JP5545913B2 - Counting device, distance meter, counting method, and distance measuring method - Google Patents

Description

  The present invention relates to a counting device that counts the number of signals, and an interference type distance meter that determines the distance from a measurement object by measuring the number of interference waveforms using the counting device.

  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. 25 shows a composite resonator model of an FP type (Fabry-Perot type) semiconductor laser. In FIG. 25, 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. 26 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. 26, 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. 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.

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

In a conventional interference type distance meter including a self-coupling type, the number of MHPs is measured using a counting device, or the frequency of the MHP is measured using FFT (Fast Fourier Transform). I try to find the distance.
However, in a distance meter using FFT, if the change in the oscillation wavelength of the laser is not linear, there is a difference between the peak frequency calculated by FFT and the average frequency of MHP that should be originally obtained, resulting in an error in the measured distance. There was a problem.

In a distance meter using a counting device, for example, noise such as ambient light is counted as MHP, or there are MHPs that cannot be counted due to signal tooth loss, resulting in an error in the number of MHPs counted by the counting device. There is a problem that an error occurs in the measured distance.
Such a counting error is not limited to the distance meter and may occur in other counting devices as well.

  The present invention has been made in order to solve the above-described problems. A counting device and a counting method capable of correcting a counting error, and a distance meter capable of improving a distance measurement accuracy by correcting a counting error of an MHP. It is another object of the present invention to provide a distance measuring method.

The present invention relates to a counting device for counting the number of signals having a linear relationship with a specific physical quantity and having a substantially single frequency when the physical quantity is constant, and counting means for counting the number of input signals in a constant counting period. A period measuring unit that measures the period of the input signal during the counting period every time a signal is input, and a frequency distribution generator that generates a frequency distribution of the signal period during the counting period from the measurement result of the period measuring unit means and analyzes the FFT the frequency distribution, a frequency analysis means of the periodic frequency distribution to determine the frequency spectrum maximum value appears in the frequency corresponding to the spacing of the maxima of the frequency distribution, the frequency of the periodic frequency distribution from the maximum value analyzing means appeared to the frequency spectrum obtained representative value deriving means for obtaining a representative value of a distribution of periods of the input signal, from the frequency distribution, a first of said representative value The sum Ns of the frequencies of the class that is less than or equal to a constant multiple and the sum Nw of the frequencies of the class that are greater than or equal to the second predetermined number times the representative value are obtained, and the counting means counts based on these frequencies Ns and Nw. Correction value calculating means for correcting the result.
Further, in one configuration example of the counting device of the present invention, the representative value deriving unit displays a local maximum value having the maximum intensity in the frequency spectrum obtained by the frequency analysis unit of the periodic frequency distribution as a representative of the period distribution of the input signal. It is assumed that the value is shown, and the representative value is obtained.
Further, in one configuration example of the counting device according to the present invention, the representative value deriving means represents a maximum value having the highest frequency in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution as a representative of the period distribution of the input signal. It is assumed that the value is shown, and the representative value is obtained.
Further, in one configuration example of the counting device of the present invention, the correction value calculating means obtains a corrected counting result N ′ by N ′ = N + Nw−Ns, where N is the counting result of the counting means. It is.

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. A laser driver that operates the semiconductor laser so that second oscillation periods including at least the second oscillation period alternately exist, and an interference signal between the laser light emitted from the semiconductor laser and the return light from the measurement object A light receiving device that converts the interference waveform generated by the laser light emitted from the semiconductor laser and the return light from the measurement object, and the interference waveform included in the output signal of the light receiving device. A period measuring means for measuring the period of the interference waveform during the counting period for counting the number of times each time the interference waveform is input, and a measurement result of the period measuring means from the measurement result of the period measuring means. A frequency distribution generating means for generating a frequency distribution of the periods of Wataru waveform, the frequency distribution by analyzing the FFT and cycle frequency for determining the frequency spectrum maxima in frequency corresponding to the spacing of the maxima of the frequency distribution appears A frequency analysis means for distribution, a representative value deriving means for obtaining a representative value of the period distribution of the interference waveform from a maximum value that appears in the frequency spectrum obtained by the frequency analysis means for the periodic frequency distribution , and the frequency distribution, A sum Ns of the frequencies of the class that is less than or equal to the first predetermined number times the representative value and a sum Nw of the frequencies of the class that are the second predetermined number of times or more of the representative value are obtained, and these frequencies Ns and Nw are obtained. A correction value calculating means for correcting the counting result of the counting means based on the calculation result, and a calculating means for calculating a distance from the measurement object from the counting result corrected by the correction value calculating means.

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. Included in the output signal of the laser receiver, the laser driver that operates the semiconductor laser so that the second oscillation period including at least the second oscillation period alternately exists, the optical receiver that converts the optical output of the semiconductor laser into an electrical signal, and Counting means for counting 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, and the interference waveform during the counting period for counting the number of the interference waveforms A period measuring means for measuring the period of the interference waveform, and a frequency distribution of the period of the interference waveform during the counting period from the measurement result of the period measuring means. A distribution creation means, and analyzed by FFT the frequency distribution, a frequency analysis means of the periodic frequency distribution to determine the frequency spectrum maximum value appears in the frequency corresponding to the spacing of the maxima of the frequency distribution, the cycle frequency distribution Representative value deriving means for obtaining a representative value of the distribution of the period of the interference waveform from the maximum value appearing in the frequency spectrum obtained by the frequency analysis means, and from the frequency distribution at a first predetermined number times or less of the representative value. A total sum Ns of frequencies of a certain class and a total frequency Nw of classes that are equal to or more than the second predetermined number times the representative value are obtained, and the counting result of the counting means is corrected based on these frequencies Ns and Nw. It has a correction value calculation means and a calculation means for obtaining a distance from the measurement object from the count result corrected by the correction value calculation means.
Further, in one configuration example of the distance meter of the present invention, the representative value deriving unit displays a maximum value having the maximum intensity in the frequency spectrum obtained by the frequency analysis unit of the periodic frequency distribution as a representative of the period distribution of the interference waveform. It is assumed that the value is shown, and the representative value is obtained.
Further, in one configuration example of the distance meter of the present invention, the representative value deriving means obtains a maximum value having the highest frequency in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution as a representative of the period distribution of the interference waveform. It is assumed that the value is shown, and the representative value is obtained.
Further, in one configuration example of the distance meter of the present invention, the correction value calculation means obtains the corrected count result N ′ by N ′ = N + Nw−Ns, where N is the counting result of the counting means. It is.

