JP2009063346A - Physical quantity sensor and physical quantity measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate control of a wavelength change of a semiconductor laser, and to reduce an effect of a transient response of a triangular wave vertex. <P>SOLUTION: A physical quantity sensor has the semiconductor laser 1; a laser driver 4 for operating the semiconductor laser 1 to repeat at least the first oscillation period wherein an oscillation wavelength is monotonously increased continuously, the second oscillation period wherein the oscillation wavelength is monotonously decreased continuously, the third oscillation period wherein the oscillation wavelength is constant at the maximum value between the first oscillation period and the second oscillation period, and the fourth oscillation period wherein the oscillation wavelength is constant at the minimum value between the second oscillation period and the first oscillation period; and a measuring means (a current-voltage conversion amplifier 5, a filter circuit 6, a counting device 7, an operation device 8) for measuring the physical quantity of a measuring object from information of interference generated by a self-coupling effect between laser light and return light included in an output from a photodiode 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a physical quantity sensor and a physical quantity measurement method for measuring a physical quantity such as a distance to an object and a speed 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. Is.

  Conventionally, as a distance meter using light interference by a laser, a laser measuring device using interference (self-coupling effect) inside a semiconductor laser between laser output light and return light from a measurement object has been proposed. (For example, refer nonpatent literature 1, nonpatent literature 2, nonpatent literature 3). FIG. 7 shows a composite resonator model of an FP type (Fabry-Perot type) semiconductor laser. In FIG. 7, 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.

When 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 from the measurement target 104 and the resonator 101 are satisfied when the following resonance condition is satisfied. The inner laser beams strengthen each other, 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 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. 8 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 = qλ / 2 shown in Expression (1) is satisfied, the phase difference between the return light and the laser light in the resonator 101 becomes 0 ° (the same phase), and the return light and the resonator 101 When L = qλ / 2 + λ / 4, the phase difference becomes 180 ° (opposite phase), and the return light and the laser light in the resonator 101 are the weakest. For this reason, when the oscillation wavelength of the semiconductor laser is changed, a place where the laser output becomes stronger and a place where the laser output becomes weaker appear alternately, and the laser output at this time is detected by the photodiode 103 provided in the resonator 101. As shown in FIG. 8, a step-like 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.
However, conventional interferometric instruments, including self-coupled instruments, have the problem that they can measure the distance to a stationary measurement object, but cannot measure the distance of a measurement object with speed. .

  In view of this, the inventor has proposed a distance / speed meter that can measure not only the distance to a stationary measurement object but also the speed of the measurement object (see Patent Document 1). The configuration of this distance / speed meter is shown in FIG. The distance / velocity meter in FIG. 9 condenses the light from the semiconductor laser 201 that emits laser light to the measurement target, the photodiode 202 that converts the light output of the semiconductor laser 201 into an electrical signal, and the light from the semiconductor laser 201. A lens 203 that irradiates the measurement target 210 and collects return light from the measurement target 210 and makes it incident on the semiconductor laser 201. A first oscillation period and an oscillation wavelength in which the oscillation wavelength continuously increases in the semiconductor laser 201. A laser driver 204 that alternately repeats a second oscillation period in which the current continuously decreases, a current-voltage conversion amplifier 205 that converts and amplifies the output current of the photodiode 202 into a voltage, and a current-voltage conversion amplifier 205 A signal extraction circuit 206 that differentiates the output voltage of the signal twice, and a counting circuit 2 that counts the number of MHPs included in the output voltage of the signal extraction circuit 206 With 7, a calculation unit 208 for calculating the distance and speed of the measurement target 210 to the measurement target 210, and 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. 10 is a diagram showing the change over time of the oscillation wavelength of the semiconductor laser 201. In FIG. 10, 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 T0 is the period of the triangular wave.

