JPH02163684A - Range finding method - Google Patents

Abstract

PURPOSE:To attain range finding with high accuracy on the wavelength level of an electro-magnetic wave or an acoustic wave by utilizing an intensity change due to interference between the irradiation and reflection of the electro-magnetic wave or acoustic wave, for which a modulation wavelength is continuously changed with amplitude modulation. CONSTITUTION:For a laser beam emitted from a laser oscillator 1, the amplitude modulation is executed by a modulator 12 and the wavelength is controlled and continuously changed by a modulating signal circuit 19. Next, this light is divided into a light toward an object 3 and a light toward a detector 18a for intensity detection by a splitter 13. A reflected light from the object 3 is condensed to the detector 18a and the intensity is detected. Detected signals by detectors 18b and 18b are added by an adder circuit 21 and an interfered waveform is obtained. This interfered waveform is shaped in a signal, smoothed and sent to a CPU 23. A signal from the circuit 19 is also sent to the CPU 23. In the CPU 23, a wavelength lambda is calculated and for this wavelength, an interfered waveform signal obtains an extremal value. After that, this value is substituted to an expression (in the expression, r: integer number, lambdam,lambdam+r: wavelength of extremal value, num,num+r: frequency of extremal value, tau,taum+r: period of extremal value) and a distance (d) can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of measuring the distance to an object using the interference effect of electromagnetic waves or ultrasonic waves.

[Prior Art] Currently, technologies using various principles have been developed to measure the distance to an object.

For example, an ultrasonic level meter has been put into practical use as a device for measuring distance using ultrasonic waves. This method determines the distance to an object by measuring the round trip time to the object when ultrasonic waves are transmitted. However, this technique has a problem with accuracy and can only obtain results that include an error of approximately ±1% (full scale).

On the other hand, as a technology similar to distance measurement technology, a technology has also been developed that applies the principle of a Michelson interferometer that uses electromagnetic waves to measure the distance traveled by an object. The technology is
Although it is possible to measure the above-mentioned immediate movement with high precision in units of wavelengths of light, it only measures the distance the object has moved, and is fundamentally different from the technique of determining the static distance to the object. They are different.

[Problem to be solved by the invention] The present invention was made under these circumstances, and
The purpose is to provide a method that can more accurately measure the distance to an object.

[Means for Solving the Problems] The present invention, which has achieved the above object, is a method for measuring the distance to an object by irradiating the object with electromagnetic waves or sound waves. to an object in
An amplitude-modulated electromagnetic wave or sound wave is irradiated while the modulation wavelength is continuously changed, and the reflected wave is incident on the receiver, and the intensity change of the electromagnetic wave or sound wave caused by interference between the emitted wave and the reflected wave reaches an extreme value. By measuring at least two modulation wavelengths when the value of The gist lies in finding the unknown distance.

However, d: unknown distance r: integer λ, λlI+r: wavelength when taking the extreme value (λ,>λ1r) vm, shi. r: Frequency when taking the extreme value (υ, <Vm+r). , τ0, - period when taking an extreme value (1I4r in τ1) The above method irradiates the target with amplitude-modulated electromagnetic waves or sound waves while continuously changing the modulation wavelength. The object of the present invention can also be achieved by emitting electromagnetic waves or sound waves whose wavelengths themselves are continuously changed without amplitude modulation, and then determining the unknown distance in the same manner [Claim (2)] .

[Function] The basic principle of interference of electromagnetic waves or ultrasonic waves (hereinafter sometimes referred to as electromagnetic waves), which plays an important role in the configuration of the present invention, will be explained with reference to the drawings.

First, in Fig. 2, 1 is the irradiation device (transmission section A), 2 is the reception device (reception section C), 3 is the object (incidence point B+, reflection point B2), 4 is the path of the irradiation wave, and 6 is the object. This is the path of the reflected wave from object 3. In the internal cause, the incident point B1 and the reflection point B2 are described separately for convenience of explanation, but it is assumed that these are substantially the same point. In this explanation, the object 3 is sufficiently spaced so that the distance 1i11D between the irradiation device 1 and the receiving device 2 is negligible compared to the distance 111d to the object (therefore, the incident angle is perpendicular to the object 3). Although it is assumed that the object is far away, if this assumption is not made, the distance d° to the object can be calculated using the following formula.