The counting method of the present invention includes a counting procedure for counting the number of input signals in a certain counting period, a period measuring procedure for measuring the period of the input signal in the counting period every time a signal is input, A frequency distribution creating procedure for creating a frequency distribution of the signal period during the counting period from the measurement result of the period measuring procedure, and the frequency distribution is analyzed by FFT to maximize the frequency corresponding to the interval between the maximum values of the frequency distribution. a frequency analyzing procedure of the periodic frequency distribution to determine the frequency spectrum value appears, the representative value determining a representative value of a distribution of periods of the input signal from the maximum value that appeared frequency spectrum obtained by the frequency analysis procedure of this cycle frequency distribution From the derivation procedure and the frequency distribution, the sum Ns of the frequencies of the class that is not more than a first predetermined number of times of the representative value and the frequencies of the class that are not less than the second predetermined number of times of the representative value It obtains a sum Nw, in which and a correction value calculation procedure for correcting the counting result of the counting procedure on the basis of the frequencies Ns and Nw.

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. Included in the oscillation procedure for operating the semiconductor laser to exist in the light source and the output signal of the light receiver that converts the interference light between the laser light emitted from the semiconductor laser and the return light from the measurement object into an electrical signal A counting procedure for counting the number of interference waveforms caused by the laser light emitted from the semiconductor laser and the return light from the measurement object, and the period of the interference waveform during the counting period for counting the number of interference waveforms as an interference waveform A period measurement procedure for measuring the frequency of each input, a frequency distribution creation procedure for creating a frequency distribution of the period of the interference waveform during the counting period from the measurement result of the period measurement procedure, And analyzed by FFT number distribution, and the frequency analyzing procedure of the periodic frequency distribution to determine the frequency spectrum maximum at a frequency appears corresponding to the spacing of the maxima of the frequency distribution, determined by the frequency analysis procedure of this cycle frequency distribution A representative value derivation procedure for obtaining a representative value of the distribution of the period of the interference waveform from the maximum value appearing in the frequency spectrum, and a sum of the frequencies of the class that is not more than a first predetermined number times the representative value from the frequency distribution. A correction value calculation procedure for determining Ns and a total sum Nw of the frequencies of the class that is a second predetermined number times or more of the representative value, and correcting the counting result of the counting procedure based on these frequencies Ns and Nw; And a calculation procedure for obtaining a distance from the measurement target from the count result corrected by the correction value calculation procedure.

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. An oscillation procedure for operating the semiconductor laser to be present in the laser beam, and a laser beam emitted from the semiconductor laser and an object to be measured included in an output signal of a light receiver that converts the optical output of the semiconductor laser into an electrical signal. Counting procedure for counting the number of interference waveforms caused by the self-coupling effect with the return light, and a period measuring procedure for measuring the period of the interference waveform during the counting period for counting the number of interference waveforms each time the interference waveform is input When the frequency distribution generating procedure for creating a frequency distribution of the periods of the interference waveforms during the counting interval from the measurement result of the cycle measuring procedure, and analyzed by FFT the frequency distribution, the The number distribution and frequency analysis procedure of the periodic frequency distribution to determine the frequency spectrum maximum value appears in the frequency corresponding to the spacing of the maxima of the local maximum value appearing in the frequency spectrum obtained by the frequency analysis procedure of this cycle frequency distribution A representative value derivation procedure for obtaining a representative value of the distribution of the period of the interference waveform, a total sum Ns of the frequencies of the class that is not more than a first predetermined number times the representative value, and a second value of the representative value from the frequency distribution. A correction value calculation procedure for obtaining a total sum Nw of class frequencies that is a predetermined number of times or more and correcting the counting result of the counting procedure based on these frequencies Ns and Nw, and a count corrected by this correction value calculation procedure And a calculation procedure for obtaining a distance from the measurement object from the result.

  According to the present invention, the period of the input signal during the counting period is measured, the frequency distribution of the signal period during the counting period is created from the measurement result, and the input signal period is representative from the analysis result of the frequency component of the frequency distribution. Since a value that can be regarded as a value is obtained, the true period of the input signal can be obtained even when, for example, the S / N ratio of the input signal is reduced. In the present invention, from the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum of the frequencies of the class Nw that is greater than or equal to the second predetermined number of times of the representative value are obtained. By obtaining and correcting the counting result of the counting means based on these frequencies Ns and Nw, the counting error of the counting device can be corrected by removing the influence of missing or excessive counting at the time of counting.

  In the present invention, the period of the interference waveform during the counting period is measured, a frequency distribution of the period of the interference waveform during the counting period is created from the measurement result, and the period of the interference waveform is calculated from the analysis result of the frequency component of the frequency distribution. Since a value that can be regarded as a representative value of the signal is obtained, the true period of the interference waveform can be obtained even when, for example, the signal-to-noise ratio of the signal is reduced during long-distance measurement. In the present invention, from the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum of the frequencies of the class Nw that is greater than or equal to the second predetermined number of times of the representative value are obtained. By finding and correcting the counting result of the counting means based on these frequencies Ns and Nw, it is possible to eliminate the influence of missing or excessive counting at the time of counting, and to correct the counting error of the interference waveform. In a distance meter that measures the number of interference waveforms using a counting means and obtains the distance to the measurement object, the distance measurement accuracy can be improved.

[First Embodiment]
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. The distance meter of FIG. 1 collects light from a semiconductor laser 1 that emits laser light to a measurement object 10, a photodiode 2 that is a light receiver that converts the optical output of the semiconductor laser 1 into an electrical signal, and light from the semiconductor laser 1. A light 3 that irradiates the measurement target 10 with light, collects return light from the measurement target 10 and makes it incident on the semiconductor laser 1, and a first oscillation period in which the oscillation wavelength continuously increases in the semiconductor laser 1 And a laser driver 4 that alternately repeats the second oscillation period in which the oscillation wavelength continuously decreases, a current-voltage conversion amplifier 5 that converts and amplifies the output current of the photodiode 2 into a voltage, and a current-voltage The filter circuit 6 that removes the carrier wave from the output voltage of the conversion amplifier 5, the counter 7 that counts the number of MHPs included in the output voltage of the filter circuit 6, and the distance to the measurement object 10 from the number of MHPs Having an arithmetic unit 8 for output, and a display device 9 for displaying the calculation result of the arithmetic unit 8.

