JPH0682552A - Electrooptical distance measurement - Google Patents

Abstract

PURPOSE:To measure a distance highly accurately by measuring the phases of measuring light and internal light having maximum modulation frequency immediately before and after switching whereas measuring the phases of measuring light and internal light having frequency other than the maximum modulation frequency prior to switching. CONSTITUTION:Light from a light source is reflected in the order of modulation frequencies F3, F2, F1 and impinges, as an internal light, on a detector and the phase thereof is measured by specified times through a phase meter thus determining an average value. The light source is then switched to emit measuring light in the order of frequencies F1, F3, F2, F1 which impinges on the detector and the phase thereof is measured by specified times through the phase meter thus determining the average value thereof. Switching is made again to the internal light and the phase is measured similarly by specified times in the order of frequencies F1, F3, F2, F1. Distance measurement data D1 is obtained from phase measurements of internal and measuring lights during an interval from first phase measurement of internal light having frequency F3 to F1 immediately after S2 whereas data D2 is obtained from phase measurements of internal light and measuring light during the interval from F3 following to S2 to F1 following to S4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring method in a light wave distance meter.

[0002]

2. Description of the Related Art Conventionally, an internal optical path and a measuring optical path are alternately switched by a switching device, and an internal light that enters a detector from a light source through the internal optical path and a measuring light that enters the detector from a light source through the measuring optical path. A distance measuring method using a light wave distance meter is known, in which the phases are sequentially obtained for lights of at least two modulation frequencies, and the distance is measured from the phase difference between the internal light and the measuring light to a target point.

This will be described in more detail. As shown in FIG. 3, when the phase measurement A of the internal light and the phase measurement B of the measurement light are sequentially performed by switching the switch, for example, three (F ₁ , F _{1 2} , F ₃ , F ₁ > F ₂ > F ₃ ), and the phase measurement A of the internal light is performed using the modulation frequency F ₃ ,
In the order of F ₂ and F ₁ , the phase measurement B of the measurement light is performed in the order of the modulation frequencies F ₁ , F ₂ , and F ₃ . (In the figure, 1,
Reference numerals ₂ and ₃ represent values measured at modulation frequencies F ₁ , F ₂ and F ₃ , respectively. In the measurement at each modulation frequency, for example, the measurement is performed 10,000 times to obtain the average value. Measurement data D ₁ , D ₂ , D ₃ , D ₄ , D ₅
Is the phase measurement of the internal light of the frequencies F ₁ , F ₂ , F ₃ and the phase measurement of the measurement light of the frequencies F ₁ , F ₂ , F ₃ performed before and after the switching from the internal optical path to the measurement optical path by the switch. (D _{1 to} D _{5 in} the figure indicate the timing at which the distance measurement data D ₁ , D ₂ ... D ₅ are obtained.)

[0004]

According to the above-described distance measuring method, there is a problem that a relatively accurate distance measuring value cannot be obtained due to drift. An object of the present invention is to solve the problems of the conventional distance measuring method.

[0005]

In order to achieve the above object, the present invention provides an internal light which is switched between an internal optical path and a measurement optical path by a switch and is incident on a detector from a light source through the internal optical path. The phase of the measuring light that enters the detector from the light source through the measuring optical path is obtained for the light of at least two modulation frequencies, and the range of the optical distance meter that measures the distance from the phase difference between the measuring light and the internal light to the target point is measured. In the distance measuring method,
The measurement of the phase is started from the measurement light or the internal light of a frequency other than the maximum modulation frequency, and the phase of the internal light of the maximum modulation frequency and the phase of the measurement light are measured immediately before and after the switching of the internal optical path and the measurement optical path by the switch. Measure and 1 immediately before the switching
Before this, the phases of the internal light and the measuring light of the same frequency other than the maximum modulation frequency are measured, and the average value of the phase data of the internal light and the measuring light of the maximum modulation frequency is obtained.

