JPH06160527A - Distance/speed predicting device - Google Patents

Abstract

PURPOSE:To evaluate the level of risk on the collision with a massive object with a simple structure by calculating the distance and speed constituents perpendicular to the reference face of a moving body from the distance and speed data obtained by a sensor. CONSTITUTION:A light beam 12 is emitted from a distance/speed sensor 11, and it is rotatively scanned centering on a point Q. An obstacle 8 approaches the moving object 10 at the relative speed V. When the light beam 12 is rotatively scanned, the distance and speed are measured at two points P1, P2, for example, and distances P1Q=L1, P2Q=L2 and the constituent V1 of the speed V in the P1Q direction and the constituent V2 in the P2Q direction are obtained. The speed V and the angle alpha are obtained from the measured values V1, V2. The speed constituent VY perpendicular to the reference face 15 is obtained from a calculation equation, and the level of risk on collision is high when an inequality VY<=Vth is satisfied between the speed constituent VY and a threshold value Vth. The angle between the vector V and the reference face 15 is given as (alpha+theta), and the level of risk on collision becomes higher as this angle approaches pi/2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance / speed predicting device, and more particularly to a distance / speed predicting device suitable for a vehicle collision predicting sensor, and more particularly to detecting a danger of a collision and a relative speed immediately before the collision. The present invention relates to a distance / speed predicting device that generates a start signal for a life protection device.

[0002]

2. Description of the Related Art Conventionally, as a vehicle collision prediction sensor,
It is known to prevent rear-end collisions during traffic jams and back sensors when moving backwards.Generally, whether a collision is dangerous to the driver's or passenger's life depends on the relative speed with the obstacle, the weight of the obstacle, the collision. It is often difficult to know these before the collision, depending on the method of. A mechanical acceleration sensor is known as a conventional method for measuring the strength of impact after a collision. When this measured value exceeds a certain threshold value, life protection devices such as an airbag and pretension are activated to mitigate the impact of the collision.

Many methods have been proposed in the past for predicting the risk of a collision before a collision, and most of them have assumed a large inter-vehicle distance as seen in a rear-end collision prevention device. However, the detection of the risk of collision and the relative speed of a moving body and an obstacle in a close state before collision has an important role in deciding whether or not to activate the life protection device.

A triangulation method is known as a conventional example of distance / velocity measurement including a state of proximity. An example of this distance measurement is shown in FIG. The line segment AB represents the baseline length,
Distance sensors are provided at both ends A and B. Point P
Represents an obstacle, the coordinate axes are as shown in the figure, and P (X,
Y). The two-dimensional position (X, Y) of the point P is the base line AB.
With reference to, for example, the angles θ and φ at both ends thereof are measured, or the lengths of the two sides BP and AP are measured.

The distance sensor may be active or passive. The former is, for example, to emit a light beam from one or both of points A and B to illuminate an obstacle P, to measure a round-trip time difference to the obstacle by pulsed light, or this time difference to an amplitude-modulated wave. Known techniques include those that are converted into a phase difference for measurement, and that the position of a point image of an illuminated obstacle P is measured by an image sensor such as a CCD or PSD.

As an example of the latter passive case, the present applicant has already proposed as Japanese Patent Application No. 3-77746,
This will be schematically described with reference to FIGS. 6 and 7. In FIG.
Passive sensor unit _{O 1 -C 1, O 2 -C} 2, O 3
-C _3, O ₄ -C ₄ shows the arrangement of the distance measuring. Passive sensor unit _{O 1 -C 1, O 2 -C} 2, and O ₃
-C _3, O ₄ -C ₄ pairs are arranged in both a short distance interval L _1, are further arranged in each pair of long distance L ₂ intervals. It is assumed that a point P on the obstacle is represented by a point P and is located at a distance from the sensor surface 1 to R and from the sensor center line 3 to S. The on the sensor surface 1 fixed focus lens _{O 1, O 2; O 3} , O 4 is arranged, an imaging element (not shown) is formed on the imaging plane 2 of the focal length near the fixed focus lens are arranged. The images of the fixed focus lenses O ₁ , O ₂ , O ₃ , and O _{4 at} point P are C ₁ , C ₂ , C ₃ , and C ₄ , respectively. C _i Q
_i (i = 1 to 4) is the image position C when the point P is at infinity
_{i (i} = _1~4) represent the lateral deviation amount of the image as measured as reference, which was a x _{i (i} = _1~4), the focal length of the fixed-focus lens f, when long base line length L ₂ The two-dimensional distances R and S can be expressed by the following equations.

