JPH0368355B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vehicle surroundings monitoring device that detects obstacles around a vehicle using ultrasonic waves, displays the distance to the obstacle, and issues an alarm when the obstacle approaches within a set distance.

The inventors of the present invention have proposed, for example, the one shown in FIG. 1 as this type of vehicle surrounding search eye device.

In FIG. 1, reference numeral 1 denotes a reference clock oscillator. Based on the clock pulses from the reference clock oscillator 1, an oscillation timing control circuit 2 generates an oscillation timing pulse with a constant period T _P and supplies it to an ultrasonic oscillation circuit 3. Ultrasonic pulses are repeatedly emitted from the ultrasonic transmitter 4 to a warning area at the rear or side of the vehicle at each period T _P. The emitted ultrasonic pulse is reflected by an obstacle and enters the ultrasonic receiver 5, where it is converted into an electrical signal and amplified by a receiving amplifier circuit 6. After that, the received signal component is detected by a detection circuit 7 with a filter. only is taken out and given to the comparator 8.

On the other hand, the timing pulse of the transmission timing control circuit 2 is applied to the set terminal S of the flip-flop 9 to set the flip-flop 9.
The counter 10 counts the reference clock pulses based on this set output. In this state, when the received signal level input to the comparator 8 reaches a predetermined threshold Th, the comparator 8 goes high.
A level output is generated to reset flip-flop 9 and counter 10 is stopped from counting. At this time, the count value of the counter 10 is the propagation time from the time the ultrasonic pulse is reflected until it is received, and the propagation speed of the ultrasonic wave is given as a constant, so the count value of the counter 10 is the distance to the obstacle. give. The count value of this counter 10 is latched by the latch circuit 10, and until the next count value is obtained,
The signal is output to each of the display section 12 and alarm section 13.

The display section 12 includes a driver 12a and a seven-segment distance display 12b, and displays the detected distance numerically, for example, in meters. In addition, alarm part 1
3 has a digital comparator 13a and an alarm distance setting device 13b, and the digital comparator 13
When it is determined in step a that the detected distance is less than the set distance, the alarm circuit 13c is activated to issue an acoustic alarm from the speaker 13d to notify that the obstacle has entered the alarm set distance.

By the way, there are various obstacles that exist around the vehicle, such as guardrails, walls, utility poles, other vehicles, and people, and the received signal level varies because the reflectivity of the ultrasonic pulse varies depending on the type of obstacle. Even for the same obstacle, the received signal level changes depending on the incident angle of the ultrasonic pulse.

For example, as shown in FIG. 2, if the reflectance of the obstacle 14 is sufficiently high, a received waveform with a sufficiently high received signal level can be obtained, as shown in received signal A in FIG. When the threshold Th of the comparator 8 is reached, the counter 10 stops counting to obtain the propagation time of the ultrasonic pulse. In this case, the true propagation time is the time Tn from the rise of the transmitted pulse to the rise of the received waveform, but the time ΔT ₁ until the threshold Th is reached is included as an error. However, since the received signal level is high and the signal waveform rises quickly, the error caused by ΔT ₁ is extremely small and poses no problem in practice.

However, when the reflectance of the obstacle 14 is small, as shown in the received signal B in FIG. 3, the received signal level is small and the rise of the signal waveform is small, so the time ΔT until reaching the threshold Th is shortened. ₂ becomes longer, and as a result, the error between the detected distance and the actual distance becomes larger.

In particular, when the distance to the ultrasonic transceivers 4 and 5 is short, as shown by the obstacle 14' in FIG. 2, even if the reflectance of the obstacle 14' is high, the obstacle 1
Since the incident angle of the ultrasonic pulse with respect to 4' increases, the received signal level decreases greatly, and at this time, an error △T ₂ shown in the received signal B in Fig. 3 occurs,
There was a problem that the percentage of error included in the detection distance increased, making it impossible to display the correct distance to the obstacle.