  Laser light emitted from the semiconductor laser 201 is collected by the lens 203 and enters the measurement object 210. The light reflected by the measurement 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 MHPs 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. The arithmetic unit 208 determines the distance from the measurement object 210 based on the minimum oscillation wavelength λa and the maximum oscillation wavelength λb of the semiconductor laser 1, the number of MHPs in the first oscillation period P1, and the number of MHPs in the second oscillation period P2. And the speed of the measuring object 210 is calculated.

JP 2006-31080 A 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

According to the self-coupled distance meter shown in FIG. 7, the distance to the measurement object can be measured. According to the distance / velocity meter shown in FIG. 9, the distance between the measurement object and the speed of the measurement object can be calculated. It can be measured simultaneously.
However, in the conventional self-coupled laser measuring instrument shown in FIGS. 7 and 9, it is necessary to stabilize the wavelength variation of the semiconductor laser and to stabilize the minimum oscillation wavelength and the maximum oscillation wavelength. There was a problem that it was difficult to control. The reason why the control is difficult is that it becomes difficult to stabilize the minimum oscillation wavelength and the maximum oscillation wavelength due to the dull shape of the apex portion of the triangular wave in FIG. 10 due to the frequency characteristics and variations of the laser driver and laser element. is there.

  Further, in the conventional self-coupled laser measuring instrument shown in FIGS. 7 and 9, since the oscillation wavelength of the semiconductor laser is changed to a triangular wave, the influence of the transient response at the apex of the triangular wave can be completely eliminated. There was a problem that it was not possible. 11A and 11B are diagrams for explaining the problems of the conventional self-coupled laser measuring instrument, and FIG. 11A is an output of the current-voltage conversion amplifier 205 in FIG. FIG. 11B schematically shows the voltage waveform, and FIG. 11B schematically shows the output voltage waveform of the signal extraction circuit 206.

  A signal extraction circuit 206 composed of a differentiation circuit or a high-pass filter removes the oscillation waveform (carrier wave) of the semiconductor laser 1 in FIG. 10 from the waveform (modulation wave) in FIG. 11A corresponding to the output of the photodiode 202. Then, the MHP waveform of FIG. 11B is extracted. At this time, a spike-like transient response waveform as shown in FIG. 11B appears at the output of the signal extraction circuit 206 at the apex timing of the triangular wave. Since the counting circuit 207 cannot count the MHP of such a transient response waveform portion, a counting error occurs. As a result, an error occurs in the distance and speed calculated by the arithmetic unit 208.

  The present invention has been made to solve the above-described problems, and can easily control the wavelength change of the semiconductor laser and reduce the influence of the transient response of the triangular wave vertex included in the output signal of the light receiver. An object of the present invention is to provide a physical quantity sensor and a physical quantity measuring method capable of performing the above.

  The physical quantity sensor according to the present invention includes a semiconductor laser that emits laser light to a measurement target, at least a first oscillation period in which the oscillation wavelength continuously monotonously increases, and a second oscillation period in which the oscillation wavelength continuously monotonously decreases. The oscillation wavelength is the minimum between the third oscillation period in which the oscillation wavelength is constant at the maximum value between the first oscillation period and the second oscillation period, and between the second oscillation period and the first oscillation period. A laser driver that operates the semiconductor laser so that a fourth oscillation period constant in value exists, and a laser beam emitted from the semiconductor laser disposed in or near the semiconductor laser and the measurement A light receiver that receives the return light from the target and converts it into an electrical signal, and information on interference generated by the self-coupling effect between the laser light and the return light contained in the output signal of the light receiver. And it has a measuring means for measuring a physical amount of a subject.

In one configuration example of the physical quantity sensor of the present invention, the physical quantity of the measurement target is at least one of a distance from the measurement target and a speed of the measurement target.
Further, in one configuration example of the physical quantity sensor of the present invention, the measuring means calculates the number of interference waveforms generated by a self-coupling effect between the laser light and the return light, which is included in an output signal of the light receiver. Counting means for counting each of the one oscillation period and the second oscillation period, the minimum oscillation wavelength and the maximum oscillation wavelength in the period in which the number of interference waveforms is counted by the counting means, and the counting result of the counting means. And calculating means for calculating at least one of the distance to the object and the speed of the measurement object.