  Hereinafter, for ease of explanation, it is assumed that a semiconductor laser 1 of a type that does not have a mode hopping phenomenon (VCSEL type, DFB laser type) is used.

  For example, the laser driver 4 supplies a triangular wave drive current that repeatedly increases and decreases at a constant change rate with respect to time to the semiconductor laser 1 as an injection current. As a result, the semiconductor laser 1 has a first oscillation period in which the oscillation wavelength continuously increases at a constant change rate in proportion to the magnitude of the injection current, and a first oscillation period in which the oscillation wavelength continuously decreases at a constant change rate. It is driven to alternately repeat the two oscillation periods.

  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, λb is the maximum value of the oscillation wavelength in each period, and T is the period of the triangular wave. 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.

  Laser light emitted from the semiconductor laser 1 is collected by the lens 3 and enters the measurement object 10. The light reflected by the measurement object 10 is collected by the lens 3 and enters the semiconductor laser 1. However, condensing by the lens 3 is not essential. The photodiode 2 is disposed in the semiconductor laser 1 or in the vicinity thereof, and converts the optical 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 filter circuit 6 has a function of extracting a superimposed signal from the modulated wave. 3A is a diagram schematically showing an output voltage waveform of the current-voltage conversion amplifier 5, and FIG. 3B is a diagram schematically showing an output voltage waveform of the filter circuit 6. As shown in 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. 3A, which is the output of the photodiode 2, and the MHP waveform (superposition) of FIG. (Wave) is extracted.

  The counting device 7 counts the number of MHPs included in the output voltage of the filter circuit 6 for each of the first oscillation periods t-1, t + 1, t + 3 and the second oscillation periods t, t + 2, t + 4. FIG. 4 is a block diagram showing an example of the configuration of the counting device 7. The counting device 7 includes a determination unit 71, an AND operation unit (AND) 72, a counter 73, a counting result correction unit 74, and a storage unit 75. The current-voltage conversion amplifier 5, the filter circuit 6, the determination unit 71 of the counting device 7, the AND 72, and the counter 73 constitute counting means.

  FIG. 5 is a block diagram showing an example of the configuration of the counting result correction unit 74. The counting result correction unit 74 includes a period measurement unit 740, a frequency distribution creation unit 741, a frequency distribution frequency analysis unit 742, a representative value derivation unit 743, and a correction value calculation unit 744.

  6A to 6F are diagrams for explaining the operation of the counting device 7. FIG. 6A schematically shows the waveform of the output voltage of the filter circuit 6, that is, the waveform of MHP. FIG. 6B is a diagram showing the output of the determination unit 71 corresponding to FIG. 6A, FIG. 6C is a diagram showing the gate signal GS input to the counting device 7, and FIG. Is a diagram showing the counting result of the counter 73 corresponding to FIG. 6 (B), FIG. 6 (E) is a diagram showing the clock signal CLK input to the counting device 7, and FIG. 6 (F) is FIG. 6 (B). It is a figure which shows the measurement result of the corresponding period measurement part 740. FIG.

  First, the determination unit 71 of the counting device 7 determines whether the output voltage of the filter circuit 6 shown in FIG. 6A is high level (H) or low level (L), as shown in FIG. Output the judgment result. At this time, the determination unit 71 determines that the output voltage of the filter circuit 6 is high level when the output voltage becomes equal to or higher than the threshold value TH1, and the output voltage of the filter circuit 6 decreases and the threshold value TH2 (TH2 <TH1) The output of the filter circuit 6 is binarized by determining the low level when it becomes below.

  The AND 72 outputs the logical product operation result of the output of the determination unit 71 and the gate signal GS as shown in FIG. 6C, and the counter 73 counts the rise of the output of the AND 72 (FIG. 6D). . Here, the gate signal GS is a signal that rises at the beginning of the counting period (in this embodiment, each of the first oscillation period and the second oscillation period) and falls at the end of the counting period. Therefore, the counter 73 counts the number of rising edges of the output of the AND 72 during the counting period (that is, the number of rising edges of MHP).

On the other hand, the period measuring unit 740 of the counting result correcting unit 74 measures the period of the rising edge of the output of the AND 72 during the counting period (that is, the MHP period) every time a rising edge occurs. At this time, the period measuring unit 740 measures the MHP period with the period of the clock signal CLK shown in FIG. In the example of FIG. 6F, the period measurement unit 740 sequentially measures Tα, Tβ, and Tγ as the MHP period. As is apparent from FIGS. 6E and 6F, the periods Tα, Tβ, and Tγ are 5 clocks, 4 clocks, and 2 clocks, respectively. The frequency of the clock signal CLK is assumed to be sufficiently higher than the highest frequency that the MHP can take.
The storage unit 75 stores the count result of the counter 73 and the measurement result of the period measurement unit 740.

After the gate signal GS falls and the counting period ends, the frequency distribution creation unit 741 of the counting result correction unit 74 creates a frequency distribution of the MHP period during the counting period from the measurement result stored in the storage unit 75. .
Subsequently, the frequency distribution frequency analysis unit 742 of the counting result correction unit 74 analyzes the frequency component of the frequency distribution created by the frequency distribution creation unit 741. Specifically, FFT (Fast Fourier Transform) may be used as the frequency analysis method.

The purpose of the frequency distribution frequency analyzing unit 742 and the representative value deriving unit 743 described later is to obtain a value that can be regarded as a true period of the MHP.
Under normal measurement conditions, a representative value (mode or median) of the signal period distribution appears in the vicinity of the true signal period. FIG. 7 shows an example of the frequency distribution of the MHP cycle under normal measurement conditions. In the example of FIG. 7, the mode value MO and the median value ME are approximately the same as the true period 30 [samplings] of the MHP.

  On the other hand, for example, when the signal to noise ratio (Signal to Noise Ratio) is lowered during long-distance measurement, a large amount of loss occurs in the MHP waveform, and the representative value of the frequency distribution of the MHP period is far from the true period. It becomes. FIG. 8 shows an example of the frequency distribution of the MHP period when the S / N ratio is lowered. In the example of FIG. 8, the mode value MO and the median value ME do not coincide with the true period 9 [samplings] of the MHP.

