JP5461762B2 - Distance meter and distance measuring method - Google Patents

Description

  The present invention relates to an interference type distance meter and a distance measurement method for measuring a distance from a measurement object using light interference.

  Distance measurement using light interference by a laser has long been used as a highly accurate measurement method without disturbing the measurement object for non-contact measurement. Recently, a semiconductor laser is being used as a light source for optical measurement in order to reduce the size of the apparatus. A typical example is one using an FM heterodyne interferometer. This is capable of relatively long distance measurement and good accuracy, but has the disadvantage that the optical system becomes complicated because an interferometer is used outside the semiconductor laser.

  On the other hand, a measuring instrument using interference (self-coupling effect) in the semiconductor laser between the laser output light and the return light from the measurement object has been proposed (for example, Non-Patent Document 1, Non-Patent Document). 2, see Non-Patent Document 3). According to such a self-coupled laser measuring instrument, the semiconductor laser with a built-in photodiode serves as the functions of light emission, interference, and light reception, so that the external interference optical system can be greatly simplified. Therefore, the sensor unit is only a semiconductor laser and a lens, and is smaller than the conventional one. In addition, the distance measurement range is wider than the triangulation method.

  FIG. 13 shows a composite resonator model of an FP type (Fabry-Perot type) semiconductor laser. In FIG. 13, 101 is a semiconductor laser, 102 is a wall opening of a semiconductor crystal, 103 is a photodiode, and 104 is an object to be measured. Part of the reflected light from the measurement object 104 easily returns to the oscillation region. The small amount of light that has returned returns to the laser beam in the resonator 101, and the operation becomes unstable, causing noise (composite resonator noise or return light noise). The change in the characteristics of the semiconductor laser due to the return light appears remarkably even if the amount of return light relative to the output light is very small. Such a phenomenon is not limited to a Fabry-Perot type (hereinafter referred to as FP type) semiconductor laser, but also other types such as a vertical cavity surface emitting laser type (hereinafter referred to as a VCSEL type) and a distributed fed back laser type (hereinafter referred to as a DFB laser type). This also appears in the same semiconductor laser.

If the oscillation wavelength of the laser is λ and the distance from the wall open surface 102 closer to the measurement target 104 to the measurement target 104 is L, the return light and the laser light in the resonator 101 are as follows when the following resonance condition is satisfied. Strengthen and slightly increase the laser power.
L = nλ / 2 (1)
In formula (1), n is an integer. This phenomenon can be sufficiently observed even if the scattered light from the measurement object 104 is very weak, because the apparent reflectance in the resonator 101 of the semiconductor laser increases, causing an amplification effect.

  Since the semiconductor laser emits laser beams having different frequencies according to the magnitude of the injection current, an external modulator is not required when modulating the oscillation frequency, and direct modulation is possible by the injection current. FIG. 14 is a diagram showing the relationship between the oscillation wavelength and the output waveform of the photodiode 103 when the oscillation wavelength of the semiconductor laser is changed at a certain rate. When L = nλ / 2 shown in Expression (1) is satisfied, the phase difference between the return light and the laser light in the resonator 101 becomes 0 ° (same phase), and the return light and the resonator 101 When L = nλ / 2 + λ / 4, the phase difference is 180 ° (opposite phase), and the return light and the laser light in the resonator 101 are the weakest. Therefore, when the oscillation wavelength of the semiconductor laser is changed, a place where the laser output becomes strong and a place where the laser output becomes weak appear alternately, and the laser output at this time is detected by the photodiode 103 provided in the resonator 101. As shown in FIG. 14, a stepped waveform having a constant period is obtained. Such a waveform is generally called an interference fringe.

  Each stepped waveform, that is, each interference fringe is called a mode pop pulse (hereinafter referred to as MHP). MHP is a phenomenon different from the mode hopping phenomenon described later. For example, if the number of MHPs is 10 when the distance to the measurement object 104 is L1, the number of MHPs is 5 at half the distance L2. That is, when the oscillation wavelength of the semiconductor laser is changed for a certain time, the number of MHPs changes in proportion to the measurement distance. Therefore, if the MHP is detected by the photodiode 103 and the frequency of the MHP is measured, the distance can be easily measured. Note that the mode hopping phenomenon peculiar to the FP type semiconductor laser is a phenomenon in which a discontinuous portion occurs in the oscillation wavelength in accordance with the continuous increase / decrease of the injection current, as shown in FIG. There is a slight hysteresis when the injection current increases and decreases.

Tadashi Ueda, Satoshi Yamada, Susumu Shito, “Distance Meter Using Self-Coupling Effect of Semiconductor Laser”, Proceedings of the 1994 Tokai Branch Joint Conference of Electrical Engineering Society, 1994 Satoshi Yamada, Susumu Shito, Norio Tsuda, Tadashi Ueda, “Study on a small rangefinder using the self-coupling effect of a semiconductor laser”, Aichi Institute of Technology research report, No. 31 B, p. 35-42, 1996 Guido Giuliani, Michele Norgia, Silvano Donati and Thierry Bosch, “Laser diode self-mixing technique for sensing applications”, JOURNAL OF OPTICS A: PURE AND APPLIED OPTICS, p. 283-294, 2002

  As described above, the distance to the measurement target can be measured by using the interference of light. However, in the conventional interference type distance meter including the self-coupling type, since the frequency of the MHP during the measurement period is extracted, the disturbance light is removed when the frequency of the disturbance light is approximately the same as the frequency of the MHP to be measured. There is a problem that measurement cannot be performed and an error occurs.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a distance meter and a distance measurement method capable of measuring a distance from a measurement object while removing the influence of ambient light. .

