JP4170878B2 - Refractive index measuring device - Google Patents

Description

  The present invention relates to a refractive index measuring apparatus that measures a refractive index by a total reflection method.

  Conventionally, there is a method of measuring a refractive index by a total reflection method using a refractive index measuring apparatus as shown in FIG. The refractive index measuring device causes the light source 103 to emit light from behind the measurement surface 102 toward the measurement surface 102 of the prism 101 on which the object to be measured is placed, and the light receiving sensor 104 receives the light reflected by the measurement surface 102. Then, the refractive index is obtained based on the output value of the light receiving sensor 104.

  The refractive index measurement device includes a window for placing a measurement object on the measurement surface 102 at a position opposite to the light source 103 with the prism 101 interposed therebetween. Depending on the refractive index measuring apparatus, the measurement accuracy of the refractive index may be reduced by external light that enters the refractive index measuring apparatus from the window.

  In the conventional simple refractive index measuring apparatus used outdoors, the refractive index is measured in a state in which the object to be measured placed on the measurement surface 102 is covered with the lid, so that the incident external light has a refractive index. It does not affect the measurement. However, in recent years, a refractive index measurement device that measures the refractive index without a lid has been commercialized in order to save the trouble of covering the lid or cleaning the object to be measured attached to the back side of the lid after the refractive index measurement. Has been. In a refractive index measuring apparatus that measures a refractive index without covering the lid, the measurement accuracy of the refractive index is reduced by incident external light.

  Conventionally, since the refractive index changes depending on the sugar content in the liquid, it has long been used for a wide range of applications such as using a refractive index measuring device to determine the sugar content of fruits. When calculating the sugar content of fruits, there are many opportunities to use a refractive index measuring device outdoors.

  When the refractive index measurement device is used in a laboratory, measures can be taken to prevent the incidence of external light in the refractive index measurement device. However, when used at an outdoor production site, external light is incident. It is difficult to take measures to prevent this.

  Since the outside light incident on the refractive index measuring device is received by the light receiving sensor 104, the output value of the light receiving sensor 104 is affected by the outside light. In order to prevent the output value of the light receiving sensor 104 from being influenced by external light, the influence of external light is based on the difference between the output values of the light receiving sensor 104 when the light source 103 is turned on and when the light source 103 is turned off. A method of calculating an output value in which is canceled and obtaining a refractive index based on the calculated output value is employed in a refractive index measuring apparatus.

  As shown in FIG. 3, the relationship between the amount of light received by the light receiving sensor and the output value exhibits linearity when the amount of received light is constant. However, for a received light amount that is larger than that range, the change in output value is small with respect to the change in the received light amount, and when the received light amount is extremely large, the output value hardly changes even if the received light amount changes.

  When external light with high intensity is incident on the refractive index measuring apparatus, if the light source 103 is turned on, the relationship between the amount of light received by the light receiving sensor 104 and the output value may be larger than the range showing linearity. When such external light is incident, it is not possible to completely cancel the external light, which may cause an error in the measured refractive index.

Therefore, there has been proposed a refractive index measurement device that notifies a measurer that a measured value is not accurate when the amount of light received by the light receiving sensor 104 when the light source 103 is turned off is equal to or greater than a certain amount of received light. .
JP 10-48130 A

  When a warning with an inaccurate measurement value is notified, a threshold value of the amount of received light that becomes a boundary of whether or not to notify the warning must be set in the refractive index measuring device. However, the range of the received light amount showing linearity varies to some extent for each light receiving sensor. The range of the amount of received light that guarantees linearity varies depending on the manufacturer of the light receiving sensor 104.

  The above threshold value is set to a very low level with a margin in consideration of the range of received light amount indicating linearity for each light receiving sensor. Therefore, even though accurate measurement is actually performed, A warning may be notified, and the performance of the refractive index measuring device cannot be fully exhibited.

  Therefore, an object of the present invention is to provide a refractive index measuring device that accurately detects whether or not the refractive index is accurately measured without hindering the performance of the refractive index measurement.

  The refractive index measuring apparatus of the present invention determines whether or not the refractive index is accurately measured by determining whether or not the amount of light received by the light receiving sensor when the light source emits light is included in the range showing linearity. Determine.

  In order to determine whether or not the amount of received light is included in the range showing the linearity, the refractive index measuring device uses the first light receiving sensor when the light source emits light at the light emission intensity at the time of measuring the refractive index and when the light source is turned off. And the second output value difference of the light receiving sensor when the light source emits weak light that is weaker than at the time of measurement and when the light source is turned off. The refractive index measuring device accurately measures the refractive index based on the ratio between the first output value difference and the emission intensity at the time of the measurement, and the second output value difference and the emission intensity ratio of the weak emission. It is determined whether or not.

  When the light source emits light with the light emission intensity at the time of measurement, when it emits weak light, or when it is turned off, the received light amount of each light receiving sensor is included in the range showing linearity, the first output value difference and the above measurement time , And the ratio of the second output value difference to the weak light emission intensity is the same. When the difference between the two ratios is within a certain allowable range, the refractive index measurement device determines that the refractive index is accurately measured.

  In the refractive index measuring apparatus of the present invention, the output value of the light receiving sensor under three conditions when the light source is made to emit light with the light emission intensity at the time of measuring the refractive index, when the light source is weakly emitted, and when the light source is turned off, It is determined whether or not the refractive index has been accurately measured based on whether or not a value corresponding to each condition is taken. Therefore, since it is not determined whether or not the measurement of the refractive index is accurately performed based on whether or not the external light amount exceeds the threshold set at a low level as in the past, the measurement of the refractive index is not performed. In spite of being performed accurately, a situation in which a warning is notified does not occur.

