JPH11153666A - Prevention method for erroneous detection of ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent mutual interference of each ultrasonic sensor arranged in the vicinity without depending on timing control of ultrasonic oscillation by synchronous lines and data communication. SOLUTION: When emitting ultrasonic wave repeatedly from an ultrasonic wave transmission element of each ultrasonic sensor 1 toward a monitoring region and receiving reflection wave appearing in a specific monitoring period from the time of ultrasonic wave emission using an ultrasonic wave reception element 20 at each time, the ultrasonic wave emission interval is made irregular for each ultrasonic wave sensor 1 and the reflection wave received in the monitoring period is stored in memory means (frame memory) 23 in turn. Based on a plurality of reflection wave data stored in the memory means 23, the existence of an object in the monitoring region is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing erroneous detection of an ultrasonic sensor, and more particularly, to an erroneous detection of an ultrasonic sensor for preventing erroneous detection due to mutual interference between a plurality of ultrasonic sensors arranged in the vicinity. It relates to a detection prevention method.

[0002]

2. Description of the Related Art Ultrasonic sensors are used for various object detection sensors because they are relatively inexpensive. For example, when applied as a vehicle detection sensor in a parking lot, the ultrasonic sensor is used for each parking area unit. It is placed on the ceiling. That is, one area is monitored by one sensor.

[0003] Since ultrasonic waves are elastic waves, when a plurality of ultrasonic sensors are arranged in the vicinity as described above, whether the reflected waves are emitted by themselves or those emitted from nearby sensors. It is difficult to distinguish between them, and a problem of erroneous detection due to mutual interference occurs.

In order to solve this problem, various countermeasures have been taken in the past, but all of them are basically designed to temporally distinguish one's own ultrasonic wave from another's ultrasonic wave. Next, three examples are introduced.

In the first method, for example, assuming that two ultrasonic sensors are arranged close to each other, one ultrasonic sensor emits ultrasonic waves every Ta seconds, while the other ultrasonic sensor emits ultrasonic waves. A different time T from the ultrasonic sensor B
Ultrasonic waves are fired every b seconds.

On the other hand, in the ultrasonic sensor, if the interval between the received reflected waves coincides with the cycle Ta transmitted by itself, it is determined that the ultrasonic wave is transmitted by itself. Similarly, if the interval between the received reflected waves of the other ultrasonic sensor coincides with the cycle Tb seconds transmitted by itself, it is determined that the transmission is due to its own transmission.

In a second method, each ultrasonic sensor has a periodic table of ultrasonic emission periods and emits ultrasonic waves according to the periodic table. If the reception interval of the reflected wave matches the periodic table, it is determined that the signal was transmitted by itself. In this method, in order to further clarify the distinction between oneself and another, the launch cycle table may be changed at least once after confirming that the reflected wave is due to one's own transmission.

As a third method, there is a method in which neighboring ultrasonic sensors are connected by a synchronous line, and ultrasonic waves are simultaneously emitted from the respective ultrasonic sensors. In this way, by causing all the ultrasonic sensors to emit ultrasonic waves at the same time, the possibility of detecting ultrasonic waves from neighboring sensors is reduced.

[0009]

However, in the first method, a means for temporally verifying whether or not the interval between the emission of the ultrasonic wave and the interval between the reception of the reflected wave is indispensable is required. Or, even if it is performed by software, the whole system becomes complicated.

In the second method, when neighboring sensors operate at the same cycle or periodic table, it is impossible to distinguish reflected waves from themselves. In addition, since this cycle is generally directly related to the object detection response speed of the sensor, it is not preferable to change the cycle unnecessarily.

In the third method, it is only necessary to operate each ultrasonic sensor at the same time, and it is the simplest in terms of control. However, it is necessary to route a synchronization line between many ultrasonic sensors, and the With difficulty. In addition, in this method, the monitoring period after oscillation is the same for all sensors, so that interference may occur depending on the position of the object to be detected.

The present invention has been made to solve such conventional problems, and its purpose is to connect each ultrasonic sensor without connecting them with a synchronous line or the like, and also in terms of hardware. An object of the present invention is to provide a method for preventing erroneous detection of an ultrasonic sensor, which can prevent mutual interference between ultrasonic sensors with a relatively simple configuration in terms of software.

