JPH01219691A - Measuring apparatus of distance by electromagnetic wave - Google Patents

Abstract

PURPOSE:To make a distance measuring apparatus small in size and low in cost, by computing a distance to an object of distance measurement from the number of times of going and returning of a light beam from a transmission circuit to a reception circuit through said object within a certain time. CONSTITUTION:When a time required for a laser light 13a to advance by a distance L is denoted by tl, a time required for the laser light (13a) to complete its travel from a transmission circuit 12 to a reception circuit 21 through an object 2 of distance measurement is 2tl. The laser light (return beam 19) returning to the reception circuit 21 turns to be a reception pulse P, and it is given a delay time td by a delay circuit 24, subjected to waveform shaping and then inputted again to the transmission circuit 12, wherefrom the laser light 13a is outputted. In this case, a distance L to the object 2 is determined by the calculation of L=ctl=cT/(2n)-cta/2. In other words, the distance to the object is determined from the number of times of an electromagnetic wave going and returning within a certain time. Accordingly, only a counter which can respond to the maximum frequency is needed, and thus an apparatus can be made small in size and low in cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electromagnetic range measuring device suitable for use in, for example, a laser radar to determine the distance to a target object.

[Summary of the invention]

The present invention is an electromagnetic range measuring device for use in, for example, a laser radar to determine the distance to a suitable target object, comprising:
The transmitting circuit consists of an electromagnetic wave transmitting circuit, a receiving circuit for electromagnetic waves reflected from the object to be measured, and a delay circuit that delays and transmits the pulse detected by the receiving circuit to the receiving circuit for retransmission. The distance to the object to be measured is calculated from the number of times that electromagnetic waves travel back and forth from the object to the receiving circuit within a certain period of time, allowing the use of a relatively slow counter, making it a small and low-cost device. It is designed so that it can be configured.

[Conventional technology]

A laser radar system is known as a device for remotely determining the distance to a target object within a certain area. This conventional laser radar system is known, for example, from Japanese Patent Application Laid-Open No. 60-1596.
As disclosed in Publication No. 66, etc., basically the fifth
The configuration is shown in the figure.

In Fig. 5, (1) shows the laser radar system as a whole, which remotely determines the distance to the object to be measured (2).Here, (3) is a pulsed laser such as a ruby laser. Yes Giant pulse laser beam (3a)
At the same time as generating a transmission pulse S, the laser beam (3a) is expanded in beam diameter by a beam expander (4) and converted into an irradiation beam (5). This irradiation beam (5) is reflected by the distance measuring object (2) and a part of it becomes a reflected beam (6) in the laser radar system (
1) Returned to the side. The reflected beam (6) is focused by a condensing lens [7] onto the light receiving surface of a photomultiplier tube (8), and photoelectrically converted into a received pulse E by the photomultiplier tube (8).

Further, (9) is a counter, which counts the reference clock F output from the clock pulse oscillator (10) from the rising edge of the transmitting pulse S to the rising edge of the receiving pulse E.

The conventional laser radar system (1) shown in FIG. 5 can measure the distance to the distance measuring object (2) in the following manner.

The first pulse laser (3) oscillates the pulse laser beam (3a) and at the same time sends the transmission pulse S to the counter (9) as shown in FIG. 6A, and the counter (9) counts the reference clock F of the frequency fo. Next, when the reflected beam (6) returns, the received pulse E (sixth
B) is sent to the counter (9), and the counter (9) stops counting. Therefore, in the counter (9), C
As shown in , the reference clock F is counted only during ΔT from the rising edge Sl of the transmitted pulse S to the rising edge El of the received pulse E, and the counted value N is obtained, but the counted value N includes a quantization error of ±1. Therefore, ΔT is (N-1)/f, <ΔT<(N+ 1)/ fo
"It is within the range of (1). This ΔT is the time for light to travel back and forth over the distance. If the speed of light is C, then the distance L (=cΔT/
2) is within the following range from equation (1).

c(N 1)/(2ro)<c(N+1)/(2fo
)...(2) Therefore, in the conventional laser radar system shown in FIG. 5, if the frequency of the reference clock F of the clock pulse oscillator (10) is fo, then ΔL=±c/ (2f o)..."
There is a measurement error ΔL expressed by (3).

