JPH08105973A - Inter-vehicle distance measuring device - Google Patents

Abstract

PURPOSE: To eliminate the effect of calibration without causing a drop in measuring accuracy by providing a calibration operation section for computing the synchronous addition value of time series data obtainable when a forward vehicle does not exit. CONSTITUTION: A transmission section 5 sends out optical pulses forward, and a receiving section 6 receives optical pulses reflected from a forward vehicle in a time series. Also, a signal processing section 2 samples optical pulse signals amplified with a signal amplification section 8 after the conversion thereof into digital signals. At the same time, the section 2 obtains the synchronous addition value of sampling data at each optical pulse transmission. Furthermore, a calibration operation section 9 computes the synchronous addition value of time series data (calibration data) about the case where a forward vehicle does not exist, and feeds the value to a controller 3. Then, a saturated addition value as reference for increasing the amplification factor of received signals is taken as equal to a value available after the deduction of the calibration data. As a result, an upper limit value for increasing the amplification factor can be made a highly accurate value, taking the calibration data into consideration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-vehicle distance measuring device for measuring an inter-vehicle distance between a host vehicle and a forward vehicle, and more particularly to a technique for improving measurement accuracy.

[0002]

2. Description of the Related Art With recent remarkable progress in automobile technology, an inter-vehicle distance measuring device for automatically measuring an inter-vehicle distance between a vehicle traveling in front of a vehicle and an alarm when the inter-vehicle distance becomes short. Is being developed.

As a conventional example of such an inter-vehicle distance measuring apparatus, one shown in FIG. 13 is known.

This device calculates the inter-vehicle distance based on the result of measurement of the time from when a pulse signal such as a radio wave or a laser is transmitted in front of the host vehicle until the pulse signal reflected from the preceding vehicle is received. To do.

The pulse signal sending means 21 sends a pulse signal such as a radio wave or a laser toward the preceding vehicle ahead, and the reflected pulse signal receiving means 22 receives a pulse signal such as a radio wave or a laser reflected from the preceding vehicle ahead. Is received and converted into an electric signal. Further, the control means 23 controls the pulse signal transmission timing, and the time measuring means 24 counts and measures the time from the pulse transmission time to the reception of the reflected pulse signal based on the command of the control means 23.

FIG. 14 is a timing chart of various signals, and the trigger signal (1) is a signal repeatedly output at predetermined intervals Tr. The sending pulse signal (2) is a signal output from the pulse signal sending means 21 controlled by the control means 23, and is output in synchronization with the trigger signal (1). The received pulse signal (3) is a signal received by the reflected pulse signal receiving means 22 by being reflected from an external obstacle, and when the amplitude of the received pulse signal (3) exceeds a predetermined threshold value Vth, The detection signal is output by the reflected pulse signal receiving means 22. Meanwhile, clock pulse (4)
Is a signal for counting the time from when the pulse signal (2) is sent out to when the detection signal is output by the time measuring means 24, and is output at every interval Δt for a certain period.

However, such a conventional signal detection method has the following problems. That is, the received output of the reflected pulse usually contains internal noise and external noise,
It is necessary to set the threshold value for detecting the reflected pulse signal to a relatively high value so as to prevent erroneous detection due to the influence of such noise. In general, noise can be regarded as random noise that follows a Gaussian distribution, where n is the instantaneous amplitude of noise.
The probability distribution P (n) is a probability density constant having a mean value of zero and a Gaussian distribution with a variance of σ ² as shown in FIG. Where σ is the standard deviation. The probability density function P (n) at this time is represented by Formula (1).

[0008]

[Equation 1] In the above equation (1), σ ² corresponds to noise power, and σ corresponds to its effective value. The probability density function P (ns) when the above noise is added to the signal of the amplitude s is given by the mathematical expression (2).
It is represented by.

