JP2010117144A - Physical quantity sensor and method for measuring physical quantity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the displacement and the speed of an object with high resolution and to shorten the time required for measurement. <P>SOLUTION: A physical quantity sensor includes: a semiconductor laser 1; a laser driver 4 which makes the laser 1 operate so that at least one of a first oscillation duration wherein an oscillation wavelength increases and a second oscillation duration wherein the oscillation wavelength decreases is present repeatedly; a photodiode 2 which detects an electric signal including an interference wavelength produced by a self-coupling effect of laser light emitted from the laser 1 and an optical return from the object 10; a current-voltage converting amplification part 5; a signal extracting part 7 which measures the period of the interference waveform included in an output of the current-voltage converting amplification part 5; and an operation part 8 which computes at least one of the displacement and the speed of the object 10, based on the variation to the reference period of the individual period measured by the signal extracting part 7 and also corrects the reference period according to the variation characteristic of the period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a physical quantity sensor and a physical quantity measuring method for measuring displacement and velocity of an object from information on interference caused by a self-coupling effect between laser light emitted from a semiconductor laser and return light from the object.

  Displacement (velocity) measurement methods using the interference principle, such as FMCW (Frequency Modulated Continuous Wave) radar, standing wave radar, and self-mixing laser sensor, In calculating the velocity, signal processing such as FFT (Fast Fourier Transform) or interference fringe counting processing is generally used. However, in order to realize high resolution by FFT, there is a problem that long sampling time and data with a high sampling period are required, and enormous processing time is required. In addition, in the interference fringe counting process, it is necessary to physically vibrate the sensor or analyze the amplitude of the interference fringe in order to measure a displacement of less than a half wavelength, which is the periodic motion of the measurement target. There is a problem that only vibrations can be measured, and there is another problem that it takes time to count interference fringes.

  On the other hand, the inventor has proposed a wavelength modulation type laser measuring instrument using the self-coupling effect of a semiconductor laser (see Patent Document 1). The configuration of this laser measuring instrument is shown in FIG. 13 includes a semiconductor laser 201 that emits laser light to an object 210, a photodiode 202 that converts the light output of the semiconductor laser 201 into an electrical signal, and the light from the semiconductor laser 201 that collects light. 210 irradiates the lens 210 and collects the return light from the object 210 and makes it incident on the semiconductor laser 201. The first oscillation period and the oscillation wavelength continuously increase in the semiconductor laser 201. A laser driver 204 that alternately repeats a second oscillation period that decreases in time, a current-voltage conversion amplifier 205 that converts and amplifies the output current of the photodiode 202 into a voltage, and an output voltage of the current-voltage conversion amplifier 205 Is extracted twice, and a counting circuit 207 that counts the number of MHPs included in the output voltage of the signal extraction circuit 206 , Having an arithmetic unit 208 which calculates the speed of the distance and the object 210 with the object 210, a display device 209 for displaying the calculation result of the arithmetic unit 208.

  The laser driver 204 supplies a triangular wave drive current that repeatedly increases and decreases at a constant change rate with respect to time to the semiconductor laser 201 as an injection current. Accordingly, the semiconductor laser 201 alternately repeats the first oscillation period in which the oscillation wavelength continuously increases at a constant change rate and the second oscillation period in which the oscillation wavelength continuously decreases at a constant change rate. To be driven. FIG. 14 is a diagram showing the change over time of the oscillation wavelength of the semiconductor laser 201. In FIG. 14, P1 is the first oscillation period, P2 is the second 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 Tt is the period of the triangular wave.

  Laser light emitted from the semiconductor laser 201 is collected by the lens 203 and enters the object 210. The light reflected by the object 210 is collected by the lens 203 and enters the semiconductor laser 201. The photodiode 202 converts the optical output of the semiconductor laser 201 into a current. The current-voltage conversion amplifier 205 converts the output current of the photodiode 202 into a voltage and amplifies it, and the signal extraction circuit 206 differentiates the output voltage of the current-voltage conversion amplifier 205 twice. The counting circuit 207 counts the number of mode pop pulses (MHP) included in the output voltage of the signal extraction circuit 206 for each of the first oscillation period P1 and the second oscillation period P2. Based on the minimum oscillation wavelength λa and the maximum oscillation wavelength λb of the semiconductor laser 201, the number of MHPs in the first oscillation period P1, and the number of MHPs in the second oscillation period P2, the arithmetic unit 208 The speed of the object 210 is calculated. According to such a self-coupled laser measuring instrument, it is possible to perform displacement measurement with a resolution of about half a wavelength of the semiconductor laser 201 and distance measurement with a resolution inversely proportional to the wavelength modulation amount of the semiconductor laser 201.

JP 2006-31080 A

  According to the self-coupled laser measuring instrument, it is possible to measure the displacement and speed of the measurement object with a higher resolution than conventional FMCW radars, standing wave radars, self-mixing laser sensors, and the like. However, a self-coupled laser measuring instrument requires a certain amount of measurement time (in the example of Patent Document 1, a half cycle of a carrier wave of oscillation wavelength modulation of a semiconductor laser) in the same manner as FFT, in calculating displacement and speed. Therefore, there is a problem that a measurement error occurs in the measurement of the measurement object whose speed change is fast. Further, since it is necessary to count the number of MHPs in signal processing, there is a problem that it is difficult to realize a resolution of less than a half wavelength of the semiconductor laser.

  The present invention has been made to solve the above-described problems, and provides a physical quantity sensor and a physical quantity measuring method capable of measuring the displacement and speed of an object with high resolution and reducing the time required for the measurement. For the purpose.