The distance meter of the present invention includes at least a semiconductor laser that emits laser light to a measurement target, a first oscillation period that includes at least a period in which the oscillation wavelength continuously increases monotonously, and a period in which the oscillation wavelength continuously decreases monotonously. The semiconductor includes the second oscillation period including at least two periods alternately, and the frequency of the oscillation waveform having the first oscillation period and the second oscillation period as one period changes for each period. A laser driver that modulates the oscillation wavelength of the laser; a light receiver that converts the laser light emitted from the semiconductor laser and the return light from the measurement object into an electrical signal; and an output signal of the light receiver over a plurality of cycles Removing means for removing a frequency component whose frequency does not change; and laser light emitted from the semiconductor laser included in the output signal of the light receiver after removing the frequency component Frequency measuring means for measuring the frequency of the interference waveform caused by the return light from the measurement object, conversion means for converting the frequency of the interference waveform to a value when the frequency of the oscillation waveform is a reference frequency, from the frequency of the interference waveform and calculating means for calculating a distance between the measurement object possess, the conversion means, the reference frequency of the oscillation waveform is f, the oscillation when the frequency measuring means to measure the frequency of the interference waveform When the frequency of the waveform is α × f, a value obtained by multiplying the frequency of the interference waveform measured by the frequency measuring means by 1 / α is used as the frequency of the converted interference waveform .
The distance meter of the present invention includes a semiconductor laser that emits laser light to a measurement target, a first oscillation period that includes at least a period in which the oscillation wavelength continuously increases monotonously, and a period in which the oscillation wavelength continuously decreases monotonously. And the second oscillation period including at least two periods alternately exist, and the amplitude of the oscillation waveform having the first oscillation period and the second oscillation period as one period changes for each period. A laser driver that modulates the oscillation wavelength of the semiconductor laser; a light receiver that converts laser light emitted from the semiconductor laser and return light from the measurement object into an electrical signal; and a plurality of output signals from the light receiver. Removal means for removing frequency components whose frequency does not change over a period, and laser light emitted from the semiconductor laser included in the output signal of the light receiver after removing the frequency components Frequency measuring means for measuring the frequency of the interference waveform caused by the return light from the measurement object, conversion means for converting the frequency of the interference waveform to a value when the amplitude of the oscillation waveform is a reference amplitude, and after the conversion And calculating means for obtaining the distance to the measurement object from the frequency of the interference waveform.
The distance meter of the present invention includes a semiconductor laser that emits laser light to a measurement target, a first oscillation period that includes at least a period in which the oscillation wavelength continuously increases monotonously, and a period in which the oscillation wavelength continuously decreases monotonously. And at least one of the frequency and the amplitude of the oscillation waveform having one cycle of the first oscillation period and the second oscillation period. A laser driver that modulates the oscillation wavelength of the semiconductor laser, a light receiver that converts laser light emitted from the semiconductor laser and return light from the measurement object into an electrical signal, and the light receiver The number of interference waveforms generated by the counting means for counting the number of signals included in the output of the laser, the laser light emitted from the semiconductor laser and the return light from the measurement object are set to a plurality of periods. Calculation means for calculating, based on the counting result of the barrel the counting means, in which the number of the interference wave and a calculating means for calculating a distance between the measurement object.

The distance meter of the present invention includes a semiconductor laser that emits laser light to a measurement target, a first oscillation period that includes at least a period in which the oscillation wavelength continuously increases monotonously, and a period in which the oscillation wavelength continuously decreases monotonously. And at least two periods alternately including at least two oscillation periods, and the frequency of the oscillation waveform having the first oscillation period and the second oscillation period as one period changes for each period. A laser driver that modulates the oscillation wavelength of the semiconductor laser, a light receiver that converts the optical output of the semiconductor laser into an electrical signal, and a removal that removes a frequency component whose frequency does not change over a plurality of periods from the output signal of the light receiver. And a self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, which is included in the output signal of the light receiver after removing the frequency component. Frequency measurement means for measuring the frequency of the interference waveform caused by the above, conversion means for converting the frequency of the interference waveform to a value when the frequency of the oscillation waveform is a reference frequency, and the measurement from the frequency of the interference waveform after conversion have a calculating means for determining the distance to the target, the conversion means, the oscillation of the reference frequency is f waveform, said frequency measuring means frequency alpha × f of the oscillation waveform when measuring the frequency of the interference waveform Then, a value obtained by multiplying the frequency of the interference waveform measured by the frequency measuring means by 1 / α is used as the frequency of the converted interference waveform .
The distance meter of the present invention includes a semiconductor laser that emits laser light to a measurement target, a first oscillation period that includes at least a period in which the oscillation wavelength continuously increases monotonously, and a period in which the oscillation wavelength continuously decreases monotonously. And the second oscillation period including at least two periods alternately exist, and the amplitude of the oscillation waveform having the first oscillation period and the second oscillation period as one period changes for each period. A laser driver that modulates the oscillation wavelength of the semiconductor laser, a light receiver that converts the optical output of the semiconductor laser into an electrical signal, and a removal that removes a frequency component whose frequency does not change over a plurality of periods from the output signal of the light receiver. And a self-coupling effect between the laser beam emitted from the semiconductor laser and the return beam from the measurement object, included in the output signal of the light receiver after removing the frequency component Frequency measurement means for measuring the frequency of the resulting interference waveform, conversion means for converting the frequency of the interference waveform to a value when the amplitude of the oscillation waveform is a reference amplitude, and the measurement from the frequency of the interference waveform after conversion It has a calculation means which calculates | requires the distance with object.
The distance meter of the present invention includes a semiconductor laser that emits laser light to a measurement target, a first oscillation period that includes at least a period in which the oscillation wavelength continuously increases monotonously, and a period in which the oscillation wavelength continuously decreases monotonously. And at least one of the frequency and the amplitude of the oscillation waveform having one cycle of the first oscillation period and the second oscillation period. A laser driver that modulates the oscillation wavelength of the semiconductor laser, a light receiver that converts the optical output of the semiconductor laser into an electrical signal, and a counting means that counts the number of signals included in the output of the light receiver. The number of interference waveforms generated by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object is counted by the counting means over a plurality of periods. Calculation means for calculating, based, in which the number of the interference wave and a calculating means for calculating a distance between the measurement object.