  The physical quantity measuring method of the present invention includes at least a first oscillation period in which the oscillation wavelength continuously monotonously increases, a second oscillation period in which the oscillation wavelength continuously monotonously decreases, and the first oscillation period to the second oscillation period. A third oscillation period in which the oscillation wavelength is constant at the maximum value during the oscillation period, and a fourth oscillation period in which the oscillation wavelength is constant at the minimum value between the second oscillation period and the first oscillation period. The laser beam emitted from the semiconductor laser and the measurement included in the oscillation procedure for operating the semiconductor laser so that the laser beam is repeatedly present, and the output signal of the light receiver disposed in or near the semiconductor laser A measurement procedure for measuring a physical quantity of the measurement target from information on interference caused by a self-coupling effect with return light from the target.

  According to the present invention, at least the first oscillation period in which the oscillation wavelength continuously monotonously increases, the second oscillation period in which the oscillation wavelength continuously monotonously decreases, and the first oscillation period to the second oscillation period. A third oscillation period having a constant maximum oscillation wavelength and a fourth oscillation period having a constant minimum oscillation wavelength between the second oscillation period and the first oscillation period. By operating the semiconductor laser, it is possible to easily control the wavelength change of the semiconductor laser, so that the wavelength change amount, the minimum oscillation wavelength, and the maximum oscillation wavelength of the semiconductor laser can be stably maintained. The measurement accuracy of physical quantities can be stabilized. In addition, in the present invention, when acquiring the interference information included in the output signal of the photoreceiver, the transient response waveform generated at the timing of switching of each oscillation period can be reduced as compared with the conventional case. Information detection errors can be reduced. As a result, in the present invention, the measurement accuracy of physical quantities can be improved.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a distance / speed meter according to the first embodiment of the present invention. The distance / velocity meter of FIG. 1 includes 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, Are collected and irradiated onto the measurement target 10, and the return light from the measurement target 10 is collected and incident on the semiconductor laser 1, the laser driver 4 that drives the semiconductor laser 1, and the photodiode 2. A current-voltage conversion amplifier 5 that converts an output current into a voltage and amplifies it, a filter circuit 6 that removes a carrier wave from the output voltage of the current-voltage conversion amplifier 5, and the number of MHPs included in the output voltage of the filter circuit 6 There is a counting device 7 that counts, a computing device 8 that calculates the distance to the measuring object 10 and the speed of the measuring object 10 from the number of MHPs, and a display device 9 that displays the calculation result of the computing device 8. That.

The current-voltage conversion amplifier 5, the filter circuit 6, the counting device 7, and the arithmetic device 8 constitute a measuring means. The current-voltage conversion amplifier 5, the filter circuit 6, and the counting device 7 constitute counting 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.

  FIG. 2 is a diagram showing the change over time of the oscillation wavelength of the semiconductor laser 1. The laser driver 4 supplies a drive current having a waveform obtained by cutting off the apex of the triangular wave to the semiconductor laser 1. Accordingly, the semiconductor laser 1 includes a first oscillation period P1 in which the oscillation wavelength continuously increases at a constant change rate, and a second oscillation period P2 in which the oscillation wavelength continuously decreases at a constant change rate, Between the first oscillation period P1 and the second oscillation period P2, the third oscillation period P3 where the oscillation wavelength is constant at the maximum value λb, and between the second oscillation period P2 and the first oscillation period P1 Thus, driving is performed so that the oscillation wavelength is a minimum value λa and a constant fourth oscillation period P4 repeatedly exists. 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.

  In order to generate a drive current having a waveform obtained by cutting off the apex of the triangular wave, for example, a digital value of the drive current preset in a memory (not shown) in the laser driver 4 is converted into an analog signal by a D / A converter (not shown). The waveform may be converted, or a waveform operation may be performed by cutting the top and bottom of the triangular wave with a limiter (not shown).