[0013]

According to the present invention, there is provided a method for preventing erroneous detection of an ultrasonic sensor for preventing erroneous detection due to mutual interference between a plurality of ultrasonic sensors arranged in the vicinity. Repeatedly emit ultrasonic waves from the ultrasonic transmission element of each ultrasonic sensor toward the monitoring area,
In receiving a reflected wave that appears within a predetermined monitoring period from the time of ultrasonic emission at each ultrasonic receiving element,
The ultrasonic emission interval is irregular for each ultrasonic sensor, and the reflected waves received during the monitoring period are sequentially stored in the storage means, and the plurality of reflected wave data stored in the storage means are stored. The presence or absence of an object in the monitoring area is detected based on the detection.

As described above, by making the ultrasonic wave emission intervals irregular, that is, random for each ultrasonic sensor, the reflected wave monitoring period becomes irregular accordingly. Therefore, the probability of continuously receiving ultrasonic waves from another ultrasonic sensor becomes extremely low.

[0015] Even if an ultrasonic wave from another ultrasonic sensor is received during the reflected wave monitoring period, in the present invention,
Since the presence / absence of an object is detected not only by the reflected wave data received this time but also by the reflected wave data received in the past, for example, the previous time, the last two times before, etc., it is possible to eliminate mutual interference.

That is, the reflected wave from the reflecting object (stationary object) which should be originally detected appears at the same time position as measured from the launching time, regardless of the state of the ultrasound launching timing. Therefore, when detecting the presence or absence of an object in the monitoring area based on a plurality of reflected wave data in the storage means, when each reflected wave data is the same, the reflected wave data is validated, and when the reflected wave data is not the same, Can be determined to include a reflected wave from another ultrasonic sensor.

In this case, the storage means is a frame memory, and each reflected wave data is stored as a reflected waveform in the same frame memory, and the reflected waveforms are compared with each other so that the reflected waves from other ultrasonic sensors can be reflected. Whether it is included can be determined easily and accurately.

In the present invention, each ultrasonic sensor is provided with random timing generating means for making the ultrasonic wave emission intervals irregular. The random timing generation means includes an address assigned to each ultrasonic sensor,
A time table having a plurality of irregular ultrasonic emission intervals set corresponding to the address is provided. A different address is set for each ultrasonic sensor, whereby each ultrasonic sensor repeats a different irregular oscillation based on the set self-address.

Further, it is preferable that the basic period of each ultrasonic sensor is the same, and the ultrasonic emission interval is irregular within the basic period. According to this, the object detection response speed of each ultrasonic sensor is reduced. The variation can be suppressed within a range that does not cause a problem in accuracy.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings for better understanding of the technical concept of the present invention.

FIG. 1 shows an ultrasonic sensor 1 used in the present invention.
In the block diagram of FIG. 7, when the application is, for example, a vehicle detection sensor in a parking lot, the ultrasonic sensor 1 having the same configuration as that of the parking sensor is provided for each parking area.

For convenience of explanation, the ultrasonic sensor 1 is divided into a transmission system including the ultrasonic transmission element 10 and a reception system including the ultrasonic reception element 20.

The transmission system is provided with a random timing data table 11 for emitting ultrasonic waves from the ultrasonic transmission element 10 irregularly (randomly). In the random timing data table 11, a data table as shown in FIG. 2 is set in advance.

That is, this data table is a time table in which a predetermined number of address numbers 1, 2,... Are arranged in the left column and the vertical line, and the rows are arranged in the order of the number of ultrasonic waves emitted (first, second, third,...). In addition, data indicating the number of milliseconds after the last emission (or reference time) of the emission of the ultrasonic waves is written in the order of the number of ultrasonic emission for each address number.

This ultrasonic emission time data has no regularity between addresses and in the order of the number of ultrasonic emission times, and in this sense, it is preferable to set, for example, using a random number.

The address of this data table is appropriately selected by the user via an address switch 12 provided in each ultrasonic sensor 1. That is, when the address of the own device is set to, for example, address 1 by the address switch 12, the central processing unit (CPU) 1
3, the time table at address 1 is read,
The timer 14 is set.

