JP2013246037A - Optical measuring apparatus and measurement light control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an error of output gain caused by temperature characteristics of a semiconductor element being a light receiving element, in optical measurement for measuring optical characteristics of an object to be measured.SOLUTION: In an optical measuring apparatus 1, pulse width modulation control is performed at a light modulation device 12 according to a modulation control signal, thereby emission light (measurement light) from a light source 10 is converted into pulse light, and divided into transmitted light and divided light by a beam splitter 18. The transmitted light is made incident on an object 200 to be measured, and the divided light is received by a photodetector 20 for light modulation. A duty ratio of the modulation control signal is changed depending on positive or negative, and an absolute value of change degree f of detected values of the photodetector 20 for light modulation in a period when the modulation control signal is at an H level.

Description

  The present invention relates to an optical measurement device that measures an optical property of a measurement object.

  By measuring the light transmitted through the substance, it is possible to know the components of the substance without directly touching the substance. For example, when the optical rotation angle is measured, the concentration of the substance can be estimated. Optical rotation refers to the property of rotating the plane of polarization when linearly polarized light passes through an optically active substance such as glucose. As a technique using this optical rotatory power, for example, in Patent Document 1, linearly polarized light passes through a sample cell and is orthogonally separated, and each orthogonally separated polarized light component is received by two light receiving elements. A technique for measuring an optical rotation angle using a difference in output level of a light receiving element is disclosed.

International Publication No. 99/30132

  In the above-described technique, a semiconductor element such as a photodiode that outputs a current corresponding to the amount of light as a detection value by photoelectric conversion is used as the light receiving element. However, there is a problem of a decrease in measurement accuracy due to temperature characteristics of the semiconductor element. There is. That is, the semiconductor element has a characteristic that, when the temperature rises, the electrical conductivity increases and the current flowing through the element increases. As a result, even if the intensity of the measurement light applied to the substance is constant, the longer the light receiving time in the light receiving element, the larger the output value due to the temperature rise, resulting in a larger measurement error. In particular, in the optical measurement that measures a change in a very small amount of measurement light such as measurement of optical rotation of glucose, an unacceptable error occurs.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an output gain due to temperature characteristics of a semiconductor element which is a light receiving element in optical measurement for measuring optical characteristics of a measurement object. Is to suppress the error.

  The 1st form for solving the above-mentioned subject is an optical measuring device which measures the optical property of the measurement object based on the passage light which passed the measurement object arranged in the optical path of measurement light, , A splitting unit that splits light in the optical path into transmitted light and split light, a light detection unit that receives the split light, and pulse width modulation control of the measurement light based on a detection value of the light detection unit And an optical modulation control unit that performs the above.

  The second form is an optical measurement device that measures the optical properties of the measurement object based on the light passing through the measurement object arranged in the optical path of the measurement light. An optical measurement device comprising: a light detection unit that receives light; and a light modulation control unit that performs pulse width modulation control of the measurement light based on a detection value of the light detection unit.

  Further, as another form, a measurement light control method in an optical measurement device that measures the optical properties of the measurement object based on the passing light that has passed through the measurement object arranged in the optical path of the measurement light, A measurement light control method is provided, wherein the measurement light is subjected to pulse width modulation control based on a divided light obtained by dividing the light in the optical path or a detection value of a light detection unit that receives the passing light. May be.

  According to the first aspect or the like, in the optical measurement device that measures the optical property of the measurement object based on the light passing through the measurement object arranged in the optical path of the measurement light, the light in the optical path is The pulse width modulation of the measurement light is performed based on the divided light or the detection value of the light detection unit that receives the passing light. By performing pulse width modulation of the measurement light, light reception in the light detection unit becomes intermittent, so that temperature rise due to light reception by the light detection unit can be suppressed, and measurement errors due to temperature characteristics of the semiconductor element can be suppressed. Further, by performing pulse width modulation based on the detection value of the light detection unit, it is possible to realize appropriate pulse width modulation by feeding back a value corresponding to the current temperature of the light detection unit.

  Further, as a third form, the optical measurement device according to the first or second form, wherein the light modulation control unit performs pulse width modulation control for changing a duty ratio based on a change degree of the detection value. An optical measurement device may be configured.

  According to the third embodiment, the pulse width modulation control for changing the duty ratio is performed based on the degree of change in the detection value of the light detection unit. By changing the duty ratio, the light receiving time of the light detection unit can be varied.

  Further, as a fourth mode, the optical measurement device according to any one of the first to third modes, wherein the light modulation control unit decreases the duty ratio when the detection value tends to increase, and tends to decrease. In this case, an optical measurement device that performs pulse width modulation control to increase the duty ratio may be configured.

