JP2008175602A - Distance meter and distance measuring method - Google Patents

Abstract

An object of the present invention is to achieve both improvement in distance resolution and extension of a measurement range.
A distance meter includes a laser driver for causing a semiconductor laser to alternately repeat a first oscillation period in which an oscillation wavelength increases and a second oscillation period in which an oscillation wavelength decreases, and an output of the semiconductor laser. And a counting device 8 that counts interference waveforms included in the output of the photodiode 2 to be converted into an electrical signal. The counting device 8 counts the interference waveform for each divided period obtained by dividing the first and second oscillation periods, and the first dividing period including at least the minimum driving current dividing period when the driving current of the semiconductor laser 1 is minimum. When the ratio of the sum of the count results in the set and the sum of the count results in the second set of the divided periods is obtained, when the ratio is outside the predetermined numerical range in both the first and second oscillation periods, The amplitude of the drive current is controlled so that the ratio is within the numerical range.
[Selection] Figure 1

Description

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

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

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

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

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

  Since the semiconductor laser emits laser beams having different frequencies according to the magnitude of the injection current, an external modulator is not required when modulating the oscillation frequency, and direct modulation is possible by the injection current. FIG. 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 = nλ / 2 shown in Expression (1) is satisfied, the phase difference between the return light and the laser light in the resonator 101 becomes 0 ° (same phase), and the return light and the resonator 101 When L = nλ / 2 + λ / 4, the phase difference is 180 ° (opposite phase), and the return light and the laser light in the resonator 101 are the weakest. Therefore, when the oscillation wavelength of the semiconductor laser is changed, a place where the laser output becomes strong and a place where the laser output becomes weak appear alternately, and the laser output at this time is detected by the photodiode 103 provided in the resonator 101. As shown in FIG. 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 described later. For example, if the number of MHPs is 10 when the distance to the measurement object 104 is L1, the number of MHPs is 5 at half the distance L2. That is, when the oscillation wavelength of the semiconductor laser is changed for a certain time, the number of MHPs changes in proportion to the measurement distance. Therefore, if the MHP is detected by the photodiode 103 and the frequency of the MHP is measured, the distance can be easily measured. Note that the mode hopping phenomenon peculiar to the FP type semiconductor laser is a phenomenon in which a discontinuous portion occurs in the oscillation wavelength in accordance with the continuous increase / decrease of the injection current, as shown in FIG. There is a slight hysteresis when the injection current increases and decreases.

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

  In a conventional interference type distance meter including a self-coupled type, the distance resolution increases as the change in the oscillation wavelength of the semiconductor laser increases. In order to increase the change in the oscillation wavelength of the semiconductor laser, the amplitude of the driving current of the semiconductor laser may be increased. Since the drive current has an upper limit defined by the semiconductor laser, to increase the amplitude of the drive current, the minimum value of the drive current is decreased while the maximum value of the drive current is fixed at the upper limit. .

  However, since the MHP signal waveform also becomes small when the drive current is small, if the amplitude of the drive current is increased, the MHP signal waveform may become smaller than the detection limit when the drive current is small, and the number of MHPs may not be measured. was there. If there is a part where the number of MHPs cannot be measured during the measurement period, the measured number of MHPs is not the original value corresponding to the distance to the object to be measured, resulting in an error in distance measurement. It was. In particular, when the distance to the measurement object is increased, the return light from the measurement object is reduced and the signal waveform of the MHP is reduced, so that the above problem may become more prominent. In other words, if the drive current amplitude of the semiconductor laser is increased to increase the distance resolution, the measurement range is shortened, and if the drive current amplitude is decreased to extend the measurement range, the distance resolution is reduced. there were.

  The present invention has been made to solve the above-described problems. In a distance meter and a distance measurement method for measuring the number of MHPs using a counter and obtaining a distance from a measurement object, an improvement in distance resolution and a measurement range are provided. The purpose is to achieve both long distances.