The physical quantity sensor of the present invention includes a semiconductor laser that emits laser light to a measurement target, a first oscillation period in which the oscillation wavelength continuously increases monotonously, and a second oscillation period in which the oscillation wavelength continuously decreases monotonously. An oscillation wavelength modulation means for operating the semiconductor laser so that at least one of them repeatedly exists, and an electrical signal including an interference waveform generated by a self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement target Detection means for detecting the signal, signal extraction means for measuring the period of the interference waveform included in the output signal of the detection means every time the interference waveform is input, and a reference period of each period measured by the signal extraction means A physical quantity calculating means for calculating at least one of a displacement and a velocity of the measurement object based on a change amount for the measurement object, and a change in the period measured by the signal extracting means. It is characterized in further comprising a period correcting means for correcting the reference period according to the characteristics.
Further, in one configuration example of the physical quantity sensor of the present invention, the physical quantity calculation means includes a sampling clock frequency for measuring a period of the interference waveform, the reference period, an average wavelength of the semiconductor laser, and the signal extraction means. And calculating at least one of the displacement and speed of the measurement object from the amount of change of the period of the interference waveform measured with respect to the reference period.

Moreover, in one configuration example of the physical quantity sensor of the present invention, the period correction unit is configured such that the time when the period of the interference waveform is equal to or greater than the reference period is equal to the time when the period of the interference waveform is equal to or less than the reference period. Thus, the reference period is corrected.
Further, in one configuration example of the physical quantity sensor of the present invention, the physical quantity calculation unit calculates at least a displacement of the measurement target, and the period correction unit includes the period when the period of the interference waveform is equal to or greater than the reference period. The reference period is corrected so that an integral value of displacement and an integral value of the displacement when the period of the interference waveform is equal to or less than the reference period are equal.
Further, in one configuration example of the physical quantity sensor of the present invention, the period correction unit obtains an average value of the period of the interference waveform in one period of the period change of the interference waveform, and uses the average value as a new reference period. It is characterized by doing.

Further, in one configuration example of the physical quantity sensor of the present invention, the physical quantity calculation means sets the period of the interference waveform when the measurement object is stationary as an initial value of the reference period. is there.
Moreover, in one configuration example of the physical quantity sensor of the present invention, the counting unit further counts the number of the interference waveforms included in the output signal of the detection unit for each of the first oscillation period and the second oscillation period. A distance calculating means for calculating a distance from the object to be measured from a minimum oscillation wavelength, a maximum oscillation wavelength and a counting result of the counting means in a period in which the number of interference waveforms is counted by the counting means, and the distance calculating means calculates Period calculation means for obtaining the period of the interference waveform from the measured distance, wherein the physical quantity calculation means uses the period obtained by the period calculation means as an initial value of the reference period.

  Further, the physical quantity measuring method of the present invention is a semiconductor in which at least one of the first oscillation period in which the oscillation wavelength continuously increases monotonically and the second oscillation period in which the oscillation wavelength continuously decreases monotonously exists. An oscillation procedure for operating the laser, a detection procedure for detecting an electrical signal including an interference waveform caused by a self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, and the detection procedure Based on the signal extraction procedure for measuring the period of the interference waveform included in the output signal every time the interference waveform is input, and the amount of change of each period measured in the signal extraction procedure with respect to the reference period, the measurement target A physical quantity calculation procedure for calculating at least one of displacement and velocity of the signal, and a period correction for correcting the reference period according to a change characteristic of the period measured by the signal extraction procedure It is characterized in further comprising an order.

  According to the present invention, the displacement and speed of the measurement target can be measured with higher resolution than before by calculating based on the amount of change of the period of each measured interference waveform with respect to the reference period. Further, in the conventional self-coupled laser measuring instrument, it takes a measurement time of a half cycle of the carrier wave, but in the present invention, the displacement and speed of the measurement object can be obtained from the period of each interference waveform. Therefore, the time required for measurement can be greatly shortened, and it is possible to deal with a measurement object whose speed changes rapidly. Further, in the present invention, it is possible to avoid a decrease in measurement accuracy of displacement and speed by correcting the reference period according to the change characteristic of the period of the interference waveform.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a physical quantity sensor according to the first embodiment of the present invention.
The physical quantity sensor in FIG. 1 condenses the light from the semiconductor laser 1 that emits laser light to the object 10 to be measured, the photodiode 2 that converts the light output of the semiconductor laser 1 into an electrical signal, and the light from the semiconductor laser 1. The lens 3 that collects the return light from the object 10 and makes it incident on the semiconductor laser 1, the laser driver 4 that serves as an oscillation wavelength modulation means for driving the semiconductor laser 1, and the output current of the photodiode 2 A current-voltage conversion amplification unit 5 that converts and amplifies the voltage, a filter unit 6 that removes a carrier wave from the output voltage of the current-voltage conversion amplification unit 5, and a self-coupled signal included in the output voltage of the filter unit 6. A signal extraction unit 7 that measures the period of a mode hop pulse (hereinafter referred to as MHP), and an operation that calculates the displacement and speed of the object 10 based on the individual periods measured by the signal extraction unit 7. Has a part 8, and a display unit 9 for displaying the calculation result of the calculating unit 8.

  The photodiode 2 and the current-voltage conversion amplification unit 5 constitute detection means. 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.

  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 P1 in which the oscillation wavelength continuously increases at a constant change rate in proportion to the magnitude of the injection current, and the oscillation wavelength continuously decreases at a constant change rate. It is driven to alternately repeat the second oscillation period P2. The time change of the oscillation wavelength of the semiconductor laser 1 at this time is as shown in FIG. In the present embodiment, the rate of change of the oscillation wavelength of the semiconductor laser 1 needs to be constant.