  According to the fourth embodiment, the pulse width modulation is performed so that the duty ratio is reduced when the detected value tends to increase, and the duty ratio is increased when the detected value tends to decrease. Since a part of the light energy due to the light reception is converted into heat, the temperature of the light detection unit rises as the light reception time increases. For this reason, when the detection value of the light detection unit tends to increase, by performing pulse width modulation of the measurement light to reduce the duty ratio, the light reception time can be shortened and the temperature rise can be suppressed. Conversely, when the detected value tends to decrease, by performing pulse width modulation that increases the duty ratio, it is possible to lengthen the light receiving time and suppress the temperature drop. Thus, by performing pulse width modulation to reduce / increase the duty ratio depending on whether the detection value is increasing or decreasing, the temperature change of the light receiving unit is suppressed and kept constant, Measurement errors due to temperature characteristics can be suppressed.

  Further, as a fifth mode, the optical measurement device according to any one of the first to fourth modes, wherein the light modulation control unit changes a duty ratio based on the detection value for a predetermined past time. You may comprise the optical measuring device which performs width modulation control.

  According to the fifth embodiment, the pulse width modulation for changing the duty ratio is performed based on the detection values for the past predetermined time.

  Further, as a sixth mode, the optical measurement device according to any one of the first to fifth modes, wherein the light modulation control unit is configured such that the detected value after the optical measurement device starts a measurement operation is You may comprise the optical measuring device which starts the said pulse width modulation control when predetermined conditions are satisfy | filled.

  According to the sixth embodiment, after the optical measuring device starts the measurement operation, the pulse width modulation control is started when the detected value satisfies the predetermined condition. Immediately after the start of the measurement operation, the operation is unstable, so pulse width modulation control is not performed on the measurement light. For example, when the detection value reaches a value that can be considered stable as a predetermined condition, pulse width modulation control is started. To do.

  Further, as a seventh form, the optical measurement device according to the first form, wherein the passing light receiving part receives the passing light, and the passing light receiving part in the period without the measuring light by the pulse width modulation control An optical measurement device may further be provided that includes a determination unit that corrects the detection value of the passing light receiving unit using the detected value to determine the optical property of the measurement object.

  According to the seventh aspect, the detection of the passing light receiving unit is performed using the detection value of the passing light receiving unit that receives the passing light that has passed through the measurement object during the period when there is no measurement light by the pulse width modulation control. The optical property of the measurement object is determined by correcting the value. In a period when there is no measurement value due to pulse width modulation, the detection value of the passing light receiving portion should be “zero”. For this reason, the detection value of the passage light receiving unit can be corrected based on the detection value of the passage light receiving unit during a period when there is no measurement value by pulse width modulation.

The block diagram of an optical measuring device. The function block diagram of a control apparatus. Calculation explanatory drawing of the change degree of the detected value of a photodetector. Calculation explanatory drawing of the change degree of the detected value of a photodetector. The flowchart of an optical modulation process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the applicable embodiment of the present invention is not limited to this.

[Constitution]
FIG. 1 is a configuration diagram of an optical measurement device 1 in the present embodiment. The optical measurement device 1 is a device that measures the optical properties of the measurement object 200. The measurement object 200 can be an arbitrary sample such as a solid or a liquid containing an optically active substance. The optical measurement device 1 receives the passing light that has passed through the measurement object 200 and measures the optical rotation angle that is an optical property of the measurement object 200.

  As shown in FIG. 1, the optical measurement device 1 includes a light source 10, a light modulation device 12, a collimator lens 14, a polarizer 16, a beam splitter 18, a light modulation photodetector 20, and a polarization beam splitter. 22, measurement photodetectors 24 and 26, subtractors 28 and 30, a differential amplifier 32, a summing amplifier 34, and a control device 100, and the beam splitter 18, the polarization beam splitter 22, and the like. In between, the measurement object 200 is placed.

  The light source 10 generates and outputs measurement light. For example, it is configured to have a semiconductor laser (laser diode), and laser light that is light having a predetermined wavelength (for example, 650 nm) and having a uniform phase is emitted from an end face that is a half mirror.

  The light modulation device 12 includes a shutter mechanism whose opening and closing is driven according to a modulation control signal (pulse signal) input from the control device 100, and performs pulse width modulation on the light emitted from the light source 10 to generate pulsed light. Convert to

  The collimating lens 14 converts the emitted light from the light modulation device 12 into parallel light. The polarizer 16 includes, for example, a polarizing optical element such as a polarizing prism, and converts parallel light emitted from the collimating lens 14 into linearly polarized light.

