line (Sp) to low level L, waiting for 12.5 μsec, and decrement the contents of register RD by 1. Repeat until. In other words, 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 signal
Since the level of the ultrasonic wave output from the ultrasonic transmitter changes depending on the number of pulses of Sp, when the sensitivity data G is an odd number, the sensitivity is higher than when it is an even number. In this example, the gain ratio between each step of the variable gain amplifier 62 is kept constant, and the pulse signal
Sensitivity ratio K between when the number of Sp is N and when the number of Sp is N+γ
is set to be the 1/2 power of the gain ratio between each step of the variable gain amplifier 62. In other words,
If the sensitivity of the entire device is Go when the sensitivity data G is 0, then the sensitivity data G is 1, 2, 3, 4, 5, 6.
The sensitivity of the entire device at 7 and 7 is, respectively.
Go・K, Go・K ² , Go・K ³ , Go・K ⁴ , Go・K ⁵ ,
Go・K ⁶ and Go・K ⁷ , which are K times each other. After emitting ultrasonic waves, first set an interval timer to count the time that has elapsed since the ultrasonic waves were 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. Also, if there is an object in a certain position,
Due to the ultrasonic waves reflected thereby, reflected waves 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 the direct wave,
Before the noise wave appears, the level of the reflected wave with low sensitivity exceeds the threshold level Vth (voltage applied to the negative input terminal of OP2), so the wave that exceeds the threshold level Vth first Although the distance of the object can be determined from the time it appears, for example, if the level of the reflected wave is lower than the noise wave as shown in FIG. 7c, there is a possibility that the noise wave will be erroneously detected. Therefore, in this embodiment, the timing T _KL at which a noise wave appears is determined in advance, and when this timing comes, a check is made to see if there is a wave that exceeds the threshold level Vth. Wait until it runs out (to point P1). Furthermore, in this embodiment, when the gain (sensitivity) G is greater than or equal to the predetermined value Gc, timing T _KH (slightly larger than T _KL ) is used instead of timing T _KL . Further, in the noise wave, a plurality of peaks (W1, W2) often appear as shown in FIG. 7d due to the superposition of a plurality of waves. In this case, if the threshold level Vth falls between the two peak levels and the valley level between them, the peak of the second noise wave will appear after the wave that appeared at timing T _KL disappears as described above. There is a possibility that W2 will appear and be detected at the timing of point P2. Therefore, in this embodiment, the sensitivity ratio K between each sensitivity step is set to be larger than the ratio (VH/VL) between the maximum peak level VH and the lowest valley level VL that can occur in a noise wave. Noise waves and reflected waves are distinguished by 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 Figure 7d, if the sensitivity is increased by one level, the sensitivity will be as shown by the dashed line. Since the level of the trough of the noise wave becomes larger than the threshold level Vth,
If the noise wave appearing at timing T _KL falls below the threshold level, 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. In addition, 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.
If the level of W3 is different, the rise time (t1 - t0 or t2 - t0) required from the timing t0 when the reflected wave W3 first arrives until the level of the reflected wave exceeds the threshold level Vth will be different. As shown by the solid line in Figure 7e, time data obtained when the reflected wave level slightly exceeds the threshold level Vth, and time data obtained when the reflected wave level is sufficiently larger than the threshold level. The measurement results differ greatly between the two, and this results 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 the results are determined to be due to reflected waves reflected by the same object. in case of,
Among them, the data obtained when the sensitivity is high is selected and the distance is calculated from that data. That is, 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. CN1...Counter that counts the number of times a wave is detected at the noise wave detection timing (T _KL , T _KH ) CN2...Counter that counts the number of times that a wave is detected at times other than the noise wave detection timing Tg max...Object measurement period RA... Register RB that holds valid time data...Register Tw that holds distance data (measurement results)...Waiting time α to avoid the effects of noise, ripples, etc. included in the signal...Is the wave reflected from the same object? This is reference time data for determining whether or not the CN2 value is set. 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 for distinguishing between noise waves such as direct waves and reflected waves tn...Time data obtained from the current measurement tn _-1 ...Time data obtained from the previous measurement Gmax...Maximum of sensitivity data Value (7) CN2max...Maximum value of CN2 After setting the interval timer, wait until the timer value reaches T _KL . Once you reach T _KL ,
Referring to the output level of the signal processing circuit 63, it is checked whether the received level of the ultrasonic wave exceeds the threshold level Vth. If it exceeds Vth, the value of counter CN1 is incremented by 1 and the ultrasonic reception level waits until it falls below the threshold level Vth. If the reception level is below Vth at timing T _KL ,
Proceed immediately to the next process. Set the value obtained by adding the wait time Tw to the timer value in the register Tmax, and wait until the timer value exceeds the value of Tmax. Next, with reference to the output level of the signal processing circuit 63, it is determined whether or not ultrasound is received (whether or not the reception level exceeds the threshold level Vth).