  Laser light emitted from the semiconductor laser 1 is collected by the lens 3 and enters the object 10. The light reflected by the 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 amplification unit 5 converts the output current of the photodiode 2 into a voltage and amplifies it.

  The filter unit 6 has a function of extracting a superimposed signal from the modulated wave. FIG. 2A is a diagram schematically showing the output voltage waveform of the current-voltage conversion amplification unit 5, and FIG. 2B is a diagram schematically showing the output voltage waveform of the filter unit 6. These figures are obtained by removing the oscillation waveform (carrier wave) of the semiconductor laser 1 of FIG. 2 from the waveform (modulated wave) of FIG. 2A corresponding to the output of the photodiode 2, and the MHP of FIG. A process of extracting a waveform (interference waveform) is shown.

Next, the signal extraction unit 7 measures the period of MHP included in the output voltage of the filter unit 6 every time MHP is generated. Here, the MHP that is a self-coupled signal will be described. As shown in FIG. 3, when the distance from the mirror layer 1013 to the object 10 is L and the oscillation wavelength of the laser is λ, the return light from the object 10 and the optical resonance of the semiconductor laser 1 are satisfied when the following resonance conditions are satisfied. The laser light in the chamber strengthens and the laser output increases slightly.
L = qλ / 2 (1)
In Formula (1), q is an integer. This phenomenon can be sufficiently observed even if the scattered light from the object 10 is extremely weak, because the apparent reflectance in the resonator of the semiconductor laser 1 increases, causing an amplification effect.

  FIG. 4 is a diagram showing the relationship between the oscillation wavelength and the output waveform of the photodiode 2 when the oscillation wavelength of the semiconductor laser 1 is changed at a certain rate. When L = qλ / 2 shown in Expression (1) is satisfied, the phase difference between the return light and the laser light in the optical resonator becomes 0 ° (the same phase), and the return light and the optical resonator The laser beam is the most intense, and when L = qλ / 2 + λ / 4, the phase difference is 180 ° (reverse phase), and the return light and the laser beam in the optical resonator are most weakened. Therefore, when the oscillation wavelength of the semiconductor laser 1 is changed, a place where the laser output becomes stronger and a place where the laser output becomes weaker appear alternately. When the laser output at this time is detected by the photodiode 2, as shown in FIG. A stepped waveform with a constant period can be obtained. Such a waveform is generally called an interference fringe. Each stepped waveform, that is, each interference fringe is MHP. As described above, when the oscillation wavelength of the semiconductor laser 1 is changed for a certain period of time, the number of MHPs changes in proportion to the measurement distance.

FIG. 5 is a block diagram illustrating a configuration example of the signal extraction unit 7. The signal extraction unit 7 includes a binarization unit 70 and a period measurement unit 71.
6 (A) to 6 (D) are diagrams for explaining the operation of the signal extraction unit 7. FIG. 6 (A) schematically shows the waveform of the output voltage of the filter unit 6, that is, the waveform of MHP. 6B is a diagram illustrating an output of the binarization unit 70 corresponding to FIG. 6A, and FIG. 6C is a diagram illustrating a sampling clock CLK input to the signal extraction unit 7. 6 (D) is a diagram illustrating a measurement result of the period measurement unit 71 corresponding to FIG. 6 (B).

  First, the binarization unit 70 of the signal extraction unit 7 determines whether the output voltage of the filter unit 6 shown in FIG. 6A is high level (H) or low level (L), and FIG. A determination result such as At this time, the binarizing unit 70 determines that the output voltage of the filter unit 6 is high level when the output voltage is equal to or higher than the threshold value TH1, and the output voltage of the filter unit 6 is decreased to decrease the threshold value TH2. By determining that the level is low when (TH2 <TH1) or less, the output of the filter unit 6 is binarized.

  The period measuring unit 71 measures the period of the rising edge (that is, the MHP period) of the output of the binarizing unit 70 every time a rising edge occurs. At this time, the period measuring unit 71 measures the MHP period with the period of the sampling clock CLK shown in FIG. 6C as one unit. In the example of FIG. 6D, the period measurement unit 71 sequentially measures Tα, Tβ, and Tγ as the MHP period. As is apparent from FIGS. 6C and 6D, the sizes of the periods Tα, Tβ, and Tγ are 5 [samplings], 4 [samplings], and 2 [samplings], respectively. The frequency of the sampling clock CLK is assumed to be sufficiently higher than the highest frequency that the MHP can take.

Next, the calculation unit 8 calculates the displacement and speed of the object 10 from the change in the cycle of each MHP based on the measurement result of the signal extraction unit 7.
FIG. 7 is a block diagram illustrating a configuration example of the calculation unit 8. The calculation unit 8 includes a physical quantity calculation unit 80, a storage unit 81, and a period correction unit 82.

When the sampling clock frequency is fad [Hz], the reference period is T0 [samplings], the oscillation average wavelength of the semiconductor laser 1 is λ [m], and the MHP period to be calculated is n [samplings] longer than the reference period T0. Then, the displacement D [m] of the object 10 in the period of the MHP to be calculated is as follows.
D = n × λ / (2 × T0) (2)

  The initial value of the reference period T0 is the MHP period when the object 10 is stationary, or the MHP period at the calculated distance. When the MHP cycle to be calculated is shortened by n [samplings] from the reference cycle T0, the sign of the period change amount n in equation (2) may be negative. In the first oscillation period P1 in which the oscillation wavelength of the semiconductor laser 1 increases, when the displacement D is positive, the moving direction of the object 10 is a direction away from the semiconductor laser 1, and when the displacement D is negative, the moving of the object 10 is performed. The direction is a direction approaching the semiconductor laser 1. In the second oscillation period P2 in which the oscillation wavelength decreases, when the displacement D is positive, the moving direction of the object 10 is a direction approaching the semiconductor laser 1, and when the displacement D is negative, the moving direction of the object 10 is. Is a direction away from the semiconductor laser 1.