R = fL ₂ / {(x ₁ + x ₂ ) / 2- (x ₃ + x ₄ ) / 2} (1) S = −R · (x ₁ + x ₂ + x ₃ + x ₄ ) / ( 4f) The lateral shift amount x _i (i = 1 to 4) is determined by extracting feature points from the correlation calculation between the image pickup elements arranged with the short base line length L ₁ . From the equation (1), it is possible to achieve a highly accurate distance with a long base line length L _{2 in} a short time by using a correlation calculation with a short base line length.

The risk of collision is divided into a plurality of areas according to the degree of risk of collision and displayed from the sign of the lateral deviation amount and the distance measurement value from FIG. In FIG. 7, the short baseline length L ₁ is sufficiently shorter than the long baseline length L ₂ and is ignored.
O ₁ and O ₂ , and O ₃ and O ₄ are shown as the same point. Also, 4 represents a car, 5 a sensor surface,
6 and 7 represent boundaries. Region I is the most dangerous region, and regions II and III are less dangerous than region I.
A, B, and C are risk rankings according to distances, and A represents the most dangerous area. R _a is _a region where the active sensor attached to the passive sensor unit works, and R _r
Represents a monitoring area.

To obtain the speed from the distance measurement by triangulation, the speed is indirectly calculated from the time series data of the distance. As an example of directly measuring the risk of collision by triangulation, the configuration of Japanese Patent Publication No. 47-22532 is shown in FIG. In the figure, 4 is a moving object such as a car, A _L and A _R are Doppler sensors provided on the moving object 4, P is an obstacle including another vehicle, V is a relative speed between the obstacle P and the moving object 4. , Θ _L , θ
Each _R represents an angle formed between the velocity vector V and PA _L , PA _R. The Doppler sensors A _L and A _R emit microwaves and detect the Doppler shift amount by heterodyne detection of the reflected wave from the obstacle.
The Doppler shift amount corresponding to θ _L and V cos θ _R is detected. In Japanese Examined Patent Publication No. 47-22532, when the ratio of the two Doppler shift amounts (cos θ _L / cos θ _R ) is within a predetermined range, the risk of collision between the moving object M and the obstacle is high.

The applicant has already filed Japanese Patent Application No. 4-8531.
In this collision prediction device, a method of obtaining an evaluation amount regarding a risk of collision and a speed immediately before the collision is shown. FIG. 9 shows this principle explanatory diagram. Point P is an obstacle, and Q and R are distance / speed measuring means provided at both ends of the moving object. V is the relative speed between the moving object and the obstacle, V ₁ and V ₂ are the speed components in the distance / speed measuring means Q and R directions, and θ is the point P.
Is an angle formed by V and V ₁ , θ ₁ is an angle formed by V and V ₁ , L is a length of a base line QR, and distances from Q and R to a point P are L ₁ and L ₂ . The risk of collision is high when θ ₁ ≤ θ,
It decreases with the degree of θ ₁ > θ. Expressed by the formula, | k | ≦ tan ² (θ / 2) (2) where θ = cos ⁻¹ (L ₁ ² + L ₂ ² −L ² ) / 2L ₁ L
₂ K = (V ₂ −V ₁ ) / (V ₁ + V ₁ ) The true relative velocity V is given by the following equation. V = (V ₁ ² + V ₂ ² -2V ₁ V ₂ cos θ) ^1/2 / sin θ (3) When the relative speed V exceeds a certain set value V _th , the life protection device is activated. There is.