[0009]

[Equation 2] Therefore, in order to correctly detect the reflected signal from the desired distance with a probability of 99.85%, the threshold is set to 3σ as shown in FIG. 15, and the amplitude of the signal is further 3 than the threshold.
The pulse signal output to be sent may be set so that a peak signal that is σ higher, that is, 6 times higher than the effective value σ of noise (15 to 16 dB in terms of SN ratio) is obtained. However, in the case of radar, it is known that the level of the received signal is attenuated in proportion to the fourth power of the distance according to the so-called radar equation, and in order to increase the distance (detection) distance, a large output and extremely high cost are required. A high special oscillation device is required. Also, in order to increase the reception intensity instead of increasing the output, it is necessary to increase the aperture area or the light receiving area of the antenna, which increases both the shape and weight of the radar head. If this is attempted, there is a problem that the vehicle mountability is extremely poor. Further, from the viewpoint of ensuring safety when irradiated to the human body, the output is limited to the safety standard or less, so it is difficult to obtain a desired detection capability.

On the other hand, since a weak signal is detected, as a means for significantly improving the receiving sensitivity, Japanese Patent Publication No. 1-46034,
A method as shown in Japanese Examined Patent Publication No. 2-2106 has been proposed. This is to convert a received signal having a constant repetition period such as the Loran C signal into a binary signal indicating whether the signal is positive or negative, sample it, and repeat it in a RAM memory for a fixed time by a microcomputer. After addition and storage, the presence / absence of a signal, the SN ratio, and its time position are detected from the memory contents. The S / N that can be detected can be significantly improved by addition, and a weak received signal can be detected. It will be possible.

However, the configuration of this conventional example is suitable when the Loran C signal has a relatively long repetition period and the time required for signal detection may be relatively long.
There are the following problems when applied to the reception of radar signals.

That is, since the reception intensity of the radar signal is attenuated in proportion to the fourth power of the distance as described above, it is necessary to improve the sensitivity 16 times in order to double the detection distance. However, since the amount of sensitivity improvement by calculation is proportional to the 1/2 power of the number of additions, the number of additions must be 16 in order to improve the sensitivity 16 times.
² = 256 times need to be increased. The radar pulse transmission repetition cycle must be made as short as possible, but in the conventional method, since the RAM memory was controlled by the microcomputer for addition and storage, the time required for sampling and addition was determined by the clock time and instruction cycle of the microcomputer. As a result, the transmission repetition cycle of the radar pulse is limited, and there is a limit to improving the high sensitivity by greatly increasing the number of additions.

Further, when the above-mentioned radar device is applied to a rear-end collision warning device of an automobile, the following problems occur.
That is, when an oncoming vehicle equipped with a similar radar device sends out to the oncoming vehicle, the pulse signal sent from the own vehicle and the pulse signal sent from the oncoming vehicle interfere with each other,
There is a risk that normal distance measurement may not be possible.

Not only the pulse signal of the oncoming vehicle but also the spark noise of the engine of the own vehicle and the noise caused by turning ON / OFF the power of electric components such as headlights, air conditioners, wipers, etc. impair normal distance measurement. Alternatively, noise may be caused by a change in power supply voltage, a change in sunshine, an environmental change such as entering a tunnel, or the like. That is, these noises of the own vehicle resonate with noises from the outside, for example, to increase the detection level, exceed the preset threshold value, and may be mistaken as a reflection signal of an impacting object that does not actually exist. is there.

On the other hand, the applicant of the present invention filed Japanese Patent Application No. 3-171.
As shown in 380, when an alarm is issued according to the proximity situation to a vehicle ahead, not only the inter-vehicle distance but also the relative speed is required. There's a problem. That is, since the pulse radar can generally measure only the distance to the impact object, it is necessary to increase the distance measurement accuracy and measure the time change rate in order to accurately obtain the relative velocity. To increase the accuracy, it is necessary to shorten the light transmission pulse width and increase the sampling points. However, for example, 130 sampling points are required for each 1 m in order to obtain the distance measuring accuracy of 1 m in the range of 130 m, and the addition process takes a very long time. Further, since the width of the light-transmitting pulse needs to be about several nanoseconds, the light-transmitting unit becomes complicated and expensive, and there is a problem that the characteristics of the conventional example are lost.