  The beam splitter 18 splits the linearly polarized light emitted from the collimating lens 14 into transmitted light and split light.

  The light modulation photodetector 20 receives one split light of the light emitted from the beam splitter 18. For example, it is configured with a photodetector such as a photodiode, and outputs a current proportional to the amount of split light received by photoelectric conversion as a detection value.

  The polarization beam splitter 22 orthogonally separates the passing light, which is the other transmitted light that has passed through the measurement object 200, from the light emitted from the beam splitter 18 into polarization components that are different from each other by 90 degrees.

  The measurement photodetectors 24 and 26 each receive the light orthogonally separated by the polarization beam splitter 22. For example, it is configured to include a photo detector such as a photodiode, and detects orthogonally polarized components (P component and S component) orthogonally separated by the polarization beam splitter 22, and receives light by performing photoelectric conversion. A current proportional to the amount of light is output as a detection value. Note that the light modulation photodetector 20 and the measurement photodetectors 24 and 26 are configured using photodetectors of the same standard.

  The subtracters 28 and 30 subtract the correction value input from the control device 100 from the detection values obtained by the measurement photodetectors 24 and 26, respectively, and output the result. The differential amplifier 32 amplifies and outputs the difference between the output values from the subtracters 28 and 30. The summing amplifier 34 amplifies and outputs the sum of the output values from the subtracters 28 and 30.

[Control device]
FIG. 2 is a functional configuration diagram of the control device 100. According to FIG. 2, the control device 100 functionally includes a processing unit 110, an operation unit 122, a display unit 124, a sound output unit 126, a communication unit 128, and a storage unit 130. Is done.

  The processing unit 110 is realized by an arithmetic device such as a CPU, for example, and comprehensively controls each unit of the control device 100 according to various programs such as programs and data stored in the storage unit 130. In the present embodiment, the processing unit 110 includes an optical rotation angle calculation unit 112 and a light modulation control unit 114.

  The optical rotation angle calculation unit 112 calculates the optical rotation angle of the measurement object 200 based on the output values of the differential amplifier 32 and the addition amplifier 34 during the period when the modulation control signal generated by the optical modulation control unit 114 is at the H level. To do.

  The light modulation control unit 114 generates a modulation control signal for performing pulse width modulation control on the measurement light emitted from the light source 10 based on the detection value of the light modulation photodetector 20. Specifically, feedback control for changing the duty ratio of the modulation control signal based on the change (fluctuation) of the detection value of the light modulation photodetector 20 during the period (light reception period) T1 when the modulation control signal is at the H level. Do.

  FIG. 3 is a waveform diagram showing an example of the modulation control signal and the detection value of the light modulation photodetector 20. In FIG. 3, the modulation control signal is shown on the upper side, and the detection value of the light modulation photodetector 20 is shown on the lower side.

  The modulation control signal is a pulse signal, and repeats an H level light receiving period T1 and an L level non-light receiving period T2 at a predetermined period T. Therefore, the duty ratio of the modulation control signal is “T1 / T2”.

  In the light receiving period T1, the emitted light (measurement light) from the light source 10 passes through the light modulation device 12 and is irradiated to the measurement object 200. In the light receiving period T2, the emitted light (measurement light) from the light source 10 is irradiated. Since the light modulation device 12 blocks the light, the light modulation photodetector 20 and the measurement photodetectors 24 and 26 do not receive light.

  First, the detection value of the light modulation photodetector 20 in the light receiving period T1 is captured at a predetermined time interval Δt (<T). Next, an average value e of these m detection values d1 to dm is calculated, and this is set as a detection average value e for one pulse.

  Subsequently, as shown in FIG. 4, the detection average value e is similarly calculated for each of a plurality of continuous pulses. Then, the degree of change f of the detection average values e1 to en for these consecutive n pulses is calculated. As a method of calculating the degree of change f, for example, a regression line (approximate line) is calculated by performing a time differentiation process on each of the detected average values e1 to en, or by performing a least square method on n detected average values. The slope of this linear function is defined as the degree of change f.

  Then, the duty ratio of the modulation control signal is changed according to the sign (sign) and the absolute value of the change degree f. Specifically, if the change degree f is within a predetermined range centered on zero, the duty ratio is not changed. On the other hand, if the degree of change is outside the predetermined range, the duty ratio is changed according to the positive / negative and absolute values. That is, if the change degree f is a positive value, it is considered that the temperature is rising, and the duty ratio is changed by a value corresponding to the absolute value of the change degree f. On the other hand, if the change degree f is a negative value, it is assumed that the temperature is decreasing, and the duty ratio is changed to be increased by a value corresponding to the absolute value of the change degree.