[Problem to be solved by the invention]

However, in such a conventional laser radar system, when trying to measure the distance to the object (2), for example, with a measurement error ΔL of 30 cm or less, c/(2f o) < 30 from equation (3). (cm), and the frequency f0 of the reference clock F is 500M)I
z or higher, which is disadvantageous in that an expensive and large-scale high-speed counter is required.

In addition, the pulsed laser beam (3
Since the delay in the rise of a) directly causes a measurement error, pulsed laser light (
The rise of 3a) has to be on the order of ins, and the pulse laser (3) requires an expensive and large-sized device such as a ruby laser.

The present invention has been made in view of the above points, and its purpose is to use a relatively low-speed counter to obtain measurement errors of the same degree as conventional methods, to use a small device, and to reduce the cost of electromagnetic waves. To provide distance measuring equipment.

[Means to solve the problem]

As shown in FIG. 1, for example, the electromagnetic wave distance measuring device according to the present invention includes a transmitting circuit (12) that outputs a light beam (17) as an electromagnetic wave, and a light beam (19) reflected from a distance measuring object (2). This receiving circuit (21) and this receiving circuit (21)
and a delay circuit (24) that transmits the received pulse P detected by the transmitter circuit (12) to the transmitter circuit (12) in order to retransmit the received pulse P after a delay.
The distance to the object to be measured (2) is calculated from the number of times n that the light beam makes a round trip within a certain period of time T to the receiving circuit (21).

[Operation] According to the present invention, the received pulses P detected at time intervals larger than the delay time t up to the delay circuit (24) need only be counted for a certain period of time T. Relatively slow counters can be used. Also, the time required for the light beam to travel back and forth to the distance measurement target (2) is 2t.
If z, the number of times the light beam travels back and forth over that distance during a certain period of time T (i.e., the count value of a relatively slow counter) is approximately n = T/(td+2 t t ) --
--The relationship (4) is satisfied. Therefore, the time t required for the light beam to travel the distance can be calculated backwards from equation (4), and the distance can be obtained by multiplying by the speed of light C. Here, by increasing the fixed time interval T in equation (4), the number of round trips n also increases proportionally, so the measurement accuracy of the time t can be improved arbitrarily.

〔Example〕

Hereinafter, one embodiment of the electromagnetic distance measuring device of the present invention will be described with reference to the drawings. In the drawings, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 1 shows an electromagnetic range measuring device (11) using electromagnetic waves and light according to the present embodiment, and an object to be measured (2). In the electromagnetic range measuring system (11), (12) is a transmitting circuit. It consists of a laser diode (13) and a drive circuit (14) for making it emit light, and generates laser light (13a). This laser light (13a) is made almost parallel by a collimator lens (15), passes through a beam splitter (16), and becomes an outgoing beam (17). Also,(
18) shows a light recursive reflector fixed on the distance measuring object (2), and this light recursive reflector (18) is attached to a mount (18).
a) Glass beads (1 mm in diameter d and 1 mm in diameter)
8b) are adhered to each other so that there are no gaps. This light recursive reflector (18
) is reflected as a backward beam (19) in substantially the same direction as the direction of incidence.

Referring now to FIG. 2, the light recursive reflector (1) of FIG.
We will explain the principle behind the fact that 8) has photoregression properties. In Figure 2, (32) is a glass bulb, and (33)
is an aluminum vapor deposited film applied to the right half of the glass bulb (32). When incident light (34) is irradiated here, the reflected light (35) is reflected almost parallel to the direction of incidence of the incident light (34) due to refraction by the glass bulb (32) and reflection by the aluminum evaporated film (33). be done. Also, if the incident light is an arrow (
34'), due to the spherical symmetry of the glass bulb (32), the reflected light (35') will reflect the direction of the arrow (34').
The light rays incident on the glass bulb (32) from the left half surface are reflected substantially parallel to the direction of incidence. This means that the glass bulb (32) has a photoreturning property, and the photoreturning glass shown in Fig. 1 is formed by covering a large number of miniaturized glass beads (18b) on the glass bulb (32). The optical reflector (18) also has optical return properties.