On the other hand, when the pulse signal sending means 21 is driven, the duty ratio of the pulse becomes low in order to ensure the durability and reliability of the light emitting element, so that the repetition time of the light sending pulse is limited. I will end up. Naturally, shortening the light-emission pulse repetition time to speed up the distance measurement reduces the durability and reliability of the light-emitting element, and conversely, increasing the light-emission pulse repetition time speeds up the distance measurement. Will be harmed.

Therefore, in order to solve such a problem,
The one described in Japanese Patent Application No. 6-146752 by the applicant of the present application has been proposed.

FIG. 5 is a block diagram showing the structure of an inter-vehicle distance measuring apparatus according to Japanese Patent Application No. 6-146752. The distance sensor head 1 mounted on the front part of the vehicle, a signal processing section 2, and a controller. 3 and an inter-vehicle distance display unit 4. The distance sensor head 1 includes a light transmitting unit 5 configured by a light emitting diode (LED), a laser diode (LD), and the like that transmits a light pulse toward a vehicle ahead, and a drive that supplies a drive voltage to the light transmitting unit 5. The circuit 7 includes a light receiving unit 6 including a photodiode that receives the light pulses reflected by the vehicle in front in time series, and a signal amplifying unit 8 that amplifies the received analog light pulse.

The signal processing unit 2 converts the amplified analog optical pulse signal into a digital signal, samples the digital signal at a predetermined sampling period, and synchronously adds sampling data for each optical pulse transmission. Find the value.

The controller 3 obtains a time having a large addition value from the addition value obtained by the signal processing circuit 2 and obtains an inter-vehicle distance based on this time and the propagation speed of the optical pulse to be transmitted. The inter-vehicle distance display unit 4 displays the obtained inter-vehicle distance on a display or the like.

The operation will be described below. First,
From the light transmitting unit 5 including an optical semiconductor device such as an LED or an LD, an optical pulse is directed forward with a predetermined pulse width (for example, 130 nsec) and a pulse interval (for example, 6 μse).
In c), the light is transmitted a predetermined number of times within a predetermined time, and the reflected light from the vehicle in front is received by the light receiving unit 6 including a light receiving element such as a photodiode (PD). FIG. 6 shows a flow of signal processing from reception of reflected light to distance calculation.

FIG. 6A shows the analog level of the received pulse signal, and the signal value is large at the portion indicated by P1 in the figure. That is, since the horizontal axis is time t,
It can be expected that a vehicle ahead is present at a distance corresponding to this time (the speed of the light pulse is known, so that the distance can be obtained from the time and speed). In addition, FIG.
6 is a diagram in which the analog signal shown in FIG. 2 is converted into digital, and the portion corresponding to P1 is "1", and the vibrations of "1" and "0" are repeated in other portions.

FIG. 3C shows data when the digital signal shown in FIG. 3B is sampled at the sampling period Δt, and this data can be obtained for the number of times of distance measurement. FIG. 11D is a bar graph showing the result of adding the sampling data, and ΔL is the distance measurement resolution.

First, the amplitude-amplified received signal shown in (a) is binarized into "0" and "1" by comparison with a predetermined reference value, and becomes digital data as shown in (b). The generated signal is transmitted for a certain period Δt (for example, 67 nsec:
(C) by sampling at a distance of 1 m)
As shown in, digital data having a predetermined number of bits can be obtained. This operation is performed many times (for example, 8192 times) within one measurement distance, and a plurality of (for example, 8192 times) digital data groups consecutive during the time obtained during each operation are synchronously added to obtain ( The characteristic of the added value level with respect to the distance shown in d) can be obtained, and from this added value level characteristic, for example, the distance to the vehicle in front can be calculated as 23 [m].

