JPWO2016046905A1 - Measuring apparatus, measuring method, computer program and recording medium - Google Patents

Abstract

The measuring device is included in the output signal of the light receiving means (120) for irradiating the measurement target (200) with the laser light, the light receiving means (130) for receiving the laser light scattered by the measurement target, and the light receiving means. The output means (170) for outputting information on the movement of the measurement target based on the beat signal resulting from the Doppler shift of the laser light, and the irradiation state of the laser light by the irradiation means based on the beat signal within a predetermined period And control means (190) for controlling. According to this measuring apparatus, it is possible to suppress the occurrence of measurement errors due to mode hops.

Description

  The present invention relates to a technical field of a measuring apparatus and a measuring method, and a computer program and a recording medium that measure, for example, information related to movement of the target to be measured using light scattered in the target to be measured.

  In a semiconductor laser used in this type of measuring apparatus, the band gap changes due to an increase in the temperature of the laser, so that the oscillation wavelength gradually changes to a long wavelength as the temperature increases. When the temperature continues to rise, the oscillation wavelength suddenly jumps to the wavelength having the maximum gain on the long wavelength side at a certain timing. This phenomenon is called mode hopping, and is known to cause a measurement error in a measuring apparatus using optical Doppler, for example.

  Patent Document 1 proposes a technique of controlling the temperature of a laser light source using a Peltier element in order to suppress the occurrence of the mode hop described above.

JP 2001-120509 A

  In the technique described in Patent Document 1 described above, a Peltier element that is a heat absorbing means is always operated. However, since the Peltier element consumes a large amount of power, it is not preferable to always operate it from the viewpoint of power saving. Moreover, since battery driving becomes difficult when the power consumption is large, there is a technical problem that an increase in cost and an increase in the size of the apparatus cannot be avoided.

  Examples of problems to be solved by the present invention include the above. It is an object of the present invention to provide a measuring apparatus and a measuring method, a computer program, and a recording medium that can suitably suppress occurrence of a measurement error due to mode hops.

  A first measuring apparatus for solving the above problems includes an irradiating means for irradiating a measurement target with laser light, a light receiving means for receiving the laser light scattered by the measurement target, and an output of the light receiving means. Based on a beat signal resulting from a Doppler shift of the laser light included in the signal, output means for outputting information on the movement of the measurement target, and on the basis of the beat signal within a predetermined period, by the irradiation means Control means for controlling the irradiation state of the laser beam.

  A second measuring apparatus for solving the above problems includes an irradiating means for irradiating a measurement target with laser light, a light receiving means for receiving the laser light scattered by the measurement target, and an output of the light receiving means. Output means for outputting information relating to the movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the signal, and the measurement target based on the beat signal within a predetermined period Detecting means for detecting a state in which an error in information relating to the movement of the image exceeds a predetermined error.

  A first measurement method for solving the above problems is obtained by an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and a light reception step. An output step of outputting information relating to movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the output signal, and the irradiation based on the beat signal within a predetermined period And a control step of controlling the irradiation state of the laser beam in the step.

  A second measurement method for solving the above problems is obtained in an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and a light reception step. An output step of outputting information relating to movement of the measurement target based on a beat signal caused by a Doppler shift of the laser light included in the output signal, and based on the beat signal within a predetermined period, A detection step of detecting a state in which an error in information relating to movement of the measurement object exceeds a predetermined error.

  A first computer program for solving the above problems is obtained in an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and the light reception step. An output step of outputting information relating to movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the output signal, and the irradiation based on the beat signal within a predetermined period And causing the computer to execute a control step of controlling the irradiation state of the laser light in the step.

  A second computer program for solving the above problems is obtained in an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and the light reception step. An output step of outputting information relating to movement of the measurement target based on a beat signal caused by a Doppler shift of the laser light included in the output signal, and based on the beat signal within a predetermined period, And causing a computer to execute a detection step of detecting a state in which an error in information relating to movement of the measurement object exceeds a predetermined error.

  A recording medium for solving the above problems is recorded with the above-described computer program (including various aspects thereof).

It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 1st Example. It is a circuit diagram which shows the specific structure of the light receiving element which concerns on 1st Example, and I-∨ converter. It is a block diagram which shows the specific structure of the blood flow calculating part which concerns on 1st Example. It is a graph which shows the specific example of a blood flow spectrum. It is a block diagram which shows the specific structure of the mode hop detection part which concerns on 1st Example. It is a flowchart which shows the flow of the mode hop detection process which concerns on 1st Example. It is a time chart which shows the mode hop detection waveform example which concerns on 1st Example. It is a time chart which shows the example of a mode hop escape waveform which concerns on 1st Example. It is a graph which shows the relationship between a count value and a blood flow measurement error. It is a flowchart which shows the flow of the blood-flow calculation process at the time of abnormality detection. It is a flowchart which shows the flow of the limit value setting of LD drive current. It is a block diagram which shows the structure of the mode hop detection part in the measuring apparatus which concerns on 2nd Example. It is a time chart which shows the mode hop detection waveform example which concerns on 2nd Example. It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 3rd Example. It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 4th Example. It is a block diagram which shows the structure of the amplitude limiter part in the measuring apparatus which concerns on 5th Example. It is a graph (the 1) which shows an example of an amplification signal and a blood-flow output. It is a graph (the 2) which shows an example of an amplification signal and a blood-flow output. It is a graph (the 3) which shows an example of an amplification signal and a blood-flow output.

<1>
The first measurement apparatus according to the present embodiment includes an irradiation unit that irradiates a measurement target with laser light, a light reception unit that receives the laser light scattered by the measurement target, and an output signal of the light reception unit. An output means for outputting information relating to movement of the measurement object based on a beat signal resulting from a Doppler shift of the laser light included; and the laser by the irradiation means based on the beat signal within a predetermined period. Control means for controlling the light irradiation state.

  According to the first measuring apparatus according to the present embodiment, the laser beam is irradiated from the irradiation unit to the measurement target during the operation. The irradiation means is configured to include, for example, a semiconductor laser element or the like, and is disposed at a position where the measurement target can be efficiently irradiated with light when used. The measurement target is a fluid such as blood of a living body. However, the measurement target is not particularly limited, and may be other than fluid (for example, an individual) as long as it moves.

  The laser light emitted from the irradiating means is scattered (specifically reflected and transmitted) in the object to be measured and then received by the light receiving means. The light receiving means includes, for example, a photodiode and outputs an output signal corresponding to the received light.

  The output signal of the light receiving means is used when outputting information related to the movement of the measurement target from the output means. Specifically, in the output means, information on the movement of the measurement target is obtained based on a beat signal resulting from a Doppler shift (hereinafter referred to as “optical Doppler” as appropriate) of the laser light included in the output signal of the light receiving means. Calculated. Here, “information relating to movement” is a broad concept including information that indirectly indicates such information in addition to the movement speed, movement amount, and movement direction of the measurement target.

  When trying to output information on the movement of the measurement target using optical Doppler, an error may occur in the measurement result due to an abnormality in the irradiation state of the irradiation means. For example, when a mode hop occurs due to an increase in the temperature of the irradiation unit, the amplitude value of the output signal of the light receiving unit varies greatly (for example, the amplitude instantaneously becomes a very large value). As a result, unnecessary fluctuation may occur in the measurement result obtained from the output signal, and an error may occur in the measurement result.