According to this time table, the first oscillation timing is 200 milliseconds, so the waiting time until oscillation is 200 milliseconds. The second oscillation waiting time is 350 milliseconds. After oscillating n times in this way, the operation returns to the first oscillation timing.

The ultrasonic emission time data read by the CPU 13 in this manner is stored in the ultrasonic drive circuit 15.
And the ultrasonic transmission element 10 is driven according to the timing.

In the receiving system, the reflected wave received by the ultrasonic receiving element 20 is given to the reflected waveform digitizing circuit 22 via the reflected wave receiving circuit 21. In this embodiment, the reflection waveform digitizing circuit 22 has a detection circuit and an A / D conversion circuit. For example, the detection circuit obtains a detection waveform as shown in FIG. The waveform is A / D converted to a digital reflected waveform as shown in FIG.

By the way, in the detected waveform of FIG. 3A, the large peak waveform on the right is from the floor surface, while the small peak waveform on the left is any of the detected object (vehicle in this embodiment) or mutual interference. It depends. A comparator is used in place of the A / D conversion circuit, and the detection waveform of the reflected wave is turned on with an appropriate threshold value.
A reflected waveform may be extracted as digital information of the off state.

As described above, the reflection waveform A / D converted by the reflection waveform digitizing circuit 22 is saved in the frame memory 23. In this case, the monitoring period timing of the reflected wave in the receiving system, that is, the digitization of the reflected waveform, is instructed to execute by using the timer 14 after the CPU 13 instructs the ultrasonic wave to be transmitted to the transmitting system. The time axis length is controlled to be constant.

That is, the digitization of the reflected waveform is performed with a certain synchronization with the transmission system, and the end of the digitizing process is controlled to be temporally constant. In this way,
Each time an ultrasonic wave is emitted from the ultrasonic transmission element 10, a reflected waveform can be obtained with a fixed time from the point of emission as a reflected wave monitoring period.

FIG. 4 exemplifies the relationship between the ultrasonic emission timings of two ultrasonic sensors 1A and 1B arranged adjacently and the reflected wave monitoring period. As shown in the figure, the ultrasonic emission intervals TA1, TA2, TA3,.
Are based on, for example, address number 1 in the data table of FIG. 2, and the ultrasonic emission intervals TB1, TB2, TB3... Of the other ultrasonic sensor 1B are based on, for example, address number 2 in the data table. Although the intervals are random, the reflected wave monitoring period RW is always constant.

The CPU 13 also writes the reflected wave data into the frame memory 23. That is, the CPU 13 sequentially stores the digitized reflection waveform in the frame memory 23 as one frame data in a fixed synchronization with the transmission system as described above. In this way, multiple reflection waveforms are saved.

In the present invention, based on the reflected waveform saved in the frame memory 23, it is determined whether or not a reflected wave due to mutual interference is included therein. In this embodiment, the CPU 13 is provided with the determination function. However, when this is processed in hardware, a separate frame memory analysis circuit or the like may be provided to calculate the frame memory data. Good.

FIG. 5 is an image diagram of the past three reflection waveforms stored in the frame memory 23. In this embodiment, the reflection waveform is originally a digital waveform, but is shown as an analog waveform for convenience of explanation.

In analyzing the frame memory, for example, the last three reflected waveforms, that is, the latest (current) received reflected waveform W1, the last received reflected waveform W2, and the received reflected waveform W3 before the last three times are compared with each other. .

In this example, the reflection peak waveform P1 is from the floor surface, and all the reflection waveforms W1 to W3 appear at the same position. In contrast, the latest received reflection waveform W1
Has another reflection peak waveform P on the left side of the reflection peak waveform P1.
Two are out.

If this reflection peak waveform P2 is caused by an immovable object such as a parked vehicle, the ultrasonic wave emission interval is on the order of milliseconds.
Although the reflection peak waveform P2 should appear at the same position in the second and last received reflection waveforms W3, the reflection waveforms W2 and W3 do not exist in this example.

Therefore, in such a case, it is determined that the reflection peak waveform P2 has a high possibility of mutual interference. In this embodiment, the past three reflected waveforms are compared, but this is a kind of filter operation, and the number of reflected waveforms to be compared for analysis is arbitrary.