In Fig. 1, the negative part of the return beam (19) reflected from the light recursive reflector (18) is separated by the beam splitter (16), and the separated part is passed through the condenser lens (20).
and is focused on the receiving circuit (21). This receiving circuit (21
) is a PIN photodiode (2) that is installed at the focal point of the condenser lens (20) and photoelectrically converts the reflected beam (19).
2) and a preamplifier (23) that amplifies the photoelectric conversion output and detects the received pulse P. Receiving circuit (21)
The received pulse P detected at is given a predetermined delay time t by a delay circuit (24) and becomes a delayed pulse Q. Here, it is assumed that the delay time t includes delays in other circuits, such as a time delay in the preamplifier (23), for example. Also (25
) is a waveform shaping circuit whose analog delayed pulse Q
At the initial rise of Δ, it becomes high level and the predetermined pulse width Δ
A digital pulse that becomes low level at t is generated and supplied to the negative input terminal of the OR gate (26).

The received pulse P detected by the receiving circuit 21) is input to the delay circuit (24) as described above, while being converted to a TTL level by the level converter (27) and processed by the AND game).
(28) is supplied to one input terminal. The other input terminal of AND game) (28) is connected to a processing circuit (3) which will be described later.
0), and the level conversion output of the received pulse P is A only while the gate pulse G is at high level.
(ND game) (28) is supplied to the counter (29). The counter (29) counts the pulses supplied from the AND gate 28) and calculates the counted value n from the processing circuit (3).
0). This processing circuit (30) is connected to the signal line (
30a) is used to clear the counter (29), and a gate pulse G that remains at a high level for a certain period of time T is supplied to the other input terminal of the AND game (28), and the first An initial pulse R having a pulse width Δt for causing oscillation is supplied via the ○R gate (26). This initial pulse R and the waveform shaping circuit (25
) becomes a transmission pulse U which is at a high level while either of them is at a high level due to the ○R agate 26). Also, when the transmission pulse U is high level, the drive circuit (1
Since current is supplied from 4) to the laser diode (13), laser light (13a) is output.

To explain the calculation contents of the processing circuit (30), first, let t be the time required for the laser beam (13a) to travel the distance, then the laser beam (13a) is sent out from the transmitting circuit (12). The time required for the signal to travel back and forth to the receiving circuit (21) via the object (2) to be measured is 2tt. Next, the laser light (return beam (19) '') that returns to the transmitting circuit (21) becomes a received pulse P, which is given a delay time t in the delay circuit (24) and waveform-shaped, and then sent to the transmitting circuit again. The laser beam (13a) is outputted manually at (12).Therefore, the counter (29) counts 2 constant periods e (=2 tz + td) during the time T when the gate pulse G is at a high level. When the number of pulses obtained by converting the TTL level of the received pulses P is n, n is approximately expressed by the following equation.

n=T/e=T/(2tz + td)...-
・(5) Solving equation (5) for t, t, = T/(2n) −td/2 −・・
(6) becomes. Here TStd is a known constant and n
is the count value at the counter (29) that changes depending on the distance, so the processing circuit (30) calculates 1. from equation (6). You can find it by calculating. Next, if the speed of light in the medium is C, the distance to the object (2) to be measured is L=c t, =
It is determined by the calculation cT/(2n) −CL+/2 −·(7). This obtained value is the display circuit shown in Figure 1 (
31).

Next, we will explain the electromagnetic range measuring device in Figure 1 ≠ the action of biting
This will be explained with reference to the figures.