[0006]

According to the distance measuring method described above, the phase of the internal light is measured in the order of the modulation frequencies F ₃ , F ₂ , and F ₁ as shown in FIG. 3, and the phase of the measurement light is measured by the modulation frequency. F ₁ ,
The measurement is performed in the order of F ₂ and F ₃ , but the measured phase data has a different drift amount of the phase data depending on the magnitude of the difference between the frequency before measurement and the frequency at the time of measurement. That is, as shown in FIG. 4, the phase data A of the internal light at the high frequency F ₁ for short distance measurement, which requires high accuracy.
₁ has a large difference between the frequency F ₂ before the measurement and the frequency F ₁ at the time of the measurement, the drift amount is large, while the high frequency F
The phase data B ₁ of the measurement light by ₁ has a small drift amount because the frequency before measurement and the frequency at the time of measurement do not change at F ₁ . This is because it takes time for the signal to settle down due to an inductance component or the like in the electric circuit of the light receiving section or the light transmitting section when the frequency difference greatly changes.

Therefore, when the phase difference data between the measurement light and the internal light at the frequency F ₁ is obtained, the drifts are not canceled out and high accuracy cannot be obtained. The present invention is derived from such consideration of the conventional distance measuring method.

As shown in FIG. 1, frequencies F ₃ , F ₂ and F
The phase data A ₃ , A ₂ and A ₁ of the internal light of ₁ are sequentially obtained, and then the switching device is switched to the phase data B ₁ ′, B ₃ of the measurement light of the frequencies F ₁ , F ₃ , F ₂ and F _1. , B ₂ and B ₁ are obtained, the switch is switched again to obtain the phase data A ₁ ′, A ₃ , A ₂ and A ₁ of the internal light of the frequencies F ₁ , F ₃ , F ₂ and F ₁ , and then the frequencies Phase data B ₁ ′, B ₃ , B ₂ , and B ₁ of the measurement lights of F ₁ , F ₃ , F _2, and F ₁ are obtained. Then, the average value of the phase data A ₁ and B ₁ ′ and the phases B ₁ and A ₁ ′ is calculated to obtain the distance measurement data D ₁ . The same measurement is repeated any number of times.

In the measurement at each frequency, for example, 500
Measure 0 times to obtain the average value. Distance measurement data D ₁ , D ₂ ...
Is the phase measurement of the internal light of frequencies F ₃ , F ₂ , F ₁ performed before and after the switching from the internal optical path to the measuring optical path by the switch and of the measuring light of frequencies F ₁ , F ₃ , F ₂ , F ₁ . It is determined from the phase measurement and the phase measurement of the internal light of the frequency F ₁ performed immediately after the switching from the measurement optical path to the internal optical path by the switch.

The drift amount of the phase data A ₁ of the internal light of the frequency F ₁ immediately before the switching from the internal optical path to the measurement optical path and the phase data B ₁ ′ of the measurement light of the frequency F ₁ immediately after the switching is due to the above-mentioned reason. Is larger (ΔD) and smaller (Δd), and the phase data B ₁ of the measuring light of the frequency F ₁ immediately before the switching from the measuring optical path to the internal optical path and the phase data A of the internal light of the frequency F ₁ immediately after the switching. drift amount of ₁ 'is greater ([Delta] D) and small ([Delta] d).

Therefore, the distance measurement data D ₁ is, for example, (Δd
If the average value is calculated as −ΔD) + (ΔD−Δd), the drift amount of the phase difference data is canceled.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a principle diagram of an optical distance meter used for implementing the distance measuring method of the present invention.

In the figure, 1 is, for example, F ₁ = 15.
An oscillator that outputs signals of three frequencies of MHz, F ₂ = 150 KHz, and F ₃ = 165 KHz. The output of the oscillator 1 is supplied to the modulator 2, and the output of the modulator 2 is supplied to the light source 3 of the laser diode, for example. It is supposed to be done.
Reference numeral 4 is a mirror for transmitting and receiving light, 5 is an objective lens, 6 is a reflecting mirror placed at a target point, 7 is a light detector, 8 is a switch, and 9 is a phase meter.

Next, the distance measuring method will be described. First, the switch 8 is set to the position shown in the figure, and the light source 3 emits light having a modulation frequency F ₃ = 165 KHz. The phase of the internal light is measured by the phase meter 9 after being made incident on the detector 7 through the internal optical path reaching the detector 7 via 10, 11, and 12. This measurement is repeated 1000 times, for example, and the average value is obtained. After that, the switch 8 is left as it is and the modulation frequency is F ₂ = 150 KH.
Light of z and F ₁ = 15 MHz is sequentially passed through the internal optical path to measure the phase of the internal light. The measurement of the phase of the internal light at the frequencies F ₂ and F ₁ is performed 2500 times, 5000 times, respectively.
It is repeated and the average value is calculated.