In order to apply a filter to the reflected waveform due to the mutual interference as described above, a method such as a logical AND between the reflected waveforms or an averaging method can be exemplified.

On the other hand, when a vehicle is present in the parking area, in the example of FIG. 5, all of the reflection waveforms W1 to W3 are added together with the reflection peak waveform P1 from the floor surface as shown in FIG. On the left side, the reflected peak waveform P3 by the parked vehicle
Will appear. Here, the left side means that the reflected wave returns earlier in time than the floor surface, and means that there is a reflector between the floor surface and the sensor.

When an object is detected as described above, the result is given to the output circuit 25. This output circuit 25
May be a relay or an LED (light emitting diode) mounted on the ultrasonic sensor.

The reflection peak waveform P3 is detected, for example, in relation to a threshold level L. In this case, the threshold level L is appropriately set based on the reflection from the ceiling of the vehicle or the like. Will be.

The reflection peak waveform P3 is higher than the floor surface,
That is, since the light is reflected by a portion close to the sensor, it reaches the ultrasonic receiving element 20 temporally faster than the reflection peak waveform P1 from the floor.

Basically, the presence or absence of a detected object is determined as “present” when the reflected wave exceeds the threshold level L, and “absent” when the reflected wave does not exceed the threshold level L. Accordingly, in order to prevent the reflection peak waveform P1 from the floor from being detected, the threshold value is released in a predetermined time width Tth in this embodiment, as shown in FIG.

Next, as another embodiment, a basic cycle is set in each ultrasonic sensor 1 and an ultrasonic wave is randomly emitted within the basic cycle. This will be described in more detail with reference to the timing chart of FIG.

First, in step ST1, the CPU 13
After the initialization of the control system of the ultrasonic sensor 1 is performed, the CPU 13 sets the basic cycle TO in step ST2.
Is set. In this example, the basic period TO is set to 750 milliseconds, and the ultrasonic wave is always emitted once within the basic period TO.

The basic period TO is set in common for all the ultrasonic sensors 1, whereby the ultrasonic sensor 1
From the ultrasonic oscillation to the reception of the reflected wave, the filtering operation, and the object detection are secured.

Next, in step ST3, the CPU 1
Numeral 3 obtains the self address set by the user from the address switch 12. In addition, the designation of this self address is based on the relationship with the ultrasonic sensor installed in the vicinity,
The user sets the ultrasonic emission timing in advance so as to be different.

When the self address is designated in this manner, each ultrasonic sensor 1 determines in step ST4 from the time table belonging to the address number the ultrasonic emission waiting time data set in the order of the ultrasonic emission frequency. Is read, and an ultrasonic wave is emitted from the ultrasonic transmission element 10 based on the data.

This operation will be described with reference to the data table of FIG. 2 and the timing chart of FIG. 8, using the ultrasonic sensor 1A as a representative. Assuming that the ultrasonic sensor 1A obtains, for example, the address number 1 from the address switch 12, in step ST4, first, 200 ms is obtained as the first firing timing data TA1.

After waiting for 200 milliseconds from the initial time of the basic period TO in step ST5, the process proceeds to step ST5.
At step 6, an ultrasonic wave is transmitted. That is, ultrasonic waves are emitted from the ultrasonic transmission element 10 toward the monitoring area 200 milliseconds after the beginning of the main processing.

Then, the reflected wave from the monitoring area is received in step ST7, and the reflected waveform is obtained by the reflected waveform digitizing circuit 22, and then the reflected waveform is stored in the frame memory 23 in step ST8.

Subsequently, in step ST9, noise filtering due to mutual interference is performed by comparison with the past several reflected waveforms. In this case, the number of ultrasonic waves emitted is the first time. After jumping from step ST11 and waiting until the TO period, which is the basic period, has elapsed in step ST12,
Return to T4. By waiting for this basic period TO time,
The response speed of the ultrasonic sensor can be kept within a certain error.

Then, at step ST4, the second firing timing data TA2 is set to 350 from the data table.
Get milliseconds. Then, 3 times from the top of the main processing this time
The ultrasonic wave is emitted after 50 milliseconds. In this way, each basic period T from the ultrasonic transmission element 10 toward the monitoring area is
Different firing timings TA1, TA from the initial time of O
2. Ultrasonic waves are sequentially emitted.