The present invention was made in view of such conventional problems, and it calculates the distance to an obstacle based on the propagation time from when an ultrasonic pulse is emitted until it is reflected by the obstacle and received. In a device for detecting, in order to reduce detection errors, a first detection means detects the time from when the ultrasonic pulse is emitted until the received signal level of the ultrasonic pulse reaches a first threshold value. On the other hand, a second
The distance to the obstacle is calculated according to the detection time obtained by subtracting the detection time of the second detection means from the detection time of the first detection means. The purpose is to solve problems.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 4 is a circuit block diagram showing one embodiment of the present invention.

First, to explain the configuration, 1 is a reference clock oscillator that oscillates a reference clock pulse of a predetermined frequency, and 2 is a reference clock oscillator that divides the reference clock pulse to have a constant period.
A transmission timing control circuit that outputs a transmission timing pulse with a constant pulse width for each T _P ; 3 is an ultrasonic transmission circuit that oscillates and outputs an ultrasonic pulse signal based on the transmission timing pulse; 4 is an ultrasonic transmission circuit that outputs an ultrasonic pulse signal to a predetermined warning area. It is an ultrasonic transmitter that emits ultrasonic pulses.

In addition to such an ultrasonic pulse transmitting system, the following ultrasonic pulse receiving system is used. That is, 5 is an ultrasonic receiver that receives ultrasonic pulses reflected by obstacles existing in the warning area and converts them into electrical signals, 6 is a receiving amplification circuit that amplifies the received signal of the ultrasonic pulses, and 7 is an ultrasonic receiver. This is a detection circuit with a filter that removes unnecessary signal components included in the received sound wave signal and extracts only the received components. The received signal extracted by this filtered detection circuit 7 is applied to comparators 15 and 16, respectively. The comparator 15 has a threshold value TL, and produces an H level output when the received signal level exceeds the threshold value TL. Further, the comparator 16 has a threshold TH that is higher than the threshold TL of the comparator 15,
When the received signal level exceeds this threshold TH, an output at H level is generated. small level threshold
The output of the comparator 15 having TL is given to the reset terminal R of the flip-flop 9, and the set terminal S of this flip-flop 9 is given the transmission timing pulse from the transmission timing control circuit 2. The flip-flop 9 is set by the second transmission timing pulse and reset by the H level output of the comparator 15. On the other hand, the output of the comparator 16 having a high level threshold TH is applied to the reset terminal R of the flip-flop 19 via an OR gate 18, and the comparator 16 having a low level threshold TL is applied to the set terminal S of the flip-flop 19.
5 outputs are given. Therefore, the flip-flop 19 is configured to be set by the H level output of the comparator 15, and reset by the H level output of the comparator 16 which is output subsequent to the H level output of the comparator 15.

That is, the flip-flop 19 detects that the received signal level of the ultrasonic pulse is equal to the threshold of the comparator 15.
The configuration is such that the time from reaching TL to reaching the threshold TH of the comparator 16 is detected to generate the H level.

Note that the output of the comparator 15 is also given to the one-shot multi 17, and the pulse width output from the one-shot multi 17 is equal to the time at which the pulse width of the transmission timing pulse output from the transmission timing control circuit 2 becomes 1/2. The flip-flop 19 can be forcibly reset when the received signal level does not reach the threshold TH of the comparator 16 and does not produce an H level output.

On the other hand, the output of the flip-flop 9, which is set at the rising edge of the transmission timing pulse and reset at the H level output of the comparator 15, is applied to the enable terminal 22a of the up-down counter 22 via the OR gate 21. When the up/down terminal 22b is at the L level, the clock pulses given from the reference clock oscillator 1 are counted up;
When is at H level, the clock pulse is down counted.