However, d is a value determined from equation (4), equation (7), or equation (8).

Assume that the 'FlFTi wave emitted from the irradiation device 1 enters the incident point Bl (=82) of the object 3 through a path 4), and then reaches the receiving device 2 through a path 6. Further, the round trip distance for the electromagnetic wave to return from the transmitter A to the receiver C is assumed to be 2d.

At this time, the phase difference δ between the electromagnetic waves in the transmitting section A and the electromagnetic waves in the receiving section C can be expressed as in the following equation (1).

Here, λ is the wavelength, and ψ is the change in phase caused by the reflection of the wave on the object 3, respectively.

Now, when an electromagnetic wave subjected to amplitude modulation is irradiated while changing the modulation wavelength continuously, the interference of the waves at the transmitter A and the receiver C is measured, and the wavelengths are λ to λ11. λ＋＋＋＋2・・
・λ0. ...(I tanshi λi>λ1 small>λm+2>...
・>λ0. 〉...), the interference intensity reaches the extreme value (
Suppose we take the local maximum value and local minimum value. At this time, the wavelength is λ1
Assuming that the interference intensity has reached its maximum value as (+,
), we can derive the following relationship.

(m, n, r: integers) The following equation (4) is obtained from the above (2) and (3).

Wavelength λ. Even if it is assumed that the interference intensity takes a minimum value when , the same result as in equation (4) can be obtained.

Therefore, if the above equation (4) is applied, at least two wavelengths λ,, λ,+ at which the interference intensity takes an extreme value.

By determining , the distance d to the object 3 can be determined with high precision in wavelength units. In the above explanation, we have described the case in which electromagnetic waves with amplitude modulation are applied while changing the modulation wavelength continuously, but electromagnetic waves or sound waves in which the wavelength of the electromagnetic wave itself is continuously changed without amplitude modulation are used. A similar conclusion can be drawn even if a configuration is adopted in which the information is transmitted from the irradiation device 1. However, when the frequency of electromagnetic waves is very high, such as light, it may be difficult to detect changes in wavelength units of electromagnetic waves using current technology.
In such cases, it is advantageous to apply amplitude modulation and then change the wavelength.

Furthermore, in the above explanation, a configuration is adopted in which the unknown pressure 11d is determined from the relationship between the wavelength λ and the distance d, but a configuration may also be adopted in which the unknown pressure 1!1d is determined from the relationship between the frequency, period, and the unknown pressure 1111d. . This point will be explained next.

The speed of electromagnetic waves or sound waves is U1, the frequency is V.

Assuming that τ is periodic, the following relationships (5) and (e) exist.

U;λ・ν...(5)τ=-...
(6) υ (5) , (From the relationship of Equation 61, the above Equation (4) can be transformed as shown in Equations (71 and (8) below).

Therefore, even if the frequency ν and period τ at which the interference intensity takes an extreme value are determined, the distance d to the object can also be determined.

However, in the present invention, the formula for determining the distance d is
, (7) or (8), and the use of mathematically modified forms of these equations is also within the technical scope of the present invention.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples. In the example below, a laser beam is used as a typical example of electromagnetic waves, and a case where the amplitude is modulated is shown, but other 1!
It goes without saying that the present invention can be carried out in the same manner even when magnetic waves or sound waves are used.

FIG. 1 is a schematic explanatory diagram showing an example of a distance measuring device configured to implement the method of the present invention.

In FIG. 1, 11 is a laser oscillator that generates laser light. The laser beam from this laser oscillator 11 is amplitude-modulated by a modulator 12, and its wavelength (amplitude wavelength here) is made to change continuously. At this time, the operation of the modulator 12 is controlled by information from the modulation signal generation circuit 19.

