JPH0113549B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a reflection type object detection device using ultrasonic waves, and particularly to failure detection of the object detection device itself. 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 of a predetermined intensity in a predetermined direction, an ultrasonic receiver is directed in the same direction, and the intensity of the signal generated at the ultrasonic receiver and The presence of reflected waves, that is, the presence of obstacles, is detected from the timing at which the signal is generated. By the way, in this type of device, if an abnormality occurs on the transmitting device side and the ultrasonic waves are no longer generated, the ultrasonic waves will not reach the receiving device side even if an obstacle actually exists. Therefore, in this case, the device will determine that there is no obstacle and will give incorrect information to the driver, which is dangerous. For example, when a vehicle backs up while checking for obstacles with a detector installed at the rear of the vehicle, if the device is malfunctioning, the driver will believe that there are no obstacles, and the driver will be able to detect obstacles. If there is, the vehicle will collide with it. For this reason, in conventional devices, it has sometimes been necessary for the driver to place an arbitrary object in the direction of the object detector to check whether the device is operating normally. However, such checks are extremely troublesome. Therefore, Japanese Patent Application Laid-Open No. 57-42866 focuses on the direct waves that reach the ultrasonic receiver directly from the ultrasonic transmitter without being reflected, and if the direct waves are not detected, an abnormality is identified as an abnormality. A detection circuit is disclosed. However, in this prior art, the received level of the direct wave is lower than the received level of the reflected wave, as mentioned above. In other words, when the levels of the direct wave and the reflected wave become equal, it becomes impossible to distinguish between the two, and the reflecting object becomes impossible to detect. However, if we try to detect a distant object, the reception level of the reflected wave will be as weak as that of the direct wave, so with conventional configurations, the distance to the detection target is limited to a short range. Therefore, the detection ability will be lower. Furthermore, in the conventional technology, it is necessary to add a special detection circuit for abnormality detection, which increases the cost of the device. The first object of the present invention is to provide a reflective object detection device that automatically detects a failure in the device itself and notifies you if there is an abnormality. The purpose of the present invention is to provide a reflective object detection device that can detect objects over a wide range of distances, and a third purpose is to provide a reflective object detection device that has a simple circuit configuration and can be manufactured at low cost. be. In order to achieve the above object, in the present invention,
A sensitivity adjustment means is provided to make the detection sensitivity of the device variable, and a plurality of operation modes are provided, and different detection sensitivities and detection timings are assigned to each operation mode. The operating modes include anomaly detection mode,
There are multiple distance measurement modes with different detection target distance areas, and in the abnormality detection mode, ultrasonic waves that reach the ultrasonic receiver directly from the ultrasonic generator without passing through obstacles,
That is, the detection sensitivity and detection timing are set to detect direct waves, and in distance measurement mode, the detection sensitivity and detection timing are set to detect reflected waves according to each distance range to be measured. . In other words, when an ultrasonic generator generates an ultrasonic wave, some of the ultrasonic wave is reflected and diffracted within the ultrasonic generator, or by traveling straight, so even if there are no obstacles, some of the ultrasonic wave becomes a direct wave. reach the receiver. Therefore, the ultrasonic generator is energized and it is monitored whether a predetermined signal is generated at a predetermined (straight wave) reception timing depending on the interval between the ultrasonic generator and the ultrasonic receiver. Then, it can be determined whether a direct wave has been received, that is, whether the transmitting device and the receiving device are operating normally. According to this, the operation of the entire device including the ultrasonic transmitter and ultrasonic receiver is checked in order to determine that the operation is normal when the ultrasonic wave is actually generated and the ultrasonic wave is received. will definitely be carried out. Also, the intensity of the direct wave reaching the ultrasonic receiver is
The intensity of the reflected wave is almost constant because there is no obstacle involved, but the intensity of the reflected wave varies greatly depending on the distance between the detection device and the object. As the distance increases, the intensity of the reflected wave decreases, and may even be smaller than the direct wave. However, in that case, the time from emitting ultrasonic waves to receiving them is significantly different between direct waves and reflected waves, so if the detection timing is shifted, direct waves and reflected waves can be distinguished, and direct waves and reflected waves can be distinguished. This can prevent errors from occurring in the measured distance. Moreover, when the measurement distance is small, the time from emitting the direct wave to receiving it is the same for the direct wave and the reflected wave. However, in that case, the reception level of the reflected wave is sufficiently higher than that of the direct wave, so by adjusting the detection sensitivity to a small value, the influence of the direct wave can be removed and only the reflected wave can be detected. Even if there is no object that generates reflected waves, by setting the detection sensitivity to a level that allows direct waves to be detected, it is possible to identify the presence or absence of direct waves and check whether the device is operating normally. In other words, in the present invention, not only can abnormalities be detected by detecting direct waves, but also direct waves and reflected waves can be completely separated by changing the detection sensitivity and detection timing. Distance can be measured accurately over a wide range of distances. Furthermore, since the circuit for detecting direct waves and the circuit for detecting reflected waves can be used in common, there is no need to add a special circuit for abnormality detection, and an inexpensive device can be constructed. Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows the exterior of a car 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. FIG. 2 shows a block diagram of the electric circuit of the obstacle detection device mounted on the vehicle shown in FIG. This will be explained with reference to FIG. The ultrasonic transmitters 20a and 30a are connected to the output ends of drive circuits 50 and 70, respectively, and a discrimination circuit 60 is connected to the output ends of the ultrasonic receivers 20b and 30b, respectively.