Further, since the cycle of the MHP to be calculated is (T0 + n) / fad, the velocity V [m / s] of the object 10 in the cycle of the MHP to be calculated is as follows.
V = n × λ / (2 × T0) × fad / (T0 + n) (3)

The physical quantity calculation unit 80 of the calculation unit 8 can calculate the displacement D of the object 10 by Expression (2), and can calculate the velocity V of the object 10 by Expression (3). For example, the frequency fad of the sampling clock is 16 [MHz], the reference period T0 is 160 [samplings], the average wavelength of the semiconductor laser 1 is 850 [nm], and the period of the MHP to be calculated is 1 [samplings] longer than the reference period T0. Then, the displacement D of the object 10 in the MHP cycle to be calculated can be calculated as 5.31 [nm], and the velocity V can be calculated as 1.05 [mm / s]. The physical quantity calculation unit 80 performs the above calculation process every time MHP occurs.
The display unit 9 displays the calculation result of the calculation unit 8.

  Here, the number of MHPs related to the distance from the object 10 per half cycle of the oscillation wavelength modulated carrier wave (triangular wave) of the semiconductor laser 1 is Nl. If the absolute value of the average velocity of the object 10 is converted to displacement per half cycle of the carrier wave, λ / 2 × Na, the number of MHPs per carrier half cycle is Nl + Na or Nl−Na. When the displacement per carrier half cycle is moving at a speed of λ / 2 × Nb, the number of MHPs per carrier half cycle is Nl + Nb or Nl−Nb, so the MHP cycle corresponding to this number is observed. . In order to obtain the displacement D and speed V of the object 10, the number of MHPs per half cycle of the carrier wave is calculated backward from each MHP period, and the displacement D and speed V of the object 10 are calculated from the number of MHPs. The above equations (2) and (3) are based on such a derivation principle. In addition, said average speed is an average speed between a certain one MHP.

  In the self-coupled laser measuring instrument disclosed in Patent Document 1, the resolution of the displacement and velocity of the object is about half the wavelength λ / 2 of the semiconductor laser. On the other hand, in the present embodiment, the resolution of the displacement D and the velocity V is λ / 2 × n / T0, so that a resolution of less than half wavelength λ / 2 can be realized, and measurement with higher resolution than in the past is possible. Can be realized.

  Next, correction of the reference period T0 will be described. As described above, according to the present embodiment, high-resolution measurement can be realized, but on the other hand, the resolution of the reference period T0 tends to be low and the accuracy tends to decrease, and the absolute accuracy of the displacement D and the velocity V is low. May be reduced. Therefore, in the present embodiment, the reference period T0 is corrected to avoid a decrease in measurement accuracy of the displacement D and the speed V.

  First, the storage unit 81 stores the measurement result of the signal extraction unit 7. The period correction unit 82 corrects the reference period T0 according to the change characteristic of the MHP period measured by the signal extraction unit 7 and stored in the storage unit 81. FIGS. 8A and 8B are diagrams for explaining the operation of the cycle correction unit 82, and are diagrams illustrating an example of a change in the cycle of MHP. When the object 10 is vibrating, the period of MHP changes in a sine wave shape as shown in FIGS. 8A and 8B.

  The displacement direction of the object 10 can be determined by the magnitude relationship with the reference period T0. In the first oscillation period P1 in which the oscillation wavelength of the semiconductor laser 1 increases, when the MHP period is longer than the reference period T0, the moving direction of the object 10 is a direction away from the semiconductor laser 1, and the MHP period is the reference period. When the period is shorter than T0, the moving direction of the object 10 is a direction approaching the semiconductor laser 1. On the other hand, in the second oscillation period P2 in which the oscillation wavelength decreases, when the MHP cycle is longer than the reference cycle T0, the moving direction of the object 10 is a direction approaching the semiconductor laser 1, and the MHP cycle is the reference cycle. When shorter than T0, the moving direction of the object 10 is a direction away from the semiconductor laser 1.

Here, if the reference period T0 deviates from the original value, as shown in FIG. 8A, a time t1 when the MHP period is equal to or greater than the reference period T0 and a time t2 when the MHP period is equal to or less than the reference period T0. There will be a difference.
Therefore, the cycle correction unit 82 corrects the reference cycle T0 so that the time t1 when the MHP cycle is equal to or greater than the reference cycle T0 is equal to the time t2 when the MHP cycle is equal to or less than the reference cycle T0. Is set in the physical quantity calculation unit 80. When the reference period T0 is corrected in this way, the times t1 and t2 become equal as shown in FIG. 8B. As a result, when the average value of the displacement D of the object 10 in one period of the MHP period change (one period of vibration of the object 10) is obtained, this average value becomes zero. The cycle correction unit 82 performs the correction of the reference cycle T0 as described above for each cycle of the MHP cycle change.

  As described above, in the present embodiment, the displacement D and the velocity V of the object 10 can be measured with higher resolution than before. Further, in the self-coupled laser measuring instrument disclosed in Patent Document 1, it takes a measurement time of a half cycle of the carrier wave, whereas in the present embodiment, the displacement of the object 10 from each MHP cycle. Since D and velocity V can be obtained, the time required for measurement can be greatly shortened, and the object 10 having a fast change in velocity can be dealt with.