[0011]

The prior art has the following disadvantages. In the case of active distance measurement by triangulation, the following difficulties arise when attempting speed detection on large obstacles. This will be described with reference to FIG. The two points A and B are separated by the baseline length,
A distance sensor is arranged at the point A, and a pair of a light transmitting unit and a distance sensor is arranged at the point B, and the light beam BP ₁ is emitted from the light transmitting unit.
It is assumed that the obstacle 8 is crossed at a point P ₁ at time T ₁ . The two-dimensional position of the point P ₁ at this time is detected by the position detecting light receiving sensors placed at the points A and B. At time T ₂ , the obstacle moves to the position of 9, and its movement vector is indicated by the arrow P ₁ P ₂ . However, P ₂ represents the position of P _{1 at} time T ₂ . However, the point that is detected by the light beam BP _1, rather than P ₂ by moving the failure Butsujo, 'since the movement vector of the apparent arrows P ₁ P _2' P ₂ becomes as actual movement It is observed that the vector P ₁ P ₂ is different in magnitude and direction. In other words, a large obstacle may detect an erroneous movement vector due to obstacle movement of the illumination point by the light beam, and thus the correct velocity may not be detected.

In Japanese Patent Application No. 3-77746 which uses passive triangulation in combination with active, a feature point on an obstacle is obtained by passive correlation calculation, and a lateral shift amount corresponding to parallax is detected for the feature point. Although there is little risk of erroneous detection as described above, the current technology still takes time, which is inconvenient in the case of requiring a short time determination immediately before a collision.
In addition, active measurement does not consider speed detection for obstacles of the above size.

In the example of Japanese Examined Patent Publication No. 47-22532, the ratio of two Doppler shift amounts (cos θ _L / cos θ _R ) is a function of the distance between the moving object and the obstacle, and if the distance changes, different set values are used. There is an inconvenience that must be taken. Further, in Japanese Patent Application No. 4-8531, two types of measuring means for distance and speed are required, so that the configuration is complicated and expensive.

The present invention has been made in view of such a situation, and has a simple structure in which the distance measuring means is installed at one place, and it is highly accurate and can be performed in a short time even for a large object. An object of the present invention is to provide a means for enabling distance / speed measurement, evaluating a risk of collision, and generating a start signal of a life protection device.

[0015]

FIG. 1 is a conceptual diagram of the present invention. In FIG. 1, 10 is a moving body, 15 is a reference plane of the moving body, 11 is a distance / speed sensor provided at a point Q on the reference plane 15, 8 is an obstacle, and 70 is predetermined from the reference plane 15. A warning line at a distance Y _th .
Light beam 1 collimated from distance / speed sensor 11
2 is radially emitted and rotationally scanned around the point Q in order to search the obstacle 8. The obstacle 8 is
It is assumed that they approach each other at a relative velocity V, and the light beam 12 is rotationally scanned to measure the distance and velocity at two points P ₁ and P ₂ , for example, P ₁ Q = L ₁ , P ₂ Q = L ₂ , Speed V
P ₁ Q component in the direction of V _1, P ₂ Q component in the direction of V ₂ is the determined of. At this time, the angles θ and θ + Δθ formed by P ₁ Q and P ₂ Q with the reference plane 15 are known, and the velocity vectors V and V ₁
When the angle formed by is α and Y _th and V _th are predetermined distance and velocity thresholds, V ₁ = V cos α, V ₂ = V cos (α + Δθ) (4) and V ₁ , V ₂ is obtained from the measured Doppler shift amount as follows.

V ₁ = f _D1 λ / 2 V ₂ = f _D2 λ / 2 (5) where f _D1 and f _D2 are Doppler shift amounts in the P ₁ Q and P ₂ Q directions λ: laser light For example, if the speed of the obstacle 8 is 50 km / h, λ = 0.8 μ
If m, f _D will be about 35 MHz.

Using the equation (4), the velocity V and the angle α can be obtained from the measured values V ₁ and V _{2 as} follows.

Α = tan ⁻¹ ((cos Δθ−V ₂ / V ₁ ) / sin Δθ) (6) V = V ₁ / cos α Further, the velocity component V _y perpendicular to the reference plane 15 is V _y = V sin (Α + θ) = V ₁ sin (α + θ) / cos α (7), and the following inequality is established between this and the threshold value V _th .

V _y ≦ V _th (8) Further, the distance L perpendicular to the reference plane 15 from the measured values L ₁ and L _2.
y is L _y = L ₁ sin θ = L ₂ sin (θ + Δθ) (9) If the following inequality is established between the distance L _y and the threshold value Y _th , the risk of collision is high.

L _y ≦ Y _th (10) Further, the angle formed by the vector V and the reference plane 15 is (α + θ).
However, the closer it is to π / 2, the higher the risk of collision.