  For this reason, in this embodiment, in particular, at the time of measurement, control of the irradiation state of the laser light by the control means is executed. The control means controls the irradiation state of the laser light based on the beat signal within a predetermined period. More specifically, the control means analyzes the beat signal within a predetermined period, and determines that a mode hop that adversely affects the measurement result has occurred, controls the laser light irradiation state. Suppresses the occurrence of mode hops. Here, the “predetermined period” is a period that is set to determine whether or not the mode hop occurs at a frequency that adversely affects the measurement result. For example, an erroneous determination occurs. It is set as a period that is long enough not to cause an adverse effect due to mode hops.

  Controlling the laser light irradiation state as described above suppresses the generation of mode hops and reduces the influence on the measurement results even if mode hops that adversely affect the measurement results occur. can do. Further, in the present embodiment, the control of the irradiation state is not always executed, and is executed when it is determined that an inappropriate mode hop has occurred based on a beat signal within a predetermined period. In other words, the irradiation state control is not always executed when a mode hop occurs, and the irradiation state control is executed when a mode hop that may have an adverse effect occurs. Therefore, the adverse effect on the measurement result can be reduced very efficiently.

  As described above, according to the measuring apparatus according to the present embodiment, it is possible to avoid inconvenience associated with the occurrence of mode hops and to perform measurement suitably.

<2>
In one aspect of the first measurement apparatus according to the present embodiment, the control unit counts the number of times that the amplitude value of the beat signal exceeds a predetermined amplitude value within the predetermined period, and the counted number of times is predetermined. When the number of times is exceeded, the irradiation state of the laser beam by the irradiation unit is controlled.

  According to this aspect, by comparing the number of times that the amplitude value of the beat signal exceeds the predetermined amplitude value with the predetermined number of times, occurrence of an inappropriate mode hop can be detected easily and accurately. The “predetermined amplitude value” is set as a value for discriminating between the amplitude value of the beat signal in a state where a mode hop has occurred and the amplitude value of a beat signal in a state where no mode hop has occurred, The “predetermined number of times” is set as a value for determining whether or not the mode hop occurs with a frequency that affects the measurement result.

<3>
In another aspect of the first measuring apparatus according to the present embodiment, the control means integrates and averages the amplitude value of the beat signal within the predetermined period, and the averaged amplitude value has a predetermined threshold value. When it exceeds, the irradiation state of the laser beam by the irradiation means is controlled.

  According to this aspect, the amplitude value of the beat signal is integrated and averaged by, for example, an LPF (low-pass filter). The averaged value is a value that increases in accordance with the frequency of occurrence of an abnormal increase in amplitude value (that is, the frequency of occurrence of mode hops). Therefore, the occurrence of an inappropriate mode hop can be detected easily and accurately by comparing the averaged value with a predetermined threshold value. The “predetermined threshold value” may be determined by a prior simulation or the like as a threshold value for discriminating a mode hop that does not affect the measurement result and a mode hop that can affect the measurement result.

<4>
In another aspect of the first measurement apparatus according to the present embodiment, the output means calculates information on the movement of the measurement target using fast Fourier transform, and the fast Fourier transform buffer is used for the predetermined period. It is set as a period according to the period.

  According to this aspect, the laser light is controlled using the data accumulated during the fast Fourier transform buffer period. That is, the occurrence of a mode hop is detected using data stored for calculating information related to the movement of the measurement target. Therefore, mode hop suppression can be realized very efficiently in practice.

  The predetermined period and the buffer period do not have to be the same value, and may be set as a period that can be derived from the buffer period (for example, a period that is an integral multiple of the buffer period).

<5>
In another aspect of the measuring apparatus according to the present embodiment, the control unit controls the irradiation state of the laser light by the irradiation unit by changing a driving current of the irradiation unit.

  According to this aspect, it is possible to reliably suppress the mode hop by changing the driving current of the irradiation unit to a value that suppresses the mode hop. Note that an AC component may be placed on the driving current of the irradiation unit so that a single mode hop is generated with a long period that does not easily affect the measurement result.

<6>
In the aspect in which the driving current of the irradiation unit is changed, the control unit may change the driving current of the irradiation unit within a predetermined range corresponding to a reference current.

  If comprised in this way, it will become possible to change the drive current of an irradiation means in the suitable range, and generation | occurrence | production of the problem accompanying the change of a drive current can be prevented. Specifically, it can be prevented that the driving current of the irradiation unit becomes too low, the power of the irradiated laser light is reduced, and the S / N ratio in measurement is deteriorated. Further, it can be prevented that the driving current of the irradiating means becomes too high, the power of the irradiated laser light increases, and the life of the irradiating means is reduced.

<7>
In the aspect in which the driving current of the irradiation unit is changed within the predetermined range described above, the control unit increases the driving current of the irradiation unit every time it determines that the irradiation state of the laser beam by the irradiation unit should be controlled. The direction may be changed step by step by a predetermined value in one direction.

  If comprised in this way, it can prevent that a drive current raises / lowers largely by control, and a hunting phenomenon will generate | occur | produce. Thereby, it is possible to prevent an increase in power consumption and an increase in measurement error due to the hunting phenomenon. Note that the “predetermined value” that is a unit of fluctuation of the drive current may be set to a value that is small enough to avoid the hunting phenomenon described above.

<8>
In the aspect in which the driving current of the irradiation unit is changed stepwise in one direction, the control unit changes the direction of change of the driving current of the irradiation unit when a change in the driving current exceeding the predetermined range is requested. It may be reversed.

  With this configuration, even when the drive current is controlled near the boundary of the predetermined range, stepwise fluctuations in the drive current can be realized. For example, even if the drive current is close to the lower limit value of the predetermined range as a result of performing the control for decreasing the drive current a plurality of times, the change direction of the drive current is reversed in the increasing direction. Continuously, stepwise drive current change can be realized.

<9>
In another aspect of the measuring apparatus according to the present embodiment, the control unit controls the irradiation state of the laser light by the irradiation unit by changing the temperature of the irradiation unit.

  According to this aspect, it is possible to reliably suppress mode hops by changing the temperature of the irradiation means using a Peltier element or the like, for example.

<10>
In another aspect of the measuring apparatus according to this embodiment, the control unit changes the refractive index of a liquid crystal window provided between the irradiation unit and the measurement target, so that the laser by the irradiation unit is used. Controls the light irradiation state.

  According to this aspect, by changing the refractive index of the liquid crystal window, it is possible to suppress the return light from the measurement target from entering the irradiation unit. Therefore, the occurrence of mode hops due to the incident return light can be reliably suppressed.

<11>
In another aspect of the measuring apparatus according to the present embodiment, when the control unit determines that the irradiation state of the laser beam by the irradiation unit should be controlled, the output so as to maintain the output before the determination. Output maintaining means for controlling the means is further provided.