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;
A buzzer 102 constituting it is connected to an output port of the 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 3-digit 7-segment display 11
1. The display 111 is driven for dynamic display by a segment drive circuit 112 and a digit drive circuit 113. 120 is a warning circuit. A warning lamp 121 that is turned on when a device malfunctions is connected to an output port of the microcomputer 90 via a lamp drive circuit 122. FIG. 3 shows a specific configuration of the drive circuit 50 shown in FIG. 2. In addition, in FIG. 2, the drive circuits 50 and 7
0 have the same configuration, the description of the configuration of the drive circuit 70 will be omitted. This will be explained with reference to FIG. 51 is a pulse oscillator constructed using an integrated circuit, with a constant duty of 50% and a frequency of 40K.
Outputs a Hz pulse signal. The output signal of the pulse oscillator 51 is applied via a NAND gate 52 and an inverter 53 to a power amplification circuit 54 composed of two transistors. nand gate 5
One input terminal of the NAND gate 52 is connected to the output port of the microcomputer 90, and when the output level of that port is high level H, the NAND gate 52 is connected to the output port of the microcomputer 90.
A pulse signal from a pulse oscillator 51 is generated at the output end of the oscillator. The power amplifier circuit 54 receives power from the battery.
A voltage Vb of 12V is applied, and a pulse signal with an amplitude of 12V appears at the output terminal of 54. The output terminal of the power amplifier circuit 54 is connected to the primary side of the step-up transformer T, and when a pulse signal is applied to the primary side of the transformer T, a signal with an amplitude of about 100V is generated on the secondary side. . This boosted 40KHz
is applied to the ultrasonic transmitter 20a. FIG. 4 shows a specific configuration of the discrimination circuit 60 shown in FIG. 2. Note that since the discrimination circuits 60 and 80 have the same configuration, a description of the discrimination circuit 80 will be omitted. Fourth
This will be explained with reference to the figures. The ultrasonic receiver 20b is
It 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 amplifier A1, A2, and A3 is an inverting amplifier configured with an operational amplifier,
A parallel resonant circuit consisting of a capacitor and an electric coil resonating at 40KHz is connected to each return path. 62 is a variable gain amplifier, ie, level changing means. This variable gain amplifier 62 is composed of an operational amplifier 62a, an analog switch (analog multiplexer) AS, and a large number of resistors. The analog switch AS used here is
It is CMOS MSI MC14051 manufactured by Motorola.
To briefly explain the variable gain amplifier 62, this circuit is configured such that a resistor selected in accordance with a signal from a microcomputer 90 applied to 3-bit control input terminals C0, C1, and C2 of an analog switch AS performs an operation. It is connected to the amplifier 62a as a feedback resistor, and amplifies the signal with an amplification degree determined by the resistor and the input resistor rin. In other words, this circuit 6
The amplification degree G of 2 is the combined resistance of the feedback resistors connected between the inverting input terminal and the output terminal of the operational amplifier 62a.