  The period T of the modulation control signal is constant, and the duty ratio is polarized by changing the light receiving period T1. In addition, a lower limit value (which can be said to be a lower limit value of the light receiving period T1) is set for the duty ratio, and is changed so as not to fall below this lower limit value.

  The duty ratio is controlled for the following reason. When the output of the light source 10 is stable, the light amount of the divided light received by the light modulation photodetector 20 is constant, so the detection value of the light modulation photodetector 20 should be constant. That is, the fluctuation of the detection value of the light modulation photodetector 20 can be considered to be caused by the temperature fluctuation of the photodetector. When the temperature rises, the electrical conductivity of the semiconductor element increases, so that the detection value of the light modulation photodetector 20 increases. Conversely, when the temperature decreases, the electrical conductivity decreases, and the detection value decreases. For this reason, the duty ratio of the modulation control signal is changed so that the change degree f becomes “zero” according to the sign of the change degree f of the detection value f of the light modulation photodetector 20 and the absolute value. Thus, the fluctuation of the detection value due to the temperature fluctuation is suppressed.

  The light modulation light detector 20 and the measurement light detectors 24 and 26 are constituted by light projectors (photodiodes) of the same standard. For this reason, both are regarded as having the same characteristics, and by changing the duty ratio of the modulation control signal based on the detection value of the light modulation photodetector 20, the measurement photodetectors 24 and 26 receive light. Variation in the detected value due to the temperature variation caused can be suppressed.

  In addition, the light modulation control unit 114 corrects the detection values of the measurement photodetectors 24 and 26 according to the detection value of the light modulation photodetector 20 in the non-light-receiving period T2 in which the modulation control signal is L level. Is calculated. In the non-light-receiving period T2 of the modulation control signal, the measurement light is blocked by the light modulation device 12 and is not received by the light modulation photodetector 20, but the output value is obtained even when the light detector such as a photodiode is not receiving light. Is not zero. This output value is called dark current and varies with temperature and the like. That is, this dark current is also included in the detection value in the light receiving period T1, which causes a measurement error of the optical rotation angle. Therefore, based on the detection value of the light modulation photodetector 20 in the non-light-receiving period T2, a correction value corresponding to the dark current is determined and input to the subtracters 28 and 30, thereby detecting the measurement light. The detection values of the devices 24 and 26 are corrected to suppress measurement errors.

  The operation unit 122 is realized by an input device such as a button switch or a touch panel, for example, and outputs an operation signal corresponding to the performed operation to the processing unit 110. The display unit 124 is realized by a display device such as an LCD, for example, and performs various displays based on a display signal input from the processing unit 110. The sound output unit 126 is realized by a sound output device such as a speaker, for example, and outputs various sounds such as a beep sound for operation confirmation based on the sound signal input from the processing unit 110. The communication unit 128 is a communication device for performing wired communication or wireless communication with an external device, and performs communication with the external device under the control of the processing unit 110.

  The storage unit 130 is realized by a storage device such as a ROM, a flash ROM, a RAM, or a hard disk, for example, and a system program for the processing unit 110 to perform overall control with the control device 100 and various programs for realizing various functions. In addition to storing data and data, it is used as a work area of the processing unit 110, and temporarily stores calculation results and the like executed by the processing unit 110 according to various programs. In the present embodiment, the storage unit 130 stores an optical modulation control program 132, detection value data 134, detection average value data 136, duty ratio data 138, and correction value data 140.

[Process flow]
FIG. 5 is a flowchart for explaining the flow of the modulation control process. This process is realized by the light modulation control unit 114 executing the light modulation control program 132.

  First, immediately after the optical measurement apparatus 1 is turned on, pulse width modulation control is not performed on the light emitted from the light source 10, and an H level signal is output as a modulation control signal.

  Then, calculation (measurement operation) of the optical rotation angle by the optical rotation angle calculation unit 112 is started, and if the detection value of the light modulation photodetector 20 reaches a value that satisfies the stability condition that the measurement operation is considered to be stable. (Step A1: YES), the duty ratio of the modulation control signal is initially set to “50%”, and the pulse modulation control for the light emitted from the light source 10 is started. (Step A3).

  Next, in the period T1 when the modulation control signal is at the H level (step A5: YES), the detection value of the light modulation photodetector 20 is captured at intervals of a predetermined time Δt (step A7).