The laser light emitted from the modulator 12 is transmitted to the beam splitter 1
3, the laser beam is split into two directions, one laser beam passing through the prism 14 toward the object 3, and the other laser beam being sent to the detector 18a where its intensity is detected.

The laser beam reflected from the object 3 is reflected by the reflecting mirror 16.
1.7, the light is focused on the detector 18b, and this detector 1
The intensity is detected by 8b. Note that the detector 18a,
Examples of the 18b include a photodiode and the like.

The signal S2 from the detector 18b is amplified by the amplifier circuit 20a and then sent to the adder circuit 21. The signal S amplified from the detector 18a via the amplifier circuit 20a is also sent to the adder circuit 21, and the adder circuit 21 adds the two signals S+ and S2 to obtain an interference waveform. This interference waveform signal S3 is sent to the smoothing circuit 22 and becomes a smoothed signal S4. Signal S4 is central processing circuit (CPU) 2
Sent to 3. The central processing circuit 23 sequentially receives the signal S4 and the signal S5 from the modulation signal generation circuit 19. The signal S is converted to a wavelength λ, and the relationship between the wavelength λ and the signal S4 at that time is arranged as shown in FIG. In the actual processing shown in FIG. 3 within the CPU, the wavelength λ and the subsequent value of the signal S4 are stored as a two-dimensional array. Next, the CPU calculates the wavelength λ (λ1, λ2, λ3, etc. in FIG. 3) at which the signal S4 takes an extreme value from the relationship shown in FIG. 3, and calculates the distance 11 [ Find d. The above explanation was made using the wavelength λ, but the frequency υ
Alternatively, it is exactly the same even if the period τ is used, and the distance 111id can be obtained from equation (7) or equation (8).

[Effects of the Invention] As described above, according to the present invention, it has become possible to measure the distance to an object with high precision such as the wavelength level of electromagnetic waves or sound waves.

[Brief explanation of the drawing]

'S1 is a schematic explanatory diagram showing an example of a distance measuring device configured to carry out the method of the present invention, Fig. 2 is a schematic explanatory diagram showing the basic principle of the present invention, and Fig. 3 is a diagram for determining the distance l11d. It is a graph showing a waveform for.

Claims (2)

[Claims] (1) In a method of measuring the distance to an object by irradiating it with electromagnetic waves or sound waves, an electromagnetic wave or sound wave with amplitude modulation applied to the object at an unknown distance from the transmitter is sent to the object at a modulated wavelength. irradiate while changing continuously, make the reflected wave enter the receiving section, and measure at least two modulated wavelengths when the intensity change of the electromagnetic wave or sound wave caused by interference between the irradiated wave and the reflected wave shows an extreme value. , the wavelength, frequency or period at this time can be expressed as (4), (7) or (
8) A distance measuring method, characterized in that the unknown distance is determined by substituting it into an equation or a mathematical variation thereof. d=(r・λ_m・λ_m_+_r)/4(λ_m−λ
_m_+_r)...(4) d=(u・r)/4(ν_
m_+_r-ν_m)...(7) d=(u・r・τ_
m・τ_m_+_r)/4(τ_m−τ_m_+_r)
...(8) However, d: unknown distance r: integer λ_m, λ_m_+_r: wavelength (λ_
m>λ_m_+_r) ν_m, ν_m_+_r: Frequency when taking the extreme value (ν
_m<ν_m_+_r) τ_m, τ_m_+_r: Period when taking the extreme value (τ_
m>τ_m_+_r) (2) In a method of measuring the distance to an object by irradiating the object with electromagnetic waves or sound waves, electromagnetic waves or sound waves of continuously changing wavelength are emitted from the transmitter to the object at an unknown distance. irradiate and make the reflected wave enter the receiving section, measure at least two wavelengths at which the intensity change of electromagnetic waves or sound waves caused by interference between the irradiated wave and the reflected wave shows an extreme value, and measure the wavelength, frequency, or A distance measuring method characterized in that the unknown distance is determined by substituting the period into equation (4), (7), or (8) of claim (1) or a mathematical variation thereof. .