  Laser light emitted from the semiconductor laser 1 is collected by the lens 3 and enters the measurement object 10. The light of the semiconductor laser 1 reflected by the measurement object 10 is collected by the lens 3 and enters the semiconductor laser 1. 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. In these figures, the oscillation waveform (carrier wave) of the semiconductor laser 1 in FIG. 2 is removed from the waveform (modulation wave) in FIG. 3A corresponding to the output of the photodiode 2, and the MHP in FIG. A process of extracting a waveform (interference waveform) is shown.

  The counting device 7 counts the number of MHPs included in the output of the filter circuit 6 for each of the first oscillation period P1 and the second oscillation period P2. The counting device 7 may use a counter composed of logic gates, or may measure an MHP frequency (that is, the number of MHPs per unit time) using FFT (Fast Fourier Transform).

  Next, the arithmetic device 8 calculates the distance to the measuring object 10 and the speed of the measuring 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 device 7. . FIG. 4 is a block diagram showing an example of the configuration of the arithmetic device 8, and FIG. 5 is a flowchart showing the operation of the arithmetic device 8. The arithmetic unit 8 calculates a distance / speed for calculating a candidate value for the distance to the measurement object 10 and a candidate value for the speed of the measurement object 10 based on the minimum oscillation wavelength λa, the maximum oscillation wavelength λb, and the number of MHPs of the semiconductor laser 1. A calculation unit 80; a history displacement calculation unit 81 that calculates a history displacement that is a difference between the distance candidate value calculated by the distance / speed calculation unit 80 and the distance candidate value calculated immediately before; and a distance / speed calculation. A storage unit 82 for storing the calculation results of the unit 80 and the history displacement calculation unit 81, a state determination unit 83 for determining the state of the measurement object 10 based on the calculation results of the distance / speed calculation unit 80 and the history displacement calculation unit 81, The distance / speed determining unit 84 determines the distance to the measuring object 10 and the speed of the measuring object 10 based on the determination result of the state determining unit 83.

  In the present embodiment, it is assumed that the state of the measuring object 10 is either a minute displacement state that satisfies a predetermined condition or a displacement state that moves more than the minute displacement state. When the average displacement of the measuring 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 The distance at time t) and the displacement state are states that satisfy (λb−λa) / λb ≦ V / Lb.

First, the distance / speed calculation unit 80 of the arithmetic unit 8 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 follows: And stored in the storage unit 82 (step S10 in FIG. 5).
Lα (t) = λa × λb × (MHP (t−1) + MHP (t))
/ {4 × (λb−λa)} (2)
Lβ (t) = λa × λb × (| MHP (t−1) −MHP (t) |)
/ {4 × (λb−λa)} (3)
Vα (t) = (MHP (t−1) −MHP (t)) × λb / 4 (4)
Vβ (t) = (MHP (t−1) + MHP (t)) × λb / 4 (5)

  In Expressions (2) to (5), 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 measurement target 10 is in a minute displacement state, and the candidate values Lβ (t) and Vβ (t) are those in which the measurement target 10 is in a displacement state. It is a value calculated assuming that there is. The arithmetic device 8 performs the calculations of the equations (2) to (5) at every time (every oscillation period) when the counting device 7 measures the number of MHPs.