In order to control the up-count and down-count of this up-down counter 22, the output of the flip-flop 19 is passed through an OR gate 20 to an up/down terminal 22b of the up-down counter.
The output of the OR gate 20 is also applied to the enable terminal 22a of the up-down counter 22 via the OR gate 21. For this reason, the up-down counter 22 first counts up the clock pulses while the flip-flop 9 is in the set state producing an H level output, and when the flip flop 9 is reset and the flip flop 19 is set simultaneously to produce an H level output, the OR gate 20 is activated. By inputting an H level to the up/down terminal 22b outputted through the flip-flop 19, the counted value up-counted in advance is down-counted while the flip-flop 19 is producing a set output, thereby correcting the counted value of the propagation time of the ultrasonic pulse. I try to do that.

The output of the up-down counter 22 is given to the latch circuit 11 to determine the emission period of the ultrasonic pulse.
A counter count value, that is, a count value corresponding to the distance to the obstacle, is latched and output for each T _P and given to the display section 12 and alarm section 13.

The configuration of the display section 12 and alarm section 13 is as follows.
Similar to the conventional device shown in the figure, the display section 12 is equipped with a driver and a seven-segment distance indicator, while the alarm section 13 is equipped with a digital comparator, an alarm distance setting device, and an alarm circuit that issues an audible alarm. It is being

Next, the operation will be explained with reference to the signal waveform diagram in FIG.

First, the ultrasonic oscillation circuit 3 repeatedly emits ultrasonic pulses with a pulse width T ₀ by the ultrasonic transmitter 4 at fixed intervals T _P based on the transmission timing pulse of the transmission timing control circuit 2. The ultrasonic pulses emitted are reflected by obstacles existing in the warning area, are received by the ultrasonic receiver 5 after a predetermined time, and are transmitted through the reception amplifier circuit 6 and the filtered detection circuit 7 as shown in FIG. 5b. Such received signal waveforms are input to each of the comparators 15 and 16.

On the other hand, the flip-flop 9 is set by the rise of the transmission timing pulse, and the enable terminal 222 of the up-down counter is set to H level via the AND gate 21. At this time, since the up-down terminal 22b is at L level, the up-down counter 22 is in an up-counting state and starts up-counting the clock pulses from the reference clock oscillator 1 in synchronization with the rising edge of the transmission timing pulse.

In this state, when the received signal first reaches the threshold TL of the comparator 15 by the filtered detection circuit 7,
The comparator 15 produces an H level output, resets the flip-flop 9 which has been in the set state, and stops the up-down counter 22 from counting up.

At this time, the count value of the up-down counter 22 is the propagation time Tn from when the ultrasonic pulse is emitted until the reflected pulse reflected by the obstacle is received by the ultrasonic receiver 5, that is, the distance to the obstacle. is in a state where it is counted.

In addition, the H level output of the comparator 15 activates the one shot multi 17 and its output is set to the L level, and this one shot multi 17
After T ₀ /2 hours, the operation is stopped and the output is returned to H level.

Further, the H level output of the comparator 15 that resets the flip-flop 9 is also applied to the flip-flop 19 at the same time.
9 and therefore flip-flop 19
The H level output of is sent to the up/down terminal 22b of the up/down counter 22 via the OR gate 20.
By setting the enable terminal 22a to H level through the OR gate 21, the up/down counter 22 enters a down count state at the same time as flip-flop 9 is reset, and the set output of flip-flop 9 causes
Start counting down the counted value.

Next, when the received signal level from the filtered detection circuit 7 reaches the threshold value TH of the comparator 16, the comparator 16 produces an H level output, and the flip-flop 19 which is in the set state is reset via the OR gate 18.

With this reset of flip-flop 19, each output of OR gates 20 and 21 goes to L level, and as a result, the operation of up-down counter 22, which was performing down-counting, is stopped. As shown in FIG. 5f, this down-counting after up-counting corresponds to the subtraction of the count value indicated by diagonal lines, which corresponds to the time during which down-counting was performed, and therefore, the up-down counter 22
The count value is corrected to the propagation time Tn' of the ultrasonic pulse corresponding to the rising portion a of the received signal from OV shown in FIG. 5b.