  In the present embodiment, the measurement accuracy of the displacement D and the speed V is reduced by correcting the reference cycle T0 so that the average value of the displacement D of the object 10 in one cycle of the MHP cycle changes to zero. It can be avoided. In this correction method of the reference period T0, correction is performed on the assumption that the center of vibration of the object 10 is not displaced. Therefore, the vibration measurement is accurately performed without being affected by the movement of the low frequency component (including constant velocity motion) of the object 10. It can be carried out. Further, the motion of the low-frequency component of the object 10 can also be obtained by calculating the distance from the object 10 using the corrected reference period T0.

  In the present embodiment, the reference period T0 is corrected based on the time of the MHP period change. However, the reference period T0 may be corrected based on the integral value of the displacement D of the object 10. In this case, the cycle correction unit 82 makes the integral value of the displacement D when the MHP cycle is equal to or greater than the reference cycle T0 equal to the integral value of the displacement D when the MHP cycle is equal to or less than the reference cycle T0. The reference period T0 may be corrected.

Note that the period of each MHP varies in a normal distribution even when the object 10 is stationary, and therefore processing such as moving average may be performed on the calculated displacement.
Moreover, in this Embodiment, although both the displacement and speed of the object 10 are measured, it cannot be overemphasized that only either one may be measured.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, another correction method for the reference period T0 will be described. Also in the present embodiment, the configuration of the physical quantity sensor is the same as that of the first embodiment, and therefore, description will be made using the reference numerals in FIGS. FIG. 9 is a diagram for explaining the operation of the cycle correction unit 82 of the present embodiment, and is a diagram illustrating an example of a change in the cycle of MHP.

  The period correction unit 82 according to the present embodiment obtains an average value of the MHP periods in one period of the MHP period change, and sets the average value in the physical quantity calculation unit 80 as a new reference period T0. At this time, as shown in FIG. 9, the period between the maximum value of the MHP cycle and the next maximum value (or between the minimum value of the MHP cycle and the next minimum value) may be set as one cycle TC of the cycle change. Then, the rising or falling edge of the MHP period change is detected using the reference period T0 before correction as a threshold value, and between the rising edge and the next rising edge (or the falling edge and the next falling edge of the period change). (Between) and 1 period TC of the period change.

In addition, the rising or falling edge of the MHP period change is detected using a predetermined appropriate value as a threshold value, and between the rising edge and the next rising edge of the periodic change (or the falling edge of the periodic change and the next rising edge). It is good also as 1 period TC of a period change between fall. In this case, the threshold value may be a value larger than the minimum value of the MHP cycle and smaller than the maximum value. The cycle correction unit 82 performs the correction of the reference cycle T0 as described above for each cycle of the MHP cycle change.
The operation of the configuration other than the period correction unit 82 is the same as that of the first embodiment.

Thus, according to the present embodiment, the same effect as that of the first embodiment can be obtained. In the correction method of the first embodiment, since the accuracy of the initial value of the reference period T0 is required to be high, the initial value of the reference period T0 is used as the MHP period when the object 10 is stationary. It cannot be applied to the object 10 that cannot be stationary.
On the other hand, in the present embodiment, the initial value of the reference period T0 may be an appropriate value determined in advance. Therefore, according to the present embodiment, the reference period T0 can be corrected even in the case of the object 10 that cannot be stationary.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In the first embodiment, the initial value of the reference period T0 is the MHP period when the object 10 is stationary. However, the present embodiment describes another method for obtaining the initial value of the reference period T0. To do. FIG. 10 is a block diagram showing a configuration example of the calculation unit 8 according to the third embodiment of the present invention. The calculation unit 8 includes a physical quantity calculation unit 80, a storage unit 81, a cycle correction unit 82, a counting unit 83, a distance calculation unit 84, and a cycle calculation unit 85. The entire configuration of the physical quantity sensor may be the same as that of the first and second embodiments, but the change speed of the oscillation wavelength of the semiconductor laser 1 is constant, and the maximum value λb of the oscillation wavelength and the minimum value λa of the oscillation wavelength are Each of them needs to be constant, and the difference λb−λa also needs to be constant.

  The counting unit 83 counts the number of MHPs included in the output of the filter unit 6 for each of the first oscillation period P1 and the second oscillation period P2. The counting unit 83 may use a counter composed of logic gates, or may measure the frequency of MHP (that is, the number of MHPs per unit time) using FFT (Fast Fourier Transform).

  Next, the distance calculation unit 84 calculates the distance to the object 10 based on the minimum oscillation wavelength λa and the maximum oscillation wavelength λb of the semiconductor laser 1 and the number of MHPs counted by the counting unit 83. In the present embodiment, it is assumed that the state of the object 10 is either a minute displacement state that satisfies a predetermined condition or a displacement state in which the movement is larger than the minute displacement state. When the average displacement of the object 10 per oscillation period P1 and oscillation period P2 is V, the minute displacement state is a state satisfying (λb−λa) / λb> V / Lb (where Lb is time (distance at time t), the displacement state is a state satisfying (λb−λa) / λb ≦ V / Lb.

First, the distance calculation unit 84 calculates the distance candidate values Lα (t) and Lβ (t) and the speed candidate values Vα (t) and Vβ (t) at the current time t as the following equations.
Lα (t) = λa × λb × (MHP (t−1) + MHP (t))
/ {4 × (λb−λa)} (4)
Lβ (t) = λa × λb × (| MHP (t−1) −MHP (t) |)
/ {4 × (λb−λa)} (5)
Vα (t) = (MHP (t−1) −MHP (t)) × λb / 4 (6)
Vβ (t) = (MHP (t−1) + MHP (t)) × λb / 4 (7)

  In Expressions (4) to (7), MHP (t) is the number of MHPs calculated at the current time t, and MHP (t−1) is the number of MHPs calculated one time before MHP (t). is there. For example, if MHP (t) is the counting result of the first oscillation period P1, MHP (t-1) is the counting result of the second oscillation period P2, and conversely, MHP (t) is the second counting period. If it is the counting result of the oscillation period P2, the MHP (t−1) is the counting result of the first oscillation period P1.