Subsequently, the history displacement calculation unit 81 of the arithmetic device 8 for each of the minute displacement state and the displacement state, the distance candidate value at the current time t, and the distance candidate value at the previous time stored in the storage unit 82. The history displacement, which is the difference between the two, is calculated by the following equation and stored in the storage unit 82 (step S11 in FIG. 5). In the equations (6) and (7), the distance candidate values calculated one time before the current time t are Lα (t−1) and Lβ (t−1).
Vcalα (t) = Lα (t) −Lα (t−1) (6)
Vcalβ (t) = Lβ (t) −Lβ (t−1) (7)

The history displacement Vcalα (t) is a value calculated on the assumption that the measurement object 10 is in a minute displacement state, and the history displacement Vcalβ (t) is a value calculated on the assumption that the measurement object 10 is in a displacement state. . The arithmetic device 8 performs the calculations of the equations (6) to (7) at each time when the number of MHPs is measured by the counting device 7. In the equations (4) to (7), the direction in which the measurement object 10 approaches the distance / speedometer of the present embodiment is defined as a positive velocity, and the direction in which the measurement object 10 moves away is defined as a negative velocity.
Next, the state determination unit 83 of the arithmetic device 8 determines the state of the measurement target 10 using the calculation results of the expressions (2) to (7) stored in the storage unit 82 (step S12 in FIG. 5). .

  As described in Patent Document 1, when the measurement object 10 is moving in a minute displacement state (equal speed movement), the history displacement Vcalα (t) calculated assuming that the measurement object 10 is in a minute displacement state. The sign is constant, and the velocity candidate value Vα (t) calculated on the assumption that the measurement object 10 is in a minute displacement state is equal to the average value of the absolute values of the history displacement Vcalα (t). When the measurement object 10 is moving at a constant velocity in a minute displacement state, the sign of the history displacement Vcalβ (t) calculated assuming that the measurement object 10 is in the displacement state is the time at which the number of MHPs is measured. Invert.

  Therefore, the state determination unit 83 calculates the hysteresis displacement Vcalα (t) calculated on the assumption that the measurement target 10 is in the minute displacement state and the calculation is performed on the assumption that the measurement target 10 is in the minute displacement state. When the speed candidate value Vα (t) and the average value of the absolute values of the history displacement Vcalα (t) are equal, it is determined that the measurement object 10 is moving at a constant speed in a minute displacement state.

  As described in Patent Document 1, when the measurement object 10 is moving in a displaced state (constant velocity motion), the sign of the history displacement Vcalβ (t) calculated assuming that the measurement object 10 is in the displaced state is The velocity candidate value Vβ (t), which is constant and calculated assuming that the measurement object 10 is in the displacement state, is equal to the average absolute value of the history displacement Vcalβ (t). In addition, when the measurement object 10 is moving at a constant speed in a displaced state, the sign of the history displacement Vcalα (t) calculated assuming that the measurement object 10 is in a minute displacement state is inverted every time the number of MHPs is measured. To do.

  Therefore, the state determination unit 83 calculates the speed calculated on the assumption that the sign of the history displacement Vcalβ (t) calculated on the assumption that the measurement object 10 is in the displacement state is constant and that the measurement object 10 is in the displacement state. Is equal to the average value of the absolute values of the history displacement Vcalβ (t), it is determined that the measurement object 10 is moving at a constant speed in the displacement state.

  As described in Patent Document 1, when the measurement object 10 is in a minute displacement state and is moving other than a uniform velocity motion, the velocity candidate value Vα calculated on the assumption that the measurement object 10 is in a minute displacement state. (T) and the average value of the absolute values of the history displacement Vcalα (t) calculated on the assumption that the measurement object 10 is in a minute displacement state do not match. Similarly, the average value of the absolute values of the velocity candidate value Vβ (t) calculated assuming that the measurement object 10 is in the displacement state and the history displacement Vcalβ (t) calculated assuming that the measurement object 10 is in the displacement state are the same. do not do.

  In addition, when the measurement object 10 is in a minute displacement state and performing a motion other than the constant velocity motion, the sign of the history displacement Vcalα (t) calculated on the assumption that the measurement object 10 is in the minute displacement state is the number of MHPs. In the history displacement Vcalβ (t) calculated by assuming that the measurement object 10 is in a displacement state, the change is not every time when the number of MHPs is measured.

