JPH0610882U - Distance measuring device - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a distance measuring device with very few errors. [Configuration] Temperature sensor (20) for measuring the temperature of the light source
And a correction value calculation means (22) for calculating a change in the refractive index of the medium due to a change in the output wavelength of the light source based on the output of the temperature sensor and creating a correction value corresponding to the change in the refractive index.
And, the optical pulse emitted from the light source is sent toward the measurement target, the reflected light pulse from the measurement target is received by the light receiver, and the propagation time of the optical pulse propagating in the medium is measured. And a calculation means (18) for calculating the distance to the measurement object from the propagation time and the correction value.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a distance measuring device using a modulated optical signal.

[0002]

[Prior art]

 This type of conventional device obtains the distance by measuring the time it takes for the light to travel back and forth to the prism reflector installed at the distance measurement target. The light source is modulated at a high frequency of about 15 MHz and obtained from the received light. In this method, the phase between the generated signal and the modulated signal is measured, and then the distance D is calculated by multiplying the refractive index n of the medium (atmosphere).

Errors caused by distance measurement using a rangefinder are divided into external factors such as meteorological conditions and internal factors resulting from the internal structure and characteristics of the machine. Normally, the distance measurement accuracy is expressed as ± (a + b × D) with a term that does not depend on the distance D and a term that depends on it. a corresponds to a term that does not depend on distance, and b corresponds to a term that depends on distance. The distance-independent term is due to the temperature stability, optical, and mechanical stability of the electric circuit. The term that depends on the distance is mainly due to the stability of the crystal oscillator used for the oscillation of the frequency synthesizer and the fluctuation of the carrier wavelength of the light source.

FIG. 4 shows the change characteristics of the center value λc of the carrier wavelength of the light emitting element when the light emitting element that emits infrared light of λc = 0.85 μm at 20 ° C. is driven with a constant drive current. . The horizontal axis represents the temperature T (° C.), and the vertical axis represents the deviation of the peak emission wavelength when the temperature at 20 ° C. is zero. As is clear from the figure, the center value λc of the carrier wavelength changes linearly with a change in temperature when the driving current is constant. The reason is that the length of the resonator in the light source and the refractive index of the active layer in the waveguide resonator change due to the temperature change, and the longitudinal mode frequency changes. The rate of change of wavelength with respect to temperature varies depending on the light emitting material, but is 0.2 to 0.4 nm / ° C.

[0005]

In the prior art, when a gas laser with a stabilized wavelength or a semiconductor laser with temperature control is used as a light source for a long-distance rangefinder, the above-mentioned error occurs. Among the items, the influence of carrier wavelength fluctuations can be ignored, but if temperature control is not performed, an error may occur especially during long-distance measurement.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a distance measuring device having an extremely small error without controlling the temperature of the light source.

[0007]

[Means for Solving the Problems]

 According to the present invention, a light pulse emitted from a light source unit is sent to an object to be measured, a light pulse reflected from the object to be measured is received by a light receiver, and the propagation time of the light pulse propagating in the medium is measured. Is a distance measuring device that calculates the distance to the measurement object by measuring the temperature of the light source unit (for example, the temperature sensor 20 of the embodiment) and the output wavelength of the light source unit. A correction value calculating means for calculating a change in the refractive index of the medium due to the change based on the output of the temperature sensor and creating a correction value corresponding to the change in the refractive index (for example, the correction value calculating circuit 22 of the embodiment). ), And a calculation means (for example, the calculation processing circuit 18 of the embodiment) for calculating the distance to the object to be measured from the propagation time and the correction value.

The light source includes a light emitting element (for example, a light emitting diode, a light emitting element 24 such as a high-intensity superluminescent diode, a semiconductor laser, etc.) and a heat dissipation member (for example, a heat dissipation container 26 of the embodiment) that holds the light emitting element. Preferably, the temperature sensor is provided on the heat dissipation member. Further, it is preferable that a hole is formed in the heat dissipation member in a position close to the light emitting element, and the temperature sensor is arranged inside the hole.