First, the 6 processing circuits (30) apply the gate pulse G at time t=t
o (FIG. 3A), and at the same time outputs an initial pulse R with a pulse width Δt (FIG. 3B). Gate pulse G
is a pulse that is kept at a high level for a time T until time t = t o + T, and specifically, T is 1
μs and ΔT are chosen to be 1Qns. At this time, the rising edge R1 of the initial pulse R becomes the rising edge Ul (FIG. 3D) of the outgoing pulse U via the OR gate (26), and the transmitting circuit (
An outgoing beam (17) is emitted from the distance measuring object (2) from the distance measuring object (2), and this outgoing beam (12) is reflected by the optical recursive reflector (18) on the ranging object (2) and becomes a backward beam ( 19)
The pulse is returned to the receiving circuit (21), and the rising edge PL of the received pulse P (FIG. 3C) is observed.

Subsequently, the received pulse P is delayed by the delay circuit (24) for a delay time of 1 d.
is given and after waveform shaping, it is again injected into the transmitting circuit (12) as an oscillating pulse U, so as shown in Figure 3, the rising edge U2 of the oscillating pulse U is excited and the transmitting circuit (12)
12) Newer forward beam (17) is the object to be measured (2)
is fired towards. Thereafter, the forward beam (17) is similarly emitted with a period of 2t□+t, and the period T of the received pulse P also becomes 2t,+1, as shown in FIG. 3C. Here, the delay time t is 70 ns, which is a value calibrated in advance.

Next, when the gate pulse G becomes low level after 2 fixed time T elapses, the counting pulse is no longer outputted from the AND game (28), and the processing circuit (30) takes in the count value n from the counter (29), ) according to the distance measurement target (2
) is calculated and displayed on the display circuit (31). After that, in order to stop outputting the forward beam (17) from the transmitting circuit (12), for example, the voltage supplied to the drive circuit (14) in the transmitting circuit (12) may be turned off.

Here, in analyzing the error of the electromagnetic wave distance measuring device of this example, the count value n of the received pulse P is an integer, but in order to obtain the true distance, it is also necessary to obtain its fraction Δn. Figure 3C
As is clear from the above, T=n e+2t, -e'=(n+
Δn) e − (8), and Q<2t,<
Since e, O<e'<e holds true, Δn is between +1. In equation (7), if we approximate n)Δn by replacing n with n+Δn, the distance is L = (cT/(2n) ] (1−Δn/n)
c t a/2...” (9), and the error ΔL
The absolute value of is IΔL l = [:cT/(2n)) (lΔnl/
n)≦cT/(2n)"...(10) Here, n-T/(2t 1 + t
When J, equation (10) becomes % equation %(11). Therefore, it can be seen that the measurement error ΔL can theoretically be arbitrarily reduced by increasing the period T of the gate pulse G.

Furthermore, the maximum counting frequency of the counter (29) in FIG.
If e, then f,=1/e≦1/td---(12) holds true from FIG. 3C and D. In this example, t, =7Qns is selected, so the formula (
12), ≦15 (MHz), which is considered to be a much lower frequency than the conventional one, so the counter (
29) can be constructed with an inexpensive and small-sized counting circuit.

Further, it is also possible to adopt a configuration in which the temperature characteristics of the pulse delay times in the transmitting/receiving circuits (12) and (21) are reversely corrected by the delay circuit (24). - Also, in this example, since the method is to count the transmission pulses P during a certain period of time T, the rise characteristics of the individual laser beams (13a) do not greatly affect the measurement accuracy due to the effect of averaging. Therefore, instead of a large and expensive device such as a ruby laser, a small and inexpensive laser diode can be used as the laser light source, making the entire device small and inexpensive. For example, even if the received pulse P becomes dull due to disturbance of reflection from the distance measuring object (2), the waveform shaping circuit (25)
Since the pulse width Δt of the transmitted pulse U is always kept at a constant value, highly accurate measurement can be maintained even if the period T of the gate pulse G is lengthened.

In addition, in this example, the measurement target (2) is a light regressive reflector (18
), a strong return beam (19) can be obtained even if the distance measurement target (2) is not directly facing the target, and a high S
/N ratio is obtained. However, this light regression reflector (18)
is not essential to the invention.