  However, since the lack of MHP has a period in the vicinity of an integral multiple of the true period of MHP, the interval between the maximum values of the frequency distribution of the MHP period is approximately equal to the true period. According to the example of FIG. 8, it can be seen that the interval between the maximum values of the frequency distribution roughly matches the true period 9 [samplings] of the MHP.

Therefore, in this embodiment, by analyzing the frequency component of the frequency distribution of the MHP cycle, a value that can be regarded as the true cycle of the MHP is obtained. When the frequency distribution frequency analysis unit 742 performs frequency analysis on the frequency distribution, a maximum value appears at a frequency corresponding to the interval between the maximum values of the frequency distribution as shown in FIG.
The representative value deriving unit 743 of the counting result correcting unit 74 regards the signal having the maximum intensity in the frequency analysis result of the frequency distribution frequency analyzing unit 742 as indicating the representative value (mode or median) of the MHP cycle, A representative value T0 of the MHP cycle is obtained.

Next, the correction value calculation unit 744 of the counting result correction unit 74 calculates the total frequency Ns of the frequencies that are 0.5 times or less of the representative value T0 of the cycle from the frequency distribution created by the frequency distribution creation unit 741, and the cycle. And a total sum Nw of class frequencies that is 1.5 times or more of the representative value T0 is corrected, and the count result of the counter 73 is corrected as follows.
N ′ = N + Nw−Ns (2)
In Equation (2), N is the number of MHPs that are the counting result of the counter 73, and N ′ is the corrected counting result.

  FIG. 10 shows an example of the frequency distribution of the MHP cycle. In FIG. 10, Ts is a class value 0.5 times the representative value T0 of the period, and Tw is a class value 1.5 times the representative value T0. Needless to say, the class in FIG. 10 is a representative value of the MHP cycle. In order to simplify the description in FIG. 10, the frequency distribution between the representative values T0 and Ts and between the representative values T0 and Tw is omitted.

FIG. 11 is a diagram for explaining the principle of correcting the counting result of the counter 73. FIG. 11A is a diagram schematically showing the waveform of the output voltage of the filter circuit 6, that is, the waveform of MHP. () Is a diagram showing the counting result of the counter 73 corresponding to FIG.
Originally, the period of MHP differs depending on the distance to the measurement object 10, but if the distance to the measurement object 10 is unchanged, the MHP appears in the same period. However, due to noise, the MHP waveform may be missing or a waveform that should not be counted as a signal may be generated, resulting in an error in the number of MHPs.

  When signal loss occurs, the MHP cycle Tw at the location where the loss occurs is approximately twice the original cycle. That is, when the MHP cycle is approximately twice or more than the representative value T0, it can be determined that the signal is missing. Accordingly, the total frequency Nw of the classes having the period Tw or more is regarded as the number of missing signals, and the missing signal can be corrected by adding this Nw to the counting result N of the counter 73.

  Further, the MHP cycle Ts at the location where noise is counted is approximately 0.5 times the original cycle. That is, when the MHP cycle is approximately 0.5 times or less of the representative value, it can be determined that the signals are excessively counted. Accordingly, the sum Ns of the frequencies of the class having a period of Ts or less is regarded as the number of times that the signal is excessively counted, and the Ns is subtracted from the count result N of the counter 73, thereby correcting the erroneously counted noise.

  The above is the correction principle of the counting result shown in Expression (2). In this embodiment, Ts is set to a value that is 0.5 times the representative value T0 of the cycle, and Tw is set to a value that is 1.5 times instead of a value that is twice the representative value T0. The reason for the five times will be described later.

  The correction value calculation unit 744 outputs the corrected count result N ′ calculated by Expression (2) to the arithmetic device 8. The counting device 7 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 arithmetic device 8 obtains the distance from the measurement object 10 based on the number N ′ of MHPs measured by the counting device 7. The number of MHPs in a certain period is proportional to the measurement distance. Therefore, the relationship between the number of MHPs and the distance in a certain counting period (in this embodiment, each of the first oscillation period and the second oscillation period) is obtained in advance and registered in a database (not shown) of the arithmetic unit 8. Then, the arithmetic device 8 can obtain the distance to the measurement object 10 by obtaining the distance value corresponding to the number N ′ of MHPs measured by the counting device 7 from the database.

Alternatively, if a mathematical expression indicating the relationship between the number of MHPs and the distance in the counting period is obtained and set in advance, the arithmetic device 8 substitutes the number N ′ of MHPs measured by the counting device 7 into the mathematical formula. The distance to the measurement object 10 can be calculated. The arithmetic unit 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.
The display device 9 displays the distance (displacement) from the measurement object 10 calculated by the arithmetic device 8 in real time.

  As described above, in the present embodiment, the MHP cycle during the counting period is measured, a frequency distribution of the MHP cycle during the counting period is created from the measurement result, and the MHP is analyzed from the frequency component analysis result of the frequency distribution. Since a value that can be regarded as a representative value of the period is obtained, the true period of the MHP can be obtained even when the S / N ratio of the signal is reduced, for example, during long-distance measurement. Then, in the present embodiment, from the frequency distribution, a total frequency Ns of class frequencies that is 0.5 times or less of the representative value and a total frequency Nw of class frequencies that are 1.5 times or more of the representative value are obtained, By correcting the counting result of the counter based on these frequencies Ns and Nw, the counting error of MHP can be corrected, so that the distance measurement accuracy can be improved.

  Note that the counting device 7 and the arithmetic device 8 in the present embodiment can be realized by, for example, a computer including a CPU, a storage device, and an interface, and a program for controlling these hardware resources. 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 this embodiment in accordance with this program.

Next, the reason why the representative value of the frequency distribution of the cycle is used as the MHP reference cycle and the reason why the threshold value of the cycle when determining the frequency Nw is 1.5 times the representative value will be described.
First, correction of the counting result when the MHP cycle is divided into two because the noise is erroneously counted will be described. When the oscillation wavelength change of the semiconductor laser is linear, the period T of MHP is normally distributed around T0 obtained by dividing the measurement period Tc by the number N of MHPs (FIG. 12).

  Next, consider the period of MHP divided into two by noise. The period of MHP divided into two as a result of excessive noise counting is divided into two at a random rate, but since the period before the division is a normal distribution centered on T0, the period is 0.5T0. On the other hand, the frequency distribution is symmetrical (a in FIG. 13).