Further , in one configuration example of the distance meter of the present invention, the conversion means sets the reference amplitude of the oscillation waveform as A, and the amplitude of the oscillation waveform when the frequency measurement means measures the frequency of the interference waveform as α × A Then, a value obtained by multiplying the frequency of the interference waveform measured by the frequency measuring means by 1 / α is used as the frequency of the converted interference waveform.
Further, in one structural example of the distance meter of the present invention, the calculating means sets the number of disturbance light signals to Nn, the frequency of the oscillation waveform before one cycle is 1 / x1 times the reference frequency, and the amplitude is y1 times the reference amplitude. At this time, the number of signals measured by the counting means is set to Nall _old , the frequency of the current oscillation waveform to be calculated for the number of interference waveforms is 1 / x2 times the reference frequency, and the amplitude is y2 times the reference amplitude At this time, when the number of signals measured by the counting means is Nall _new , the number N of the interference waveforms is N = (Nall _old− Nn × x1) / y1 = (Nall _new− Nn × x2) / It is calculated by y2.

Further , the distance measuring method of the present invention radiates a wave whose wavelength is modulated so that the amplitude changes every period to the measurement object, and generates interference between the wave reflected by the measurement object and returning to the measurement object. A frequency component whose frequency does not change over a plurality of periods from the detected interference information, and a value obtained when the amplitude of the wavelength-modulated wave is a reference amplitude after removing the frequency component. The distance to the measurement object is obtained based on the information on the interference after the conversion.
Further, the distance measuring method of the present invention includes a wave that is wavelength-modulated so that at least one of frequency and amplitude changes for each period, and is included in an output of a light receiver that converts the wave into an electric signal. And calculating the number of interference waveforms generated between the wave reflected back to the object to be measured and the radiated wave based on the result of the counting over a plurality of periods. The distance to the measurement object is obtained based on the number.

In the distance measuring method of the present invention, the first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonically are alternated. And an oscillation procedure for modulating the oscillation wavelength of the semiconductor laser so that the amplitude of the oscillation waveform having at least two periods in the first oscillation period and the second oscillation period is changed every period. A removal procedure for removing a frequency component whose frequency does not change over a plurality of periods from an output signal of a light receiver that converts an optical output of the semiconductor laser into an electrical signal, and an output signal of the light receiver after removing the frequency component A frequency measurement procedure for measuring a frequency of an interference waveform generated by a self-coupling effect between a laser beam emitted from the semiconductor laser and a return beam from the measurement object, A conversion procedure for converting the frequency of the interference waveform into a value when the amplitude of the oscillation waveform is a reference amplitude, and a calculation procedure for obtaining a distance from the measurement object from the frequency of the interference waveform after conversion. .
In the distance measuring method of the present invention, the first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonically are alternated. And the oscillation of the semiconductor laser so that at least one of the frequency and the amplitude of the oscillation waveform having one period of the first oscillation period and the second oscillation period changes for each period. An oscillation procedure for modulating the wavelength, a counting procedure for counting the number of signals included in the output of the light receiver for converting the optical output of the semiconductor laser into an electrical signal, the laser light emitted from the semiconductor laser, and the measurement object A calculation procedure for calculating the number of interference waveforms caused by the self-coupling effect with the return light based on a counting result of the counting procedure over a plurality of periods, and the measurement from the number of the interference waveforms In which and a calculation procedure for obtaining the distance to the elephants.

  According to the present invention, the oscillation wavelength of the semiconductor laser is modulated so that the frequency (or amplitude) of the oscillation waveform changes with each period, and the frequency component whose frequency does not change over a plurality of periods from the output signal of the light receiver is disturbed. The frequency of the interference waveform contained in the output signal of the receiver after removing the frequency component is converted to the value when the frequency (or amplitude) of the oscillation waveform is the reference frequency (or reference amplitude). By obtaining the distance from the object to be measured from the frequency of the interference waveform after conversion, the influence of the disturbance light can be removed even when the frequency of the disturbance light is approximately the same as the frequency of the interference waveform.

  In the present invention, the oscillation wavelength of the semiconductor laser is modulated so that at least one of the frequency and amplitude of the oscillation waveform changes every period, the number of signals included in the output of the light receiver is counted, and the number of interference waveforms is calculated. By calculating based on the counting results over a plurality of cycles and obtaining the distance from the object to be measured from the number of interference waveforms, even if the disturbance light frequency is approximately the same as the interference waveform frequency, The influence can be removed.