Next, another example of the electromagnetic wave distance measuring device of the present invention will be explained with reference to FIG.

Figure 4 shows SHF as an electromagnetic wave with a frequency of about 10 GHz.
This shows a part of an electromagnetic range measuring device that uses waves, where (36) is a transmitting antenna for emitting an outgoing beam (37) of SHF waves, and (38) is a transmitting antenna installed on the ranging object (2) to emit that outgoing beam. A small parabolic antenna for reflecting (37) to obtain a return beam (39), (40) is the return beam (39)
e.g. satellite method (BS) for receiving and obtaining electrical signals.
This is a BS antenna used for reception. The other circuit configurations are basically the same as those in the example shown in FIG. 1, so detailed explanations will be omitted.

According to this example, the spread of the forward beam (37) is larger than that in the example shown in FIG. 1, so there is a margin in the installation accuracy of the transmitting antenna (36).

Similarly, in the electromagnetic wave distance measuring device of the present invention, UHF is used as the electromagnetic wave.
It is also possible to use electromagnetic waves in the band or VHF band. In this case, normal antennas are used as the transmitting antenna (36) and BS antenna (40) in Figure 4, and a small parabolic antenna (38) is used as a resonance antenna. You can use a container etc. In this case, even if visibility is somewhat poor, the approximate distance to the location can be determined.

Further, since the electromagnetic wave distance measuring device of the present invention can be made small and lightweight, it is possible to easily construct a portable laser system that detects the direction at the same time by rotating the entire device or by deflecting the optical path of the forward beam. It can also be applied to automobile collision prevention systems, etc.

It should be noted that the electromagnetic wave distance measuring device of the present invention is not limited to the above-described embodiments, and it goes without saying that changes can be made without departing from the gist of the present invention.

〔Effect of the invention〕

The electromagnetic wave ranging device of the present invention is provided with a delay circuit that delays the pulse detected by the receiving circuit and transmits it to the transmitting circuit for retransmission, so that the electromagnetic wave is transmitted for a certain period of time from the transmitting circuit to the receiving circuit via the object to be measured. Since the distance to the object to be measured is calculated from the number of times it makes a round trip within a certain period of time, it is only necessary to have a counter that can respond to at least the maximum frequency determined by the reciprocal of the delay time. can be made smaller and lower in price.

Furthermore, by lengthening the certain period of time, the distance to the object to be measured can be determined with arbitrary precision.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an example of the electromagnetic wave distance measuring device of the present invention, Fig. 2 is a diagram explaining the principle of the optical return property of the light return reflector 18) shown in Fig. 1, and Fig. 3 The figures are signal waveform diagrams of various parts of the example shown in Fig. 1, Fig. 4 is a block diagram showing the main parts of another example of the electromagnetic wave distance measuring device of the present invention, Fig. 5 is a block diagram showing the conventional laser radar system, and Fig. 6 The figure is a diagram of signal waveforms at various parts in FIG. (2) is the object to be measured, (12) is the transmitting circuit, (13) is the laser diode, (16) is the beam splitter, (1
8) is a light recursive reflector, (21) is a receiving circuit, (22)
is a PIN photodiode, (24) is a delay circuit, (2
5) is a waveform shaping circuit, (29) is a counter, and (30) is a processing circuit. Agent Mamukai Ito
MATSU KUMA Hide Sheng'l + + Σ signal; 1 and 3 (Kure 3)

Claims (1)

[Claims] It is composed of a transmitting circuit for electromagnetic waves, a receiving circuit for receiving electromagnetic waves reflected from an object to be measured, and a delay circuit for delaying and transmitting the pulse detected by the receiving circuit to the transmitting circuit for retransmission. An electromagnetic wave distance measuring device characterized in that the distance to the distance measuring object is calculated from the number of times that electromagnetic waves travel back and forth from a circuit to the receiving circuit via the distance measuring object within a certain period of time.