However, in reality, even when there is no vehicle or other obstacle in front of the vehicle, the transmitted light is reflected by the road surface or the like and is received by the light receiving section 6. Therefore, in order to improve the measurement accuracy, this light receiving component (hereinafter referred to as calibration data) must be removed. Therefore, conventionally, a method of subtracting the calibration data from the measured added value level is used. Hereinafter, this method will be described.

FIG. 9 is an explanatory view showing the reflection of light when there is no obstacle in front of the vehicle. Light is transmitted to the light transmission range 12 by the light transmission from the distance sensor head 1 mounted on the front surface of the vehicle 11. Is sent, reflected on the road surface, etc. and reflected light 13
Occurs. As a result of this addition, for example, a characteristic curve D1 as shown in FIG. 10 is obtained. Then, if the characteristic curve D1 is used as a calibration and subtracted from the addition result obtained in the actual distance measurement, the addition result is calibrated.

As the calibration data, the minimum value of the synchronous addition result group at the time of no hit (non-detection state) is stored as a reference value, and the addition result at each sampling point is constantly higher than the reference value. It is memorized whether or not it is coming out, and the noise component is removed by constantly subtracting the added value component that is coming out high at each sampling point, and calibration is performed. Although the calibration using the calibration data is performed every time the distance is measured, the detection and storage of the calibration are not constantly performed, and the stored value is stored in a non-volatile memory or the like. FIG. 11 shows the synchronous addition result in the no-hit state after the calibration has been performed. By subtracting the characteristic curve D1, the addition result at the no-hit time is set to a constant reference value regardless of the distance R, as indicated by D2.

Next, the state of the addition result when the synchronous addition result is saturated and the distance to the target cannot be measured will be described with reference to FIG. As shown in the figure, when the synchronous addition result is saturated (see D3), the peak of the addition result cannot be detected, so that the distance to the target cannot be measured. Such a situation can be avoided by lowering the amplification factor of the received signal. FIG. 8 shows a flowchart for controlling the signal amplification factor when the total number of additions is 8192. Step ST
When 8192 times of synchronous addition are completed in step 1, step S
At T2, the peak value is detected from the synchronous addition results at each sampling point and is substituted into MAX, and the step S
At T3, MAX is compared with 7900, and if MAX is larger than 7900, the reception signal amplification factor is lowered at step ST5. If MAX is 7900 or less, the process goes to step ST4, and at step ST4, MAX is compared with 5000 and M is compared.
If AX is smaller than 5000, the received signal amplification factor is increased in step ST6, and if MAX is 5000 or more (50
When 00 <MAX <7900) In step ST7, the distance to the target is obtained from the synchronous addition result. Step ST4
The reason why the lower limit value of the addition result peak value is set to 5000 is that, when the total number of additions is 8192 times, the measurement distance accuracy sharply deteriorates when the addition result peak value falls below 5000.

Here, when the total number of additions is 8192, the relationship between the peak value of the addition result and the 3σ value variation of the measured distance data of the sensor (σ: standard deviation of the measured distance data) is 1
An example is shown in FIG. In the figure, the target is set at 25 m and measured, and the standard deviation σ is obtained from the distance measurement result of 256 times. According to the figure, the peak value of the addition result is
When it is less than 5000, 3σ rapidly increases and the measurement distance accuracy deteriorates. Therefore, the lower limit of the addition result peak value in step ST4 of FIG. 8 is set to 5000.

[0030]