The distance meter of the present invention includes at least a semiconductor laser that emits laser light to a measurement target, a first oscillation period that includes at least a period in which the oscillation wavelength continuously increases monotonously, and a period in which the oscillation wavelength continuously decreases monotonously. A laser driver for operating the semiconductor laser so that the second oscillation period including the alternating current exists, and interference light between the laser light emitted from the semiconductor laser and the return light from the measurement target is converted into an electrical signal And the number of interference waveforms generated by the laser light emitted from the semiconductor laser and the return light from the measurement object included in the output signal of the light receiver, and the first oscillation period and the second First counting means for counting each of the oscillation periods, computing means for obtaining a distance from the measurement object from the counting result of the first counting means, the first oscillation period and the first Second counting means for counting the number of the interference waveforms for each divided period obtained by dividing each counting period of the oscillation period, and the driving current supplied from the laser driver to the semiconductor laser is minimum. The sum of the counting results of the second counting means in the first set of divided periods including at least the minimum drive current divided period, and the division different from the first set including at least the minimum drive current divided period When the ratio of the sum of the counting results of the second counting means in the second set of periods is determined for each of the first oscillation period and the second oscillation period, the first oscillation period and Control means for controlling the amplitude of the drive current via the laser driver so that the ratio is within a numerical range when the ratio is outside a predetermined numerical range in both of the second oscillation periods; Those having.
Further, the distance meter of the present invention includes the semiconductor laser, the laser driver, a light receiver that converts an optical output of the semiconductor laser into an electric signal, and radiation from the semiconductor laser included in the output signal of the light receiver. A first counting means for counting the number of interference waveforms caused by the self-coupling effect between the laser beam and the return light from the measurement object for each of the first oscillation period and the second oscillation period; Means, the second counting means, and the control means.
In one configuration example of the distance meter of the present invention, the control means performs amplitude control of the drive current only when the ratio is substantially equal between the first oscillation period and the second oscillation period. is there.

Further, the present invention provides a distance measurement method for emitting laser light to a measurement object using a semiconductor laser, wherein the first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonously and the oscillation wavelength continuously monotonously. An oscillation procedure for operating the semiconductor laser so that second oscillation periods including at least a decreasing period alternately exist, and interference light between laser light emitted from the semiconductor laser and return light from the measurement target The number of interference waveforms generated by the laser light emitted from the semiconductor laser and the return light from the measurement object, included in the output signal of the light receiver that converts the signal into an electrical signal, is calculated as the first oscillation period and the second A first counting procedure for counting each oscillation period, a calculation procedure for obtaining a distance from the measurement object from the counting result of the first counting procedure, the first oscillation period and the previous A second counting procedure for counting the number of the interference waveforms for each divided period obtained by dividing each counting period of the second oscillation period, and when the drive current supplied from the laser driver to the semiconductor laser is minimum The sum of the counting results of the second counting procedure in the first set of divided periods including at least the minimum drive current divided period as the divided period is different from the first set including at least the minimum drive current divided period. When the ratio of the counting result of the second counting procedure in the second set of divided periods is determined for each of the first oscillation period and the second oscillation period, the first oscillation period And a control procedure for controlling the amplitude of the drive current via the laser driver so that the ratio falls within the numerical range when the ratio is outside the predetermined numerical range in both the second oscillation period and the second oscillation period. It is as it has.
Further, the distance measuring method of the present invention includes a laser beam emitted from the semiconductor laser and an object to be measured, which are included in the oscillation procedure and an output signal of a light receiver that converts an optical output of the semiconductor laser into an electrical signal. The first counting procedure, the calculation procedure, and the second counting procedure for counting the number of interference waveforms caused by the self-coupling effect with the return light of each of the first oscillation period and the second oscillation period And the control procedure.