Up-down counter 2 corrected in this way
The count value 2 is given to the latch circuit 11, and the latch output of the latch circuit 11 causes the display unit 12 to display the distance to the obstacle digitally, and the alarm unit 13 to indicate that the detected distance is within the alarm setting distance. It will determine whether the vehicle is within the warning setting distance and will issue an audible alarm.

Next, if the reflectance of the obstacle is low or the distance to the obstacle is too short, the incident angle of the ultrasonic pulse is large, and the received signal level is the threshold of the comparator 16.
If it does not reach TH, as shown in the signal waveform of FIG. 6, when the received signal level reaches the threshold TL, the comparator 15 similarly produces an H level output, and the flip-flop 9 is reset to stop up-counting. with flipflop 1
9 starts counting down, and at the same time the one-shot multi 17 is activated to produce an L level output for T ₀ /2 hours, and even if the received signal level does not reach the threshold TH of the comparator 16, T ₀ /2 After an hour, the one-shot multi 17 stops working and
Forcibly resetting flip-flop 19 via OR gate 18 by producing a level output;
The up-down counter 22 counts down during the operating time T ₀ /2 of the one-shot multi 17.
The count value of will be corrected. Therefore, even if the received signal level of the ultrasonic pulse is small, the maximum
The count value is corrected by subtracting the propagation time of the ultrasonic pulse over T ₀ /2, and even if the rise time from when the received signal is received to when it reaches the threshold TL becomes longer, the count value of the up-down counter 22 remains unchanged. is corrected to the counting time that is the rising edge of the received signal from OV, greatly reducing distance detection errors.

As explained above, according to the present invention, in a device that detects the distance to an obstacle based on the propagation time from when an ultrasonic pulse is emitted until it is reflected by the obstacle and received, The first detection means detects the time from when the ultrasonic pulse is emitted until the received signal level of the ultrasonic pulse reaches a first threshold, while the received signal level of the ultrasonic pulse is set to the first threshold. A second detection means detects the time from the time when the threshold value exceeds the threshold value to a second threshold value higher than the first threshold value, and from the detection time of the first detection means to the detection time of the second detection means. Since the distance to the obstacle is calculated according to the detection time obtained by subtracting the By increasing the angle of incidence of the sound wave pulse, even if the received signal level is small, the detection distance is corrected according to the signal level, so the distance to the obstacle can always be detected more accurately, resulting in high accuracy. Since distance detection can be performed, the reliability of the device can be greatly improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the applicant's prior art, Fig. 2 is an explanatory diagram showing the obstacle detection state, and Fig. 3 is a signal showing the detection error due to the magnitude of the received signal level. FIG. 4 is a circuit block diagram showing an embodiment of the present invention, and FIGS. 5 and 6 are signal waveform diagrams showing the operation of the present invention. 1... Reference clock oscillator, 2... Transmission timing control circuit, 3... Ultrasonic oscillation circuit, 4... Ultrasonic transmitter, 5... Ultrasonic receiver, 6... Reception amplifier circuit, 7... Detection Circuit (with filter), 9,1
9...Flip-flop, 11...Latch circuit,
12...Display section, 13...Alarm section, 15, 16...
...Comparator, 17...One-shot multi,
18, 20, 21...OR gate, 22...Up-down counter, 22a...Enable terminal,
22b...Up/down terminal.

Claims (1)

[Claims] 1. In a vehicle surroundings monitoring device that detects the distance to an obstacle based on the propagation time from when an ultrasonic pulse is emitted until it is reflected by an obstacle and received, a first detection means for detecting the time from when the pulse is emitted until the received signal level of the ultrasonic pulse reaches a first threshold; and when the received signal level of the ultrasonic pulse exceeds the first threshold. a second detection means for detecting the time from time to when a second threshold higher than the first threshold is reached; and subtracting the detection time of the second detection means from the detection time of the first detection means. A vehicle surroundings monitoring device comprising: a subtraction means; and a distance calculation means for calculating a distance to an obstacle according to the detection time obtained by the subtraction means.