[0021]

The distance / speed predicting device of the present invention uses the single distance / speed sensor provided on the reference plane of the moving body and the arithmetic unit to detect the distance and speed of an obstacle having a size immediately before the collision, particularly the reference surface. Vertical distance and velocity components can be measured and calculated accurately in real time with a simple configuration.
The velocity component can be compared to a predetermined threshold and an activation signal of the life protection device can be provided if the predetermined threshold is exceeded. In addition, the risk of collision can be easily predicted from the measured distance signal.

[0022]

FIG. 2 shows the first embodiment of the present invention. In FIG. 2, the reference plane of the moving body is indicated by 15, the obstacle is indicated by 8, and the
20 is an objective lens that also serves as a light receiving device, and 21i and 22i are fibers for projecting and receiving light that are arranged in the focal plane of the objective lens 20.
(I represents the case of a, b, c, d, e, f6 lines.
The same applies hereinafter), the other end of the light projecting fiber 21i is 25i, the other end of the light receiving fiber 22i is 27i, a coherent light source for illuminating 25i is 23i, and a cementing lens is 24i.
i, the reference fiber 26i arranged in parallel with the light projecting fiber 25i, the other end of the reference fiber 26i is 33i, the optical switch 40 provided at the other end 33i is 40, and the optical switch 40
34i on one end and 35 on the other end
i, the other end of the fiber end 34i is 28i, the other end of 35i is 42i, and the light absorbing member provided at the other end 42i is 41. Reference numeral 45 denotes a drive signal for switching the optical path of the optical switch 40. The fiber end 28i is juxtaposed with the other end 27i of the signal light fiber 22i. 29i is a coupling lens, 30i
Represents a photodetector.

Next, the operation will be described. Coherent light source 2
3i undergoes amplitude modulation by a drive source (not shown), and alternately emits light in time series. Coherent light source 2
The light emitted from 3i is coupled to the light projecting fiber 25i and the reference fiber 26i by the coupling lens 24i. The light emitted from the other end 21i of the light projecting fiber 25i is collimated by the lens 32 and the objective lens 20 and emitted as a light beam 31i. The coherent light source 23i alternately emits the light beam 31i in a time-sequential manner, so that the light beam 31i equivalently performs rotational scanning. Light beam 31
Among i, for example, two of 31b and c are obstacles 8 and two points P
It is assumed that they intersect at _j (j = 1, 2) and are scattered by the obstacle 8. It is assumed that the intersection P _j is inside the warning line 70 at a distance Y _th from the reference plane 15, and the scattered light undergoes Doppler shift according to the moving speed V of the obstacle 8 and corresponds to the round trip distance to the obstacle 8. A signal light with a phase delay is given. The signal light is collected by the objective lens 20 and the lens 32 and is coupled to the light receiving fibers 22b and 22c.
The other ends 27b, c of the light receiving fibers 22b, c are juxtaposed with the other ends 28b, c of the reference fibers 26b, c, and when the drive signal 45 to the optical switch 40 connects the fiber end 33i to the fiber end 34i. The signal light and the reference light from the reference light fibers 28 b and c are collimated by the collimator lens 29.
Collimated by b and c, and coherently detected by the photodetectors 30b and 30c. When the fiber end 33i is connected to the fiber end 35i by the drive signal 45, the reference light is absorbed by the light absorbing member, and the signal light is incoherently detected.

Next, the signal flow will be described with reference to the block diagram of FIG. Signal detected by the optical detector 30i has been made coherent measurement or incoherent measured by the function of the optical switch, its amplitude is modulated at a frequency f _d or amplitude modulation frequency f _m of the Doppler shift. In the latter case, the higher the constant frequency f _m , the higher the resolution of the distance. Therefore, in the case of a close distance, about 100 MHz is usually preferable. The former is at most 60 km as the relative speed of the moving body.
/ H or less is 40 MHz or less, and about 20 MHz is selected as the threshold value for starting the life protection device. The signal detected by the photodetector 30i is the preamplifier 50.
It is amplified by i, temporally integrated by the multiplexer 51, and supplied to the filters 53 and 55 via the capacitor 52. In the case of coherent measurement, the path of the filter 53 is used. The filter 53 is a bandpass filter, and passes only the peripheral band of the Doppler shift frequency corresponding to the activation threshold of the life protection device. In the incoherent measurement, the path of the filter 55 is selected. Filter 55
Is a narrow band filter that passes only the frequency f _{m of} amplitude modulation. The signal passed through the filter 53 has its shift frequency determined by the Doppler shift detector 54 and is sent to the CPU 57. By rotating the light beam 31i once, the measurement results V ₁ and V ₂ by the light beams 31b and 31c are obtained.
The PU 57 calculates the equations (6) and (7) to obtain the velocity component V _y perpendicular to the reference plane 15. As a result, the velocity component V _y is compared with the threshold value, in other words, the determination of the above equation (8) is made, and if it exceeds this, the output of the phase detector 56 to be described later is used as a reference for the activation signal 60 of the life protection device. Output is done.