  According to the present invention, the number of interference waveforms is counted for each divided period obtained by dividing each counting period of the first oscillation period and the second oscillation period, and the drive current supplied from the laser driver to the semiconductor laser is The total sum of the counting results of the second counting means in the first set of divided periods including at least the minimum drive current divided period that is the minimum divided period is different from the first set including at least the minimum drive current divided period. When the ratio of the counting result of the second counting means in the second set of the divided periods is obtained for each of the first oscillation period and the second oscillation period, the first oscillation period and the second oscillation period The range in which the measurable distance does not become too short by controlling the amplitude of the drive current via the laser driver so that the ratio is within the numerical range when the ratio is outside the predetermined numerical range in both oscillation periods With drive current Can be kept large amplitude, it is possible to achieve both the improvement of resolution of the distance between the long range of the measurement range.

  Further, in the present invention, the amplitude of the drive current is controlled only when the ratio is substantially equal between the first oscillation period and the second oscillation period, so that the measurement object is in an acceleration motion. It can be excluded and an error in amplitude control can be prevented.

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

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a distance meter according to an embodiment of the present invention. The distance meter of FIG. 1 measures a semiconductor laser 1 that emits laser light to a measurement object 12, a photodiode 2 that converts the optical output of the semiconductor laser 1 into an electrical signal, and the light from the semiconductor laser 1 is collected. A lens 3 that irradiates the object 12 and collects return light from the object 12 to be incident on the semiconductor laser 1, and a first oscillation period and an oscillation wavelength in which the oscillation wavelength continuously increases in the semiconductor laser 1 A laser driver 4 that alternately repeats a continuously decreasing second oscillation period, a current-voltage conversion amplifier 5 that converts and amplifies the output current of the photodiode 2 into a voltage, and a current-voltage conversion amplifier 5 The signal extraction circuit 11 that differentiates the output voltage twice and the number of MHPs included in the output voltage of the signal extraction circuit 11 are counted, and the amplitude of the drive current of the semiconductor laser 1 is inappropriate from the counting result. A counting device 8 that controls the laser driver 4 so that the amplitude is appropriate when set, a computing device 9 that calculates the distance to the measurement object 12 from the number of MHPs, and a display that displays the calculation results of the computing device 9 Device 10.

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

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

  FIG. 2 is a diagram showing the change over time of the oscillation wavelength of the semiconductor laser 1. In FIG. 2, t-1 is the t-1th oscillation period, t is the tth oscillation period, t + 1 is the t + 1th oscillation period, t + 2 is the t + 2nd oscillation period, t + 3 is the t + 3th oscillation period, and t + 4 is The t + 4th oscillation period, λa is the minimum value of the oscillation wavelength in each period, λb is the maximum value of the oscillation wavelength in each period, and T is the period of the triangular wave.

  Laser light emitted from the semiconductor laser 1 is collected by the lens 3 and enters the measurement object 12. The light reflected by the measurement object 12 is collected by the lens 3 and enters the semiconductor laser 1. However, condensing by the lens 3 is not essential. The photodiode 2 converts the light output of the semiconductor laser 1 into a current. The current-voltage conversion amplifier 5 converts the output current of the photodiode 2 into a voltage and amplifies it.

  The signal extraction circuit 11 has a function of extracting a superimposed signal from a modulated wave. For example, two differentiation circuits 6 and 7 are used. The differentiation circuit 6 differentiates the output voltage of the current-voltage conversion amplifier 5, and the differentiation circuit 7 differentiates the output voltage of the differentiation circuit 6. 3A schematically shows the output voltage waveform of the current-voltage conversion amplifier 5, FIG. 3B schematically shows the output voltage waveform of the differentiating circuit 6, and FIG. 6 is a diagram schematically showing an output voltage waveform of a circuit 7. FIG. These are obtained by removing the oscillation waveform (carrier wave) of the semiconductor laser 1 of FIG. 2 from the waveform (modulated wave) of FIG. 3A, which is the output of the photodiode 2, and the MHP waveform (superposition) of FIG. (Wave) is extracted.

  FIG. 4 is a block diagram showing an example of the configuration of the counting device 8. The counting device 8 includes counters 81 and 82, a storage unit 83, and a control unit 84. The current-voltage conversion amplifier 5, the signal extraction circuit 11 and the counter 81 constitute first counting means, and the current-voltage conversion amplifier 5, the signal extraction circuit 11 and the counter 82 constitute second counting means. is doing.