[First Embodiment]
The present invention is a method for measuring a distance based on an interference signal between a wave emitted in sensing using wavelength modulation and a wave reflected by an object. Therefore, the present invention can also be applied to an optical interferometer other than the self-coupling type and an interferometer other than light. More specifically, the case where the self-coupling of the semiconductor laser is used will be described. When the laser oscillation wavelength is changed while irradiating the measurement target from the semiconductor laser, the oscillation wavelength changes from the minimum oscillation wavelength to the maximum oscillation wavelength. The displacement of the measurement object during the change (or during the change from the maximum oscillation wavelength to the minimum oscillation wavelength) is reflected in the number of MHPs. Therefore, the state of the measurement object can be detected by examining the number of MHPs when the oscillation wavelength is changed. The above is the basic principle of the present invention.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a distance meter according to the first embodiment of the present invention. 1 includes a semiconductor laser 1 that emits laser light to a measurement target, a photodiode 2 that converts the optical output of the semiconductor laser 1 into an electrical signal, and a light that is collected from the semiconductor laser 1 to be measured. 12, the lens 3 that collects the return light from the measurement target 12 and makes it incident on the semiconductor laser 1, the first oscillation period in which the oscillation wavelength continuously increases monotonically, and the oscillation wavelength continuously monotonously. The semiconductor laser 1 is arranged such that there are at least two alternating second oscillation periods that decrease, and the frequency of the oscillation waveform in which the first oscillation period and the second oscillation period are one period changes for each period. A laser driver 4 that modulates the oscillation wavelength of the laser, a current-voltage conversion amplifier 5 that converts and amplifies the output current of the photodiode 2 into a voltage, and a signal extraction circuit that differentiates the output voltage of the current-voltage conversion amplifier 5 twice. 1 Then, the disturbance light frequency component included in the output voltage of the signal extraction circuit 11 is removed, and the interference information included in the output voltage of the signal extraction circuit 11 is converted to a value when the frequency of the oscillation waveform is the reference frequency. It has the frequency measuring device 8, the calculating device 9 which calculates the distance with the measuring object 12 from the frequency of the interference waveform after conversion, and the display device 10 which displays the calculation result of the calculating device 9. The current-voltage conversion amplifier 5, the signal extraction circuit 11, and the frequency measuring device 8 constitute a removing means, a frequency measuring means, and a converting means.

  Hereinafter, for ease of explanation, it is assumed that a semiconductor laser 1 of a type that does not have the above-described mode hopping phenomenon (VCSEL type, DFB laser type) is used. In the case of using a type (FP type) semiconductor laser 1 having a mode hopping phenomenon, this fact is noted.

  For example, the laser driver 4 supplies the semiconductor laser 1 with a triangular wave drive current that repeatedly increases and decreases at a constant change rate with respect to time and whose frequency changes every period as an injection current. Thus, the semiconductor laser 1 alternately repeats the first oscillation period in which the oscillation wavelength continuously increases in proportion to the magnitude of the injection current and the second oscillation period in which the oscillation wavelength continuously decreases, And it drives so that the frequency of the triangular wave which makes 1st oscillation period and 2nd oscillation period 1 period changes for every period.

  FIG. 2 is a diagram showing the change over time of the oscillation wavelength of the semiconductor laser 1. In FIG. 2, t-1 is the t-1th oscillation period, t is the tth oscillation period, t + 1 is the t + 1th oscillation period, t + 2 is the t + 2nd oscillation period, t + 3 is the t + 3rd oscillation period, and t + 4 is The t + 4th oscillation period, λa is the minimum value of the oscillation wavelength in each period, and λb is the maximum value of the oscillation wavelength in each period. In the present embodiment, the maximum value λb of the oscillation wavelength and the minimum value λa of the oscillation wavelength are always constant, and the difference λb−λa is also always constant. As is clear from FIG. 2, the frequency of the triangular wave is not constant and changes every period T. In the example of FIG. 2, assuming that the frequency of the triangular wave in the period t−1 and t is fHz, the frequency in the period t + 1 and t + 2 is 2 × fHz, and the frequency in the period t + 3 and t + 4 is fHz. That is, the frequency of the triangular wave changes as f, 2 × f, f, 2 × f,.

  The drive current is a drive current having a waveform in which the first oscillation period and the second oscillation period are alternately continued for at least three periods, and the oscillation wavelength continuously monotonously increases in the first oscillation period. If the drive current has a waveform including at least a period during which the oscillation wavelength continuously includes a period during which the oscillation wavelength continuously decreases monotonically, a drive current having a waveform other than the triangular wave illustrated (for example, a sine wave) Can be used. For example, in order to suppress current consumption, a driving current having an intermittent waveform with a pause period every two peaks (that is, every four periods) can be used (FIG. 3).

  Laser light emitted from the semiconductor laser 1 is collected by the lens 3 and enters the measurement object 12. The light reflected by the measurement object 12 is collected by the lens 3 and enters the semiconductor laser 1. However, condensing by the lens 3 is not essential. The photodiode 2 converts the light output of the semiconductor laser 1 into a current. The current-voltage conversion amplifier 5 converts the output current of the photodiode 2 into a voltage and amplifies it. The signal extraction circuit 11 has a function of extracting a superimposed signal from a modulated wave. For example, two differentiation circuits 6 and 7 are used. The differentiation circuit 6 differentiates the output voltage of the current-voltage conversion amplifier 5, and the differentiation circuit 7 differentiates the output voltage of the differentiation circuit 6. 4A schematically shows the output voltage waveform of the current-voltage conversion amplifier 5, FIG. 4B schematically shows the output voltage waveform of the differentiation circuit 6, and FIG. 4C shows the differentiation. 6 is a diagram schematically showing an output voltage waveform of a circuit 7. FIG. These are obtained by removing the oscillation waveform (carrier wave) of the semiconductor laser 1 of FIG. 2 from the waveform (modulated wave) of FIG. 4A, which is the output of the photodiode 2, and the MHP waveform (superimposition) of FIG. (Wave) is extracted.

  The frequency of the MHP generated by the laser light emitted from the semiconductor laser 1 and the return light from the measurement object 12 has a property of being proportional to the frequency and amplitude of the triangular wave. On the other hand, the frequency of disturbance light does not depend on the frequency and amplitude of the triangular wave. Therefore, by using such a property, it is possible to distinguish between MHP and disturbance light and remove the influence of disturbance light.