As a result, each reflected waveform is stored in the frame memory 23 every time the ultrasonic wave is emitted, and in the second and subsequent times, filtering of noise due to mutual interference is performed in step ST9 by comparing with the past several reflected waveforms. Done.

Thereafter, it is determined whether or not a vehicle (object) is detected in step ST10. If YES, in step ST11a, for example, a relay of a display lamp for displaying the presence or absence of the vehicle is turned on, and the display lamp is turned on.
If no vehicle is detected, the relay of the display lamp is turned off in step ST11b.

[0059]

As described above, according to the present invention,
For example, when a plurality of ultrasonic sensors are installed close to each parking area of a parking lot, malfunctions due to mutual interference are caused by making the ultrasonic emission intervals of each ultrasonic sensor irregular (random). It can be significantly reduced.

Further, the reflected wave data is sequentially stored in the storage means, and the respective reflected wave data are compared with each other. If the respective reflected wave data are the same, the reflected wave data is validated, and In this case, it can be determined that a reflected wave from another ultrasonic sensor is included.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an ultrasonic sensor used in the present invention.

FIG. 2 is a schematic diagram for explaining a data table of a random timing generation circuit in the ultrasonic sensor.

FIG. 3 is a waveform diagram schematically showing an ultrasonic waveform received by the ultrasonic sensor.

FIG. 4 is an ultrasonic emission tine Mig chart of the ultrasonic sensor according to the present invention.

FIG. 5 is an image diagram showing a reflected waveform stored in a frame memory of the ultrasonic sensor.

FIG. 6 is a schematic diagram for explaining a threshold set for an ultrasonic waveform received by the ultrasonic sensor.

FIG. 7 is an operation flowchart for another embodiment of the present invention.

FIG. 8 is an ultrasonic emission tine Mig chart in the another embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 ultrasonic transmitting element 11 random timing data table 12 address switch 13 CPU 14 timer 15 ultrasonic driving circuit 20 ultrasonic receiving element 21 ultrasonic receiving circuit 22 reflected waveform digitizing circuit 23 frame memory

Claims (5)

[Claims] 1. An ultrasonic sensor erroneous detection prevention method for preventing erroneous detection due to mutual interference between a plurality of ultrasonic sensors arranged in the vicinity, wherein the ultrasonic sensors of each ultrasonic sensor are directed to a monitoring area. Repeatedly emit ultrasonic waves,
In receiving a reflected wave that appears within a predetermined monitoring period from the time of ultrasonic emission at each ultrasonic receiving element,
The ultrasonic emission interval is irregular for each ultrasonic sensor, and the reflected waves received during the monitoring period are sequentially stored in the storage means, and the plurality of reflected wave data stored in the storage means are stored. Detecting the presence or absence of an object in the monitoring area based on the detection error of the ultrasonic sensor. 2. When detecting the presence / absence of an object in the monitoring area based on a plurality of reflected wave data in the storage means, if the respective reflected wave data are the same, the reflected wave data is validated; 2. The method according to claim 1, wherein it is determined that a reflected wave from another ultrasonic sensor is included when the two ultrasonic waves are not the same. 3. The storage means comprises a frame memory, and the reflected wave data is stored as a waveform in the same frame memory, and a comparison between the waveforms indicates whether a reflected wave from another ultrasonic sensor is included. 3. The method according to claim 2, wherein the determination is made as to whether or not the ultrasonic sensor is erroneously detected. 4. An ultrasonic sensor according to claim 1, wherein each of said ultrasonic sensors comprises a random timing generating means for making said ultrasonic wave emitting intervals irregular, said random timing generating means comprising: an address assigned to each of said ultrasonic sensors; A time table having a plurality of irregular ultrasonic emission interval data set corresponding to the address, wherein the ultrasonic emission interval is controlled based on the time table. The method for preventing erroneous detection of the ultrasonic sensor according to claim 1. 5. An ultrasonic wave according to claim 1, wherein said ultrasonic sensors have the same basic period, and ultrasonic emission intervals are irregular within said basic period. A method for preventing sensor misdetection.