Assuming that the frequency distribution of the MHP cycle including noise is such that n% of the MHP is divided into two by the noise, the average value and the median value of the MHP cycle are calculated.
The sum of all the periods is always the measurement period Tc, and there is no change. However, when n% of MHP is divided into two periods by noise, the integral value of the frequency becomes (1 + n [%]) N. The average value of the period is (1 / (1 + n [%])) T0.

  On the other hand, when ignoring the noise distribution that overlaps the normal distribution, the cumulative frequency of the noise divided into two is twice the frequency included in the class between the median and T0. The median is a position where the area of b in FIG. 14 is twice the area of a.

Excel (registered trademark), which is Microsoft software, has an internal ratio of two-sided values between the mean value of α distribution and ασ as “(1- (1-NORMDIST (α)) * 2) * 100 [%]”. There is a function called NORMSDIST () that can be expressed. By using this function, the median value of the MHP cycle can be expressed by the following equation.
(1- (1-NORMDIST ((median-T0) / σ)) * 2)
* (100-n) / 2 = n [%] (3)

Based on the above, when the standard deviation σ is 0.02T0, and the average value T0 ′ and median value T0 ′ of the MHP period when 10% of MHP is divided into two periods by noise, the following values are calculated. It becomes like this.
T0 ′ = (1 / (1 + 0.1)) T0 = 0.91T0 (4)
T0 '= 0.995T0 (5)
Here, both the average value and the median value are represented by T0 ′. The counter value (frequency integrated value) is 1.1 N, and the count error is 10%.

  Here, consider the probability of a period that can be taken by two periods T1 and T2 (T1 ≧ T2) after an MHP of a certain period Ta is divided into two. Assuming that noise occurs randomly, T2 can take a value of 0 <T2 ≦ Ta / 2 with the same probability as shown in FIG. Similarly, T1 can take the value of T / 2 ≦ T1 <Ta with the same probability. In FIG. 15, the area of the probability distribution that T1 can take and the area of the probability distribution that T2 can take are both 1.

Since the period Ta has a normal distribution centered on T0, if Ta is regarded as a set, the frequency distribution of the probability that T2 can take is the accumulation of normal distributions with an average value of 0.5T0 and a standard deviation of 0.5σ. It has the same shape as the frequency distribution.
Further, as shown in FIG. 16, the frequency distribution of the probability that T1 can take is a cumulative frequency distribution of a normal distribution with an average value of 0.5T0 and a standard deviation of 0.5σ, and a normal distribution with an average value of T0 and a standard deviation of σ. The shape is such that the cumulative frequency distribution is superimposed. Here, the number of each of T1 and T2 is equal to the number n [%] · N of MHPs whose period is divided into two.

If the number n [%] · N of MHPs whose period is divided into two by noise can be counted, the number N of MHPs can be derived using the following equation.
N = N′−n [%] · N (6)
As shown in FIG. 17, if Tb can be set so that the number Ns of MHPs having a period equal to or less than Tb is equal to the number n [%] · N of MHPs divided into two, the period is equal to or less than Tb. By counting the number Ns of MHPs, the number n [%] · N of MHPs whose periods are divided into two can be indirectly counted.

In FIG. 17, when the frequency of the MHP cycle T2 having a cycle of Tb or more (c in FIG. 17) and the frequency of the MHP cycle T1 having a cycle of less than Tb (d in FIG. 17) are equal to or less than Tb The number of MHPs having a period is equal to the number of T2, that is, the number Ns (= n [%] · N) of MHPs whose periods are divided into two. That is, the number N of MHPs can be expressed by the following formula.
N = N′−n [%] · N = N′−Ns (7)
Since the frequency shapes of T1 and T2 are symmetric shapes with 0.5 Ta, if the determination is made with 0.5 Ta as a threshold value, the frequency Ns (= n [%] · N) of the MHP whose period is divided into two Can be counted accurately.

  Next, by counting the number of MHPs having a period of 0.5T0 or less, the number of MHPs n [%] · N whose period is divided into two can be indirectly counted. T0 cannot be calculated from the frequency distribution of the period (FIG. 13). If the MHP population is ideal and the parameter is large enough that the mode (mode) is equal to T0 as in the frequency distribution of FIG. 13, the mode can be used as T0 '.

  Here, the counting of the number n [%] · N of MHPs using the average value or the median value T0 ′ will be described. T0 ′ = y · T0 and substituting T0 ′ for T0 to obtain Ns, the frequency Ns ′ having a period smaller than 0.5T0 ′, which is determined as the number of MHPs whose periods are divided into two, is y · n [%] · N (FIG. 18).

When the average value or the median value T0 ′ is used, the corrected count value Nt is expressed as follows.
Nt = N′−Ns ′ = (1 + n [%]) N−yn [%] N
= (1+ (1-y) n [%]) N = N + (1-y) n [%] N (8)
Note that (1-y) n [%] N, which is an error after correction, is the frequency of the portion e in FIG.

Here, an example of correcting the counting result of the counter 73 using the average value or the median value T0 ′ will be described.
Assuming that the standard deviation is σ = 0.02T0 and 10% of the MHP is divided into two periods by noise (the count result is an error of 10%), the average value T0 ′ of the MHP period is 0.91T0, and the median value T0 Since 'is 0.9949T0, y when using the average value T0' is 0.91, and y when using the median value T0 'is 0.9949, and the corrected count result N' is as follows: Is calculated.
N ′ = (1 + 0.1 (1−0.91)) N = 1.09N (9)
N ′ = (1 + 0.1 (1−0.995)) N = 1.0005N (10)

  Equation (9) shows the corrected count result N 'when the average value T0' is used, and Equation (10) shows the corrected count result N 'when the median value T0' is used. The error of the count result N ′ when the average value T0 ′ is used is 0.9%, and the error of the count result N ′ when the median value T0 ′ is used is 0.05%.