  When the modulation control signal changes to the L level (step A9: YES), the detection value change degree f for the consecutive n pulses including the current pulse is calculated (step A11). That is, the average value e of the m detected values d (d1 to dm) taken in is calculated, and then the degree of change in the detection average value e (e1 to en) for the past consecutive n pulses including the current pulse. Is calculated. Subsequently, the duty ratio of the modulation control signal is changed according to the calculated change degree f (step A13).

  Further, the detection value of the light modulation photodetector 20 is regarded as a dark current, and the correction value is set / updated (step A15).

  Thereafter, it is determined whether or not the process is to be terminated due to power-off or the like. If the process is not terminated (step A17: NO), the process returns to step A5 and the same process is repeated. If the process ends (step A17: YES), this process ends.

[Function and effect]
As described above, in the optical measurement device 1 of the present embodiment, the pulse width modulation control is performed on the emitted light (measurement light) from the light source 10 according to the modulation control signal, and the light is converted into pulse light. Further, the divided light obtained by dividing the measurement light by the beam splitter 18 is received by the light modulation photodetector 20, and the change in the detection value of the light modulation photodetector 20 in the light receiving period T1 when the modulation control signal is at the H level. The duty ratio of the modulation control signal is changed according to the sign of the degree f and the absolute value. Thereby, the measurement error resulting from the temperature rise of the measurement photodetectors 24 and 26 due to the reception of the measurement light can be suppressed.

[Modification]
It should be noted that embodiments to which the present invention can be applied are not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention.

(A)
For example, in the above-described embodiment, pulse width modulation is performed on the emitted light (measurement light) of the light source 10 using the detection value of the light modulation photodetector 20, but the measurement photodetectors 24 and 26 are used. The detected value may be used. Specifically, using the detection values of one or both of the measurement photodetectors 24 and 26, similarly, the degree of change of the detection value is calculated and the duty ratio of the modulation control signal is changed. To do.

DESCRIPTION OF SYMBOLS 1 Optical measuring device, 10 Light source, 12 Light modulation device, 14 Collimating lens, 16 Polarizer, 18 Beam splitter, 20 Light modulation photodetector, 22 Polarization beam splitter, 24, 26 Measurement photodetector, 28, 30 Subtractor, 32 differential amplifier, 34 summing amplifier, 100 control device, 110 processing unit, 112 optical rotation angle calculation unit, 114 light modulation control unit, 122 operation unit, 124 display unit, 126 sound output unit, 128 communication unit, 130 Storage unit, 132 Light modulation control program, 134 Detection value data, 136 Detection average value data, 138 Duty ratio data, 140 Correction value data, 200 Measurement object

Claims (8)

An optical measurement device that measures the optical properties of the measurement object based on the passing light that has passed through the measurement object arranged in the optical path of the measurement light,
A splitting unit that splits light in the optical path into transmitted light and split light;
A light detector that receives the split light; and
A light modulation control unit that performs pulse width modulation control of the measurement light based on a detection value of the light detection unit;
Optical measuring device with An optical measurement device that measures the optical properties of the measurement object based on the passing light that has passed through the measurement object arranged in the optical path of the measurement light,
A light detector for receiving the passing light;
A light modulation control unit that performs pulse width modulation control of the measurement light based on a detection value of the light detection unit;
Optical measuring device with The light modulation control unit performs pulse width modulation control for changing a duty ratio based on the degree of change in the detection value.
The optical measuring device according to claim 1 or 2. The light modulation control unit performs pulse width modulation control to decrease the duty ratio when the detection value tends to increase and increase the duty ratio when the detection value tends to decrease.
The optical measuring device as described in any one of Claims 1-3. The light modulation control unit performs pulse width modulation control for changing a duty ratio based on the detection value for a predetermined time in the past.
The optical measuring device as described in any one of Claims 1-4. The light modulation control unit starts the pulse width modulation control when the detection value after the optical measurement device starts a measurement operation and satisfies a predetermined condition.
The optical measuring device as described in any one of Claims 1-5. A passing light receiving portion for receiving the passing light;
A determination unit that corrects the detection value of the passing light receiving unit and detects the optical property of the measurement object using the detection value of the passing light receiving unit during a period in which there is no measurement light by the pulse width modulation control. When,
The optical measurement device according to claim 1, further comprising: A measurement light control method in an optical measurement device that measures the optical properties of the measurement object based on the passing light that has passed through the measurement object arranged in the optical path of the measurement light,
A measurement light control method, wherein the measurement light is subjected to pulse width modulation control based on a divided light obtained by dividing the light in the optical path or a detection value of a light detection unit that receives the passing light.

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