  FIGS. 5A and 5B are diagrams for explaining the operation of the counting device 8, and schematically show the output voltage waveform of the signal extraction circuit 11. FIG. 5A shows a case where the amplitude of the triangular wave driving current of the semiconductor laser 1 is appropriate, and FIG. 5B shows a case where the amplitude of the triangular wave driving current is excessive. 5A and 5B, t-1 is shown as an example of the first oscillation periods t-1, t + 1, t + 3, and t is shown as an example of the second oscillation periods t, t + 2, t + 4. Is shown.

First, the counter 81 of the counting device 8 determines the number of MHPs included in the output voltage of the signal extraction circuit 11 for each counting period of the first oscillation periods t-1, t + 1, t + 3 and the second oscillation periods t, t + 2, and so on. Count every t + 4 counting period. The counting result of the counter 81 is output to the arithmetic unit 9. 5A and 5B, the first and second oscillation periods are the same as the counting period for ease of description, but the actual counting period is the first, second, Of the two oscillation periods, this is a period excluding a portion where the triangular wave drive current is maximum. It is preferable that the counting period of the first oscillation period and the counting period of the second oscillation period have the same length.
On the other hand, the counter 82 divides the counting periods of the first oscillation period t-1 and the second oscillation period t, respectively, into divided periods At _-1 , _Bt-1 , _Ct-1 , _Ct. , B _t, each a _t, count the number of MHP included in the output voltage of the signal extraction circuit 11.

Divided period A _t-1, B _t-1, C _t-1 is the first counting interval of the oscillation period t-1 may be those obtained by dividing at irregular intervals, divided period C _t, B _t, A _t Alternatively, the counting period of the second oscillation period t may be divided at unequal intervals. However, the first and the oscillation period t-1 the number of divisions of the second oscillation period t are identical, divided period _{A t-1, B t-} 1, C t-1, C t, B t, A t is It is necessary that the time interval be symmetric with respect to the midpoint P of the period T of the triangular wave including the first oscillation period t-1 and the second oscillation period t.
The storage unit 83 stores the count result of the counter 82.

  The control unit 84 controls the laser driver 4 so that the amplitude is appropriate when it is determined from the count result of the counter 82 stored in the storage unit 83 that the amplitude of the triangular wave drive current of the semiconductor laser 1 is inappropriate. The control unit 84 includes the sum of the counting results of the counter 82 in the first set of divided periods including at least the minimum driving current dividing period in which the triangular wave driving current is minimum, and the first including at least the minimum driving current dividing period. The result obtained for each of the first oscillation period t-1 and the second oscillation period t with respect to the ratio of the count results of the counter 82 in the second set of the divided period different from the set is approximately equal, and When the ratio is outside the predetermined numerical range in both the first oscillation period t-1 and the second oscillation period t, it is determined that the amplitude of the triangular wave drive current of the semiconductor laser 1 is excessive, and the ratio is in the numerical range. The amplitude of the triangular wave drive current is controlled through the laser driver 4 so as to be within.

Minimum drive current divided period triangular wave driving current is minimum, in the first oscillation period t-1 A _t-1, a second oscillation interval t in A _t. A first set of at least including divided period the minimum drive current divided period, the first oscillation period in t-1 for example A _t-1 + B _t-1, and the second oscillation period t in A _t + B _t . On the other hand, the second set of divided periods including at least the minimum drive current divided period is, for example, A _t-1 + B _t-1 + C _t-1 in the first oscillation period t ₋₁ , and in the second oscillation period t. A _t + B _t + C _t Divided period _{A t-1, B t-} 1, C t-1, C t, B t, count results respectively nA _t-1 of the counter 82 in the _{A t, nB t-1,} nC t-1, nC t , NB _t , nA _t , the ratio of the sum of the counting results in the first oscillation period t−1 is (nA _t−1 + nB _t−1 ) / (nA _t−1 + nB _t−1 + nC _{t− 1} ), and the ratio in the second oscillation period t is (nA _t + nB _t ) / (nA _t + nB _t + nC _t ).