Check. If not received, this check is repeated until the timer value reaches Tg max. If the timer value reaches Tg max before ultrasonic waves are received, the sensitivity of gain data G is increased by one step and the processing after ultrasonic emission is executed again. When ultrasonic waves are received, first check the contents of counter CN2. Since the contents of the counter CN2 are cleared to 0 for the first time, the value of the timer at that time is stored in the register RA. Since ultrasonic waves have been detected, the contents of counter CN2 are incremented by 1. If the value of counter CN2 is not greater than CN2max,
Wait until the timer value reaches Tg max, update the gain G by one step to increase the sensitivity, and execute the processing after ultrasonic emission again. If the contents of counter CN2 are 1 or more when ultrasonic waves are received in step S42, the value α of the memory table is read according to the contents of CN2. In addition,
The values α1, α2, and
α3...αn are set to satisfy the following relationship. α1＞α2＞α3＞…＞αn In other words, the reflected wave level is at the threshold level for the first time.
There is a possibility that there will be a relatively large difference between the time data when Vth is exceeded and the time data measured at the next gain, so the value of counter CN2 is 1.
In the case of , the reference value α1 is set relatively large, and as the value of CN2 becomes larger, the difference in time data becomes smaller, so the reference value is also set smaller. Time data tn _-1 obtained in the previous measurement (with lower sensitivity than the current one) and time data tn obtained this time
Compare with. If tn<tn _-1 and tn+α>tn _-1 , for example, the time data t1 shown in Fig. 7e should be changed to tn _-1 and t2 to
As can be understood by associating them with tn, it can be determined that the time data is the result of receiving waves 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. Further, if the content of the counter CN2 is 2, it is determined whether the following condition B is satisfied. In other words, if the value of counter CN2 is 2, the previously measured time data tn _-1 (contents of RA) is invalid, which corresponds to point P2, where unnecessary wave W2 was detected, as shown by the solid line in Figure 7d. There is a possibility that the data is the actual time data. Therefore, if the content of CN2 is 2, it is determined whether tn-β>tn _-1 (condition B) is satisfied. If the time data tn _-1 corresponds to point P2, the time data tn measured this time corresponds to point P
3, it 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 neither conditions A nor B are satisfied and the current time data is smaller than the previous time,
For example, there may be a case where an object that generates a large level of reflected waves exists relatively far away, and an object that only generates small reflected waves exists closer to it.In this case, in this example, the current time data is It is regarded as valid, clears counter CN2, updates the contents of register RA to the current time data, and continues measurement. However, if the value of counter CN1 is 1
In this case, the current time data tn is, for example, the 7th d.
Since there is a possibility that the data corresponds to point P2 shown in the figure, this condition is ignored. If none of conditions A, B and tn < tn _-1 are satisfied, if the value of counter CN2 exceeds its maximum value, or if gain G exceeds its maximum value and there is no valid data in register RA. If it exists, calculate the distance of the object from the time data stored in register RA and send the result to register RB.