The signal that has passed through the filter 55 is detected by the phase detector 56 at the reference frequency that is amplitude-modulating the light source, and the phase delay corresponding to the time when the light travels back and forth to the obstacle is detected. The detected result is sent to the CPU 57, and the vertical distance is calculated from the reference line 15 in FIG.
In other words, the calculation of the equation (9) is performed, and after the comparison with the distance threshold value Y _th of the equation (10), if it is less than this, when a warning signal is generated or the activation signal 60 of the life protection device is generated, Provide judgment information. The measurement procedure is usually coherent measurement, and when a velocity component exceeding the threshold is detected as a result, a drive signal 45 is generated by a command from the CPU 57, the optical path is switched, incoherent measurement is performed, and the distance component is measured. Is measured.

The feature of this embodiment is that the relative moving speed of the obstacle can be obtained by one scanning with a single distance / speed sensor.
It is judged whether the collision is dangerous to life. This is because the margin time from the subsequent measurement of the distance to the collision with the obstacle is required.

This embodiment can be modified in several ways. In FIG. 2, the objective lens 20 and the lens 32 are used for both transmission and reception, but they can be separately provided. Similarly in FIG. 2, a plurality of light sources 2 are used to rotate and scan the light beam 31a.
Although 3i is switched over time, it is also possible to mechanically rotate and scan the light beam from a single light source. It is also possible to insert a modulator in place of the optical switch 40, give a constant frequency shift f _s , and always perform coherent measurement. At this time, the beat frequency f _s carrier wave and the Doppler shift frequency f _d are observed. The distance measurement is achieved by _obtaining the phase difference between the basic beat frequency f _s0 formed by the reference light separately drawn from the light source 23i and the output light of the modulator and the beat frequency of the signal light. At this time, both velocity and distance can be obtained simultaneously by one measurement.

The second embodiment of the present invention is shown in FIGS. 4 (a) and 4 (b).
Shown in. The positional relationship between the obstacle and the speed / distance sensor, the signal processing system and other parts not shown are the same as those in the first embodiment.

FIG. 4A comprises an objective lens 100 and a light-transmitting / light-receiving fiber 90. The objective lens 100 is composed of a concave lens represented by I, an equivalent convex lens represented by II, and a diaphragm S, and typically represents an optical system used as an objective lens of a so-called medical endoscope. The thin parallel light flux 71 near the principal ray from the outside passes through the concave lens I, the diaphragm S, and the convex lens II to become a convergent light flux 72 parallel to the optical axis 91, and is coupled to the light receiving fiber 22i. On the contrary, the light beam emitted from the light transmitting fiber 21i passes through the objective lens 100 and is emitted as a thin parallel light beam (not shown). In other words, the function of the diaphragm S is such that only a thin parallel light beam near the principal ray is transmitted and received, and only the principal rays corresponding to the light receiving fibers 22i are selected.

FIG. 4B shows a coherent light source 75, a collimator lens 76, and a fiber bundle 77. The fiber bundle 77 consists of a light transmitting fiber 25i (shown in white) and a reference fiber 26i (shown in black). In the first embodiment shown in FIG. 2, a plurality of collimating light sources 23i are used and the fiber 25 is used.
i, 26i are sequentially illuminated in the order of a, b, c ... F, and the light beam 31i is rotationally scanned, but in the present embodiment, the fiber bundle 77 is collectively illuminated by the coherent light source 75 and the collimator lens 76. .