  According to this aspect, when it is determined that the laser beam irradiation state by the irradiation unit should be controlled (that is, when an inappropriate mode hop is detected), the output unit detects the mode hop. The previous output is maintained. For this reason, even if the output of the output means becomes an inappropriate value due to the mode hop, it is possible to continue outputting an appropriate value. Note that the output maintenance of the output unit may be canceled when the mode hop is no longer detected by controlling the irradiation state of the laser beam by the control unit, for example.

<12>
In another aspect of the measuring apparatus according to the present embodiment, the measuring device further includes a limiting unit that limits an amplitude value of an output signal of the light receiving unit within a predetermined amplitude range, and the output unit receives the light reception limited by the limiting unit. Information relating to the movement of the object to be measured is output based on a beat signal caused by the Doppler shift of the laser light included in the output signal of the means.

  According to this aspect, the amplitude value of the output signal of the light receiving unit is limited within a predetermined range by the limiting unit. For this reason, the output signal is output in a state where a portion exceeding the predetermined amplitude range is cut. The “predetermined amplitude range” here is an amplitude range (in other words, an upper limit value of amplitude) set as a reference for amplitude limitation in order to suppress the influence on the measurement result due to mode hopping. is there. The predetermined amplitude range is set as a range in which the influence by the mode hop can be effectively suppressed by a prior simulation or the like. The predetermined amplitude range may be a fixed value, or may be a value that can be changed according to a measurement situation or the like.

  If the amplitude value is limited as described above, even if a mode hop occurs, the fluctuation portion due to the mode hop is removed from the output signal of the light receiving means. As a result, the output signal used when outputting the information related to the movement of the measurement target is in a state in which it is not influenced by mode hops at all or almost. Therefore, even in a situation where a mode hop occurs, information regarding the movement of the measurement target is output as accurate.

  Note that the effect of suppressing the effect of mode hops by limiting the amplitude value of the output signal is effective when the frequency of mode hops is relatively moderate, although it depends on the value of the predetermined amplitude range. If the frequency increases significantly, it may not be sufficient. However, in the present embodiment, as described above, the mode hop occurrence frequency can be reduced by controlling the irradiation state of the laser light. Therefore, it is possible to effectively suppress the influence according to the state of occurrence of mode hops.

<13>
The second measuring apparatus according to the present embodiment includes an irradiating unit that irradiates a measurement target with laser light, a light receiving unit that receives the laser light scattered by the measurement target, and an output signal of the light receiving unit. Output means for outputting information related to movement of the measurement target based on a beat signal resulting from the Doppler shift of the laser light included, and movement of the measurement target based on the beat signal within a predetermined period Detecting means for detecting a state in which an error in information relating to the error exceeds a predetermined error.

  According to the second measuring apparatus of the present embodiment, at the time of measurement, it is detected whether or not the error of information relating to the movement of the measurement target exceeds a predetermined error. Here, the “predetermined error” is a value set as a threshold value for determining whether or not an error in information related to the movement of the measurement target is acceptable in the usage environment. Note that whether or not the error in the information related to the movement of the measurement target exceeds a predetermined error is detected based on the beat signal. Specifically, the occurrence frequency of the mode hop in the irradiation means is detected from the beat signal, and an error occurring in the measurement result is estimated from the occurrence frequency.

  According to the second measuring apparatus according to the present embodiment, it is possible to suitably detect a state in which an error occurring in the measurement result exceeds an allowable range. Therefore, it is not accurate by executing, for example, mode hop suppression control. It is possible to prevent the measurement result from being continuously output.

<14>
The first measurement method according to this embodiment includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and an output obtained in the light reception step. In the irradiation process, based on the beat signal included in the signal, based on the beat signal resulting from the Doppler shift of the laser light, and on the basis of the beat signal within a predetermined period And a control step for controlling the irradiation state of the laser beam.

  According to the first measurement method of the present embodiment, as in the first measurement apparatus of the present embodiment described above, the generation of mode hops is suppressed by controlling the irradiation state of the laser light, and the measurement result is obtained. Can be reduced.

  In addition, also in the 1st measuring method which concerns on this embodiment, it is possible to take the various aspects similar to the various aspects in the 1st measuring apparatus which concerns on this embodiment mentioned above.

<15>
The second measurement method according to this embodiment includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and an output obtained in the light reception step. An output step of outputting information relating to movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the signal, and the measurement target based on the beat signal within a predetermined period And a detection step of detecting a state in which an error in information relating to the movement of the image exceeds a predetermined error.

  According to the second measurement method of the present embodiment, similarly to the above-described second measurement apparatus of the present embodiment, it is possible to suitably detect a state where an error occurring in the measurement result exceeds an allowable range. .

<16>
The first computer program according to the present embodiment includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and an output obtained in the light reception step. In the irradiation process, based on the beat signal included in the signal, based on the beat signal resulting from the Doppler shift of the laser light, and on the basis of the beat signal within a predetermined period The computer executes a control process for controlling the irradiation state of the laser beam.

  According to the first computer program of the present embodiment, by causing the computer to execute the same steps as those of the first measurement method according to the present embodiment described above, the occurrence of mode hops is suppressed, and the measurement results are displayed. The influence can be reduced.

<17>
The second computer program according to the present embodiment includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and an output obtained in the light reception step. An output step of outputting information relating to movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the signal, and the measurement target based on the beat signal within a predetermined period And a detection step of detecting a state in which an error in information relating to movement of the image exceeds a predetermined error.

  According to the second computer program of the present embodiment, by causing the computer to execute the same steps as those of the second measurement method according to the present embodiment described above, an error occurring in the measurement result exceeds the allowable range. It is possible to suitably detect the state.

<18>
The recording medium according to the present embodiment records the above-described computer program (including various aspects thereof).

  According to the recording medium of the present embodiment, inconvenience due to the mode hop can be suitably avoided by causing the computer to execute the first computer program or the second computer program of the present embodiment.

  The measuring apparatus and measuring method according to the present embodiment, the operation of the computer program and the recording medium, and other gains will be described in more detail in the following examples.

  Hereinafter, embodiments of a measuring apparatus and a measuring method, a computer program, and a recording medium will be described in detail with reference to the drawings. In the following, a case where the measurement device according to the present invention is configured as a blood flow measurement device that measures blood flow will be described as an example.

<First embodiment>
A measuring apparatus according to the first embodiment will be described with reference to FIGS.

<Overall configuration>
First, the overall configuration of the measuring apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of the measuring apparatus according to the first embodiment.

  In FIG. 1, the measuring apparatus according to the present embodiment includes a laser driving unit 110, a semiconductor laser 120, a light receiving element 130, an IV conversion unit 140, an amplifier 150, an A / D converter 160, and a buffer. The processing unit 165, the blood flow calculation unit 170, the mode hop detection unit 180, and the mode hop suppression processing unit 190 are configured.

  The laser driver 110 generates a current for driving the semiconductor laser 120.

  The semiconductor laser 120 is a specific example of “irradiation means”, and irradiates the measurement target 200 (for example, skin of a living body) with laser light corresponding to the drive current generated in the laser drive unit 110. .

  The light receiving element 130 is a specific example of “light receiving means”, and receives scattered light scattered by the blood 200 out of the laser light emitted from the semiconductor laser 120. The light receiving element 130 outputs a detection current according to the intensity of the received scattered light.

