JPS607839B2 - Ultrasonic vehicle detection device - Google Patents

Description

[Detailed Description of the Invention] This invention provides a method for transmitting ultrasonic waves toward the road surface from an ultrasonic transducer installed at a required height above the road surface, and the time it takes for the reflected waves to be received. The present invention relates to a vehicle detection device that detects a vehicle.

In this type of ultrasonic vehicle detection device, from the viewpoint of reducing sampling errors, it is preferable to make the transmission cycle of the ultrasonic waves transmitted from the transducer as short as possible. However, when the transmission period is shortened, multiple reflections from the road surface occur, that is, the ultrasonic waves reflected from the road surface are reflected by the transducer, propagate toward the road again, and are reflected again from the road surface and received by the transducer. This phenomenon occurs, and if this multiple reflected wave from the road surface is received by the transducer during the detection time period when the detection gate is open, it will cause false detection. This multiple reflection does not occur in exactly the same way for all detection devices, and the occurrence state differs depending on the height position of the transducer, how it is mounted, the shape of the road surface, etc. This invention was made in view of the above-mentioned circumstances, and the transmission period of ultrasonic waves is adjusted as much as possible according to the special circumstances of each vehicle detection device, such as the mounting state of the ultrasonic transducer and the shape of the road surface. An object of the present invention is to provide an ultrasonic vehicle detection device that can avoid false detection based on multiple reflections while keeping the distance short.

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

In FIG. 1, the ultrasonic transducer 15 is installed at a required height above the road surface L.

The ultrasonic wave transmitted from the transducer 15 toward the road surface L is
The waves are reflected by the road surface L or the vehicle CA and are received by the transducer 15. In principle, when an ultrasonic wave is reflected above the virtual vehicle determination limit level above the road surface L, the ultrasonic vehicle detection device assumes that the ultrasonic wave is reflected from the vehicle CA and detects the vehicle. Outputs a detection signal. In FIGS. 2 and 3, the ultrasonic signal from the ultrasonic signal generator 11 is transmitted only during the time period T when the transmitting gate 12 is open, through the gate 12, the transmitting multiplier 13, and the limiter. The ultrasonic waves are sent to the transducer 15 via the transducer 14, and the ultrasonic waves are transmitted toward the road surface L from the transducer 15.

The reflected wave from the road surface L or the vehicle CA is received by the transducer 15 and then sent to the detection gate 19 via the limiter 16, the received wave multiplier 17, and the waveform shaping circuit 18. The detection gate 19 is open only during the detection time period T4, and if there is a reflected wave signal within this time period L, this signal passes through the gate 19 and is output as a vehicle detection signal. Let L be the time required for the ultrasonic waves to travel back and forth between the transducer 15 and the bell day, and let T2 be the time required to eliminate malfunctions due to the reverberation of the transmitted ultrasonic waves being received by the transducer 15. In this case, the detection time period T4 is set to a time period from the time when the ultrasonic waves are transmitted until time T3 is reached after time T2 has elapsed. The opening and closing of the gates 12 and 19 are controlled by a gate control circuit 20'. The gate control circuit 2 receives a transmission period timing pulse of a required period To from a transmission period pulse generation circuit 40 to be described later, and this pulse resets the counter 21 and sets the flip-flop 22. .

A series of pulses are inputted to the counter 21 from the pulse generation circuit 24, and the counter 21 starts counting these pulses from the time it is reset, and the counted value corresponds to the above times T, , T2, and T3. When the value reaches that value, the count output is output as a set or reset signal for the flip-flops 22 and 23. The flip-flop 22 is set by the transmission periodic pulse and reset by the count output corresponding to the time m of the counter 21, and outputs a control signal for opening the gate 12 while being set.
The flip-flop 23 is set by the counting output of the counter 21 corresponding to the time L and reset by the counting output corresponding to the time L, and outputs a control signal for opening the gate 19 while being set. The period To of the transmission period timing pulse can be changed as appropriate by the transmission period change control circuit 30 and the transmission period pulse generation circuit 40'.

The transmission periodic pulse generation circuit 4 includes a pulse generation circuit 45 such as an astable multipipelator. This pulse generation circuit 45 has a plurality of periods To,
, T side To3, t4 are set. This is achieved by connecting a plurality of elements, such as resistors, in parallel, which determine the period (oscillation constant) of the generated pulses, and setting the values of these resistors to different values. These periods are h, Tm, To3<To4, for example, 3
They are set to 0, 40, 50, and 60 msec, respectively.
Gates 41 to 44 are connected in series to each resistor, and by closing any gate to make it conductive, a transmission period timing pulse with a period determined by the resistor corresponding to that gate is generated. is obtained. These gates 41 to 44 are controlled by the period change control circuit 3. The wave transmission cycle change control circuit 30 is reset by the vehicle detection signal, and each time it is reset, it starts a timing operation and keeps the set time T, . a timer 31 that outputs a signal when the timer 31 reaches the timer 31; a NOT circuit 32 that outputs an inverted signal of the output of the timer 31; and a NOT circuit 32 that is set by the rising edge of the output signal of the NOT circuit 32 and starts timing operation from the time it is set. A timer 33 outputs a signal when the set time T,2 has been reached, a monostable multipipelator 34 generates one pulse after the signal is output from the timer 33, and the multipipelator 34 outputs a signal. The counter 35 counts the pulses of , generates a count output from an output terminal according to each count value, and closes the gates 41 to 44, respectively.