Next, the operation will be described. In the first embodiment, FIG.
In the above, the light beam 31i was rotationally scanned in order to search for the obstacle 8. However, in this embodiment, since the light source 75 collectively illuminates, the light beam 31i is emitted at the same time. Therefore, in FIG. 2, the light beams 31b and c simultaneously generate P ₁ and P
Illuminate ₂ . Due to the nature of the objective lens 100, only the components of the scattered light that have traveled substantially parallel to the light beams 31b and 31c are converged on the light receiving fibers 22b and 22c, respectively, and are detected by the photodetectors 30b and 30c. The detected signal is shown in Fig. 3.
Is processed according to the flow shown in the block diagram of
It is converted into a time series signal by the multiplexer 52 via the preamplifier 50i. In other words, although the obstacles are illuminated at the same time, the nature of the objective lens 100 and the multiplexer 5
This is equivalent to rotationally scanning the light beam equivalently received by the combination of 1.

The feature of this embodiment is that a single coherent light source can illuminate an obstacle at the same time, so that the apparatus can be downsized, the angle of view can be widened, and the obstacle can be detected at high speed.

[0033]

As described above, according to the distance / velocity predicting apparatus of the present invention, the velocity of an obstacle immediately before a collision, especially the velocity component perpendicular to the base line, is applied to an obstacle having a large size. It is possible to accurately measure in real time with a simple configuration using only the distance / speed sensor, and to provide the activation signal of the life protection device when the speed component exceeds a predetermined threshold value. Further, the risk of collision can be easily predicted from the measured distance signal.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of the present invention.

FIG. 2 is a diagram illustrating a first embodiment.

FIG. 3 is a block diagram showing the flow of signals.

FIG. 4 is a diagram illustrating a second embodiment.

FIG. 5 is a diagram illustrating a distance / speed measurement method by triangulation.

FIG. 6 is a diagram illustrating a distance / speed measuring method using a passive sensor unit.

FIG. 7 is a diagram illustrating a distance / speed measurement method using a passive sensor unit.

FIG. 8 is a diagram illustrating a method of obtaining a velocity from distance measurement by triangulation.

FIG. 9 is a diagram illustrating a method of obtaining an evaluation amount related to the risk of collision and a speed immediately before the collision.

FIG. 10 is a diagram illustrating speed detection for an obstacle having a size by triangulation.

[Explanation of symbols]

 8 ... Obstacle 10 ... Moving object 11 ... Distance sensor 12 ... Light beam 15 ... Moving object reference plane 70 ... Warning line

[Procedure amendment]

[Submission date] March 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

FIG. 2 shows the first embodiment of the present invention. In FIG. 2, the reference plane of the moving body is indicated by 15, the obstacle is indicated by 8, and the
20 is an objective lens that also serves as a light receiving device, and 21i and 22i are fibers for projecting and receiving light that are arranged in the focal plane of the objective lens 20.
(I represents the case of a, b, c, d, e, f6 lines.
The same applies hereinafter), the other end of the light projecting fiber 21i is 25i, the other end of the light receiving fiber 22i is 27i, a coherent light source for illuminating 25i is 23i, and a coupling lens is 24i.
i, a reference fiber 26i juxtaposed with the light projecting fiber 25i, the other end of the reference fiber 26i is 33i, and the optical switch 40 provided at the other end 33i is 40.
34i on one end and 35 on the other end
i, the other end of the fiber end 34i is 28i, the other end of 35i is 42i, and the light absorbing member provided at the other end 42i is 41. Reference numeral 45 denotes a drive signal for switching the optical path of the optical switch 40. The fiber end 28i is juxtaposed with the other end 27i of the signal light fiber 22i. 29i is a coupling lens, 30i
Represents a photodetector.

Claims (2)

[Claims] 1. A light emitter provided on a reference plane of a moving body, which radially emits a light beam for obstacle detection, and a light receiving section having a distance / velocity sensing function, and the moving body reference based on the obtained distance / velocity data. A distance / velocity prediction device comprising a calculation unit for calculating a distance and a velocity component perpendicular to a plane. 2. A starting unit that compares a distance component and a velocity component perpendicular to the reference plane of the moving body with a predetermined threshold value and generates a starting signal of the life protection device when the comparison result satisfies a predetermined reference. The distance / speed predicting device according to claim 1.