  The IV converter 140 converts the detection current output from the light receiving element 130 into a voltage and outputs a detection voltage.

The amplifier 150 amplifies the detection voltage output from the IV converter 140 and outputs it as an amplified signal. The A / D converter 160 quantizes the input analog amplified signal and outputs it as digital data.

  The buffer processing unit 165 stores a specified number of data output from the A / D converter 160.

  The blood flow calculation unit 170 is a specific example of “output means”, and outputs blood flow (specifically, information relating to movement of the blood 200 such as a flow rate) based on input data. The blood flow calculation unit 170 is configured as a DSP (Digital Signal Processor), for example, and can execute digital signal processing such as frequency analysis on input data.

  The mode hop detection unit 180 detects that a mode hop has occurred in the semiconductor laser 120 (at a high frequency) based on the input buffer data. Further, when the mode hop detection unit 180 detects the occurrence of the mode hop, the mode hop detection unit 180 outputs a signal permitting the execution of the processing in the mode hop suppression processing unit 190 and also sends a previous value hold signal (ie, a blood flow calculation unit 170). , A command to maintain the previous output). A specific configuration of the mode hop detection unit 180 will be described in detail later.

  The mode hop suppression processing unit 190 is a specific example of “control means”, and executes suppression processing for suppressing mode hops according to the detection result in the mode hop detection unit 180. The suppression process will be described in detail later.

<Description of overall operation>
Hereinafter, the overall operation of the above-described measuring apparatus will be described in detail with reference to FIG.

  In FIG. 1, during the operation of the measuring apparatus according to the present embodiment, first, the laser driving unit 110 generates a specified operating current that is equal to or higher than the threshold current of the semiconductor laser 120 and supplies it to the semiconductor laser 120. Thereby, the semiconductor laser 120 oscillates.

  The semiconductor laser 120 is fixed to the measurement target 200 with a clip or the like (not shown) so as to emit laser light to the measurement target 200. When the measurement target 200 is living body skin, the irradiated laser light becomes scattered light scattered by a skin tissue that is a fixed object and scattered light scattered by red blood cells in a capillary that is a moving object, Both of them are received by the light receiving element 130.

  Here, the scattered light scattered by the skin tissue is the reference light, and the scattered light scattered by the red blood cells is scattered light that has caused an optical Doppler shift corresponding to the moving speed of the red blood cells. These two scattered lights cause interference due to the coherence of the laser light. The light receiving element 130 generates a detection current corresponding to the intensity of the optical beat signal as a result of this interference.

  Similar to the semiconductor laser 120, the light receiving element 130 is fixed to the measurement target 200 with a clip or the like (not shown) so as to receive scattered light from the measurement target 200. The detection current corresponding to the optical beat signal detected by the light receiving element 130 is converted into a current voltage by the IV converter 140 and output as a detection voltage.

  Hereinafter, specific configurations and operations of the light receiving element 130 and the IV converter 140 will be described with reference to FIG. FIG. 2 is a circuit diagram showing a specific configuration of the light receiving element and the IV converter according to the first embodiment.

  In FIG. 2, the light receiving element 130 according to the present embodiment includes two light receiving elements 130a and 130b. The light receiving elements 130a and 130b are configured as, for example, photodetectors using PIN type semiconductors. The light receiving elements 130a and 130b have cathodes connected to each other and are connected in series in opposite directions. If comprised in this way, DC component can be suppressed and AC component which is a signal component can be detected efficiently.

  Specifically, a current component corresponding to a steady light component included in the input light (hereinafter appropriately referred to as a “DC (direct current) component”) among currents output from each of the light receiving elements 130a and 130b is reduced or removed. Thus, a current mainly including a current component corresponding to the signal light component included in the input light (hereinafter appropriately referred to as “AC (alternate current) component”) can be output as the detection current. That is, the DC component of the output current of the light receiving element 130a and the DC component of the current output of the light receiving element 130b can be canceled, and a detection current mainly including an AC component corresponding to the signal light component included in the input light is obtained. Can be output.

  For example, if the detection current of the light receiving element 130a is Id1 and the detection current of the light receiving element 130b is Id2, the polarity is reversed and the series connection is made.

Idt = Id2-Id1 (1)
Further, since the scattered light received by the light receiving element 130a and the scattered light received by the light receiving element 130b are different from each other, if the wavelength of the light is used as a reference length, the signal is approximately uncorrelated. Therefore, the intensity of the optical beat signal, which is a signal component, is multiplied by √2 by subtraction.

  On the other hand, since the DC current is canceled out by subtraction, saturation can be prevented even when the detection sensitivity of the transimpedance amplifiers Amp1 and Amp2 is set high. Specifically, the resistance values of the feedback resistors Rf1 and Rf2 can be set high, and the current-voltage conversion sensitivity is improved. As a result, a high detection S / N (Signal-to-Noise ratio) is obtained.

  The non-inverting input terminals of Amp1 and Amp2 are grounded. Due to the negative feedback action of the feedback resistors Rf1 and Rf2 of Amp1 and Amp2, the non-inversion terminal and the inversion terminal are in an imaginary shoot state and have approximately the same potential. Therefore, the anode of the light receiving element 130a and the anode of the light receiving element 130b are at the same potential, and the P light receiving element 130a and the light receiving element 130b operate in a so-called power generation mode. With this power generation mode, dark current is suppressed, and noise increase due to dark current fluctuation can be suppressed.

  The detection voltage Vd1 of Amp1 and the detection voltage Vd2 of Amp2 are as shown in the following equations (2) and (3).

Vd1 = Rf1 · Idt (2)
Vd2 = Rf2 · (−Idt) (3)
Amp3 differentially amplifies the detection voltage of Amp1 and Amp2 and outputs it as Vout. This differential amplification removes common mode noise such as power supply noise and hum.

  Here, when the resistance value is set such that Ra1 = Ra2 = Ra and Rb1 = Rb2 = Rb, Vout is expressed by the following formula (4).

Vout = (Rb / Ra) (Vd1-Vd2) (4)
From the above equations (2), (3), and (4), when the resistance value is set so that Rf1 = Rf2 = Rf, Vout is expressed by the following equation (5).

Vout = 2Rf (Rb / Ra) Idt (5)
From the above equation (5), it can be seen that the detection voltage Vout corresponding to the intensity of the optical beat signal as the signal component can be obtained.

  Returning to FIG. 1, the detected voltage output from the IV converter 140 is input to the amplifier 150. The amplifier 150 amplifies the detection voltage to an amplitude level that matches the input dynamic range of the A / D converter 160, and outputs an amplified signal.

  The amplified signal that is the output of the amplifier 150 is input to the A / D converter 160. The A / D converter 160 quantizes the input amplified signal at a specified sampling frequency and outputs data as a digital value.

  The data output from the A / D converter 160 is input to the buffer processing unit 165 in order to accumulate the number of data used for the frequency analysis of the blood flow calculation unit 170. The buffer processing unit 165 accumulates n-point data necessary for FFT (Fast Fourier Transform), for example. The buffer data accumulated by the buffer processing unit 165 is subjected to digital signal processing by the blood flow calculation unit 170, and information relating to blood flow is output.