Setting time of the timer 31 m, . is preferably variable according to the wave transmission period ~, ~To4, and in that case, it is set to a time slightly longer than the selected wave transmission period. This is easily realized using the counting output of the counter 35.
When setting timer 31, . If it is fixed, it is set to a time slightly longer than the longest transmission period L4. The timer 33 detects whether the vehicle detection signal is continuously output for a set time T,2, and
The set time m,2 is set to, for example, 3 hours. This timer 33 is reset by the fall of the output of the NOT circuit 32 and the output pulse of the monostable multipipulator 34. When the count value of the counter 35 is 1, an output is generated from the output terminal 1, the gate 41 is closed by this power, and the period of the wave transmission period pulse of the wave transmission period pulse generation circuit 40 becomes L. Similarly, when the count value is 2, 3, 4, output is generated from the output terminals 2, 3, 4, and the gate 42
, 43 and 44 are closed, respectively, and the transmission period is L2, h
3, L4. At the start of the operation, the start button ST is pressed, one pulse is generated from the monostable multipipelator 34, an output is generated at the output terminal 1 of the counter 35, and the wave transmission period is set to To. Referring to FIG. 4, the shortest transmission period is first set, and the transducer 1
5, ultrasonic waves are transmitted at a period To. Assuming that the vehicle detection signal is generated continuously, the period of this signal is also To. In this case, the timer 31 is reset for each detection signal, and when setting eyebrows m, . Since the timer 31 does not reach , no output is generated from the timer 31. Therefore, NOT circuit 32
An output is generated from the timer 33, and the timer 33 performs a timing operation. The vehicle detection signal continues for the set time of the timer 31, . Assuming that there is no output for the above period, the timer 31 generates an output, the NOT circuit 32 outputs no more, and the timer 33 is reset. Then, when the vehicle detection signal is outputted again, the timer 31 is reset and the output of the timer 31 disappears, an output is generated from the NOT circuit 32, and the timer 33 is set and starts timing operation again. In this way, when two or more vehicle detection signals are output in succession at the time of setting of the timer 33, an output is generated from the timer 33, and one pulse is sent from the monostable multipipulator 34 to the counter 35. The gate 42 is activated by a signal from the counting output terminal 2 of 35. Gate 41 will of course be opened. Therefore, the period of the transmission period timing pulse is T
o2, and this time the ultrasonic wave is transmitted at the wave transmission cycle no2. The timer 33 is reset by the output pulse of the monostable multipipulator 34, and if an output is generated from the NOT circuit 32, it is immediately set and starts timing again. In this way, if the vehicle detection signal continues to be output for the required time T,2 or more, the wave transmission interval is sequentially switched from a short cycle to a long cycle. and,
If no output is generated from the timer 33 in a certain wave transmission cycle, the timer 33 settles to that wave transmission cycle. Even in the longest cycle T, if the vehicle detection signal continues to be output for the required time T, 2 or more, the counter 35 is reset and returns to the cycle 'o' again. In this case, a vehicle detection undetectable signal may be output. Note that "the vehicle detection signal continues to be output continuously" means that the timer 31 is set at the specified time, . It should be noted that this varies depending on the

Setting situation m,. is less than twice the transmission period, and if even one pulse of the vehicle detection signal is not output, the timer 33
is reset and the set time T, . If the timer 33 is between twice and three times the transmission period, the timer 33 is not reset even if only one pulse of the vehicle detection signal is not output, but is reset when two pulses are not output. In this specification, "the vehicle detection signal continues to be output continuously" includes both of the above two examples, and includes both of the above two examples, and includes the set times T, . shall be set arbitrarily within a practically possible range. Usually, there is a gap between two vehicles running on a road surface, and there is always a reflected wave from the road surface between the vehicle detection signal from the preceding vehicle and the vehicle detection signal from the following vehicle.