When the amplitude of the triangular wave drive current of the semiconductor laser 1 is appropriate, the MHP signal waveform is sufficiently large as shown in FIG. 5A, so that the counters 81 and 82 can correctly count the number of MHPs. . For this reason, the ratio of the sum of the counting results of the counter 82 is within a predetermined numerical range. If the counting periods of the first oscillation period t-1 and the second oscillation period t are divided into equal intervals and are not affected by noise or the like during the measurement period, the ratio (nA _t-1 + NB _t-1 ) / (nA _t-1 + nB _t-1 + nC _t-1 ) and (nA _t + nB _t ) / (nA _t + nB _t + nC _t ) are both 2/3. Therefore, 2/3 ± α considering the error ± α such as noise with respect to the predetermined value 2/3 is a predetermined numerical range.

On the other hand, when the amplitude of the triangular wave drive current is excessive, the MHP signal waveform becomes smaller than the detection limit and disappears when the drive current is small as shown in FIG. Cannot correctly count the number of MHPs. For this reason, the ratio of the sum of the counting results of the counter 82 is outside the numerical range. In the example of FIG. 5B, the ratios (nA _t-1 + nB _t-1 ) / (nA _t-1 + nB _t-1 + nC _t-1 ) and (nA _t + nB _t ) / (nA _t + nB _t + nC _t ) Is smaller than 2/3.

  FIG. 6 is a diagram showing a waveform of a triangular wave driving current supplied from the laser driver 4 to the semiconductor laser 1, FIG. 6A shows a case where the amplitude of the triangular wave driving current is excessive, and FIG. 6B shows a triangular wave. This shows a case where the amplitude of the drive current is appropriate. As shown in FIG. 6A, when the amplitude of the triangular wave drive current is excessive, the ratio of the sum of the count results of the counter 82 is out of the numerical range, so the control unit 84 controls the laser so that the ratio is within the numerical range. The amplitude of the triangular wave drive current is controlled through the driver 4. At this time, the laser driver 4 keeps the maximum value of the drive current fixed at a constant value (the upper limit value CL of the drive current defined by the semiconductor laser 1 in the example of FIGS. 6A and 6B), The amplitude AMP of the drive current is reduced by increasing the minimum value of the drive current. Thus, the amplitude of the drive current can be set to an appropriate value.

The counting device 8 performs the above-described processing every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4.
In the present embodiment, the signal waveform of the MHP shown in FIG. 5B has been described as the case where the amplitude of the triangular wave drive current is excessive (when the minimum value of the drive current is too small), but FIG. ) Also occurs when the distance to the measurement object 12 is long. Also in this case, since the ratio of the sum of the counting results of the counter 82 is outside the numerical range, the measurable distance can be extended by controlling the amplitude of the triangular wave drive current so that the ratio is within the numerical range. it can.

  In addition, the control unit 84 sets the ratio of the first oscillation period t−1 and the second oscillation period t to be approximately equal as a condition for performing the amplitude control of the triangular wave drive current. The reason for providing such a condition is that the acceleration motion of the measurement object 12 is taken into consideration. When the measurement object 12 is accelerating, the ratio is different between the first oscillation period t-1 and the second oscillation period t. Therefore, it is necessary to control the amplitude of the triangular wave drive current after excluding such a case.

In the present embodiment, as examples of the ratio, (nA _t-1 + nB _t-1 ) / (nA _t-1 + nB _t-1 + nC _t-1 ), (nA _t + nB _t ) / (nA _t + nB _t + NC _t ), but the present invention is not limited to this. If the combination of the divided periods is selected so that the first set and the second set of the divided periods including at least the minimum drive current divided period are different, You may obtain | require a ratio by the combination of.
In the present embodiment, the number of divisions of the first oscillation periods t-1, t + 1, t + 3 and the second oscillation periods t, t + 2, t + 4 is 3, but the number of divisions may be two or more.