  The candidate values Lα (t) and Vα (t) are values calculated on the assumption that the object 10 is in a minute displacement state, and the candidate values Lβ (t) and Vβ (t) are obtained when the object 10 is in a displacement state. This is a calculated value. The distance calculation unit 84 performs the calculations of the equations (4) to (7) at each time (every oscillation period) when the counting unit 83 measures the number of MHPs.

Subsequently, the distance calculation unit 84 calculates, for each of the minute displacement state and the displacement state, a history displacement that is a difference between the distance candidate value at the current time t and the distance candidate value at the immediately preceding time as follows: calculate. In the equations (8) and (9), the candidate distance values calculated one time before the current time t are Lα (t−1) and Lβ (t−1).
Vcalα (t) = Lα (t) −Lα (t−1) (8)
Vcalβ (t) = Lβ (t) −Lβ (t−1) (9)

The history displacement Vcalα (t) is a value calculated on the assumption that the object 10 is in a minute displacement state, and the history displacement Vcalβ (t) is a value calculated on the assumption that the object 10 is in a displacement state. The distance calculation unit 84 performs calculations of Expressions (8) to (9) at each time when the number of MHPs is measured by the counting unit 83. In Expressions (6) to (9), the direction in which the object 10 approaches the physical quantity sensor of the present embodiment is defined as a positive speed, and the direction in which the object 10 moves away is defined as a negative speed.
Next, the distance calculation unit 84 determines the state of the object 10 using the calculation results of Expressions (4) to (9).

  As described in Patent Document 1, the distance calculation unit 84 has a constant sign of the history displacement Vcalα (t) calculated on the assumption that the object 10 is in a minute displacement state, and the object 10 is in a minute displacement state. If the velocity candidate value Vα (t) calculated on the assumption that the velocity is equal to the average value of the absolute values of the history displacement Vcalα (t) is equal, it is determined that the object 10 is moving at a constant velocity in a minute displacement state. .

  Further, as described in Patent Document 1, the distance calculation unit 84 has a constant sign of the history displacement Vcalβ (t) calculated on the assumption that the object 10 is in the displacement state, and the object 10 is in the displacement state. If the velocity candidate value Vβ (t) calculated on the assumption that the average displacement is equal to the absolute value of the absolute value of the history displacement Vcalβ (t), it is determined that the object 10 is moving at a constant velocity in the displacement state.

  Further, as described in Patent Document 1, the distance calculation unit 84 measures the number of MHPs with the sign of the history displacement Vcalα (t) calculated on the assumption that the object 10 is in a minute displacement state. When the velocity 10 calculated by assuming that the object 10 is in a minute displacement state and the average value of the absolute values of the history displacement Vcalα (t) do not coincide with each other, the object 10 is It is determined that a movement other than a constant speed movement is performed in a minute displacement state.

  Focusing on the velocity candidate value Vβ (t), the absolute value of Vβ (t) is a constant, and this value is equal to the wavelength change rate (λb−λa) / λb of the semiconductor laser 1. Therefore, the distance calculation unit 84 assumes that the absolute value of the velocity candidate value Vβ (t) calculated on the assumption that the object 10 is in the displacement state is equal to the wavelength change rate, and that the object 10 is in the minute displacement state. If the velocity candidate value Vα (t) calculated in this way and the average value of the absolute values of the history displacement Vcalα (t) do not match, it is determined that the object 10 is moving in a minute displacement state other than the constant velocity motion. May be.

  Further, as described in Patent Document 1, the distance calculation unit 84 calculates the number of MHPs at which the sign of the history displacement Vcalβ (t) calculated on the assumption that the object 10 is in the displacement state is measured. When the velocity candidate value Vβ (t) calculated on the assumption that the object 10 is in the displacement state does not match the average value of the absolute values of the history displacement Vcalβ (t), the object 10 is in the displacement state. It is determined that the person is exercising other than the uniform speed movement.

  When attention is paid to the velocity candidate value Vα (t), the absolute value of Vα (t) is a constant, and this value is equal to the wavelength change rate (λb−λa) / λb of the semiconductor laser 1. Therefore, the distance calculation unit 84 assumes that the absolute value of the velocity candidate value Vα (t) calculated on the assumption that the object 10 is in the minute displacement state is equal to the wavelength change rate, and that the object 10 is in the displacement state. If the calculated velocity candidate value Vβ (t) and the average value of the history displacement Vcalβ (t) do not coincide with each other, it is determined that the object 10 is moving in a displaced state other than the uniform velocity motion. May be.

  The distance calculation unit 84 determines the distance from the object 10 based on the determination result. That is, when it is determined that the object 10 is moving at a constant velocity in a minute displacement state, the distance calculation unit 84 sets the distance candidate value Lα (t) as the distance from the object 10, and the object 10 is in a displacement state, etc. When it is determined that the vehicle is moving at a speed, the distance candidate value Lβ (t) is set as the distance to the object 10.

  The distance calculation unit 84 sets the distance candidate value Lα (t) as the distance from the object 10 when it is determined that the object 10 is moving in a minute displacement state other than the constant velocity movement. However, the actual distance is an average value of the distance candidate values Lα (t). Further, when it is determined that the object 10 is moving other than the constant velocity motion in the displaced state, the distance calculation unit 84 sets the distance candidate value Lβ (t) as the distance to the object 10. However, the actual distance is an average value of the distance candidate values Lβ (t).