If rt, it is expressed by the following formula. G=-rt/rin...(1) Analog switch AS has its ports X0, X1,
Select one of X2,
Connect Y0 electrically. For example, if the data of the gain setting signal is "0", which is L, L, and L for input terminals C0, C1, and C2, respectively, port X0 is selected and the combined resistance rt is
r0, so the gain G becomes -r0/rin. Similarly, the data of the gain setting signal is "1", "2",
When "3", "4", "5", "6" and "7",
Ports X1, X2, X3, X4, X5, X6 and respectively
X7 is selected and the combined resistance rt is r0 and r0+, respectively.
r1, r0+r1+r2, r0+r1+r2+r3, r0+r1+r2+
r3+r4, r0+r1+r2+r3+r4+r5, r0+r1+r2+
r3+r4+r5+r6, and r0+r1+r2+r3+r4+r5+
It becomes r6 + r7. Therefore, variable gain amplifier 62
The gain G of can be set in eight stages using a gain setting signal. In this embodiment, the maximum gain when the gain setting signal data is "7" is set to about 128 times the minimum gain when the gain setting signal data is "0". 63 is an inverting amplifier, 64 is a rectifying and smoothing circuit, 65
is a comparator. A reference voltage Vr obtained by dividing the voltage Vb by a resistor is applied to one input terminal of the comparator 65, and a DC voltage Vs obtained by the rectifying and smoothing circuit 64 is applied to the other input terminal of the comparator 65. has been done. 66 is a level conversion circuit, ie, an interface circuit, the output end of which is connected to the microcomputer 90. Voltage Vcc is 5V. The general operation of the obstacle detection device will be explained. As shown in Fig. 5, this device generates ultrasonic waves from both ends of the rear bumper 2 of the automobile 1, so when an obstacle 3 is present, the ultrasonic waves reflected by the obstacle 3 are transmitted to the ultrasonic receiver. This is detected by the electrical circuit to detect the presence of an obstruction. In reflective obstacle detection using ultrasonic waves,
The intensity of reflected waves varies greatly depending on the location of the obstacle, and if the detection sensitivity is too high, even objects that are not obstacles may be detected as obstacles. In addition, there are reflected waves that reach the receiver after being reflected multiple times, and if the distance is calculated by detecting these reflected waves, a large error will occur. Therefore, in this embodiment, the area to be detected is divided into multiple areas based on distance, different sensitivities are set for each area, and the time for detecting obstacles is regulated by setting a time window. By doing so, we have achieved high reliability. Regarding the sensitivity setting, specifically, the data of the gain setting signal used to set the analog switch AS mentioned above is changed. Furthermore, the time is determined by changing the reference data to be compared with the data counted by the interval timer inside the microcomputer 90. Table 1 below shows the gain setting signal data Dg in each region and the reflected wave detection inhibition period data ΔTinh.
and detection end time data Tg max.

[Table] In Table 1, the numerical values shown with the alphabet H are shown in hexadecimal notation. The numbers in parentheses are decimal numbers. The data in Table 1 is stored in advance in a ROM (read-only memory) within the microcomputer 90. A numerical value of 1 for the time data ΔTinh and Tg max shown in Table 1 corresponds to a time of 80 μs in this example. The operation of the microcomputer 90 is shown in FIGS. 6a, 6b, and 6c. 6a is the main routine, FIG. 6b is a subroutine for its failure detection processing operation, and FIG. 6c is a subroutine for the obstacle detection processing operation shown in the main routine. First, the general operation will be explained with reference to FIG. 6a.
Also execute step S1 to initialize. This writes predetermined data into the RAM (random access memory) inside the microcomputer 90 and sets the level of each output port of the microcomputer to the initial level. That is, the ports that control the energization of the drive circuits 50 and 70 are set to low level L, the ports that energize the warning circuit 120 are set to high level H, and the ports that energize the buzzer circuit 100 are set to high level H. and each port that energizes the distance display circuit 110 is set to a de-energized level. Next, the microcomputer 90 performs step S2.
is executed, the state of the port to which the activation circuit 40 is connected is checked, and this process is repeated until the state reaches the level indicating the state in which the switch 41 is operated. When the start switch 41 is operated, the microcomputer 90 executes a failure check subroutine at step S3. This process will be explained in detail later, but briefly, it generates an ultrasonic wave, checks whether its direct wave is detected by the ultrasonic receivers 20b and 30b,
The state of flag S is set according to the result of the check. In other words, the detection of direct waves indicates that the ultrasonic waves are being reliably transmitted and that the ultrasonic receiver is also operating normally. You can judge whether it is normal or not. Actually, in this process, if the operation is normal, the flag S is set to "0", and if the operation is abnormal, that is, no direct wave is detected, the flag S is set to "1". Next, the microcomputer 90 steps
Execute S4, check the state of flag S obtained as a result of the previous failure check routine, and select the next process to be executed based on the state. If the operation is abnormal, the microcomputer 9
0 proceeds to step S5, where the state of the output port is set so that the buzzer 102 and the warning lamp 121 are energized. If the operation is normal, the microcomputer 9
0, the program proceeds to step S6 and executes an obstacle detection subroutine that will be explained in detail later. With this process,
If an obstacle is detected, the distance between the vehicle and the obstacle is calculated, and the result is stored in a predetermined register. When no obstacle is detected, "0" is stored in that register. In step S7, the microcomputer 90
The distance data obtained in the obstacle detection subroutine is output to display drive circuits 112 and 113, and the distance between the vehicle and the obstacle is displayed as a three-digit numerical value. After completing the above processing, return to step S2,
Repeat the following steps. The fault check subroutine will now be described in detail with reference to FIG. 6b. When the microcomputer 90 proceeds to step S31, it outputs the numerical value 4 to the analog switch AS as a gain setting signal.