  Therefore, the state determination unit 83 reverses the sign of the history displacement Vcalα (t) calculated on the assumption that the measurement target 10 is in a minute displacement state at each time when the number of MHPs is measured, and the measurement target 10 is When the velocity candidate value Vα (t) calculated on the assumption of the minute displacement state and the average value of the absolute values of the history displacement Vcalα (t) do not coincide with each other, the measurement object 10 is in the minute displacement state and other than the constant velocity motion. Determine that you are exercising.

  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 state determination unit 83 has an absolute value of the velocity candidate value Vβ (t) calculated on the assumption that the measurement target 10 is in the displacement state, and the measurement target 10 is in the minute displacement state. When the velocity candidate value Vα (t) calculated on the assumption that the average value of the absolute values of the history displacement Vcalα (t) does not coincide with each other, the object to be measured 10 performs a motion other than the constant velocity motion in a minute displacement state. It may be determined that

  As described in Patent Document 1, when the measurement object 10 is in a displacement state and is moving other than a constant velocity motion, a velocity candidate value Vα (calculated assuming that the measurement object 10 is in a minute displacement state) t) and the average value of the absolute values of the history displacement Vcalα (t) calculated on the assumption that the measurement object 10 is in the minute displacement state, and the velocity candidate values calculated on the assumption that the measurement object 10 is in the displacement state The average value of the absolute values of the history displacement Vcalβ (t) calculated on the assumption that Vβ (t) is the displacement state of the measurement object 10 does not match.

  Further, when the measurement object 10 is in a displacement state and is moving other than a constant velocity motion, the sign of the history displacement Vcalβ (t) calculated on the assumption that the measurement object 10 is in the displacement state is the number of MHPs. The history displacement Vcalα (t), which is inverted at each time and calculated on the assumption that the measurement target 10 is in a minute displacement state, has a change in sign, but this change is not at every time when the number of MHPs is measured.

  Therefore, the state determination unit 83 reverses the sign of the history displacement Vcalβ (t) calculated on the assumption that the measurement target 10 is in the displacement state at each time when the number of MHPs is measured, and the measurement target 10 is displaced. When the velocity candidate value Vβ (t) calculated on the assumption that the state is in the state and the average value of the absolute values of the history displacement Vcalβ (t) do not coincide with each other, a motion other than the constant velocity motion is performed when the measurement object 10 is in the displacement state. It is determined that

  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 state determination unit 83 has the absolute value of the velocity candidate value Vα (t) calculated on the assumption that the measurement object 10 is in the minute displacement state equal to the wavelength change rate, and the measurement object 10 is in the displacement state. When the velocity candidate value Vβ (t) calculated on the assumption that the average value of the absolute values of the history displacement Vcalβ (t) does not coincide with each other, the measurement object 10 is moving in a displacement state other than the constant velocity movement. May be determined.

The distance / speed determining unit 84 of the computing device 8 determines the speed of the measuring object 10 and the distance from the measuring object 10 based on the determination result of the state determining unit 83 (step S13 in FIG. 5).
That is, when it is determined that the measurement target 10 is moving at a uniform speed in a minute displacement state, the distance / speed determination unit 84 sets the speed candidate value Vα (t) as the speed of the measurement target 10 and uses the distance candidate value. When it is determined that Lα (t) is a distance from the measurement object 10 and the measurement object 10 is moving at a constant speed in a displaced state, the velocity candidate value Vβ (t) is the velocity of the measurement object 10 and the distance The candidate value Lβ (t) is set as the distance from the measurement object 10.

  Further, when it is determined that the measurement target 10 is moving in a minute displacement state other than the uniform speed movement, the distance / speed determination unit 84 sets the speed candidate value Vα (t) as the speed of the measurement target 10, The distance candidate value Lα (t) is set as the distance to the measurement object 10. However, the actual distance is an average value of the distance candidate values Lα (t). Further, when it is determined that the measurement object 10 is moving in a displaced state other than the constant velocity movement, the distance / speed determination unit 84 sets the speed candidate value Vβ (t) as the speed of the measurement object 10 and sets the distance. The candidate value Lβ (t) is a distance from the measurement object 10. However, the actual distance is an average value of the distance candidate values Lβ (t).