In such a conventional vehicle-to-vehicle distance sensor, as shown in step ST3 of FIG. 8, the timing of lowering the reception signal amplification factor when the synchronous addition result is saturated is as follows. It is uniformly set as "when the peak value of the synchronous addition result exceeds 7900". Therefore, when there is a peak (for example, 4400) due to noise that is constantly generated in the synchronous addition result due to the influence of road surface reflection, etc., and the reference value when performing noise calibration is the natural noise level (for example, 4000), The addition result at the sampling point where the addition result was 4400 is always the value obtained by subtracting 400 after the noise calibration. Then, the saturated addition value at the sampling point where 400 is always subtracted is 8192-400 = 7792, and the saturation addition value does not reach 7900. Therefore, if the signal amplification width is switched according to the flowchart shown in FIG. Even though the result is saturated at 7792, the amplification factor does not decrease, which causes a problem that distance measurement becomes impossible. Further, if 7900 is lowered to 7600 in step ST3 of FIG. 8, when the addition result at the sampling point where 400 is always subtracted reaches 7600, the amplification factor is lowered and the addition result is saturated. The problem is solved, but the sampling points where 400 is not subtracted (the maximum value of the addition result reaches 7900) do not saturate the addition result, and the high received signal S / N ratio and high ranging accuracy are measured. The area (7600 to 7900) that allows distance is discarded. Therefore, if the upper limit value 7900 of the addition result peak value in step ST4 of FIG. 8 is uniformly lowered, there arises a problem that the performance of the inter-vehicle distance sensor cannot be utilized to the maximum.

The present invention has been made to solve such a conventional problem, and an object thereof is to provide an inter-vehicle distance measuring apparatus capable of removing the influence of calibration without lowering the measurement accuracy. To provide.

[0032]

In order to achieve the above object, the present invention provides a transmitting means for repeatedly transmitting a predetermined pulse signal toward the front of a vehicle, and a reflection of the pulse signal reflected by an object in front of the vehicle. Receiving means for receiving a signal, amplifying means for amplifying the received reflected signal, data converting means for converting the signal amplified by the amplifying means into digital data, and sampling the digital data at a predetermined cycle, Time-series data forming means for forming time-series data, synchronous addition means for synchronously adding the time-series data of a predetermined number of times continuous in time, and from the peak value of the synchronous addition value by the synchronous addition means to the object Distance calculation means for calculating the distance of the calibration data and the synchronous addition value of the time-series data obtained when the object does not exist. As a calibration means for calibrating the calculation by the distance calculation means, and a comparison value according to the calibration data is determined, and the comparison value and the peak value of the synchronous addition value by the addition means are amplified based on the comparison result. Amplification rate control means for controlling the amplification rate of the means.

[0033]

According to the present invention constructed as described above, the calibration data is obtained in advance, and the saturation addition value which is a reference when increasing the amplification factor of the received signal is calculated from the saturation addition value. The reduced value or a value obtained by further subtracting a predetermined value. As a result, the upper limit value for increasing the amplification factor of the received signal can be made a highly accurate value in consideration of the calibration data, and the accuracy of the inter-vehicle distance measurement can be improved.

[0034]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an inter-vehicle distance measuring apparatus according to an embodiment of the present invention. The distance sensor head 1, the signal processing unit 2, the controller 3, and the inter-vehicle distance display unit 4 in the figure are the same as those in FIG. 5 described in the conventional example, except that a calibration calculation unit 9 is provided. There is. Therefore, only the configuration of the calibration calculation unit 9 will be described, and the other description will be omitted.

The calibration calculator 9 calculates the added value when there is no vehicle or other obstacle in front of the host vehicle, and supplies the added value to the controller 3.

Next, the operation of this embodiment will be described.

First, a control signal is output from the controller 3 shown in FIG. 1 to the signal processing unit 2, and the signal processing unit 2 receives the control signal and the signal processing unit 2 sends a predetermined pulse width (eg, 133 nse) to the drive circuit 7.
c), a pulse signal having a predetermined cycle (for example, 6.25 μsec) is output as a light-transmitting trigger signal, and the drive circuit 7 causes the light-transmitting unit 5 to perform pulse light emission with the same pulse width (for example, 6.25 μsec) as the pulse signal.