The amplification degree of the variable gain amplifier 62 is now set to a predetermined level. This level is the signal obtained at one input terminal of the comparator 65 by the ultrasonic signals received by the ultrasonic receivers 20b and 30b when the obstacle detection device emits ultrasonic waves when the operation is normal. The level of Vs is set to be slightly higher than the reference voltage Vr, that is, the threshold level. Next, the microcomputer 90 steps
Proceeding to S32, the level of the output port connected to the NAND gate 52 is set for a predetermined time (80 μs in this example).
to a high level H. During this period, the output terminal of the NAND gate 52 receives 40KHz from the pulse oscillator 51.
Since a pulse signal appears, a predetermined level of 40 KHz voltage is applied from the output of the transformer T to the ultrasonic transmitters 20a and 30a. Then, the microcomputer 90
Proceeding to S33, the microcomputer (8748) starts the internal programmable interval timer. In step S34, the microcomputer 90 checks the time since starting the interval timer, that is, the time since the generation of ultrasonic waves has finished, and checks the time Tmin, that is, when the direct waves reach the ultrasonic receiver 20b and Wait until the minimum time that can be determined to have reached 30b has elapsed. In step S35, the microcomputer 90 checks whether the time since starting the interval timer has passed Tmax, that is, the maximum time for determining that the direct waves have reached the ultrasonic receivers 20b and 30b. Depending on the result, the next process to be executed is selected. If the time is between Tmax and Tmin, the microcomputer 90 proceeds to step S39. In this process, the state of the port connected to the output end of the level conversion circuit 66 is read, and it is checked whether it is at the ultrasonic detection level, that is, whether Vs>Vr. If no ultrasound is detected, the time Tmax
The process returns to step S35 and repeats this process until it exceeds . When ultrasonic waves are detected, the next step S40
Proceed to. In step S40, the microcomputer 90
sets the failure check flag S to "0" and proceeds to step S37. If the time Tmax elapses before a direct wave is detected, the process advances to step S36 and the fault check flag S is set.
is set to "1". When these processes are completed, the microcomputer 90 waits in step S37 until the time exceeds Tc max. This time Tc max is long enough so that if the ultrasonic waves emitted in this fault check subroutine are reflected by an arbitrary object, the reflected waves will not affect obstacle detection after this process is completed. It is a time when The microcomputer 90 resets the interval timer in step S38 and returns to the main routine. Next, the obstacle detection subroutine will be explained with reference to FIG. 6c. First, the microcomputer 90
In step S61, the gain setting signal is set to "0" and the amplification degree of the variable gain amplifier 62 is set to the lowest level "0". Next, the process proceeds to step S62, where the microcomputer 90 outputs a high level H to the port connected to the NAND gate 52 for 80 μs. As a result, a 40KHz pulse signal from the pulse generator 51 is generated at the output end of the NAND gate 52 only during the high level period, thereby energizing the ultrasonic transmitters 20a and 30a, and the 40KHz ultrasonic signal is generated. Sent. Next, the process proceeds to step S63, where the microcomputer 90 sets the internal interval timer to start. In the next step S64, the microcomputer 90 reads the state of the port connected to the output end of the level conversion circuit 66, and selects the next step according to the result. When the port is at the low level L, that is, Vs>Vr and the ultrasonic detection level, the process proceeds to step S65, and when no ultrasonic waves are detected, the process proceeds to step S69. When the microcomputer 90 detects the reflected wave and proceeds to step S65, it checks whether the time since starting the interval timer, that is, the time since the ultrasonic wave was emitted, is between Tmax and Tmin. do. Time for this process
Tmax and Tmin are the longest and shortest times set by the time data ΔTinh shown in Table 1 above, and these times are the maximum and shortest times set in the time data ΔTinh shown in Table 1 above, and these times are the maximum and shortest times set by the time data ΔTinh shown in Table 1 above. This is the time during which detection of reflected waves is prohibited in order to monitor one of the regions divided into a plurality of regions according to the distance between the devices 20b and 30b and the obstacle.