Store in. In the embodiment described above, the sensitivity can be adjusted in multiple steps by combining the gain adjustment of the receiving side amplifier and the transmission level adjustment of the ultrasound transmitting side, but the sensitivity can be adjusted in a predetermined step by just adjusting the transmission level of the ultrasound transmitting side. can be carried out. 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, fine sensitivity adjustment can be made by using the frequency characteristics of an ultrasonic oscillator, ultrasonic receiver, amplifier, etc., for example. 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 number N is set to match the center frequency of the ultrasonic transmitter, and the number N+
γ is set to match a frequency shifted by a predetermined amount from the center frequency, so that when the sensitivity data is an even number, the ultrasonic emission level is low, and when the sensitivity data is an odd number, the ultrasonic emission level is high. In addition, 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, change the interval between pulses, and change the high-level period. The ultrasonic emission level can be similarly adjusted by adjusting the duty between the low level period and the low level period. Furthermore, the adjustment may be made by combining these means, for example, pulse number adjustment and frequency adjustment. [Effects] As described above, according to the present invention, reflected waves and unnecessary waves such as direct waves can be distinguished, so there is no false detection.
Moreover, it can reliably detect objects that are located at close range.

[Brief explanation of drawings]

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 shows the drive circuit 50 shown in FIG.
FIG. Figure 5 shows the third
FIG. 2 is an electrical circuit diagram showing the configuration of a discrimination circuit 60 shown in the figure. Figures 6a, 6b, 6c and 6
Figure d shows the microcomputer 90 shown in Figure 3.
1 is a flowchart showing a schematic operation of the Chapter 7a
The figure is a waveform diagram showing the signal waveform of each part of the electric circuit shown in Figure 5, Figure 7b is a waveform diagram showing the correlation between the number of pulses of the energizing pulse Sp and the reflected wave level, and Figure 7c is a waveform diagram showing the correlation between the number of pulses of the energizing pulse Sp and the reflected wave level.
7d and 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 flowchart of an ultrasonic emission subroutine in another embodiment. 1: Car, 2: Rear bumper, 3: Obstacle, 2
0a, 30a: Ultrasonic transmitter (ultrasonic generating means),
20b, 30b: Ultrasonic receiver (ultrasonic receiving means), 40: Starting circuit, 50, 70: Drive circuit,
60, 80: Discrimination circuit, 61: Narrowband amplifier (amplification means), 62: Variable gain amplifier, 63: Signal processing circuit, 90: Microcomputer (electronic control means), 111: Display.

Claims (1)

[Claims] 1. Ultrasonic wave generating means for generating ultrasonic waves; Force means for energizing the ultrasonic wave generating means; Ultrasonic wave receiving means disposed near the ultrasonic wave generating means; Said ultrasonic wave receiving means Amplifying means for amplifying the signal from; and the amplitude of the signal applied to the ultrasonic energizing means, the frequency of the signal applied to the ultrasonic energizing means, the wave number of the signal applied to the ultrasonic energizing means, and the ultrasonic energizing means. Sensitivity adjustment for adjusting at least one of the duty of the pulse signal applied to the ultrasonic wave energizing means, the interval of the pulse signal applied to the ultrasonic energizing means, the degree of amplification of the amplification means, and the level for determining whether or not ultrasonic waves are received. When a detection instruction is received, the ultrasonic generation means is activated, and the presence or absence of an object and the distance from the object detection device are determined according to the time from emission to reception of ultrasonic waves, and the ultrasonic wave generation means is provided. The output signal of the ultrasonic receiving means is monitored at an unnecessary wave detection timing a predetermined time after the means is energized, and if a wave is detected at this timing, detection of reflected waves is prohibited until it becomes non-detected. After that, when the wave detection state is reached, read the first time data obtained at that time, raise the sensitivity to a predetermined level at least higher than the peak-to-trough level ratio that can occur in unnecessary waves, and then detect waves again. electronic control means for comparing second time data obtained as a result with the first time data to identify unnecessary waves and reflected waves; 2. The reflective object detection device according to claim 1, wherein the electronic control means gradually increases the sensitivity from the lowest sensitivity upon receiving an object detection instruction. 3. The reflective object detection device according to claim 1 or 2, wherein the electronic control means sets the unnecessary wave detection timing according to detection sensitivity.