Since the vehicle detection signal is not output depending on the reflected wave from the road surface, it is impossible for the vehicle detection signal to continue to be output for the required period of time during normal operation. The fact that the vehicle detection signal continues to be output for the required period of time means that false detection is being performed due to multiple reflection waves from the road surface. As mentioned above, when the vehicle detection signal continues to be output for the required time, the output from the timer 33 changes the primary transmission period, and the road surface period is changed to prevent false detection due to multiple reflections from the road surface. A value that does not occur is selected. Since the road surface period is changed from a short period to a long period, the transmission period is set to the shortest period that does not cause false detection due to multiple reflections on the road surface, and care is taken to operate at the shortest possible period. It should also be noted that there are Cases in which false detection due to multiple road surface reflections do not occur are: (1) When the wave transmission period and the period in which the road surface reflections reach the transducer 15 after being transmitted, (2) The detection time period when the detection gate 19 is open. When the road surface reflected wave reaches the transducer 15 at a time other than L,
- A possible case is that the wave transmission period is very long and the multiple reflected waves from the road surface are attenuated during that period. Among these, the situation in case (2) above is shown in FIG. The transmitted wave P, is reflected by the road surface, and the first reflected wave is R, . The road surface reflected waves R, . The second reflected wave that is reflected by the transducer 15 and then reflected again from the road surface is R,2, and the third reflected wave is R,3. These road surface reflected waves R, .
, R, 2, R, and 3 all reach the transducer 15 at a time other than the time period T4 when the detection gate 19 is open. Mainly, the transmission period will be automatically set to satisfy such conditions. Furthermore, in FIG. 3, the transmitted wave P2 is reflected by the vehicle, and the reflected wave Q2 reaches the transducer 15 in the detection time period T4. This reflected wave Q
2, a vehicle detection signal is output. FIG. 5 shows a modification of the transmission periodic pulse generation circuit. This circuit 50
consists of a pulse generating circuit 56 that generates a series of pulses, and a counter 55 that counts these pulses. The counter 55 has a wave transmission period To,,T. 2, T's, T
A count output is generated when the count value corresponding to o4 is counted.

Gates 51 to 54 controlled by the output of the counter 35 are connected to each count output terminal, respectively, and the corresponding count output passes through the open gates and is sent to the gate control circuit 20 as a transmission cycle timing pulse. 'This will be sent. The counter 55 is reset by this timing pulse and starts counting every time it is reset. As described above, in the present invention, the detection of a mistake due to multiple reflections from the road surface is detected based on the continuous output state of the vehicle detection signal, and the ultrasonic wave transmission cycle is sequentially changed to eliminate the detection of mistake due to multiple reflections from the road surface. Therefore, it is possible to prevent unintentional detection caused by road surface multiple reflected waves being received by the transducer during the detection time period when the detection gate is open. Moreover, since the transmission period is changed from short to long, the shortest transmission period that does not cause false detection due to multiple reflections from the road surface is automatically selected, reducing sampling errors. <To satisfy the requirement of shortening the transmission period as much as possible. Road surface multiple reflections do not occur in exactly the same way in all detection devices, and the occurrence state differs depending on the height position of the transducer, how it is mounted, the shape of the road surface, etc., but in this invention, The prevention of false detection due to multiple reflections from the road surface has been achieved depending on the special circumstances.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the vehicle detection principle of the present invention, Fig. 2 is a block diagram showing an embodiment, Fig. 3 is a time chart showing the vehicle detection operation, and Fig. 4 is a time chart showing the road surface period changing operation.・Chart, FIG. 5 is a block diagram showing a modification of the transmission periodic pulse generation circuit. 12...Transmission gate, 15...Ultrasonic transducer, 19...Detection gate, 20...
Gate control circuit, 30... Transmission cycle change control circuit, 40... Transmission cycle pulse generation circuit, L...
...road surface. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. When ultrasonic waves are transmitted toward the road surface from an ultrasonic transducer installed at a required height above the road surface, and the reflected waves are received within the required detection time period. In an ultrasonic vehicle detection device that outputs a vehicle detection signal, multiple stages of transmission cycles are set, and a transmission cycle generation circuit that outputs a transmission cycle timing signal of the selected cycle and a vehicle detection signal are required. a cycle change control circuit that detects that the wave is continuously output for a time and switches the wave transmission cycle of the wave transmission cycle generation circuit from a short cycle to a sequentially long cycle each time the wave transmission cycle generation circuit is detected; An ultrasonic vehicle detection device that performs vehicle detection by transmitting ultrasonic waves every time. 2 The above-mentioned wave transmission cycle generation circuit consists of a pulse generation circuit,
This pulse generation circuit includes a plurality of elements each having a different value that determines the period of the generated pulse, and a gate controlled by the period change control circuit is connected in series to each of these elements. The ultrasonic vehicle detection device according to item 1. 3 The above-mentioned wave transmission cycle generation circuit includes a pulse generation circuit that generates a series of pulses, and counts the pulses from this pulse generation circuit so that the counted value becomes a value corresponding to a plurality of preset wave transmission cycles. It consists of a counter that generates a count output when the count output occurs, and a gate that is connected to each count output terminal of this counter and controlled by the period change control circuit, and the counter is reset by the count output that passes through the gate. The ultrasonic vehicle detection device according to claim 1, which starts a counting operation every time it is reset.