The light pulse-transmitted from the light transmitting unit 5 is reflected by the target and received by the light receiving unit 6, and the received analog reception signal is amplitude-amplified by the signal amplifying unit 8 and compared with a predetermined reference value. Is binarized into 0 and 1, and the binarized received signal is subjected to a predetermined number (for example, 8192 times) of synchronous addition in the signal processing unit 2 and the synchronous addition result is output to the controller 3 to input the synchronous addition result. Controller 3
Judges the necessity of control of the received signal amplification factor from the peak value of the addition result, and when it judges that the control is not necessary, calculates the distance to the target and outputs the distance data to the inter-vehicle distance display unit 4. Then, the inter-vehicle distance display unit 4 which has input the distance data displays the distance on the monitor. Here, the flow of signal processing from reception of reflected light to distance calculation by synchronous addition will be described with reference to FIG. First, the reflected light for one pulse emission is received and amplitude-amplified as an analog signal.
The received light signal shown in (a) is obtained, which is binarized into "0" and "1" by comparison with the reference value, as shown in FIG. 6B, and the binarized signal is converted into a certain period Δt (for example, 6.67
nsec), and as shown in FIG. 6C, digital data of a predetermined number of bits (for example, Δt
If 6.67nsec is set, it becomes fixed bit data at 1m intervals.
Then, by performing a synchronous addition process on a plurality of consecutive digital data groups (for example, 8192 times), the characteristic of the added value level with respect to the distance as shown in FIG. 6D is obtained. The resolution of the horizontal axis (distance) at this time is determined by Δt (for example, if Δt = 6.67 nsec, the resolution is 1 m). In FIG. 7D, the distance at which the added value reaches a peak is output as the distance to the target.

Next, the entire flow from the start of distance measurement to the distance calculation will be described with reference to the flow charts shown in FIGS.

First, in step ST11, a distance measurement start signal is output from the controller 3 shown in FIG. 1 to the signal processing unit 2, the signal processing unit 2 inputs the signal, and in step ST12 the signal processing unit 2 amplifies the signal. The amplification factor of the unit 8 is initialized, the number of additions is cleared to 0 in step ST13, the inside of the addition processing circuit is initialized in step ST14, and the signal processing unit 2 outputs a light transmission trigger to the drive circuit 7 in step ST15. . Then, in step ST16, the signal received by the light receiving unit 6 is amplified and binarized by the amplification factor set in the signal amplifying unit 8, and in step ST17, the signal processing unit 2 converts the binarized received signal. Predetermined sampling period (eg 6.67nse
In step ST18, the signal processing unit 2 performs synchronous addition processing at each sampling point by sampling in c) and dividing into a predetermined number of bits (for example, 160 bits). Next, in step ST19, the number of additions is incremented. If the number of additions is less than the total number of additions, 8192, in step ST20, the process returns to step ST15.
In step ST22, a predetermined margin (for example, 50: judgment margin) is subtracted from the synchronous addition result at each sampling point (160 points in this example) and the saturation addition value at that sampling point in step ST22. If there is even one sampling point at which the synchronous addition result exceeds the saturation addition value −50, the reception signal amplification factor is reduced in step ST23, and if there is no one point, step S
Go to T24. Then, in step ST24,
A peak value is detected from the results of synchronous addition at each sampling point, and the peak value is assigned to the variable MAX, and step S
At T25, MAX is compared with 5000. If MAX is less than 5000, the process goes to step ST26. Then step ST
In step 26, the distance R to the target is calculated from the result of 8192 times of synchronous addition, and the flow returns to step ST24.

Next, an example of the result of synchronous addition is shown in FIG.
A curve D4 shown in the figure is a saturation addition value at each sampling point when the calibration is taken into consideration, and a curve D5 is
This is a value obtained by subtracting 50 from this saturation addition value, and curves D6 and D7 are sampling results having maximum values in MAX1 and MAX2, respectively. And in this example the curve D
5 is the switching line of the amplification factor.

According to the figure, the saturated addition value does not reach 7900 after the noise calibration is performed (eg 779).
2) Regarding the sampling points, the amplification factor can be lowered when the maximum value (MAX1) of the synchronous addition results exceeds 7792-50 = 7742. Therefore, even if there is a sampling point at which the saturated addition value does not reach 7900, the addition result will not be saturated, thus solving the problem in the conventional example.