  Further, the buffer data accumulated by the buffer processing unit 165 is also input to the mode hop detection unit 180. The mode hop detection unit 180 detects the occurrence of a mode hop (more accurately, the occurrence of a mode hop that affects the measurement result) based on the buffer data. When the mode hop detection unit 180 detects the occurrence of a mode hop, the mode hop suppression processing unit 190 executes a mode hop suppression process (here, drive current control of the laser drive unit 110).

<Blood flow calculation>
Next, a specific configuration and operation of the blood flow calculation unit 170 will be described with reference to FIGS. 3 and 4. FIG. 3 is a block diagram showing a specific configuration of the blood flow calculation unit according to the first embodiment. FIG. 4 is a graph showing a specific example of a blood flow spectrum.

  In FIG. 3, data input to the blood flow calculation unit 170 is first input to the Hanning window processing unit 171. The Hanning window processing unit 171 executes Hanning window processing as preprocessing for FFT (Fast Fourier Transform).

  The FFT processing unit 172 performs frequency analysis on the data limited by the window function by FFT processing.

  The square calculation unit 173 performs complex conjugate processing on the frequency analysis data, and acquires the power spectrum P (f).

  The primary moment accumulating unit 174 multiplies the obtained power spectrum P (f) by the frequency vector f and further accumulates within the specified band to obtain Σ {f · P (f)}.

  The LPF unit 175 removes the high frequency component of the Σ {f · P (f)} signal and multiplies it by a specified gain. Thereby, a blood flow output is obtained.

  As shown in FIG. 4, when the blood flow is low, that is, when the velocity of blood cells, which are scatterers flowing in capillaries, is slow, the power spectrum P (f) of the optical beat signal is indicated by a dotted line in the figure. Thus, the low frequency component is included more than the high frequency component. On the other hand, when the blood flow is high, that is, when the flow velocity of blood cells, which are scatterers flowing in the capillaries, is fast, the power spectrum P (f) of the optical beat signal has the characteristics shown by the solid line in the figure. As a result, the high frequency component is contained more than the low frequency component.

  Thus, when the speed of the moving body is high, the Doppler shift amount of the scattered light increases. Therefore, in the frequency spectrum of the optical beat signal, the components in the high frequency region are increased, and the characteristics as shown in FIG. 4 are exhibited.

  The blood flow calculation unit 170 performs calculation to efficiently detect a change in the power spectrum of the optical beat signal. In this embodiment, a method using frequency analysis by FFT has been described, but the present invention is not limited to this method.

<Mode hop detection>
Next, a specific configuration of the mode hop detection unit 180 will be described in detail with reference to FIG. FIG. 5 is a block diagram showing a specific configuration of the mode hop detection unit according to the first embodiment.

  As shown in FIG. 5, the mode hop detection unit 180 includes an absolute value conversion unit 181, a peak detection unit 182, a level comparison unit 183, a counter unit 184, and a number comparison unit 185. .

  The absolute value converting unit 181 converts the n-point buffer data accumulated by the buffer processing unit 165 into an absolute value and outputs an ABS signal.

  The peak detection unit 182 detects the positive maximum value of the ABS signal input from the absolute value conversion unit 181 and outputs a PEK signal.

  The level comparison unit 183 compares the specified peak value THLVL with the PEK signal, and when the PEK signal is large, outputs CMP = 1 as a comparison result. On the other hand, when PEK is equal to or smaller than THLVL, CMP = 0 is output as a comparison result.

  The counter unit 184 changes the counter value based on the comparison result CMP input from the level comparison unit 183. Specifically, the counter unit 184 increments the count value when the comparison result is CMP = 1, and maintains the counter value when CMP = 0. The counter unit 184 is supplied with a CLR signal for initializing the counter value. The CLR signal is generated only once when n points of data are accumulated in the buffer processing unit, and the counter value is cleared (CNT = 0).

  The number comparison unit 185 compares the counter value CNT input from the counter unit 184 with a specified counter value THCNT input from the other input, and outputs an abnormality detection signal. Specifically, when CNT <THCNT, the number comparison unit 185 determines that the counter value CNT has not reached the specified number of times, and outputs an abnormality detection signal with the abnormality detection flag MDHP = 0. On the other hand, when CNT> = THCNT, the number comparison unit 185 determines that the counter value CNT has reached a predetermined number of times, and outputs an abnormality detection signal with the abnormality detection flag MDHP = 1.

  Next, processing executed when detecting a mode hop will be described with reference to FIGS. FIG. 6 is a flowchart showing the flow of the mode hop detection process according to the first embodiment. FIG. 7 is a time chart showing an example of a mode hop detection waveform according to the first embodiment, and FIG. 8 is a time chart showing an example of a mode hop escape waveform according to the first embodiment. FIG. 9 is a graph showing the relationship between the count value and the blood flow measurement error.

  As shown in FIG. 6, when measurement by the blood flow measurement device according to the present embodiment is started, the semiconductor laser 120 (hereinafter referred to as “LD” as appropriate) is driven with a specified amount of current (step S101). . Subsequently, in the A / D converter 160, the amplified signal is A / D converted at a specified frequency (step S102). The buffer processing unit 165 determines whether or not the number of accumulated data after A / D conversion has reached n points (step S103). If the number of accumulated data has not reached n points (step S103: NO), the process returns to step S102. On the other hand, when the number of accumulated data has reached n points (step S103: YES), the abnormal counter value CNT is cleared (step S104).

  Next, the absolute value conversion unit 181 converts the accumulated data of n points into absolute values and stores them as ABS values (step S105). The peak detection unit 182 detects a plurality of peaks of the ABS value corresponding to the accumulated data of n points, and stores them as a plurality of PEK values (step S106). The level comparison unit 183 determines whether or not all peak values have been compared with the specified peak value THLVL (step S107). Here, when the comparison of all the peak values is completed (step S107: YES), the process proceeds to step S112. On the other hand, when the comparison of all peak values is not completed (step S107: NO), the process proceeds to step S108.

  When PEK> THLVL is satisfied (step S108: YES), the level comparison unit 183 determines that an abnormal peak value has been detected, and sets a comparison flag (CMP = 1) (step S109). In the counter unit 184, the counter value is incremented (step S110), and the process returns to step S107. On the other hand, when PEK> THLVL is not satisfied (step S108: NO), the level comparison unit 183 determines that an abnormal peak value is not detected, and the comparison flag is reset (CMP = 0) (step S111). . Note that the counter unit 184 returns to step S107 while maintaining the counter value.

  The number comparison unit 185 determines whether or not the counter value CNT has reached the specified number THCNT (step S112). When CNT> THCNT is satisfied, the number comparison unit 185 determines that a number of abnormal peak values have been detected, and sets an abnormal flag (MDHP = 1) (step S113). In this case, the number comparison unit 185 outputs an LD drive current change command (step S114), and the process returns to step S102. On the other hand, when CNT> THCNT is not satisfied, the number comparison unit 185 determines that an abnormal peak value is not detected or a large number is not detected, and the abnormality flag is reset (MDHP = 0) (step S115). ). In this case, the LD drive current is maintained and the process returns to step S102.