[0009]

[Action]

 In the distance measuring device of the present invention having the above structure, the temperature of the light source unit is measured by the temperature sensor, and the output wavelength of the light source unit is calculated. Since the carrier wavelength of the light pulse that is actually emitted is obtained, the accurate phase index or group index in the medium can be calculated, and the correction value created based on this can be used to measure the propagation time. The distance to the object is corrected.

[0010]

【Example】

 Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of a distance measuring device according to the present invention. The trigger generation circuit 2 outputs a trigger signal. When the pulse drive circuit 4 receives the trigger signal, it is switched to the ON state to supply a current pulse to the light source unit 6 and cause the light source unit 6 to generate an optical pulse.

The light pulse is sent by the light sending optical system 8 toward the object to be measured. A part of the light reflected by the object to be measured is detected by the light receiver 12 via the light receiving optical system 10. In this embodiment, the light receiver 12 converts the light receiving pulse into a light receiving signal which is an electric signal. The light receiving signal output from the light receiver 12 is amplified by the amplifier circuit 14 and then input to the time measuring circuit 16.

The time measuring circuit 16 starts the time measurement at the same time as receiving the trigger signal from the trigger generating circuit 2, and ends the time measurement when receiving the light receiving signal. The propagation time of the optical pulse thus measured is supplied to the arithmetic processing circuit 18. The light source unit 6 is provided with a temperature sensor 20, and the measurement output of the temperature sensor 20 is input to the correction value calculation circuit 22. The correction value calculation circuit 22 calculates the weather correction coefficient K according to the method described later. The calculated weather correction coefficient K is converted into a correction signal which is an electric signal and input to the arithmetic processing circuit 18. The arithmetic processing circuit 18 calculates the distance D to the measurement object based on the supplied propagation time measurement value and the correction signal.

FIG. 2 shows an example of the configuration of the light source unit 6. A light emitting element 24 including a light emitting diode, a high brightness super luminescent diode, a semiconductor laser, or the like is arranged inside a cylindrical heat dissipation container 26. The heat dissipation container 26 is made of a metal having a high thermal conductivity, and has an internal thread formed on the inner circumference. A retaining ring 28 having a male screw on the outer periphery is screwed into the heat dissipation container 26, and the light emitting device 24 is fixed so that the bottom surface of the light emitting device 24 is brought into close contact with the inner surface of the heat dissipation container 26. A small hole 30 is provided in the heat dissipation container 26, and the temperature sensor 20 is inserted therein. The temperature sensor 20 is a temperature measuring element such as a thermistor, and measures the temperature change of the light emitting element 24 through the heat dissipation container 20.

Next, the operation of the embodiment of FIG. 1 will be described with reference to the flowchart of FIG. When the distance measurement is started, the meteorological conditions such as the temperature, atmospheric pressure, water vapor pressure at the distance measuring point are measured, and the results are sent to the correction value calculation circuit 22 from, for example, an operation unit (not shown) provided in the apparatus body. Input (step 1). Next, the correction value calculation circuit 22 reads the measurement output of the temperature sensor 20 (step 2), and calculates the center wavelength λc of the light emitted from the light source unit 6 in step 3 as follows.

First, the rate of change of wavelength with respect to temperature is obtained. Since the center wavelength of the spectrum of the light source can be measured by using an optical spectrum analyzer or the like, if the center wavelength at any two arbitrary temperatures is obtained, the rate of change of the wavelength with respect to temperature can be obtained from the result. For example, assuming that the central wavelength at 20 ° C. is 0.85 μm and the rate of change of the wavelength with respect to temperature is α, the central wavelength λc at a certain temperature T (° C.) can be calculated by Formula 1.

[0016]

[Equation 1]

In the next step 4, the correction value calculation circuit 22 calculates the weather correction coefficient K. A light wave of a single wavelength travels in the atmosphere at a phase velocity, and the refractive index in the atmosphere at this time is called the phase refractive index np. A light wave having a plurality of wavelengths travels in the atmosphere at a group velocity, and the refractive index at this time is referred to as a group refractive index ng. When a light emitting diode or a super luminescent diode is used as a light source as in the present embodiment, the spectral width thereof is wide, so that the group refractive index ng is used as the refractive index in the atmosphere.