  FIG. 5 is a block diagram showing an example of the configuration of the frequency measuring device 8. The frequency measurement device 8 uses the Fast Fourier Transform (hereinafter referred to as FFT) to change the frequency characteristics of the output of the signal extraction circuit 11 (FIG. 4C) for each of the first oscillation periods t−1, t + 1, t + 3 and the first. The frequency of disturbance light is removed from the frequency characteristics of the output of the FFT unit 81 that measures every two oscillation periods t, t + 2, and t + 4, the storage unit 82 that stores the measurement result of the FFT unit 81, and the signal extraction circuit 11. The determination unit 83 that measures the frequency of the MHP and the conversion unit 84 that converts the frequency of the MHP measured by the determination unit 83 into a value when the frequency of the triangular wave is the reference frequency.

First, the FFT unit 81 of the frequency measuring device 8 measures the frequency characteristics of the output of the signal extraction circuit 11 every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4. .
The storage unit 82 stores the measurement result of the FFT unit 81. The determination unit 83 compares the measurement result of the FFT unit 81 with the measurement result of the previous cycle stored in the storage unit 82 and removes the frequency of disturbance light from the frequency characteristic of the output of the signal extraction circuit 11.

  FIG. 6 is a diagram showing the triangular wave frequency dependence of MHP and disturbance light. FIG. 6 (A) schematically shows the waveform of MHP at the output of the signal extraction circuit 11, and FIG. 6 (B) is the signal extraction circuit 11. The waveform of the disturbance light in the output of is schematically shown. 7A shows the frequency spectrum of the output of the signal extraction circuit 11 when the frequency of the triangular wave is fHz, and FIG. 7B shows the output of the signal extraction circuit 11 when the frequency of the triangular wave is 2 × fHz. The frequency spectrum of is shown.

  When the frequency of the triangular wave is changed every period T, the frequency of the MHP changes in proportion to the frequency of the triangular wave as shown in FIG. That is, when observed in the frequency spectrum, when the frequency of the triangular wave is fHz, the frequency of the MHP that was fsHz as shown in FIG. 7A becomes 2 × fHz as shown in FIG. 7B. 2 × fsHz as shown in FIG. On the other hand, the frequency of disturbance light is constant even if the frequency of the triangular wave changes as shown in FIGS. 6B, 7A, and 7B.

  Therefore, the determination unit 83 obtains a signal strength difference between the measurement result of the FFT unit 81 and the measurement result of the previous cycle stored in the storage unit 82 for each frequency, and the measurement result of the FFT unit 81 and the measurement of the previous cycle are measured. A signal whose frequency does not change as a result, that is, a signal whose signal intensity difference is equal to or smaller than a predetermined intensity difference threshold is determined as a signal due to the influence of disturbance light, and this signal is removed from the measurement result of the FFT unit 81. Then, the determination unit 83 determines the signal having the maximum intensity as the MHP signal in the measurement result of the FFT unit 81 after removing the disturbance light signal, and measures the MHP frequency.

  Next, the conversion unit 84 multiplies the MHP frequency measured by the determination unit 83 by a coefficient corresponding to the frequency of the triangular wave when the MHP frequency is measured. If the reference frequency of the triangular wave is fHz and the frequency of the triangular wave when the MHP frequency is measured is α × fHz, the coefficient by which the MHP frequency is multiplied is 1 / α. For example, when the frequency of the triangular wave when the MHP frequency is measured is 2 × fHz, the frequency of the MHP is twice that when the frequency of the triangular wave is fHz. Therefore, the coefficient 1 / α = By multiplying by 1/2, the frequency of MHP can be converted to a value when the triangular wave is constant at the reference frequency fHz. The frequency of the triangular wave is notified from the laser driver 4. The conversion unit 84 determines the coefficient value according to the frequency of the triangular wave notified from the laser driver 4.

  In this way, the influence of disturbance light can be removed from the output voltage of the signal extraction circuit 11, and the frequency of the MHP can be measured. The frequency measuring device 8 performs the above-described processing every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4.

  Next, the arithmetic unit 9 obtains the distance from the measuring object 12 based on the frequency of the MHP measured by the frequency measuring device 8. As described above, since the frequency of MHP is proportional to the measurement distance, the frequency and distance of MHP have a linear relationship as shown in FIG. Therefore, if the relationship between the frequency of the MHP and the distance when the triangular wave is constant at the reference frequency fHz is obtained in advance and registered in a database (not shown) of the arithmetic device 9, the arithmetic device 9 is used by the frequency measuring device 8. By obtaining a distance value corresponding to the measured frequency of the MHP from the database, the distance to the measurement object 12 can be obtained.

Or if the numerical formula which shows the relationship between the frequency of MHP and distance is calculated | required beforehand and it sets, the arithmetic unit 9 will substitute the measurement object 12 by substituting the frequency of MHP measured by the frequency measuring device 8 to a numerical formula. Can be calculated. The arithmetic unit 9 performs the above processing every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4.
The display device 10 displays the distance (displacement) from the measurement object 12 calculated by the arithmetic device 9 in real time.

  As described above, in the present embodiment, the oscillation wavelength of the semiconductor laser 1 is modulated so that the frequency of the triangular wave changes every period, and the frequency changes over a plurality of periods from the output signal of the photodiode 2 (light receiver). The frequency component of the interference wave included in the output signal of the receiver after removing the frequency component is converted to the value when the triangular wave frequency is the reference frequency. By obtaining the distance to the measurement object from the frequency of the interference waveform, the influence of disturbance light can be removed.