Further, the saturation addition value reaches 7900 (for example,
8100) Regarding sampling points, MAX2 is 8100-50
It is possible to lower the amplification factor when the value exceeds 8050.
In this way, since the timing for switching the reception signal amplification factor is determined for each sampling point, the other sampling points are not affected by the sampling points on which noise is steadily placed during noise calibration.
Therefore, it is possible to maximize the performance of the sensor without throwing away the area where the distance can be measured with a high received signal S / N ratio and high distance measuring accuracy without being saturated. Therefore, the problem in the conventional example is solved.

[0044]

As described above, according to the present invention,
Change the upper limit value of the synchronous addition result that is set to prevent saturation of the synchronous addition result for each sampling point, and change the value to the saturation addition value for each sampling point determined by calibration, or a predetermined value from the saturation addition value for each sampling point. By setting the value obtained by subtracting, even if there is a sampling point at which the saturated addition value after calibration is lower than the saturation addition value at another sampling point, the effect that the addition result is not saturated is obtained. Also, since the upper limit value of the addition result is determined for each sampling point, it is possible to use all the addition value areas for which distance measurement can be performed accurately at each sampling point for distance measurement.
The effect of maximizing the sensor performance can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an inter-vehicle distance measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a first partial diagram of a flowchart showing the operation of the present embodiment.

FIG. 3 is a second partial diagram of the flowchart showing the operation of the present embodiment.

FIG. 4 is an explanatory diagram showing an example in which a saturated addition value of addition values is changed for each sampling point.

FIG. 5 is a block diagram showing a configuration of a conventional inter-vehicle distance measuring device.

FIG. 6 is an explanatory diagram showing a procedure for obtaining an inter-vehicle distance from a received light pulse.

FIG. 7 is an explanatory diagram showing a state when a synchronous addition result is saturated.

FIG. 8 is a flowchart showing a conventional operation of changing the amplification factor of a received signal.

FIG. 9 is an explanatory diagram showing how calibration occurs.

FIG. 10 is a characteristic diagram showing calibration data.

FIG. 11 is a characteristic diagram when the calibration data is calibrated.

FIG. 12 is a characteristic diagram showing a relationship between a peak value of a synchronous addition result and 3σ.

FIG. 13 is a block diagram showing a configuration of a conventional inter-vehicle distance measuring device.

FIG. 14 is a timing chart showing a conventional operation.

FIG. 15 is a diagram showing a probability density function.

[Explanation of symbols]

1 distance sensor head 2 signal processing unit 3 controller 4 vehicle distance display unit 5 light transmitting unit 6 light receiving unit
7 Drive circuit 8 Signal amplifier 9 Calibration calculator
11 Own vehicle 12 Light transmission range 13 Reflected light

Claims (3)

[Claims] 1. A transmission means for repeatedly transmitting a predetermined pulse signal toward the front of the vehicle, a reception means for receiving a reflection signal reflected by an object existing in front of the pulse signal, and an amplification of the received reflection signal. Amplifying means, data converting means for converting the signal amplified by the amplifying means into digital data, time-series data creating means for sampling the digital data at a predetermined cycle to form predetermined time-series data, and Synchronously adding means for synchronously adding the time series data of a predetermined number of consecutive times, distance calculating means for calculating the distance to the object from the peak value of the synchronous addition value by the synchronous adding means, and the object does not exist The calculation by the distance calculating means is calibrated by using the synchronous addition value of the time series data obtained at this time as calibration data. An amplification factor control that determines a comparison value according to the calibration data and corrects the comparison value and the peak value of the synchronous addition value by the addition device based on the comparison result. An inter-vehicle distance measuring device comprising: 2. The inter-vehicle distance measuring device according to claim 1, wherein the pulse signal is an optical pulse. 3. The inter-vehicle distance measuring device according to claim 1, wherein the pulse signal is an ultrasonic pulse.