To determine the group refractive index ng of the atmosphere, the phase refractive index np is calculated and converted. That is, first, the phase refractive index np is obtained according to the equation (2).

[0019]

[Equation 2]

Here, σ = 1 / λc (μm ⁻¹ ), P is atmospheric pressure (Torr), t is temperature (° C.), and f is water vapor pressure (Torr). Then, the group refractive index ng is obtained according to the equation (3).

[0021]

[Equation 3]

In Equation 3, σ ² is set to Σ, Equation 2 is substituted into Equation 3, and the group refractive index ng is obtained, which is calculated as Equation 4.

[0023]

[Equation 4]

The meteorological correction coefficient K when the group refractive index (ng = 1.000273770) at the industrial standard (temperature of 20 ° C., atmospheric pressure of 760 Torr, water vapor pressure of 10 Torr, carbon dioxide gas of 0.03%) is used is It becomes like

[0025]

[Equation 5]

In the next step 5, the distance measurement value D is calculated as follows. That is, the trigger generation circuit 2 outputs a trigger signal. When the pulse drive circuit 4 receives the trigger signal, it is turned on to supply a current pulse to the light source unit 6 and cause the light source unit 6 to generate an optical pulse. The light pulse is sent to the object to be measured by the light sending optical system 8. Part of the light reflected by the measurement object is detected by the light receiver 12 via the light receiving optical system 10. The light receiver 12 converts the light reception pulse into a light reception signal which is an electric signal and outputs the light reception signal. The received light signal is amplified by the amplifier circuit 14 and then input to the time measuring circuit 16.

On the other hand, the time measuring circuit 16 starts the time measurement in synchronization with the trigger signal of the trigger generating circuit 2 and ends the time measurement when receiving the amplified light receiving signal. The propagation time of the optical pulse thus measured is supplied to the arithmetic processing circuit 18. The arithmetic processing circuit 18 calculates the distance measurement value D based on the supplied propagation time measurement value. In the next step 6, the arithmetic processing circuit 18 calculates the weather-corrected distance D ′ according to Equation 6 using the distance measurement value D and the weather correction coefficient K calculated by the correction value calculation circuit 22. .

[0028]

[Equation 6]

Then, the arithmetic processing circuit 18 outputs the weather corrected distance D'as a final distance measurement value (step 7).

[0030]

[Effect of device]

 As described above, according to the present invention, since the central output wavelength of the light source can be measured in real time, the distance measurement error caused by the wavelength fluctuation caused by the temperature change can be avoided, and the long distance measurement can be performed. Also enables extremely highly accurate distance measurement.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a high precision distance measuring device according to an embodiment of the present invention.

FIG. 2 is a sectional view of an embodiment of a light source unit.

FIG. 3 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 4 is a graph showing the temperature dependence of the center wavelength of the light emitted from the light source.

[Explanation of symbols]

 6 ... Light source unit 16 ... Time measurement circuit 18 ... Calculation processing circuit 20 ... Temperature sensor 22 ... Correction value calculation circuit 24 ... Light emitting element 26 ...・ Radiation container 30 ・ ・ ・ ・ Small hole

Claims (3)

[Scope of utility model registration request] 1. A light pulse emitted from a light source unit is sent to an object to be measured, a reflected light pulse from the object to be measured is received by a photoreceiver, and the optical pulse of the light pulse propagating in the medium is received. In the distance measuring device for calculating the distance to the measurement object by measuring the propagation time, a temperature sensor for measuring the temperature of the light source unit, and the refractive index of the medium accompanying the change in the output wavelength of the light source unit. A correction value calculating unit that calculates a change based on the output of the temperature sensor and creates a correction value corresponding to the change in the refractive index, and calculates a distance to the measurement object from the propagation time and the correction value. A distance measuring device comprising: 2. The distance measuring device according to claim 1, wherein the light source unit has a light emitting element and a heat radiating member that holds the light emitting element, and the temperature sensor is provided on the heat radiating member. apparatus. 3. The heat radiating member has a hole formed in a position close to the light emitting element, and the temperature sensor is arranged inside the hole. Distance measuring device.