JPH09113624A - Range finder using light wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the range finding accuracy of a range finder using light wave by eliminating the range finding error of the range finder which is caused by multipath reflection expressed by the function of the range to be found. SOLUTION: A range finder using light wave is provided with a light emitting means (2) which emits an intensity-modulated signal toward a reflecting mirror (4) set at a measuring point, a light receiving means (5) which receives the modulated light reflected by the mirror (4), and a phase measuring means (6) which measures the phase difference between the modulated signal emitted from the means (2) and that received by the means (5). A correcting arithmetic means (7),which stores the range finding error expressed by the function of the range to be found performs correcting calculation for removing an error component from the range to the measuring point found as a result of the phase difference measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightwave distance measuring device. More specifically, the present invention relates to a new optical distance measuring device useful for measuring and measuring a phase difference generated when an intensity-modulated signal is reciprocated to an object to be measured.

[0002]

2. Description of the Related Art Conventionally, there has been known an optical distance measuring device for measuring a phase difference generated when an intensity modulated signal is reciprocated to an object to be measured. In this optical distance measuring device, for example, as shown in FIG. 6, the modulated light generated by the modulation signal creating means (1) and output from the light emitting means (2) is collimated by the objective lens (3). Then, the light is emitted toward a reflecting mirror (4) such as a corner cube / ref sheet placed at the measurement point. Then, the reflecting mirror (4) reflects the modulated light, and the reflected light passes through the objective lens (3) again and is condensed on the light receiving means (5).

The reflected light is photoelectrically converted by the light receiving means (5), the phase proportional to the round trip distance to the measurement point is measured by the phase measuring means (6), and the measured object is measured based on the phase measurement result. The distance to the measurement point is obtained by calculating the distance to the object. With this device, for example,
If the frequency of the intensity-modulated signal is 15 MHz, its wavelength is λ = 20 m. The optical signal modulated by this frequency and transmitted from the light emitting means (2) is transmitted by the reflecting mirror (4) at a distance of 10 m.
When the distance is, the light receiving means (5) receives the signal with a phase delay of about 1 cycle. And generally, this λ / 2 = 10 m = 2π (rad) is called a unit distance. If the position of the reflecting mirror (4) is displaced further than 10 m, one cycle (2π (ra
d)) is exceeded and the optical signal is received. When the position of the reflecting mirror (4) is displaced closer than 10 m, the light receiving means (5) receives an optical signal of less than one cycle (2π (rad)). That is, the position of the measurement point can be measured by measuring the delay of the propagation time of the optical signal that is proportional to the position of the reflecting mirror (4).

In a general optical distance measuring device, an internal optical path (transmitted light from the light emitting means (2) is directly or indirectly via a mirror between the light emitting means (2) and the light receiving means (5). A reference optical path of a fixed path length that reaches the receiving means (5) and an external optical path (transmitted light from the light emitting means (2) is reflected by a reflecting mirror (4) placed at the measurement point and reciprocates between measurement distances. A measurement optical path) is formed, and an optical signal from the external optical path and an optical signal from the internal optical path are selectively incident on the light receiving means (5),
Each phase measurement removes phase fluctuations in the electrical system.

However, in such a conventional lightwave distance measuring device, the measuring light may be reflected by the light emitting means (2) and the light receiving means (5), and light of two or more round trips may be generated. The light other than the regular measurement light of may cause the measurement error. That is, for example, when the light emitting means (2) or the light receiving means (5) has a large reflection, the light returning from the reflecting mirror (4) and reaching the light receiving means (5) or the light emitting means (2) is reflected again. Since it is sent out to the mirror (4), it becomes two reciprocating lights that reciprocate with the reflecting mirror (4), and as a result of superimposing this with the regular measuring light that passes through the external optical path only once, the phase of the measuring light is changed. It changes and causes a measurement error. For this reason, in order to construct a highly accurate lightwave distance measuring device, this error factor (multiple reflection: an error caused by reciprocating the reflecting mirror twice or more) must be minimized. Therefore, conventionally, the light emitting means and the light receiving means are installed obliquely to reduce the reflectance, or an optical filter or shutter coating is arranged to block the multiple reflected light, and the amount of error measured in advance is stored inside the device. However, measures such as performing correction calculation were needed.