For example, in Table 1, the level of gain (Dg)
When is set to 2, Tmax is 2400 μs, corresponding to 1EH, and Tmin is 0 μs, corresponding to 00H. Then, during this time, even if a reflected wave is detected, the detection is invalidated, and the process then proceeds to step S69. If a reflected wave is detected during the period during which reflected wave detection is valid, the process proceeds to step S66. When the microcomputer 90 proceeds to step S69, it checks whether the time from the timer start exceeds Tg max. This time Tg max
is the time set by the time data Tg max shown in Table 1 above, and this time is the time at which the ultrasonic waves emitted for one obstacle detection will not affect the next obstacle detection. It's set to a sufficient amount of time even though it's not. For example, in the case of a region where the gain level is set to 2, Tg max is 3520 μs corresponding to 2CH. If the time does not exceed Tg max, the process returns to step S64. When the time exceeds Tgmax, the process proceeds to step S70. In step S70, the microcomputer 90 updates the gain setting and raises the level by one. For example, if the gain level G is 0,
Next, set G to 1. In the next step S71, the gain level G set in the previous step S70 is set to the maximum level, that is, 7.
Check whether it has been exceeded. If G is 7 or less, the process proceeds to step S72, and if G is 8, the process returns to the main routine. In step S72, the microcomputer 90 resets the interval timer and then returns to step S62. If a reflected wave is detected after the detection prohibition period Tmax has elapsed, this is processed as valid data in step S66, and the ultrasonic wave is transmitted to the ultrasonic transmitter 20.
The time from when the ultrasonic waves are emitted by the ultrasonic waves a and 30a until the reflected waves are detected by the ultrasonic detectors 20b and 30b is determined from the count value of the interval timer, and from this value and the speed of the ultrasonic waves. The distance between the vehicle and the obstacle is calculated and the result is stored in a predetermined register. In the next step S67, the microcomputer 90 waits until the time elapses above Tgmax,
Next, the process advances to step S68. In step S68, the microcomputer 90
resets the interval timer and returns to main routine processing. In the above embodiment, the sensitivity of the obstacle detection device is changed by changing the amplification degree of the amplifier on the receiving device side, but the sensitivity can also be changed by changing the reference voltage Vr of the comparator 65, and vice versa. Sensitivity can also be changed by changing the ultrasonic transmission intensity on the transmitting device side. FIG. 7 shows an embodiment in which the reference voltage Vr of the comparator is changed. This will be explained with reference to FIG. In this embodiment, the variable gain amplifier 62 shown in FIG. 3 is omitted, and instead, one end of the comparator 65 is connected to the common port Y0 of the analog switch AS. Each port of analog switch AS
Different voltages obtained by dividing voltage Vb by resistors rx, r0 to r7 are applied to X7. Therefore, by connecting a microcomputer to the control input ports C0, C1, and C2, you can adjust the reference voltage by changing the data output to those ports.
Since Vr changes, the ultrasonic detector 20b or 30
The detection level, that is, the sensitivity at which the reflected wave received at point b is determined to be a reflected wave changes. FIG. 8 shows an embodiment in which the ultrasonic transmission intensity on the transmitting device side is changed. This will be explained with reference to FIG. In this embodiment, the intensity of the transmitted ultrasonic waves is changed by changing the voltage applied to the power amplification circuit 54. In this embodiment, the voltage is generated by the power supply PW. This power supply PW
This is a modification of the commonly used series control type constant voltage power supply device. In other words, the analog switch AS switches the voltage applied to the transistor Q1, that is, the error amplifier, thereby changing the output voltage of the power supply. In other words, different voltages obtained by dividing the output voltage of the power supply PW using multiple resistors are applied to each port X0 to X7 of the analog switch AS.