  As shown in FIG. 7, the buffer data is a signal close to a random signal having various frequencies, amplitudes, and phases. However, in the normal case where the LD is not mode-hopped, the amplitude is within a specified range. However, when the LD is mode-hopped, the wavelength of the light shifts, so the optical beat signal by the optical Doppler is disturbed, and the amplitude of the buffer data obtained by quantizing the amplified signal obtained by amplifying the optical beat signal is from the disturbance of the optical beat signal. An abnormal peak is shown.

  Here, when a discontinuous single mode hop occurs, the disturbance section of the optical beat signal is short, the abnormal peak is also single, and finally there is little adverse effect on the blood flow signal output (left side of FIG. 7). On the other side). However, when a continuous intense mode hop occurs, the disturbance section of the optical beat signal is long, the abnormal peak becomes continuous, and finally the adverse effect on the blood flow signal output becomes large (see the right side of FIG. 7). .

  The ABS value that is converted into an absolute value to detect the amplitude value of the buffer data is a positive value. The abnormal peak value portion of the buffer data also has an abnormal ABS value. In order to detect an abnormal state of the amplitude value of the buffer data, the ABS value is compared with a specified peak value THLVL, and the comparison result CMP is CMP = 1 in the abnormal peak value portion, and in other normal states, CMP = 1

  In order to initialize the counter, a CLR signal is generated for every n points of data. The cycle of the CLR signal is the same as the cycle in which n-point data subjected to A / D conversion is accumulated by buffer processing. However, mode hop detection may use data of a period different from the buffer processing period (for example, a period that is an integral multiple of the buffer processing period, a rate at which blood flow is output to the outside, or the like).

  On the left half of FIG. 7, once an abnormal peak due to mode hops occurs once, CMP = 1 and the counter value CNT is incremented. However, since the mode hops are not continuously generated here, the counter value CNT is cleared by the CLR signal before reaching the prescribed number of times THCNT. Therefore, MDHP = 0 remains and no abnormality is detected.

  On the other hand, on the right half of FIG. 7, continuous abnormal peaks due to continuous mode hops occur, and in a long section, CMP = 1 and the counter value CNT is incremented a plurality of times. As a result, the counter value CNT reaches the specified number of times THCNT. Therefore, MDHP = 1 and an abnormality is detected.

  FIG. 8 shows that a continuous intense mode hop is detected due to a change in the temperature of the LD, so that MDHP = 1, an LD drive current change command is issued, and then the LD drive current changes, resulting in a continuous intense An example is shown in which the mode hop state is escaped and the mode hop is changed to a stable state.

  The continuous intense mode hop state is, for example, that the wavelength mode in which the gain of the semiconductor laser is maximized exists close to the specific drive current at a specific temperature, and mode competition occurs alternately between modes. This is the case. At this time, if the drive current is changed, the mode is stabilized in one of the modes and cannot be returned to the other mode. That is, it is possible to escape from a continuous mode hop state.

  FIG. 9 shows the result of an experiment to grasp the relationship between the abnormal peak count value CNT shown in FIGS. 7 and 8 and the measurement error that finally occurred in the blood flow output. As can be seen from the figure, when the count value CNT exceeds the specified count value THCNT, the measurement error increases rapidly. Thus, experimental results have been obtained in which the measurement error increases exponentially as the count value CNT increases. The region where CNT is equal to or less than THCNT is a case where no mode hop occurs or a single modest mode hop occurs. On the other hand, the region where CNT exceeds THCNT is a case where continuous intense mode hops occur.

  As a result of the above, it can be determined that if the process for suppressing the mode hop is performed when the count value CNT exceeds the specified count value THCNT, the adverse effect of the mode hop can be reduced very efficiently. In the present embodiment, since the mode hop state of the semiconductor laser 120 can be quantitatively grasped from the count value CNT corresponding to the number of abnormal peaks in the n-point data used for frequency analysis of blood flow calculation, the final When the influence on the blood flow measurement result is small, the LD drive current is maintained. On the other hand, only when the influence on the blood flow measurement result is finally large, the LD drive current is changed to escape from the mode hop state. It becomes possible. Therefore, more appropriate LD drive current control can be realized, and the blood flow can be accurately measured by exiting the mode hop state while suppressing power consumption.

  Further, in the case of continuous intense mode hop states in the mode competition state, it is possible to escape from the mode competition by detecting an abnormality and changing the drive current. On the other hand, since a single modest mode hop state does not detect an abnormality, a drive current can be maintained and a stable laser oscillation state can be maintained. Therefore, it is possible to prevent the mode hop state from being promoted due to an excessive drive current change.

  It can be said that the CNT value corresponding to the number of abnormal peaks in the n-point data is a value corresponding to the probability of causing a mode hop. Therefore, an index that quantitatively indicates whether a mode hop is likely to occur or a mode hop is unlikely to occur is the count value CNT. The specified count number THCNT can be optimized based on data as shown in FIG. 9, for example.

<Maintaining blood flow output when an abnormality is detected>
Next, a blood flow calculation method at the time of detecting an abnormality will be specifically described with reference to FIG. FIG. 10 is a flowchart showing the flow of blood flow calculation processing when an abnormality is detected.

As shown in FIG. 10, when the number of accumulated data reaches n points (step S103: YES), the mode hop detection process already described with reference to FIG. 6 is performed (step S201). Thereafter, when the abnormality detection flag MDHP is confirmed and the mode hop abnormality state is not detected (step S202: NO), MDHP = 0 and the normal blood flow calculation process shown in FIG. 3 is executed (step S203).
On the other hand, when the mode hop abnormal state is detected (step S202: YES), MDHP = 1, and it is determined that the current blood flow calculation has low reliability of the input data. In this case, in order to hold the previous calculation result, the previous blood flow calculation result is set as the current blood flow calculation result, and a command to change the LD drive current is issued (step S204).

  As a result, when the mode hop abnormal state is not detected, the blood flow obtained by the normal blood flow calculation process is output. When the mode hop abnormal state is detected, the previous blood flow calculation process is performed. The obtained blood flow is output (step S205). When a mode hop abnormal state is detected, an increase in measurement error during mode hop (see FIG. 9) can be prevented by maintaining the previous blood flow calculation result. The data shown in FIG. 9 is an experimental result when the above-described processing is not executed.

<Drive current limit setting>
Next, setting of the limit value for the LD drive current controlled by the mode hop suppression process will be described in detail with reference to FIG. FIG. 11 is a flowchart showing the flow of setting the limit value of the LD drive current.

  FIG. 11 shows an example in which the process (step S204) at the time of abnormality detection in FIG. 10 is partially changed. In the example shown here, when the LD drive current set value is changed (down or up) (step S301), it is determined whether the LD drive current set value is within a limit value (step S302).

  Here, when the LD drive current set value is within the limit value, an LD drive current change command is issued (step S303), and a blood flow value is output (step S205). On the other hand, when the LD drive current set value exceeds the limit value, the drive current change direction is reversed (up or down) and the LD drive current set value is changed again (step 304), and then the LD drive current change is performed. A command is issued (step S303), and a blood flow value is output (step S205).

  The LD drive current is adjusted in order to obtain an appropriate laser beam power in the initial stage. The limit value of the LD drive current change is set, for example, as a range of ± 5% with respect to the adjustment value in the initial stage. When the limit value for changing the LD drive current is set in this way, the LD drive current is changed within an appropriate range.