[Second Embodiment]
In the first embodiment, the frequency of the triangular wave is changed every period T. However, since the frequency of the MHP is also proportional to the amplitude of the triangular wave, the laser driver 4 changes the amplitude of the triangular wave as shown in FIG. It may be changed every T. In the example of FIG. 9, when the amplitude of the triangular wave in the period t−1 and t is A, the amplitude in the period t + 1 and t + 2 is 2 × A.

  In the present embodiment, the amplitude of the triangular wave is notified from the laser driver 4. Assuming that the reference amplitude of the triangular wave is A and the amplitude of the triangular wave when the MHP frequency is measured is α × A, the coefficient by which the MHP frequency is multiplied is 1 / α. Therefore, the conversion unit 84 may multiply the MHP frequency measured by the determination unit 83 by a coefficient 1 / α corresponding to the amplitude of the triangular wave when the MHP frequency is measured. Other configurations and processes of the distance meter are the same as those in the first embodiment. Thus, also in this embodiment, the same effect as that of the first embodiment can be obtained.

[Third Embodiment]
In the first and second embodiments, the distance to the measurement object is obtained from the MHP frequency, but the distance can also be obtained from the number of MHPs in a certain period. FIG. 10 is a block diagram showing the configuration of a distance meter according to the third embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In the present embodiment, a counting device 13 is provided instead of the frequency measuring device 8 of the first and second embodiments. The counting device 13 constitutes counting means and calculation means.

  FIG. 11 is a block diagram showing an example of the configuration of the counting device 13. The counting device 13 counts the number of signals output from the signal extraction circuit 11 every first oscillation period t−1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4. The storage unit 87 stores the result, and the calculation unit 88 calculates the number of MHPs from the count result of the counter 86 and the past count result stored in the storage unit 87.

First, the counter 86 of the counting device 13 counts the number of signals output from the signal extraction circuit 11 every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4. The storage unit 87 stores the count result of the counter 86.
FIG. 12 is a diagram showing the triangular wave amplitude dependence of MHP and disturbance light. FIG. 12 (A) schematically shows the waveform of MHP at the output of the signal extraction circuit 11, and FIG. 12 (B) is the signal extraction circuit 11. The waveform of the disturbance light in the output of is schematically shown.

The number N of MHPs does not depend on the frequency of the triangular wave as shown in FIG. 6 (A), but as shown in FIG. 12 (A), the amplitude of the triangular wave is multiplied by y to increase the number to y times. Can do. In contrast, the number of disturbance light signals Nn is inversely proportional to the frequency of the triangular wave as shown in FIG. 6B, but does not depend on the amplitude of the triangular wave as apparent from FIG.
Therefore, by changing the amplitude and frequency of the triangular wave for each period T, the number N of MHPs and the number of disturbance light signals Nn can be changed for each period T. The influence can be removed.

The number of signals Nall combining MHP and disturbance light when the triangular wave frequency is 1 / x times and the amplitude is y times can be expressed as follows.
Nall = N × y + Nn × x (8)
This number of signals Nall is a value observed by the counter 86. From Expression (8), the number N of MHPs can be obtained as the following expression.
N = (Nall−Nn × x) / y (9)

Here, it is assumed that the triangular wave before one cycle is the reference frequency and the reference amplitude, and at this time, the number of signals measured by the counter 86 and stored in the storage unit 87 is Nall _old, and the frequency of the current triangular wave after one cycle is set. Is 1 / x times the reference frequency and the amplitude is y times the reference amplitude, and the number of signals measured by the counter 86 at this time is Nall _new , the following simultaneous equations are obtained.
N = (Nall _old− Nn × 1) / 1 = (Nall _new− Nn × x) / y
(10)

  The calculation unit 88 can obtain the number N of MHPs by solving the simultaneous equations of Expression (10). Thus, the number of MHPs can be acquired by removing the influence of disturbance light from the output voltage of the signal extraction circuit 11. The counting device 13 performs the above processing every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4.

  Next, the operation of the arithmetic device 9a of the present embodiment will be described. The arithmetic device 9a obtains the distance from the measuring object 12 based on the number of MHPs measured by the counting device 13. The number of MHPs in a certain period is proportional to the measurement distance. Therefore, the database of the arithmetic unit 9a is obtained by obtaining in advance the relationship between the number of MHPs and the distance during a certain period (in this embodiment, the first oscillation period or the second oscillation period) when the triangular wave is constant at the reference frequency fHz. If registered in (not shown), the computing device 9a obtains the distance to the measurement object 12 by acquiring the distance value corresponding to the number of MHPs measured by the counting device 13 from the database. it can.

Alternatively, if a mathematical expression indicating the relationship between the number of MHPs and the distance in a certain period is obtained and set in advance, the arithmetic unit 9a performs measurement by substituting the number of MHPs measured by the counting device 13 into the mathematical expression. The distance to the object 12 can be calculated. The arithmetic unit 9a performs the above processing every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4.
Other configurations and processes of the distance meter are the same as those in the first embodiment. Thus, also in this embodiment, the same effect as that of the first embodiment can be obtained. In the present embodiment, at least one of the frequency and amplitude of the triangular wave may be changed for each period.

In the first to third embodiments, the frequency or amplitude of the triangular wave is changed to 1 time, 2 times, 1 time, 2 times,... It goes without saying that it is not limited to twice.
In addition, when the appearance frequency of disturbance light periodically changes, it becomes difficult to remove disturbance light when it coincides with the modulation period of the triangular wave. Therefore, the frequency or amplitude of the triangular wave is increased by one, two, one, two, or two. It is preferable to change at random instead of a fixed rule such as double.