Next, the switch 8 is moved upward, and the light of the frequency F ₁ is used as the measurement light. From the light source 3, the prism 12, the transmission / reception mirror 4, the objective lens 5, the reflecting mirror 6, the objective lens 5, and the mirror. It is incident on the detector 7 through the measuring optical path reaching the detector 7 via 4 and the phase of this measuring light is measured by the phase meter 9
To measure. This frequency F ₁ is repeated 5000 times, for example, and the average value is obtained. After that, the switching device 8 is left as it is and the modulation frequency is F ₃ = 165 KHz and F ₂ = 150.
Light of KHz and F ₁ = 15 MHz is sequentially passed through the measurement optical path to measure the phase of the measurement light. This frequencies F ₃ , F ₂ and F
The measurement of the phase of the measurement light at ₁ is, for example, 1000
Repeat 2500 times and 10000 times and calculate the average value. After the above measurement, the average value of the phase data A ₁ , B ₁ ′ and B ₁ , A ₁ ′ is calculated to cancel the drift amount,
D ₁ is obtained as the distance measurement data. The switch 8 is again switched to the internal optical path side, the modulation frequency is changed in the order of F ₁ , F ₃ , F ₂ and F ₁ , and the phase of the internal light is measured for each. The internal light phase measurement at each frequency is the same as before.
₁ times 5000 times, F ₃ 1000 times, F
Repeat 2500 times for _{2 and} 5000 times for F ₁ .

The distance measurement data D ₁ is the second from the phase measurement of the internal light of the frequency F _{3 which is} two before the phase measurement of the internal light of the frequency F ₁ immediately before the _first switching S ₁ of the switch 8. It is obtained from the phase measurement of the internal light and the phase measurement of the measurement light performed until the phase measurement of the internal light of the frequency F ₁ immediately after the _second switching S ₂ . The distance measurement data D ₂ is the _second data of the switching device 8.
From the phase measurement of the internal light of frequency F ₂ after the _second switching S ₂ , the frequency F ₁ after the _fourth switching S ₄ of the switching device 8
It is obtained from the internal light phase measurement and the measurement light phase measurement performed up to the internal light phase measurement.

[0018]

As described above, according to the present invention, the phase measurement is started from the measuring light or the internal light having a frequency other than the maximum modulation frequency, and immediately before and after the switching of the internal optical path and the measuring optical path by the switch. Measures the phases of the internal light having the maximum modulation frequency and the measurement light, and immediately before the switching, measures the phases of the internal light and the measurement light having the same frequency other than the maximum modulation frequency. This has the effect of offsetting the drift amount and obtaining a highly accurate distance measurement value.

[Brief description of drawings]

FIG. 1 is a time chart explaining an embodiment of a distance measuring method according to the present invention.

FIG. 2 is a principle diagram of a lightwave rangefinder used for implementing the distance measuring method of the present invention.

FIG. 3 is a time chart explaining a distance measuring method in a conventional optical distance meter.

FIG. 4 is a time chart showing the relationship between phase data and drift measured by a conventional lightwave distance meter.

[Explanation of symbols]

 1 oscillator 2 modulator 3 light source 7 light detector 8 switcher 4 phase meter

Claims (1)

[Claims] 1. A phase of an internal light which is switched between an internal optical path and a measurement optical path by a switch, and which is incident on a detector from a light source through the internal optical path, and a phase of measurement light which is incident on a detector from a light source through the measurement optical path. Is obtained for light of at least two modulation frequencies, and a distance measuring method of a light wave range finder for measuring a distance from a phase difference between measurement light and internal light to a target point
The measurement of the phase is started from the measurement light or the internal light of a frequency other than the maximum modulation frequency, and immediately before and after the switching of the internal optical path and the measurement optical path by the switch, the phase of the internal light of the maximum modulation frequency and the measurement light is changed. Measure and 1 immediately before the switching
In the light distance meter characterized by measuring the phase of the internal light of the same frequency other than the maximum modulation frequency and the measurement light before and the average value of the phase data of the internal light of the maximum modulation frequency and the measurement light Distance measuring method.