Changing the data output to the control input ports C0, C1, and C2 of the circuit changes the voltage applied to the error amplifier, which changes the output voltage. If the voltage output by the voltage PW changes, the amplitude of the output pulse of the power amplifier circuit 54 changes, so the intensity of the emitted ultrasonic waves changes, and this changes the intensity of the ultrasonic waves that reach the ultrasonic receiver, so there is no obstacle. Detection sensitivity changes. In the above embodiment, two sets of ultrasonic transmitters and ultrasonic detectors are provided at the rear of the vehicle, but the ultrasonic transmitter and the ultrasonic receiver may also be provided on the side of the vehicle. Alternatively, the ultrasonic transmitter and the ultrasonic receiver may be provided in a fork of a forklift truck to detect cargo.The number of ultrasonic transmitters and ultrasonic receivers may be one or three or more. Further, in the above embodiment, each ultrasonic transmitter is provided with a drive circuit, and each ultrasonic receiver is provided with a discrimination circuit, but the number of these drive circuits and discrimination circuits is at least one. It's good to have both. When connecting multiple ultrasonic receivers to one discrimination circuit, use an analog switch, for example, to switch the signals from each ultrasonic receiver and connect one of them to the discrimination circuit. Bye. As described above, according to the present invention, the direct wave of the ultrasonic waves emitted from the ultrasonic generating means is detected by the ultrasonic receiving means to determine the presence or absence of a failure. You can check the operation of the device. Furthermore, by setting different detection sensitivities and detection timings for each operation mode, direct waves and reflected waves can be reliably separated, allowing reflections to be made from short to long distances without being affected by direct waves. Distance can be accurately measured by detecting only waves. Furthermore, since the circuit that detects direct waves for failure detection and the circuit that detects reflected waves for distance measurement can share the same circuit, there is no need to add a special circuit for failure detection. , it is possible to provide an inexpensive reflective object detection device.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an automobile equipped with a reflective object detection device according to one embodiment, FIG. 2 is a block diagram of an electric circuit of the device according to the embodiment installed in the automobile of FIG.
This figure is a block diagram showing one drive circuit 50 in FIG. 2, FIG. 4 is a block diagram showing one discrimination circuit 60 in FIG. 2, and FIG. 5 is a schematic diagram showing the operation of the device shown in FIG. 2. The plan view, FIG. 6a, FIG. 6b, and FIG. 6c are flowcharts showing the operation of the microcomputer 90 shown in FIG. 2, respectively. FIGS. 7 and 8 are block diagrams showing a part of the electric circuit of the object detection device of other embodiments, respectively. 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 (energizing means), 60, 80: Discrimination circuit, 51: Pulse transmitting circuit, 61: Narrowband amplifier (amplification means),
62: Variable gain amplifier (sensitivity adjustment means), 6
4: rectifier and smoothing circuit, 65: comparator, 66: level conversion circuit, 90: microcomputer (control means), 102: buzzer (alarm means), 121: lamp (alarm means).

Claims (1)

[Claims] 1. Ultrasonic generation means for generating ultrasonic waves; Urging means for urging the ultrasonic generation means; Arranged at a predetermined interval from the ultrasonic generation means, for receiving ultrasonic waves. Ultrasonic receiving means; Amplifying means for amplifying the signal from the ultrasonic receiving means; Sensitivity adjusting means for adjusting detection sensitivity; and Different control states are assigned to at least one of detection sensitivity and detection timing of each mode. It has an abnormality detection mode and a plurality of distance measurement modes with different detection target distance areas, and in each mode, the sensitivity adjustment means is controlled to set the detection sensitivity, and the ultrasonic wave generation means is energized, The ultrasonic detection signal output from the amplification means is monitored when the elapsed time from the time when the ultrasonic generation means is energized corresponds to the assigned detection time, and in the abnormality detection mode, a direct wave is detected. Detection sensitivity and detection timing are assigned, and when an ultrasonic detection signal is not obtained, an abnormality is identified and an alarm is issued, and when an ultrasonic detection signal is obtained, the mode is shifted to the ranging mode,
In each ranging mode, a detection sensitivity and detection timing for detecting reflected waves are assigned, and a control means identifies the distance to the object according to the time from transmitting ultrasonic waves to receiving ultrasonic waves. A reflective object detection device comprising; 2. The reflective object detection device according to claim 1, wherein the sensitivity adjustment means adjusts the urging level of the urging means according to the set detection sensitivity. 3. The reflective object detection device according to claim 1, wherein the sensitivity adjustment means adjusts the amplification degree of the amplification means according to the set detection sensitivity. 4. The reflective object detection device according to claim 1, wherein the sensitivity adjustment means adjusts the discrimination level of the ultrasonic detection signal according to the set detection sensitivity.