  In addition, since the MHP signal is not a sine wave, it generally includes odd harmonics. Therefore, if the frequency or amplitude of the triangular wave is changed to an odd multiple when the frequency of the disturbance light and the frequency of the MHP match, the disturbance light harmonic and the MHP become the same frequency. It becomes difficult to remove. Therefore, the amount of change in the frequency (or amplitude) for each period of the triangular wave is preferably an even multiple of the reference frequency (or reference amplitude).

  Moreover, the frequency measuring device 8, the arithmetic devices 9, 9a, and the counting device 13 in the first to third embodiments are, for example, a computer having a CPU, a storage device, and an interface, and a program that controls these hardware resources. Can be realized. A program for operating such a computer is provided in a state of being recorded on a recording medium such as a flexible disk, a CD-ROM, a DVD-ROM, or a memory card. The CPU writes the read program into the storage device, and executes the processing described in the first to third embodiments according to this program.

  The present invention can be applied to a technique for measuring a distance from a measurement object.

It is a block diagram which shows the structure of the distance meter used as the 1st Embodiment of this invention. It is a figure which shows one example of the time change of the oscillation wavelength of the semiconductor laser in the 1st Embodiment of this invention. It is a figure which shows the other example of the time change of the oscillation wavelength of the semiconductor laser in the 1st Embodiment of this invention. It is a figure which shows typically the output voltage waveform of the current-voltage conversion amplifier in the 1st Embodiment of this invention, and the output voltage waveform of a differentiation circuit. It is a block diagram which shows one example of a structure of the frequency measuring device in the 1st Embodiment of this invention. It is a figure which shows the triangular wave frequency dependence of a mode pop pulse and disturbance light. It is a frequency spectrum figure which shows the frequency change of the mode pop pulse and disturbance light when a triangular wave frequency changes. It is a figure which shows the relationship between the frequency of a mode pop pulse, and distance. It is a figure which shows one example of the time change of the oscillation wavelength of the semiconductor laser in the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the distance meter used as the 3rd Embodiment of this invention. It is a block diagram which shows one example of a structure of the counting device in the 3rd Embodiment of this invention. It is a figure which shows the triangular wave amplitude dependence of a mode pop pulse and disturbance light. It is a figure which shows the compound resonator model of the semiconductor laser in the conventional laser measuring device. It is a figure which shows the relationship between the oscillation wavelength of a semiconductor laser, and the output waveform of a built-in photodiode. It is a figure which shows the magnitude | size of the width of the frequency which became discontinuous by the mode hopping phenomenon.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Photodiode, 3 ... Lens, 4 ... Laser driver, 5 ... Current-voltage conversion amplifier, 6, 7 ... Differentiation circuit, 8 ... Frequency measuring device, 9, 9a ... Arithmetic unit, 10 ... Display 11 ... Signal extraction circuit, 12 ... Measurement target, 13 ... Counter, 81 ... FFT unit, 82 ... Storage unit, 83 ... Determination unit, 84 ... Conversion unit, 86 ... Counter, 87 ... Storage unit, 88 ... Calculation Department.

Claims (12)