However, in the optical distance measuring device improved by the above means, there is a restriction that the light emitting means or the light receiving means having a low reflectance must be selected, or the light emitting means or the light emitting means with respect to the optical axis must be selected. Since the light receiving means is obliquely installed, the light emitting / light receiving efficiency is lowered, the maximum measurement distance is limited, and the addition of optical parts makes the device expensive and enormous. There was a point.

Further, in the lightwave distance measuring apparatus improved by the above means, since the error amount measured in advance is stored inside the device, the data of the error amount at each measurement point must be calculated, and the work process There was a problem that the amount of time in the process became very large. Therefore, the present invention has been made in view of the circumstances as described above, solves the problems of the conventional device, and accurately measures at any measurement distance without adding a special component for multiple reflection countermeasures. It is an object of the present invention to provide an optical wave distance measuring device that can obtain a result.

[0008]

In order to solve the above problems, the present invention provides a light emitting means for emitting an intensity-modulated signal toward a reflecting mirror placed at a measuring point, and a reflecting means reflected by the reflecting mirror. A light wave distance measuring device that includes a light receiving unit that receives the returned modulated light and a phase measuring unit that measures the phase difference between the light emitting unit and the modulation signal of the light receiving unit, and that calculates the distance from the phase measurement result to the measurement point. Therefore, the distance measurement error, which is expressed as a function of the measured distance, is stored internally, and the correction calculation means is provided to remove the error component from the distance to the measurement point obtained from the phase measurement result. Provided is a lightwave distance measuring device characterized by performing a correction calculation.

Further, according to the present invention, in the above-described optical distance measuring device, the correction calculation is performed by the following approximate expression.

[0010]

(Equation 2)

There is also provided a lightwave distance measuring device characterized by: That is, according to the present invention, the correction calculation means stores the correction calculation expression represented by the function of the measurement distance, and the correction calculation means performs the correction calculation of the measurement value obtained by the phase measurement means. There is. At this time, by performing an appropriate correction calculation for the measured distance,
A measurement error due to a large amount of reflected light can be completely eliminated.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in more detail below with reference to examples.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the basic construction of a lightwave distance measuring apparatus according to the present invention. In this figure, a modulation signal generating means (1) is generally an original oscillator using a crystal oscillator or the like, or an original oscillator output is a frequency divider / PLL (Phas).
e Locked Loop) circuit or the like. The modulation signal creating means (1) in this case is L
In the light emitting means (2) including a light emitting element such as ED and laser,
Input the light source modulation signal. The photoelectrically converted modulated signal input to the light emitting means (2) is selected in the internal optical path or the external optical path via the objective lens (3) and is input to the light receiving means (5).

The received signal photoelectrically converted by the light receiving means (5) is a signal having phase information proportional to the distance to the measurement point determined by the installation of the reflecting mirror (4). Therefore, the phase calculation means (6) compares the phase of the modulated signal obtained from the modulated signal generating means (1) with the received signal obtained from the light receiving means (5), whereby the distance calculation can be performed. .

Generally, when measuring the external optical path, the phase angle θe between the modulated signal and the received signal changes following the measurement distance. On the other hand, when measuring the internal optical path, the phase angle θi between the modulated signal and the received signal has a substantially constant value. By subtracting the phase angle between the external optical path measurement and the internal optical path measurement,
Phase angle θl = θ proportional to the measurement distance to the reflector (4)
e-θi can be obtained.

For example, as shown in FIG. 2, a received signal holding distance information is a vector SIF, and an error signal not having accurate distance information due to the multiple reflected light is a vector NIF.
If defined as IF, the vector SIF shown in polar coordinates
For the above reason, the phase angle θl changes in proportion to the distance. On the other hand, since the vector NIF has no distance information, it maintains a phase angle different from that of the vector SIF.

When the error signal NIF is present, the received signal input to the phase measuring means (6) of FIG.
Since it is the vector sum of IF and vector NIF, as shown in FIG. 2, a mutual difference of Δφ from the actual distance information, that is, the phase angle θl occurs. This phase difference is maximum,

[0018]

(Equation 3)

It becomes as follows. As described above, FIG. 2 shows the case where the error vector NIF is superimposed on the vector SIF due to the multiple reflection, and a phase error of Δφ occurs. In the case of FIG. 2, the measurement error is the vector SIF and the vector NIF.
Will be determined by the relationship between the light amount ratio of ## EQU1 ## and the phase angle.