  Note that Vβ (t) is always a positive value and Vα (t) is either a positive value or a negative value depending on the magnitude relationship between MHP (t−1) and MHP (t). It does not represent the direction of speed of the object 10. When the number of MHPs of the semiconductor laser whose oscillation wavelength is increasing is larger than the number of MHPs of the semiconductor laser whose oscillation wavelength is decreasing, the velocity of the measuring object 10 is positive (approaching the laser). Direction).

The arithmetic device 8 performs the processing of steps S10 to S13 at every time (every oscillation period) when the number of MHPs is measured by the counting device 7.
The display device 9 displays the distance to the measurement object 10 and the speed of the measurement object 10 calculated by the arithmetic device 8 in real time.

As described above, in the present embodiment, at least the first oscillation period P1 in which the oscillation wavelength continuously increases at a constant change rate, and the second oscillation in which the oscillation wavelength continuously decreases at a constant change rate. A period P2, a third oscillation period P3 in which the oscillation wavelength is constant at the maximum value λb between the first oscillation period P1 and the second oscillation period P2, and the second oscillation period P2 to the first oscillation period Since the semiconductor laser 1 is driven so that the fourth oscillation period P4 in which the oscillation wavelength is the minimum value λa repeatedly exists between P1 and the minimum oscillation wavelength λa and the maximum oscillation wavelength λb of the semiconductor laser 1, Since it becomes easy to clearly define the wavelength variation that is the difference between the wavelengths λb and λa, the wavelength variation of the semiconductor laser 1 can be easily controlled. As a result, in the present embodiment, the wavelength change amount, the minimum oscillation wavelength λa, and the maximum oscillation wavelength λb of the semiconductor laser 1 can be stably maintained, and the distance and speed measurement accuracy can be stabilized.
As a method for defining the amount of wavelength change, for example, the photocurrent of the photodiode 2 in the periods P3 and P4 during which the optical output of the semiconductor laser 1 is stabilized and the calculated physical quantity for a known object are fed back to the laser driver 4. The drive current of the semiconductor laser 1 may be controlled, or the upper and lower limiters of the triangular wave may be controlled. Alternatively, the calculated physical quantity may be corrected.

  In the present embodiment, since the transient response waveform generated at the output of the filter circuit 6 at the timing of switching of each oscillation period can be made smaller than in the case of FIG. Counting errors can be reduced. As a result, in this embodiment, the distance and speed measurement accuracy can be improved as compared with the conventional self-coupled laser measuring instrument shown in FIGS.

[Second Embodiment]
In the first embodiment, the drive current having a waveform obtained by cutting off the apex of the triangular wave is supplied to the semiconductor laser 1. You may make it supply. The time change of the oscillation wavelength of the semiconductor laser 1 in this case is shown in FIG.

  In the first embodiment, there is a possibility that a transient response waveform is generated in the output of the filter circuit 6 at the switching timing of each oscillation period. Although the magnitude of the transient response waveform is smaller than that in the case of FIG. 12B, there is a possibility that a counting error occurs in the counting device 7. The transient response waveform can be significantly reduced by processing the drive current with a low-pass filter and blunting the oscillation waveform of the semiconductor laser 1 as in the present embodiment, so that it can be compared with the first embodiment. Counting errors can be further reduced.

  Even when the oscillation waveform is blunted as shown in FIG. 6, the third oscillation period P3 and the fourth oscillation period P4 are necessary to stabilize the wavelength change. In order to leave the third oscillation period P3 and the fourth oscillation period P4, the time of the third oscillation period P3 and the fourth oscillation period P4 before processing by the low-pass filter is set to T, and the time constant of the low-pass filter is set. The time constant of the low-pass filter may be set so that T ≧ t, where τ.