Next, assuming that the standard deviation is σ = 0.05T0 and the period of the MHP is divided into two by noise (the counting result is an error of 20%), the average value T0 ′ of the MHP period is 0.83T0, Since the median value T0 ′ is 0.9682T0, y when using the average value T0 ′ is 0.83, and y when using the median value T0 ′ is 0.968, and the corrected count result N ′ is It is calculated as follows.
N ′ = (1 + 0.2 (1−0.83)) N = 1.304N (11)
N ′ = (1 + 0.2 (1−0.968)) N = 1.0064N (12)

Equation (11) shows the corrected count result N ′ when the average value T0 ′ is used, and Equation (12) shows the corrected count result N ′ when the median value T0 ′ is used. The error of the count result N ′ when the average value T0 ′ is used is 3.4%, and the error of the count result N ′ when the median value T0 ′ is used is 0.64%.
From the above, it can be seen that if the count result N is corrected using the representative value of the MHP cycle, the error in the corrected count result N ′ can be reduced.

Next, correction of the counting result when a loss occurs in the MHP waveform will be described. The period of MHP when a loss occurs during counting because the intensity of MHP is small is a normal distribution centered on T0 of the original MHP period, and therefore a normal distribution with an average value of 2T0 and a standard deviation of 2σ ( It becomes f) of FIG. Assuming that m [%] MHP is missing, the frequency of the MHP period whose period is doubled due to this missing is Nw (= m [%] · N). Further, the frequency of the period of approximately T0 after being decreased due to omission at the time of counting is g shown in FIG. 20, and the decrease in the frequency shown in h of FIG. 20 is 2Nw (= 2m [%]). Therefore, the original number N ′ of MHPs when no MHP is lost during counting can be expressed by the following equation.
N ′ = N + m [%] = N + Nw (13)

  Next, let us consider the threshold of the period when counting Nw for correcting the counting result. Here, it is assumed that p [%] is divided into two by noise out of the frequency Nw of the MHP period whose period is doubled due to omission at the time of counting. Of the missing MHPs, the frequency of the MHP period divided into two is Nw ′ (= m · p [%] · N). The frequency distribution of the period of the MHP divided into two again is as shown in FIG. When the threshold value of the period regarded as Nw is 1.5T0, the frequency of the MHP period with a period of 0.5T0 or less is 0.5Nw ′ (= 0.5p [%] · Nw), and the period is from 0.5T0. The frequency of the MHP period up to 1.5T0 is Nw ′ (= p [%] · Nw), and the frequency of the MHP period of 1.5T0 or more is 0.5 Nw ′ (= 0.5 p [%] · Nw). )

Therefore, the frequency distribution of all MHP cycles is as shown in FIG. 22. When the threshold value of Ns is 0.5T0 and the threshold value of Nw is 1.5T0, the counting result N is expressed by the following equation. Can do.
N = (N′−2Nw) + (Nw−Nw ′) + 2Nw ′ = N′−Nw + Nw ′
(14)

The corrected result from the equation (14) is as follows, and it can be seen that the original number N ′ of MHPs is calculated when no MHP is lost during the counting.
N−0.5Nw ′ + (0.5Nw ′ + (Nw−Nw ′))
= (N-Nw + Nw ') + (0.5Nw' + (Nw-Nw '))
= N '(15)

  From the above, it can be seen that the counting result N can be corrected by setting the threshold value of the cycle for obtaining the frequency Nw to 1.5 times the representative value. Similar to the case where the period of MHP is divided into two by noise, correction is performed using a representative value instead of T0, so that the same error occurs.

In the above description, the case where the MHP cycle is divided into two as a result of excessive noise counting and the case where the MHP cycle is doubled due to omission at the time of counting have been described separately, but these occur independently. Therefore, these cases are expressed as one frequency distribution as shown in FIG. When the threshold value of Ns is 0.5T0 and the threshold value of Nw is 1.5T0, the count result N can be expressed by the following equation.
N = (N′−2Nw−Ns) + (Nw−Nw ′) + 2Nw ′ + 2Ns
= N'-Nw + Nw '+ Ns (16)

The corrected result from the equation (16) is as follows, and it can be seen that the original number N ′ of MHPs when there is no omission or excessive counting at the time of counting is calculated.
N− {0.5Nw ′ + Ns} + {0.5Nw ′ + (Nw−Nw ′)}
= {N−Nw + Nw ′ + Ns} − {0.5Nw ′ + Ns}
+ {0.5 Nw ′ + (Nw−Nw ′)}
= N '(17)

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the first embodiment, the signal having the maximum intensity in the frequency analysis result of the frequency distribution frequency analysis unit 742 is regarded as indicating the representative value of the MHP cycle. However, in an extremely noisy environment, as shown in FIG. 24, not the frequency 1 / T0 corresponding to the maximum value interval of the frequency distribution of the MHP cycle, but the frequency corresponding to twice the maximum value of the frequency distribution. In some cases, 1 / (2T0) has the maximum intensity.

  Therefore, in an environment that is considered to be extremely noisy, the representative value deriving unit 743 of the counting result correcting unit 74 outputs a signal having the highest frequency among a plurality of maximum values in the frequency analysis result of the frequency distribution frequency analyzing unit 742 to the MHP. The representative value T0 of the MHP period may be obtained by regarding the representative value of the period.

In the first and second embodiments, the case where the counting device of the present invention is applied to a distance meter has been described. However, the present invention is not limited to this, and the counting device of the present invention is also applied to other fields. be able to. When the counting device of the present invention is effective, the signal to be counted has a linear relationship with a specific physical quantity (distance in the case of the first and second embodiments), and the physical quantity is constant. This is the case where the signal has a substantially single frequency.
Even if the signal is not a single frequency, the specific physical quantity to be counted is sufficiently low compared to the counting period, for example, the speed of an object vibrating at a frequency of 1/10 or less. Even when the spread of the periodic distribution is small, the counting device of the present invention is effective as a substantially single frequency.

In the first and second embodiments, the correction of the missing MHP has been described for the case where the MHP period is approximately twice the original period due to one missing. Thus, the present invention can be applied even when two or more missing parts occur. If two MHPs are missing in succession, the MHP with a period three times the median is considered to be a combination of three MHPs. In this case, if the frequency of the class that is approximately three times or more the median value of the period is obtained and this frequency is doubled, the missing MHP can be corrected. If such a way of thinking is generalized, the following equation may be used instead of equation (2).
N ′ = N + Nw1 + Nw2 + Nw3 +... -Ns (18)
Nw1 is the sum of the frequencies of the class that is 1.5 times or more of the median of the period, Nw2 is the sum of the frequencies of the class that is 2.5 or more of the median of the period, and Nw3 is about 3 of the median of the period. It is the sum of the frequency of the class that is 5 times or more.
In the first and second embodiments, the case where the present invention is applied to a self-coupled interferometer has been described. However, the present invention can also be applied to interferometers other than the self-coupled interferometer.