  Next, the arithmetic device 9 obtains the distance from the measurement object 12 based on the number of MHPs measured by the counter 81 of the counting device 8. The number of MHPs in a certain period is proportional to the measurement distance. Therefore, if the relationship between the number of MHPs and the distance in a certain counting period is obtained in advance and registered in the database (not shown) of the arithmetic device 9, the arithmetic device 9 counts the number of MHPs measured by the counter device 8. The distance to the measurement object 12 can be obtained by acquiring the distance value corresponding to.

Alternatively, if a mathematical expression indicating the relationship between the number of MHPs and the distance in the counting period is obtained and set in advance, the arithmetic device 9 performs measurement by substituting the number of MHPs measured by the counting device 8 into the mathematical formula. The distance to the object 12 can be calculated. The arithmetic unit 9 performs the above processing every first oscillation period t-1, t + 1, t + 3 and every second oscillation period t, t + 2, t + 4.
The display device 10 displays the distance (displacement) from the measurement object 12 calculated by the arithmetic device 9 in real time.

  As described above, in the present embodiment, by controlling the amplitude of the drive current based on the ratio of the count results of the counter 82, the amplitude of the drive current is kept large within a range in which the measurable distance is not too short. Therefore, it is possible to achieve both the improvement of the distance resolution and the extension of the measurement range.

  Note that the counting device 8 and the computing device 9 in the present embodiment can be realized by, for example, a computer having a CPU, a storage device, and an interface and a program for controlling these hardware resources. A program for operating such a computer is provided in a state of being recorded on a recording medium such as a flexible disk, a CD-ROM, a DVD-ROM, or a memory card. The CPU writes the read program into the storage device, and executes the processing described in this embodiment in accordance with this program.

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

It is a block diagram which shows the structure of the distance meter used as 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 embodiment of this invention. It is a figure which shows typically the output voltage waveform of the current-voltage conversion amplifier in embodiment of this invention, and the output voltage waveform of a differentiation circuit. It is a block diagram which shows an example of a structure of the counting device in embodiment of this invention. It is a figure for demonstrating operation | movement of the counting apparatus of FIG. It is a figure which shows the waveform of the triangular wave drive current supplied to a semiconductor laser from a laser driver in 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 figure which shows the magnitude | size of the width of the frequency which became discontinuous by the mode hopping phenomenon.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Photodiode, 3 ... Lens, 4 ... Laser driver, 5 ... Current-voltage conversion amplifier, 6, 7 ... Differentiation circuit, 8 ... Counting device, 9 ... Arithmetic device, 10 ... Display device, 11 ... Signal extraction circuit, 12 ... Measurement object, 81, 82 ... Counter, 83 ... Storage part, 84 ... Control part.

Claims (6)