Therefore, according to the present invention, first, according to the flowchart showing the calculation of the distance measurement error based on the theory represented by the function of the measured distance in FIG. 3, first, in the optical system as shown in FIG. With respect to the location of the cause, a signal reaching the light receiving means (5) via the regular optical path with the light emitting means (2) as a reference, and a signal reaching the light receiving means (5) via the incorrect optical path due to multiple reflection. The ratio with the signal is calculated (step 1 in FIG. 3). The maximum value Δφ of the phase error in FIG. 2 is calculated from the signal ratio in step 1, and Δφ
Is converted into a distance measurement error corresponding to the wavelength λ of the intensity modulated signal (step 2). Next, the distance measurement error based on the theoretical function represented by the function of the measurement distance is calculated. For example, assuming that the cause of multiple reflection is the light emitting portion in FIG. 4, the light receiving means (5) is transmitted from the light emitting means (2) through the reflecting mirror (4).
The normal optical path length (8a) of the modulated light up to and the erroneous optical path length (8b) due to multiple reflection are calculated. When the optical path length difference {(8a)-(8b)} is an integral multiple of the wavelength λ of the intensity modulation signal, the vector SIF shown in FIG.
Since the phase angle of the error vector NIF coincides with that of the error vector NIF, a ranging error due to multiple reflection does not occur. Therefore, the distance measurement error due to multiple reflection is obtained in step 2 of FIG. 3 and a function of the measurement distance with 1/2 of the wavelength λ of the intensity-modulated signal as one cycle with reference to the integral multiple measurement point. Maximum phase error Δφ
Is expressed as the product of the distance measurement error and the converted value (step 3 in FIG. 3).

Next, according to a flow chart showing a procedure for performing a correction calculation by theoretically analyzing the multiple reflection theory of FIG.
First, a measurement distance including a distance measurement error due to multiple reflection components is calculated (step 1). From the measurement distance calculated in step 1, a distance measurement error corresponding to the measurement distance is calculated and correction calculation is performed (step 2). The value calculated in step 2 is output as the distance measurement value (step 3).

Accurate optical distance measurement is realized by the above process.

[0023]

As described in detail above, in the present invention, the correction calculation formula for theoretically analyzing the multiple reflected light is stored in advance in the correction calculation means, and the correction calculation is performed on the measurement value obtained by the phase measuring means. , Eliminates the distance measurement error of the light wave distance measuring device caused by the multiple reflection expressed by the function of the measurement distance,
It is possible to improve the ranging accuracy. Therefore, it becomes possible to manufacture a long-distance optical wave distance measuring device with low cost and high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a vector diagram showing the principle of error generation.

FIG. 3 is a flowchart showing a procedure of theoretical analysis of distance measurement error in the embodiment of the present invention.

FIG. 4 is a schematic diagram showing theoretical analysis of distance measurement error in the embodiment of the present invention.

FIG. 5 is a flowchart showing a procedure of correction calculation in the embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional basic configuration.

[Explanation of symbols]

 1 Modulation Signal Creating Means 2 Light Emitting Means 3 Objective Lens 4 Reflecting Mirror 5 Light Receiving Means 6 Phase Measuring Means 7 Correction Calculating Means 8a Regular Optical Path Length 8b Incorrect Optical Path Length

Claims (2)

[Claims] 1. A light emitting means for emitting an intensity-modulated signal toward a reflecting mirror placed at a measuring point, a light receiving means for receiving the modulated light reflected by the reflecting mirror and returning, a light emitting means and a light receiving means. A lightwave distance measuring device comprising a phase measuring means for measuring the phase difference of the modulated signal of, and calculating the distance to the measurement point based on the result of the phase measurement. An optical wave distance measuring apparatus, comprising: a correction calculation unit that stores an error component from a distance to a measurement point obtained from a phase measurement result and performs the distance measurement correction calculation by the correction calculation unit. 2. The correction calculation is performed by the following approximate expression: The lightwave distance measuring device according to claim 1, wherein