  The present invention can be applied to a counting device that counts the number of signals and an interference-type distance meter that measures the number of interference waveforms by using the counting device and obtains 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 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 filter circuit. It is a block diagram which shows one example of a structure of the counting device in the 1st Embodiment of this invention. It is a block diagram which shows one example of a structure of the count result correction | amendment part in the counting device of FIG. It is a figure for demonstrating operation | movement of the counting apparatus of FIG. It is a figure which shows an example of the frequency distribution of the period of the mode hop pulse in normal measurement conditions. It is a figure which shows an example of the frequency distribution of the period of the mode hop pulse at the time of S / N ratio fall. It is a frequency spectrum figure which shows the general | schematic result which frequency-analyzed the frequency distribution of the period of the mode hop pulse. It is a figure which shows one example of the frequency distribution of the period of the mode hop pulse in the 1st Embodiment of this invention. It is a figure for demonstrating the correction principle of the count result of the counter in the 1st Embodiment of this invention. It is a figure which shows frequency distribution of the period of a mode hop pulse. It is a figure which shows frequency distribution of the period of the mode hop pulse containing noise. It is a figure which shows the median of the period of the mode hop pulse containing a noise. It is a figure which shows the probability distribution of the period of the mode hop pulse by which the period was divided into two. It is a figure which shows frequency distribution of the period of the mode hop pulse by which the period was divided into two. It is a figure which shows frequency distribution of the period of the mode hop pulse by which the period was divided into two. It is a figure which shows frequency distribution of the period of the mode hop pulse by which the period was divided into two. It is a figure which shows the error after counter value correction | amendment. It is a figure which shows the frequency distribution of the period of the mode hop pulse which became a 2 times period. It is a figure which shows frequency distribution of the period of the mode hop pulse divided into two among the mode hop pulses lost at the time of counting. It is a figure which shows frequency distribution of the period of the mode hop pulse divided into two among the mode hop pulses lost at the time of counting. It is a figure which shows the frequency distribution of the period of a mode hop pulse when a loss and an excessive count generate | occur | produce simultaneously at the time of a count. It is a frequency spectrum figure which shows the other general result which frequency-analyzed the frequency distribution of the period of the mode hop pulse. 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.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Photodiode, 3 ... Lens, 4 ... Laser driver, 5 ... Current-voltage conversion amplifier, 6 ... Filter circuit, 7 ... Counting device, 8 ... Arithmetic unit, 9 ... Display device, 10 ... Measurement Object 71, determination unit 72, logical product operation unit 73, counter, 74, counting result correction unit, 75, storage unit, 740, period measurement unit, 741, frequency distribution creation unit, 742, frequency distribution frequency analysis unit 743 ... representative value deriving unit, 744 ... correction value calculating unit.

Claims (18)