  Note that the counting device 7 and the computing device 8 in the first and second embodiments 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 the embodiment in accordance with this program.

  In the first and second embodiments, a distance / speed meter is described as an example of the physical quantity sensor. However, the present invention is not limited to this, and a distance meter or a speed meter may be used. It may be a sensor that measures other physical quantities.

  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 distance and speedometer 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 arithmetic unit in the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the arithmetic unit in 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 2nd Embodiment of this invention. It is a figure which shows the compound resonator model of the semiconductor laser in the conventional laser measuring device. It is a figure which shows the relationship between the oscillation wavelength of a semiconductor laser, and the output waveform of a built-in photodiode. It is a block diagram which shows the structure of the conventional distance and speedometer. It is a figure which shows one example of the time change of the oscillation wavelength of a semiconductor laser in the distance and speedometer of FIG. It is a figure for demonstrating the problem of the conventional self-coupling type laser measuring device.

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: 80 ... distance / speed calculation unit, 81 ... history displacement calculation unit, 82 ... storage unit, 83 ... state determination unit, 84 ... distance / speed determination unit.

Claims (6)

A semiconductor laser that emits laser light to the object to be measured;
The oscillation wavelength is at least between the first oscillation period in which the oscillation wavelength continuously increases monotonously, the second oscillation period in which the oscillation wavelength continuously decreases monotonously, and the first oscillation period to the second oscillation period. The semiconductor laser has a third oscillation period that is constant at the maximum value and a fourth oscillation period at which the oscillation wavelength is constant at the minimum value between the second oscillation period and the first oscillation period. A laser driver to operate,
A light receiving device that is disposed in or near the semiconductor laser, receives the laser light emitted from the semiconductor laser and the return light from the measurement object, and converts it into an electrical signal;
A physical quantity sensor comprising: measurement means for measuring a physical quantity of the measurement target from information on interference caused by a self-coupling effect between the laser light and the return light contained in an output signal of the light receiver. The physical quantity sensor according to claim 1,
The physical quantity sensor according to claim 1, wherein the physical quantity of the measurement target is at least one of a distance from the measurement target and a speed of the measurement target. The physical quantity sensor according to claim 2,
The measuring means includes
Counting means for counting the number of interference waveforms generated by the self-coupling effect between the laser beam and the return beam included in the output signal of the light receiver for each of the first oscillation period and the second oscillation period; ,
From the calculation means for calculating at least one of the distance to the measurement object and the velocity of the measurement object from the minimum oscillation wavelength and the maximum oscillation wavelength in the period of counting the number of interference waveforms by the counting means and the counting result of the counting means A physical quantity sensor characterized by comprising: In a physical quantity measurement method for emitting laser light to a measurement object using a semiconductor laser,
The oscillation wavelength is at least between the first oscillation period in which the oscillation wavelength continuously increases monotonously, the second oscillation period in which the oscillation wavelength continuously decreases monotonously, and the first oscillation period to the second oscillation period. The semiconductor laser has a third oscillation period that is constant at the maximum value and a fourth oscillation period at which the oscillation wavelength is constant at the minimum value between the second oscillation period and the first oscillation period. Oscillation procedure to operate
From the information of interference caused by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, which is included in the output signal of the light receiver disposed in or near the semiconductor laser, A physical quantity measurement method comprising: a measurement procedure for measuring the physical quantity of the measurement target. The physical quantity measuring method according to claim 4,
The physical quantity of the measurement object is at least one of a distance to the measurement object and a speed of the measurement object. The physical quantity measuring method according to claim 5,
The measurement procedure is as follows:
A counting procedure for counting, for each of the first oscillation period and the second oscillation period, the number of interference waveforms generated by the self-coupling effect between the laser light and the return light, included in the output signal of the light receiver; ,
A calculation procedure for calculating at least one of the distance to the measurement object and the velocity of 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 physical quantity measuring method characterized by comprising.

Images