  Here, if the LD drive current is too low, the LD light emission power is reduced, resulting in a problem that the measurement S / N cannot be secured. Further, if the LD drive current is excessively increased, the LD light emission power increases, resulting in a problem that the life of the LD is reduced. However, according to the present embodiment, the LD driving current is changed in an appropriate range, the above-described problems can be prevented, and the driving current is changed by appropriately inverting the current changing direction, so that a continuous intense mode hop state can be obtained. You can escape.

  As described above, according to the measurement apparatus of the first embodiment, it is possible to suppress the occurrence of mode hopping of the semiconductor laser 120 and perform more accurate blood flow measurement. In the measurement apparatus according to the present embodiment, the suppression process is executed only when a mode hop occurs at such a frequency as to cause an adverse effect. Therefore, the mode hop can be suppressed extremely efficiently.

<Second embodiment>
Next, a measuring apparatus according to the second embodiment will be described with reference to FIGS. FIG. 12 is a block diagram illustrating the configuration of the mode hop detection unit in the measurement apparatus according to the second embodiment. FIG. 13 is a time chart showing a mode hop detection waveform example according to the second embodiment.

  The second embodiment is different from the first embodiment described above only in part of the configuration and operation, and many parts are the same as the first embodiment. For this reason, below, a different part from 1st Example is demonstrated in detail, and description is abbreviate | omitted suitably about the overlapping part.

  As shown in FIG. 12, the mode hop detection unit 180b according to the second embodiment includes an absolute value conversion unit 181, an LPF unit 186, and a level comparison unit 187.

  The LPF unit 186 integrates and averages the ABS (that is, the absolute valued buffer data) output from the absolute value conversion unit 181 and outputs the result as RMS.

  The level comparison unit 187 compares the RMS output from the LPF unit 186 with the specified average level RMSLVL. When RMS> RMSLVL is established, it is determined that the amplitude value is abnormal due to the LD mode hop, and abnormality is detected with MDHP = 1.

  As shown in FIG. 13, the RMS value gradually increases when there is an abnormal peak in the buffer data, and gradually decreases when the abnormal peak disappears. Also, when continuous intense mode hops occur, the RMS value continues to rise and eventually reaches RMSLVL. Using such RMS characteristics, in the second embodiment, when RMS> RMSLVL is established, MDHP changes from 0 to 1, and an abnormality is detected.

  As described above, according to the measurement apparatus of the second embodiment, it is possible to suitably detect the occurrence of a mode hop as in the first embodiment in which the mode hop is detected using the abnormal peak counter value CNT. Therefore, the generation of mode hops can be suppressed and more accurate blood flow measurement can be performed.

<Third embodiment>
Next, a measuring apparatus according to the third embodiment will be described with reference to FIG. FIG. 14 is a block diagram showing the overall configuration of the measuring apparatus according to the third embodiment.

  Note that the third embodiment differs from the first and second embodiments described above only in part of the configuration and operation, and many parts are the same as in the first and second embodiments. For this reason, below, a different part from 1st and 2nd Example is demonstrated in detail, and description shall be abbreviate | omitted suitably about the overlapping part.

  As shown in FIG. 14, in the measuring apparatus according to the third embodiment, the laser driving unit 110 is provided with a Peltier element 300 for controlling the temperature. And the mode hop suppression process part 190b which concerns on 2nd Example controls the generation of the mode hop by controlling the Peltier device 300. FIG.

  Specifically, the mode hop suppression processing unit 190b receives a suppression processing permission signal from the mode hop detection unit 180 (that is, when it is determined that mode hops occur frequently), the Peltier element A control signal is output, and the Peltier device 300 absorbs heat from the laser driving unit 110. In this way, the temperature of the laser driving unit 110 decreases, and mode hops that have occurred due to the temperature increase are suppressed.

  As described above, according to the measurement apparatus of the third embodiment, the generation of mode hops in the semiconductor laser 120 is suppressed, as in the first and second embodiments that control the drive current of the laser drive unit 110. Thus, more accurate blood flow measurement can be performed.

<Fourth embodiment>
Next, a measuring apparatus according to the fourth embodiment will be described with reference to FIG. FIG. 15 is a block diagram showing the overall configuration of the measuring apparatus according to the fourth embodiment.

  Note that the fourth embodiment differs from the first to third embodiments described above only in part of the configuration and operation, and many parts are the same as in the first to third embodiments. For this reason, below, a different part from 1st-3rd Example is demonstrated in detail, and description is abbreviate | omitted suitably about the overlapping part.

  As shown in FIG. 15, in the measuring apparatus according to the fourth example, a liquid crystal 400 is provided between the semiconductor laser 120 and the measurement target 200. Then, the mode hop suppression processing unit 190c according to the fourth embodiment controls the liquid crystal 400 to suppress the occurrence of mode hops.

  Specifically, when the suppression processing permission signal is input from the mode hop detection unit 180 (that is, when it is determined that mode hops occur frequently), the mode hop suppression processing unit 190c performs liquid crystal control. By outputting a signal, the refractive index of the liquid crystal 400 is changed, and an environment in which return light from the measurement target 200 does not enter the semiconductor laser 120 is realized. In this way, the mode hop that has occurred due to the return light entering the semiconductor laser 120 is suppressed.

  As described above, according to the measurement apparatus according to the third embodiment, as in the first to third embodiments, the generation of mode hops in the semiconductor laser 120 is suppressed and more accurate blood flow measurement is performed. Is possible.

<Fifth embodiment>
Next, a measuring apparatus according to a fifth example will be described with reference to FIGS. FIG. 16 is a block diagram illustrating the configuration of the amplitude limiter unit in the measurement apparatus according to the fifth embodiment. FIGS. 17 to 19 are graphs showing examples of the amplified signal and the blood flow output, respectively. Note that the horizontal axis of the graphs shown in FIGS. 17 to 19 is time, which corresponds to 0 to 27 seconds.

  As shown in FIG. 16, the measurement apparatus according to the fifth example is configured to include an amplitude limiter unit 500 in the previous stage of the blood flow calculation unit 170. The amplitude limiter unit 500 includes a polarity determination unit 501, a selection unit 502, a −1 multiplication unit 503, and a data exchange unit 504.

  The polarity determination unit 501 determines the polarity of input buffer data. The determination result in the polarity determination unit 501 (that is, the polarity of the buffer data) is output to the selection unit 502.

  When the polarity of the buffer data is positive, the selection unit 502 selects the limit level THLVL as it is and outputs it to the data replacement unit 504. On the other hand, when the polarity of the buffer data is negative, the selection unit 502 selects a level obtained by inverting the limit level THLVL by −1 by the −1 multiplication unit 503 and inverting it, and outputs the selected level to the data replacement unit 504. The limit level THLVL may be the same as or different from the specified peak value THLVL (that is, the amplitude threshold for detecting the mode hop in the mode hop detection unit 180).