  Next, the cycle calculating unit 85 obtains the MHP cycle from the distance calculated by the distance calculating unit 84, and sets this cycle in the physical quantity calculating unit 80 as an initial value of the reference cycle T0. The frequency of MHP is proportional to the measurement distance, and the period of MHP is inversely proportional to the measurement distance. Therefore, if the relationship between the MHP cycle and the distance is obtained in advance and registered in the database (not shown) of the cycle calculation unit 85, the cycle calculation unit 85 may correspond to the distance calculated by the distance calculation unit 84. Is obtained from the database, the MHP cycle can be obtained. Alternatively, if a mathematical expression indicating the relationship between the MHP cycle and the distance is obtained and set in advance, the cycle calculation unit 85 substitutes the distance calculated by the distance calculation unit 84 into the mathematical formula, thereby changing the MHP cycle. Can be calculated.

The operations of the physical quantity calculation unit 80, the storage unit 81, and the cycle correction unit 82 are as described in the first and second embodiments.
According to the present embodiment, even if the object 10 cannot be stationary, the initial value of the reference period T0 can be obtained.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. In the first to third embodiments, the semiconductor laser 1 is oscillated in a triangular wave shape. However, the present invention is not limited to this, and the semiconductor laser 1 in the first and second embodiments as shown in FIG. May be oscillated in a sawtooth shape. That is, in the present embodiment, the semiconductor laser 1 may be operated so that either the first oscillation period P1 or the second oscillation period P2 exists repeatedly. However, in the third embodiment, it is necessary to oscillate the semiconductor laser 1 in a triangular wave shape.

  Even when the semiconductor laser 1 oscillates in a sawtooth shape as in the present embodiment, the rate of change of the oscillation wavelength of the semiconductor laser 1 needs to be constant. The operation in the first oscillation period P1 or the second oscillation period P2 is the same as in the case of triangular wave oscillation. As shown in FIG. 11, in the case of sawtooth oscillation in which only the first oscillation period P1 exists repeatedly, the processing of the first oscillation period P1 may be repeated, and the saw in which only the second oscillation period P2 exists repeatedly. Needless to say, in the case of wavy oscillation, the processing of the second oscillation period P2 may be repeated.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. In the first to fourth embodiments, the photodiode 2 and the current-voltage conversion amplifying unit 5 are used as detection means for detecting an electrical signal including an MHP waveform. However, the MHP waveform is not used without using a photodiode. It is also possible to extract. FIG. 12 is a block diagram showing a configuration of a physical quantity sensor according to the fifth embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIG. The physical quantity sensor of the present embodiment uses a voltage detection unit 12 as detection means instead of the photodiode 2 and the current-voltage conversion amplification unit 5 of the first to fourth embodiments.

  The voltage detector 12 detects and amplifies the voltage between the terminals of the semiconductor laser 1, that is, the anode-cathode voltage. When interference occurs between the laser light emitted from the semiconductor laser 1 and the return light from the object 10, an MHP waveform appears in the voltage between the terminals of the semiconductor laser 1. Therefore, it is possible to extract the MHP waveform from the voltage between the terminals of the semiconductor laser 1.

The filter unit 6 removes the carrier wave from the output voltage of the voltage detection unit 12. Other configurations of the physical quantity sensor are the same as those in the first to fourth embodiments.
Thus, in this embodiment, an MHP waveform can be extracted without using a photodiode, and the physical quantity sensor components can be reduced as compared with the first to fourth embodiments. The cost can be reduced. In this embodiment, since no photodiode is used, the influence of disturbance light can be eliminated.

  In the first to fifth embodiments, at least the signal extraction unit 7 and the calculation unit 8 can be realized by, for example, a computer having a CPU, a memory, and an interface, and a program for controlling these hardware resources. . The CPU executes the processes described in the first to fifth embodiments according to the program stored in the memory.

  The present invention can be applied to a technique for measuring a physical quantity of an object from information on interference caused by a self-coupling effect between laser light emitted from a semiconductor laser and return light from the object.

It is a block diagram which shows the structure of the physical quantity sensor which concerns on the 1st Embodiment of this invention. It is a wave form diagram showing typically the output voltage waveform of the current-voltage conversion amplification part in the 1st embodiment of the present invention, and the output voltage waveform of a filter part. It is a figure for demonstrating a mode hop pulse. It is a figure which shows the relationship between the oscillation wavelength of a semiconductor laser, and the output waveform of a photodiode. It is a block diagram which shows the structural example of the signal extraction part in the 1st Embodiment of this invention. It is a figure for demonstrating operation | movement of the signal extraction part in the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the calculating part in the 1st Embodiment of this invention. It is a figure for demonstrating operation | movement of the period correction | amendment part in the 1st Embodiment of this invention. It is a figure for demonstrating operation | movement of the period correction | amendment part in the 2nd Embodiment of this invention. It is a block diagram which shows the structural example of the calculating part in the 3rd 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 4th Embodiment of this invention. It is a block diagram which shows the structure of the physical quantity sensor which concerns on the 5th Embodiment of this invention. It is a block diagram which shows the structure of the conventional laser measuring device. It is a figure which shows one example of the time change of the oscillation wavelength of a semiconductor laser in the laser measuring device of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Photodiode, 3 ... Lens, 4 ... Laser driver, 5 ... Current-voltage conversion amplification part, 6 ... Filter part, 7 ... Signal extraction part, 8 ... Calculation part, 9 ... Display part, 10 ... object, 11 ... carrier wave adjustment unit, 12 ... voltage detection unit, 70 ... binarization unit, 71 ... period measurement unit, 80 ... physical quantity calculation unit, 81 ... storage unit, 82 ... cycle correction unit, 83 ... counting unit, 84: Distance calculation unit, 85: Period calculation unit.