A semiconductor laser that emits laser light to the object to be measured;
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and A laser driver that modulates the oscillation wavelength of the semiconductor laser such that the frequency of an oscillation waveform having one oscillation period and the second oscillation period as one period changes for each period;
A light receiver that converts laser light emitted from the semiconductor laser and return light from the measurement object into an electrical signal;
Removing means for removing a frequency component whose frequency does not change over a plurality of periods from the output signal of the light receiver;
A frequency measuring means for measuring a frequency of an interference waveform generated by the laser light emitted from the semiconductor laser and the return light from the measurement object, included in the output signal of the light receiver after removing the frequency component;
Conversion means for converting the frequency of the interference waveform into a value when the frequency of the oscillation waveform is a reference frequency;
Have a calculating means for determining the distance between the measurement object from the frequency of the interference waveform after the conversion,
The conversion means has an interference waveform measured by the frequency measurement means when the reference frequency of the oscillation waveform is f and the frequency of the oscillation waveform when the frequency measurement means measures the frequency of the interference waveform is α × f. A distance meter obtained by multiplying a frequency obtained by multiplying 1 / α by a frequency of the converted interference waveform . A semiconductor laser that emits laser light to the object to be measured;
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and A laser driver that modulates an oscillation wavelength of the semiconductor laser so that an amplitude of an oscillation waveform having one oscillation period and the second oscillation period as one period changes for each period;
A light receiver that converts laser light emitted from the semiconductor laser and return light from the measurement object into an electrical signal;
Removing means for removing a frequency component whose frequency does not change over a plurality of periods from the output signal of the light receiver;
A frequency measuring means for measuring a frequency of an interference waveform generated by the laser light emitted from the semiconductor laser and the return light from the measurement object, included in the output signal of the light receiver after removing the frequency component;
Conversion means for converting the frequency of the interference waveform into a value when the amplitude of the oscillation waveform is a reference amplitude;
A distance meter comprising: a calculation unit that obtains a distance from the measurement object based on the frequency of the converted interference waveform. A semiconductor laser that emits laser light to the object to be measured;
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and A laser driver that modulates the oscillation wavelength of the semiconductor laser so that at least one of the frequency and the amplitude of the oscillation waveform having one oscillation period and the second oscillation period as one period changes for each period;
A light receiver that converts laser light emitted from the semiconductor laser and return light from the measurement object into an electrical signal;
Counting means for counting the number of signals included in the output of the light receiver;
Calculating means for calculating the number of interference waveforms generated by the laser light emitted from the semiconductor laser and the return light from the measurement object based on the counting result of the counting means over a plurality of periods;
A distance meter comprising: calculating means for obtaining a distance to the measurement object from the number of the interference waveforms. A semiconductor laser that emits laser light to the object to be measured;
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and A laser driver that modulates the oscillation wavelength of the semiconductor laser such that the frequency of an oscillation waveform having one oscillation period and the second oscillation period as one period changes for each period;
A light receiver for converting the optical output of the semiconductor laser into an electrical signal;
Removing means for removing a frequency component whose frequency does not change over a plurality of periods from the output signal of the light receiver;
Frequency measurement for measuring the frequency of the interference waveform generated by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, which is included in the output signal of the light receiver after removing the frequency component Means,
Conversion means for converting the frequency of the interference waveform into a value when the frequency of the oscillation waveform is a reference frequency;
Have a calculating means for determining the distance between the measurement object from the frequency of the interference waveform after the conversion,
The conversion means has an interference waveform measured by the frequency measurement means when the reference frequency of the oscillation waveform is f and the frequency of the oscillation waveform when the frequency measurement means measures the frequency of the interference waveform is α × f. A distance meter obtained by multiplying a frequency obtained by multiplying 1 / α by a frequency of the converted interference waveform . A semiconductor laser that emits laser light to the object to be measured;
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and A laser driver that modulates an oscillation wavelength of the semiconductor laser so that an amplitude of an oscillation waveform having one oscillation period and the second oscillation period as one period changes for each period;
A light receiver for converting the optical output of the semiconductor laser into an electrical signal;
Removing means for removing a frequency component whose frequency does not change over a plurality of periods from the output signal of the light receiver;
Frequency measurement for measuring the frequency of the interference waveform generated by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, which is included in the output signal of the light receiver after removing the frequency component Means,
Conversion means for converting the frequency of the interference waveform into a value when the amplitude of the oscillation waveform is a reference amplitude;
A distance meter comprising: a calculation unit that obtains a distance from the measurement object based on the frequency of the converted interference waveform. A semiconductor laser that emits laser light to the object to be measured;
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and A laser driver that modulates the oscillation wavelength of the semiconductor laser so that at least one of the frequency and the amplitude of the oscillation waveform having one oscillation period and the second oscillation period as one period changes for each period;
A light receiver for converting the optical output of the semiconductor laser into an electrical signal;
Counting means for counting the number of signals included in the output of the light receiver;
A calculation means for calculating the number of interference waveforms caused by a self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, based on the counting result of the counting means over a plurality of periods;
A distance meter comprising: calculating means for obtaining a distance to the measurement object from the number of the interference waveforms. The distance meter according to claim 2 or 5,
The conversion means has an interference waveform measured by the frequency measurement means when the reference amplitude of the oscillation waveform is A and the amplitude of the oscillation waveform when the frequency measurement means measures the frequency of the interference waveform is α × A. A distance meter obtained by multiplying a frequency obtained by multiplying 1 / α by a frequency of the converted interference waveform. The distance meter according to claim 3 or 6,
The calculation means sets the number of disturbance light signals to Nn, the frequency of the oscillation waveform one cycle before is 1 / x1 times the reference frequency and the amplitude is y1 times the reference amplitude, and the number of signals measured by the counting means at this time was a Nall _old, with y2 times the current reference amplitude amplitude at 1 / x2 times the frequency of the reference frequency of the oscillation waveform to be calculated the number of the interference waveform, the number of signals measured by the counting means at this time Is a _new distance meter, wherein the number N of the interference waveforms is calculated by N = (Nall _old− Nn × x1) / y1 = (Nall _new− Nn × x2) / y2.   Waves that have been wavelength-modulated so that the amplitude changes every period are radiated to the measurement object, and interference generated between the wave reflected back to the measurement object and the radiated wave is detected, and the detected interference information is used. Removes frequency components whose frequency does not change over a plurality of periods, converts the interference information after removing the frequency components into a value when the amplitude of the wavelength-modulated wave is a reference amplitude, and information about interference after conversion A distance measurement method characterized in that a distance to a measurement object is obtained based on the method.   A wave that has been wavelength-modulated so that at least one of frequency and amplitude changes every period is radiated to the measurement object, and the number of signals included in the output of the light receiver that converts the wave into an electrical signal is counted. The number of interference waveforms generated between the reflected wave and the radiated wave is calculated based on the result of the counting over a plurality of periods, and the distance to the measurement object is calculated based on the number of the interference waveforms. A distance measuring method characterized by obtaining. In a distance measurement method for emitting laser light to a measurement object using a semiconductor laser,
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and An oscillation procedure for modulating the oscillation wavelength of the semiconductor laser so that the amplitude of an oscillation waveform with one oscillation period and the second oscillation period as one period changes for each period;
A removal procedure for removing a frequency component whose frequency does not change over a plurality of cycles from an output signal of a light receiver that converts an optical output of the semiconductor laser into an electrical signal;
Frequency measurement for measuring the frequency of the interference waveform generated by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, which is included in the output signal of the light receiver after removing the frequency component Procedure and
A conversion procedure for converting the frequency of the interference waveform into a value when the amplitude of the oscillation waveform is a reference amplitude,
A distance measurement method comprising: a calculation procedure for obtaining a distance to the measurement object from the frequency of the converted interference waveform. In a distance measurement method for emitting laser light to a measurement object using a semiconductor laser,
The first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist alternately for at least two periods, and An oscillation procedure for modulating the oscillation wavelength of the semiconductor laser so that at least one of the frequency and the amplitude of the oscillation waveform having one oscillation period and the second oscillation period as one period changes for each period;
A counting procedure for counting the number of signals contained in the output of a light receiver that converts the optical output of the semiconductor laser into an electrical signal;
A calculation procedure for calculating the number of interference waveforms caused by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object based on the counting result of the counting procedure over a plurality of periods;
A distance measuring method comprising: a calculation procedure for obtaining a distance to the measurement object from the number of the interference waveforms.

Images