A semiconductor laser that emits laser light to the object to be measured;
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. A laser driver,
A light receiver that converts interference light between laser light emitted from the semiconductor laser and return light from the measurement object into an electrical signal;
The number of interference waveforms generated by the laser light emitted from the semiconductor laser and the return light from the measurement object included in the output signal of the light receiver is determined for each of the first oscillation period and the second oscillation period. First counting means for counting about;
A calculation means for obtaining a distance from the measurement object from a counting result of the first counting means;
Second counting means for counting the number of the interference waveforms for each divided period obtained by dividing each counting period of the first oscillation period and the second oscillation period;
Sum of count results of the second counting means in the first set of divided periods including at least the minimum drive current divided period which is the divided period when the drive current supplied from the laser driver to the semiconductor laser is minimum And a ratio between the first oscillation period and the sum of the counting results of the second counting means in a second set of different divided periods from the first set including at least the minimum drive current divided period, When calculated for each of the second oscillation periods, the ratio is within a numerical range when the ratio is outside a predetermined numerical range in both the first oscillation period and the second oscillation period. And a control means for controlling the amplitude of the drive current via the laser driver. A semiconductor laser that emits laser light to the object to be measured;
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. A laser driver,
A light receiver for converting the optical output of the semiconductor laser into an electrical signal;
The number of interference waveforms generated by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, included in the output signal of the light receiver, is calculated as the first oscillation period and the second oscillation period. First counting means for counting for each of the oscillation periods;
A calculation means for obtaining a distance from the measurement object from a counting result of the first counting means;
Second counting means for counting the number of the interference waveforms for each divided period obtained by dividing each counting period of the first oscillation period and the second oscillation period;
Sum of count results of the second counting means in the first set of divided periods including at least the minimum drive current divided period which is the divided period when the drive current supplied from the laser driver to the semiconductor laser is minimum And a ratio between the first oscillation period and the sum of the counting results of the second counting means in a second set of different divided periods from the first set including at least the minimum drive current divided period, When calculated for each of the second oscillation periods, the ratio is within a numerical range when the ratio is outside a predetermined numerical range in both the first oscillation period and the second oscillation period. And a control means for controlling the amplitude of the drive current via the laser driver. The distance meter according to claim 1 or 2,
The distance meter according to claim 1, wherein the control means performs amplitude control of the drive current only when the ratio is substantially equal between the first oscillation period and the second oscillation period. In a distance measurement method for emitting laser light to a measurement object using a semiconductor laser,
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. Oscillation procedure
The laser light emitted from the semiconductor laser and the measurement object included in the output signal of the light receiver that converts the interference light between the laser light emitted from the semiconductor laser and the return light from the measurement object into an electrical signal. A first counting procedure for counting the number of interference waveforms caused by the return light of each of the first oscillation period and the second oscillation period;
A calculation procedure for obtaining a distance from the measurement object from the counting result of the first counting procedure;
A second counting procedure for counting the number of the interference waveforms for each divided period obtained by dividing each counting period of the first oscillation period and the second oscillation period;
The sum of the counting results of the second counting procedure in the first set of divided periods including at least the minimum driving current divided period that is the divided period when the drive current supplied from the laser driver to the semiconductor laser is the minimum; The ratio between the first oscillation period and the second sum of the counting results of the second counting procedure in the second group of the divided period different from the first group including at least the minimum drive current dividing period, When each of the two oscillation periods is obtained, the ratio is within a numerical range when the ratio is outside a predetermined numerical range in both the first oscillation period and the second oscillation period. And a control procedure for controlling the amplitude of the drive current via a laser driver. In a distance measurement method for emitting laser light to a measurement object using a semiconductor laser,
The semiconductor laser is operated so that a first oscillation period including at least a period in which the oscillation wavelength continuously increases monotonically and a second oscillation period including at least a period in which the oscillation wavelength continuously decreases monotonously exist. Oscillation procedure
The number of interference waveforms generated by the self-coupling effect between the laser light emitted from the semiconductor laser and the return light from the measurement object, included in the output signal of the light receiver that converts the optical output of the semiconductor laser into an electrical signal. A first counting procedure counting for each of the first oscillation period and the second oscillation period;
A calculation procedure for obtaining a distance from the measurement object from the counting result of the first counting procedure;
A second counting procedure for counting the number of the interference waveforms for each divided period obtained by dividing each counting period of the first oscillation period and the second oscillation period;
The sum of the counting results of the second counting procedure in the first set of divided periods including at least the minimum driving current divided period that is the divided period when the drive current supplied from the laser driver to the semiconductor laser is the minimum; The ratio between the first oscillation period and the second sum of the counting results of the second counting procedure in the second group of the divided period different from the first group including at least the minimum drive current dividing period, When each of the two oscillation periods is obtained, the ratio is within a numerical range when the ratio is outside a predetermined numerical range in both the first oscillation period and the second oscillation period. And a control procedure for controlling the amplitude of the drive current via a laser driver. In the distance measuring method according to claim 4 or 5,
The distance measurement method according to claim 1, wherein the control procedure performs amplitude control of the drive current only when the ratio is substantially equal between the first oscillation period and the second oscillation period.

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