In a counting device that counts the number of signals having a linear relationship with a specific physical quantity and having a substantially single frequency when the physical quantity is constant,
Counting means for counting the number of input signals in a certain counting period;
Period measuring means for measuring the period of the input signal during the counting period each time a signal is input;
Frequency distribution creating means for creating a frequency distribution of the signal period during the counting period from the measurement result of the period measuring means,
And analyzed by FFT the frequency distribution, a frequency analysis means of the periodic frequency distribution to determine the frequency spectrum maximum value appears in the frequency corresponding to the spacing of the maxima of the frequency distribution,
Representative value deriving means for obtaining a representative value of the distribution of the period of the input signal from the maximum value appearing in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution;
From the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum Nw of the frequencies of the class that are greater than or equal to the second predetermined number of times of the representative value are obtained, and And a correction value calculating means for correcting the counting result of the counting means based on the frequencies Ns and Nw. The counting device according to claim 1, wherein
The representative value deriving means regards the maximum value having the maximum intensity in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution as a representative value of the period distribution of the input signal, and obtains the representative value. A counting device characterized by. The counting device according to claim 1, wherein
The representative value deriving means regards the maximum value having the highest frequency in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution as the representative value of the period distribution of the input signal, and obtains the representative value. A counting device characterized by. The counting device according to any one of claims 1 to 3,
The said correction value calculation means calculates | requires the count result N 'after correction | amendment by N' = N + Nw-Ns when the count result of the said count means is set to N. The counting apparatus characterized by the above-mentioned. A semiconductor laser that emits laser light to the object to be measured;
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. A laser driver,
A light receiver that converts interference light between 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 interference waveforms 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;
A period measuring means for measuring a period of the interference waveform during a counting period for counting the number of the interference waveforms every time the interference waveform is input;
Frequency distribution creating means for creating a frequency distribution of the period of the interference waveform during the counting period from the measurement result of the period measuring means,
And analyzed by FFT the frequency distribution, a frequency analysis means of the periodic frequency distribution to determine the frequency spectrum maximum value appears in the frequency corresponding to the spacing of the maxima of the frequency distribution,
Representative value deriving means for obtaining a representative value of the period distribution of the interference waveform from the maximum value appearing in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution;
From the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum Nw of the frequencies of the class that are greater than or equal to the second predetermined number of times of the representative value are obtained, and Correction value calculating means for correcting the counting result of the counting means based on the frequencies Ns and Nw of
A distance meter comprising: a calculation unit that obtains a distance from the measurement object from a count result corrected by the correction value calculation unit. A semiconductor laser that emits laser light to the object to be measured;
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. A laser driver,
A light receiver for converting the optical output of the semiconductor laser into an electrical signal;
Counting means for counting 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, included in the output signal of the light receiver,
A period measuring means for measuring a period of the interference waveform during a counting period for counting the number of the interference waveforms every time the interference waveform is input;
Frequency distribution creating means for creating a frequency distribution of the period of the interference waveform during the counting period from the measurement result of the period measuring means,
And analyzed by FFT the frequency distribution, a frequency analysis means of the periodic frequency distribution to determine the frequency spectrum maximum value appears in the frequency corresponding to the spacing of the maxima of the frequency distribution,
Representative value deriving means for obtaining a representative value of the period distribution of the interference waveform from the maximum value appearing in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution;
From the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum Nw of the frequencies of the class that are greater than or equal to the second predetermined number of times of the representative value are obtained, and Correction value calculating means for correcting the counting result of the counting means based on the frequencies Ns and Nw of
A distance meter comprising: a calculation unit that obtains a distance from the measurement object from a count result corrected by the correction value calculation unit. The distance meter according to claim 5 or 6,
The representative value deriving means regards the maximum value having the maximum intensity in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution as a representative value of the period distribution of the interference waveform, and obtains the representative value. Distance meter characterized by. The distance meter according to claim 5 or 6,
The representative value deriving means regards the maximum value having the highest frequency in the frequency spectrum obtained by the frequency analysis means of the periodic frequency distribution as a representative value of the period distribution of the interference waveform, and obtains the representative value. Distance meter characterized by. The distance meter according to any one of claims 6 to 8,
The correction value calculating means obtains the corrected count result N ′ by N ′ = N + Nw−Ns, where N is the count result of the counting means. In a counting method for counting the number of signals having a linear relationship with a specific physical quantity and having a substantially single frequency when the physical quantity is constant,
A counting procedure for counting the number of input signals in a certain counting period;
A period measurement procedure for measuring the period of the input signal during the counting period each time a signal is input;
A frequency distribution creating procedure for creating a frequency distribution of the signal period during the counting period from the measurement result of the period measuring procedure;
Analyzing the frequency distribution by FFT to obtain a frequency analysis procedure of a periodic frequency distribution to obtain a frequency spectrum in which a maximum value appears at a frequency corresponding to the interval between the maximum values of the frequency distribution;
A representative value derivation procedure for obtaining a representative value of the period distribution of the input signal from the maximum value that appears in the frequency spectrum obtained by the frequency analysis procedure of the periodic frequency distribution;
From the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum Nw of the frequencies of the class that are greater than or equal to the second predetermined number of times of the representative value are obtained, and And a correction value calculation procedure for correcting the counting result of the counting procedure based on the frequencies Ns and Nw. The counting method according to claim 10, wherein
In the representative value deriving procedure, the maximum value having the maximum intensity in the frequency spectrum obtained by the frequency analysis procedure of the periodic frequency distribution is regarded as indicating the representative value of the period distribution of the input signal, and the representative value is obtained. A counting method characterized by the above. The counting method according to claim 10, wherein
In the representative value derivation procedure, the maximum value having the highest frequency in the frequency spectrum obtained by the frequency analysis procedure of the periodic frequency distribution is regarded as indicating the representative value of the period distribution of the input signal, and the representative value is obtained. A counting method characterized by the above. The counting method according to any one of claims 10 to 12,
In the correction value calculating procedure, when the counting result of the counting procedure is N, the corrected counting result N ′ is obtained by N ′ = N + Nw−Ns. In a distance measurement method for emitting laser light to a measurement object using a semiconductor laser,
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. Oscillation procedure
The laser light emitted from the semiconductor laser and the measurement object included in the output signal of the light receiver that converts the interference light between the laser light emitted from the semiconductor laser and the return light from the measurement object into an electrical signal. A counting procedure for counting the number of interference waveforms caused by the return light of
A period measurement procedure for measuring a period of the interference waveform during a counting period for counting the number of the interference waveforms every time the interference waveform is input;
A frequency distribution creating procedure for creating a frequency distribution of the period of the interference waveform during the counting period from the measurement result of this cycle measuring procedure,
Analyzing the frequency distribution by FFT to obtain a frequency analysis procedure of a periodic frequency distribution to obtain a frequency spectrum in which a maximum value appears at a frequency corresponding to the interval between the maximum values of the frequency distribution;
A representative value derivation procedure for obtaining a representative value of the period distribution of the interference waveform from a local maximum value appearing in the frequency spectrum obtained by the frequency analysis procedure of the periodic frequency distribution;
From the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum Nw of the frequencies of the class that are greater than or equal to the second predetermined number of times of the representative value are obtained, and A correction value calculation procedure for correcting the counting result of the counting procedure based on the frequencies Ns and Nw of
A distance measurement method comprising: a calculation procedure for obtaining a distance to the measurement object from a count result corrected by the correction value calculation procedure. In a distance measurement method for emitting laser light to a measurement object using a semiconductor laser,
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. Oscillation procedure
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, included in the output signal of the light receiver that converts the optical output of the semiconductor laser into an electrical signal. Counting procedure;
A period measurement procedure for measuring a period of the interference waveform during a counting period for counting the number of the interference waveforms every time the interference waveform is input;
A frequency distribution creating procedure for creating a frequency distribution of the period of the interference waveform during the counting period from the measurement result of this cycle measuring procedure,
Analyzing the frequency distribution by FFT to obtain a frequency analysis procedure of a periodic frequency distribution to obtain a frequency spectrum in which a maximum value appears at a frequency corresponding to the interval between the maximum values of the frequency distribution;
A representative value derivation procedure for obtaining a representative value of the period distribution of the interference waveform from a local maximum value appearing in the frequency spectrum obtained by the frequency analysis procedure of the periodic frequency distribution;
From the frequency distribution, the sum Ns of the frequencies of the class that is less than or equal to the first predetermined number of times of the representative value and the sum Nw of the frequencies of the class that are greater than or equal to the second predetermined number of times of the representative value are obtained, and A correction value calculation procedure for correcting the counting result of the counting procedure based on the frequencies Ns and Nw of
A distance measurement method comprising: a calculation procedure for obtaining a distance to the measurement object from a count result corrected by the correction value calculation procedure. The distance measuring method according to claim 14 or 15,
In the representative value deriving procedure, the maximum value having the maximum intensity in the frequency spectrum obtained by the frequency analysis procedure of the periodic frequency distribution is regarded as indicating the representative value of the period distribution of the interference waveform, and the representative value is obtained. A distance measurement method characterized by The distance measuring method according to claim 14 or 15,
In the representative value derivation procedure, the maximum value having the highest frequency in the frequency spectrum obtained by the frequency analysis procedure of the periodic frequency distribution is regarded as a representative value of the period distribution of the interference waveform, and the representative value is obtained. A distance measurement method characterized by The distance measuring method according to any one of claims 14 to 17,
In the correction value calculation procedure, when the counting result of the counting procedure is N, the corrected counting result N ′ is obtained by N ′ = N + Nw−Ns.

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