  When an abnormal peak occurs in the buffer data (that is, when the level comparison result is CMP = 1), the data replacement unit 504 replaces the buffer data with the output of the selection unit 502 and outputs it as limit data. Further, the data replacement unit 504 outputs the buffer data as limit data as it is when the amplitude is normal (that is, when CMP = 0 as the level comparison result). The limit data is input to the blood flow calculation unit 170 including signal processing including frequency analysis shown in FIG.

  The waveform shown in FIG. 17 is an example of a waveform obtained when the semiconductor laser 120 is stably oscillating in a single mode, that is, when no mode hop occurs. In this case, since no mode hop occurs, almost no noise is present in the amplified signal. For this reason, an accurate blood flow output is obtained without performing the amplitude limiter process.

  The waveform shown in FIG. 18 is an example of a waveform obtained when the semiconductor laser 120 is in an unstable oscillation state due to mode hopping. In this case, as can be seen from comparison with FIG. 17, a lot of noise is present in the amplified signal due to the occurrence of mode hops. For this reason, if the amplitude limiter process is not performed, the pulse wave of the blood flow output is disturbed.

  The waveform shown in FIG. 19 is an example of the waveform obtained when the semiconductor laser 120 is in an unstable oscillation state due to the mode hop, as in the case of FIG. 18, but the amplitude limiter processing according to this embodiment is performed. Demodulating. For this reason, the noise component is suppressed by the amplitude limiting action of the amplitude limiter unit 500. As a result, the disturbance of the pulse wave in the blood flow output is suppressed to a minimum, and a waveform close to a state in which mode hopping is not performed (that is, no noise) is obtained as in the case of FIG.

  As described above, according to the measurement apparatus of the fifth embodiment, even if noise due to the mode hop of the semiconductor laser 120 occurs, the influence can be suppressed and more accurate blood flow measurement can be performed. It is. Note that the effect of suppressing the influence of mode hops by the amplitude limiter process is effective when the mode hop occurrence frequency is relatively moderate, and there is a possibility that it will not be sufficient if the mode hop occurrence frequency is greatly increased. However, in this embodiment, as described above, when a mode hop occurs frequently, the mode hop is generated by controlling the driving current of the laser driving unit 110, controlling the temperature, or controlling the return light by the liquid crystal 400. The frequency can be reduced. Therefore, it is possible to effectively suppress the influence according to the state of occurrence of mode hops.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification. A method, a computer program, and a recording medium are also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 110 Laser drive part 120 Semiconductor laser 130 Light receiving element 140 IV conversion part 150 Amplifier 160 A / D converter 165 Buffer process part 170 Blood flow calculation part 171 Hanning window process part 172 FFT process part 173 Square calculation part 174 Primary Moment accumulating unit 175 LPF unit 180 Mode hop detection unit 181 Absolute value conversion unit 182 Peak detection unit 183 Level comparison unit 184 Counter unit 185 Number comparison unit 186 LPF unit 187 Level comparison unit 190 Mode hop suppression processing unit 200 Measurement target 300 Peltier Element 400 Liquid crystal 500 Amplitude limiter unit 501 Polarity determination unit 502 Selection unit 503 -1 times unit 504 Data switching unit

Claims (18)

Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
An output means for outputting information on the movement of the measurement target based on a beat signal caused by a Doppler shift of the laser light included in the output signal of the light receiving means;
And a control unit that controls an irradiation state of the laser light by the irradiation unit based on the beat signal within a predetermined period. The control means counts the number of times that the amplitude value of the beat signal exceeds a predetermined amplitude value within the predetermined period, and when the counted number exceeds the predetermined number of times, the laser light by the irradiation means The measuring apparatus according to claim 1, wherein the irradiation state is controlled. The control means integrates and averages the amplitude value of the beat signal within the predetermined period, and when the averaged amplitude value exceeds a predetermined threshold, the irradiation state of the laser light by the irradiation means is determined. The measuring device according to claim 1, wherein the measuring device is controlled. The output means calculates information on the movement of the measurement object using a fast Fourier transform,
The measuring apparatus according to any one of claims 1 to 3, wherein the predetermined period is set as a period corresponding to a buffer period of the fast Fourier transform.   5. The measurement apparatus according to claim 1, wherein the control unit controls the irradiation state of the laser beam by the irradiation unit by changing a driving current of the irradiation unit. 6. .   The measuring apparatus according to claim 5, wherein the control unit changes a driving current of the irradiation unit within a predetermined range corresponding to a reference current.   Each time the control means determines that the irradiation state of the laser light by the irradiating means should be controlled, it changes the driving current of the irradiating means stepwise in a predetermined direction in one direction of increasing or decreasing. The measuring apparatus according to claim 6.   8. The measuring apparatus according to claim 7, wherein the control unit reverses the change direction of the drive current of the irradiation unit when a change in the drive current exceeding the predetermined range is requested.   The measurement apparatus according to claim 1, wherein the control unit controls an irradiation state of the laser light by the irradiation unit by changing a temperature of the irradiation unit.   The said control means controls the irradiation state of the said laser beam by the said irradiation means by changing the refractive index of the liquid crystal window provided between the said irradiation means and the said to-be-measured object. Item 10. The measuring device according to any one of Items 1 to 9.   The control means further comprises output maintaining means for controlling the output means so as to maintain the output before the determination when it is determined that the irradiation state of the laser light by the irradiation means should be controlled. The measuring device according to claim 1. Further comprising limiting means for limiting the amplitude value of the output signal of the light receiving means within a predetermined amplitude range;
The output means outputs information related to movement of the measurement target based on a beat signal caused by a Doppler shift of the laser light included in an output signal of the light receiving means restricted by the restriction means. The measuring apparatus according to claim 1, wherein the measuring apparatus is characterized. Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
An output means for outputting information on the movement of the measurement target based on a beat signal caused by a Doppler shift of the laser light included in the output signal of the light receiving means;
And a detection unit that detects a state in which an error in information relating to movement of the measurement target exceeds a predetermined error based on the beat signal within a predetermined period. An irradiation step of irradiating a measurement target with laser light;
A light receiving step for receiving the laser light scattered by the measurement object;
An output step of outputting information relating to the movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the output signal obtained in the light receiving step;
And a control step of controlling an irradiation state of the laser light in the irradiation step based on the beat signal within a predetermined period. An irradiation step of irradiating a measurement target with laser light;
A light receiving step for receiving the laser light scattered by the measurement object;
An output step of outputting information relating to the movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the output signal obtained in the light receiving step;
And a detection step of detecting a state in which an error in information relating to movement of the measurement target exceeds a predetermined error based on the beat signal within a predetermined period. An irradiation step of irradiating a measurement target with laser light;
A light receiving step for receiving the laser light scattered by the measurement object;
An output step of outputting information relating to the movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the output signal obtained in the light receiving step;
A computer program causing a computer to execute a control step of controlling an irradiation state of the laser beam in the irradiation step based on the beat signal within a predetermined period. An irradiation step of irradiating a measurement target with laser light;
A light receiving step for receiving the laser light scattered by the measurement object;
An output step of outputting information relating to the movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the output signal obtained in the light receiving step;
A computer program causing a computer to execute a detection step of detecting a state in which an error in information relating to movement of the measurement target exceeds a predetermined error based on the beat signal within a predetermined period.   18. A recording medium on which the computer program according to claim 16 or 17 is recorded.

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