Claims (14)

A semiconductor laser that emits laser light to the object to be measured;
Oscillation wavelength modulation means for operating the semiconductor laser so that at least one of a first oscillation period in which the oscillation wavelength continuously increases monotonously and a second oscillation period in which the oscillation wavelength continuously decreases monotonously exists ,
Detection means for detecting an electrical signal including an interference waveform generated by a self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object;
Signal extraction means for measuring the period of the interference waveform included in the output signal of the detection means every time the interference waveform is input;
A physical quantity calculating means for calculating at least one of the displacement and the velocity of the measurement object based on the amount of change of each period measured by the signal extracting means with respect to the reference period;
A physical quantity sensor comprising: a period correction unit that corrects the reference period according to a change characteristic of a period measured by the signal extraction unit. The physical quantity sensor according to claim 1,
The physical quantity calculation means includes a sampling clock frequency for measuring the period of the interference waveform, the reference period, an average wavelength of the semiconductor laser, and a change in the period of the interference waveform measured by the signal extraction means with respect to the reference period. A physical quantity sensor that calculates at least one of a displacement and a velocity of the measurement object from a quantity. The physical quantity sensor according to claim 1 or 2,
The period correction means corrects the reference period so that a time when the period of the interference waveform is equal to or greater than the reference period is equal to a time when the period of the interference waveform is equal to or less than the reference period. Physical quantity sensor. The physical quantity sensor according to claim 1 or 2,
The physical quantity calculating means calculates at least a displacement of the measurement object;
The period correction unit is configured such that an integral value of the displacement when the period of the interference waveform is equal to or greater than the reference period is equal to an integral value of the displacement when the period of the interference waveform is equal to or less than the reference period. In addition, the physical quantity sensor is characterized by correcting the reference period. The physical quantity sensor according to claim 1 or 2,
The physical quantity sensor according to claim 1, wherein the period correction means obtains an average value of the period of the interference waveform in one period of the period change of the interference waveform and sets the average value as a new reference period. The physical quantity sensor according to claim 1 or 2,
The physical quantity sensor is characterized in that the period of the interference waveform when the measurement object is stationary is an initial value of the reference period. The physical quantity sensor according to claim 1 or 2,
And counting means for counting the number of the interference waveforms included in the output signal of the detection means for each of the first oscillation period and the second oscillation period;
A distance calculating means for calculating a distance from the object to be measured from a minimum oscillation wavelength and a maximum oscillation wavelength and a counting result of the counting means in a period of counting the number of interference waveforms by the counting means;
A period calculating means for determining the period of the interference waveform from the distance calculated by the distance calculating means,
The physical quantity sensor, wherein the physical quantity calculation means uses the period obtained by the period calculation means as an initial value of the reference period. An oscillation procedure for operating the semiconductor laser so that at least one of the first oscillation period in which the oscillation wavelength continuously increases monotonously and the second oscillation period in which the oscillation wavelength continuously decreases monotonously exists;
A detection procedure for detecting an electrical signal including an interference waveform caused by a self-coupling effect between laser light emitted from the semiconductor laser and return light from a measurement object;
A signal extraction procedure for measuring the period of the interference waveform included in the output signal obtained by the detection procedure every time the interference waveform is input;
A physical quantity calculation procedure for calculating at least one of the displacement and the velocity of the measurement object based on the change amount of each period measured in the signal extraction procedure with respect to the reference period;
A physical quantity measurement method comprising: a period correction procedure for correcting the reference period in accordance with a change characteristic of a period measured in the signal extraction procedure. The physical quantity measuring method according to claim 8,
The physical quantity calculation procedure includes a sampling clock frequency for measuring a cycle of the interference waveform, the reference cycle, an average wavelength of the semiconductor laser, and a cycle of the interference waveform measured in the signal extraction procedure with respect to the reference cycle. A physical quantity measuring method, wherein at least one of a displacement and a speed of the measurement target is calculated from a change amount. The physical quantity measuring method according to claim 8 or 9,
The period correction procedure corrects the reference period so that a time in which the period of the interference waveform is equal to or greater than the reference period and a time in which the period of the interference waveform is equal to or less than the reference period are equal. Physical quantity measurement method. The physical quantity measuring method according to claim 8 or 9,
The physical quantity calculation procedure calculates at least a displacement of the measurement object,
In the period correction procedure, the integral value of the displacement when the period of the interference waveform is equal to or greater than the reference period is equal to the integral value of the displacement when the period of the interference waveform is equal to or less than the reference period. And correcting the reference period. The physical quantity measuring method according to claim 8 or 9,
In the period correction procedure, an average value of the period of the interference waveform is obtained in one period of the period change of the interference waveform, and this average value is used as a new reference period. The physical quantity measuring method according to claim 8 or 9,
In the physical quantity calculation procedure, the period of the interference waveform when the measurement object is stationary is set as an initial value of the reference period. The physical quantity measuring method according to claim 8 or 9,
A counting procedure for counting the number of the interference waveforms included in the output signal obtained by the detection procedure for each of the first oscillation period and the second oscillation period;
A distance calculation procedure for calculating the distance to the measurement object from the minimum oscillation wavelength and the maximum oscillation wavelength in the period of counting the number of interference waveforms by this counting procedure and the counting result of the counting procedure;
A cycle calculation procedure for determining the cycle of the interference waveform from the distance calculated by the distance calculation procedure,
In the physical quantity calculating procedure, the period obtained by the period calculating procedure is set as an initial value of the reference period.

Images