  The method of measuring the refractive index in the refractive index measuring apparatus 200 of the present embodiment is performed using the total reflection method described with reference to the background art and FIG.

  In the present embodiment, the refractive index measuring apparatus 200 causes the light source 103 to emit light and measure the refractive index in order to determine whether or not the refractive index has been accurately measured. Further, the light source 103 is turned off. The refractive index measuring apparatus 200 accurately measures the refractive index based on the output values of the three light receiving sensors 104 when the refractive index is measured, when the light source 103 is weakly emitted, and when the light source 103 is turned off. It is determined whether or not it has been done.

  The procedure will be described in detail below. First, the refractive index measuring apparatus 200 starts measuring the refractive index according to a measurement instruction from the measurer. For example, when the start key 210 provided in the refractive index measuring apparatus 200 is pressed, the light emission control unit 201 shown in FIG. 1 measures the refractive index of the object to be measured placed on the measurement surface 102 of the prism. The light source 103 is caused to emit light. The light emission control unit 201 causes the light source 103 to emit light and instructs the calculation unit 204 to acquire output values of all the light receiving elements of the light receiving sensor 104. The computing means 204 uses the output value of each light receiving element acquired based on the instruction as the output value v1 (see FIG. 3) when measuring the refractive index.

  Next, the light emission control means 201 weakens the light emission intensity of the light source 103 and causes the light source 103 to emit light weakly. In the present embodiment, the light emission intensity of weak light emission is 80% of the light emission during measurement of the refractive index, but the light emission intensity of weak light emission may be weaker than the light emission during measurement of the refractive index.

  In the weak light emission state, the light emission control means 201 instructs the calculation means 204 to acquire the output values of all the light receiving elements of the light receiving sensor 104 as the output value v2 at the time of weak light emission. Based on the instruction, the arithmetic means 204 obtains the output values of all the light receiving elements by setting the output value of each light receiving element as the output value v2 at the time of weak light emission. Further, the light emission control means 201 inputs to the determination means 205 that the light emission intensity of weak light emission is 80% of the light emission at the time of measuring the refractive index.

  Next, the light emission control means 201 turns off the light source 103. In the light-off state, the light emission control unit 201 instructs the calculation unit 204 to acquire the output values of all the light receiving elements of the light receiving sensor 104 as the output value v3 when the light is turned off. Based on the instruction, the arithmetic means 204 acquires the output value of each light receiving element as the output value v3 when the light is extinguished.

  When external light is incident on the refractive index measuring apparatus 200, the output value v1 at the time of refractive index measurement and the output value v2 at the time of weak light emission are the sum of the light reflected by the measurement surface 102 and the incident external light. The output value v3 when the light is extinguished is an output value corresponding to the amount of received external light.

  When the calculation means 204 obtains the output value v1 at the time of measuring the refractive index of each light receiving element, the output value v2 at the time of weak light emission, and the output value v3 at the time of extinction, it next cancels the external light quantity. In the present embodiment, as the light amount canceling means, the calculating means 204 is configured to turn off each light receiving element from the output value v1 when measuring the refractive index of each light receiving element and the output value v2 when each light receiving element emits weak light. Is subtracted from the output value v3. Hereinafter, the value obtained by subtracting the output value v3 at the time of extinction from the output value v1 at the time of refractive index measurement is referred to as a first output value difference ΔV1, and the output value v3 at the time of extinction is subtracted from the output value v2 at the time of weak light emission. The value is referred to as a second output value difference ΔV2.

  The calculating means 204 inputs the first output value difference ΔV1 and the second output value difference ΔV2 to the determining means 205, and inputs the first output value difference ΔV1 to the measuring means 207.

  When the first output value difference ΔV1 is input, the measuring unit 207 measures the refractive index based on the first output value difference ΔV1.

  On the other hand, when the first output value difference ΔV1 and the second output value difference ΔV2 are input, the determination unit 205 indicates that the light emission intensity of weak light emission is 80% in the present embodiment. Since it is input from the means 201, it is determined whether or not the relationship between the first output value difference ΔV1 and the second output value difference ΔV2 corresponding to each light receiving element is ΔV1 = ΔV2 / 0.8. When this equation is established, the relationship between the amount of light received and the output value of the light receiving element for which this equation is established indicates linearity between the amount of received light when the refractive index is measured and the amount of received light when the light is emitted weakly. It is proved that.

  When the first output value difference ΔV1 and the second output value difference ΔV2 of all the light receiving elements satisfy the relationship of the above equation, the determination unit 205 determines that the refractive index has been accurately measured. Since the adjustment of the light source quantity and the measurement of the amount of received light include an adjustment error and a measurement error, even if the values of ΔV1 and ΔV2 / 0.8 are slightly different, the determination means 205 accurately measures the refractive index. It is desirable to determine that it has been done.

  When the determination unit 205 determines whether or not the refractive index is accurately measured, the determination unit 205 notifies the notification unit 206 of the determination result. The notification means 206 displays the notified determination result on the display panel or notifies the measurer by sound or voice.

  The measurer can know whether the refractive index measured by the measuring unit 207 is accurate by knowing the determination result.

  In the above, the light emission control means 201 emits the light source 103 for measuring the refractive index and then performs weak light emission and extinguishing. Is not limited.

  A typical example of the external light incident on the refractive index measuring device is light from a fluorescent lamp. A light source using an AC voltage such as a fluorescent lamp is repeatedly turned on and off at a predetermined cycle. For this reason, when the refractive index measuring device is used in an environment where a fluorescent lamp is installed, the intensity of external light incident on the refractive index measuring device is not constant, but changes according to the emission intensity of the fluorescent lamp. In the present invention, the first output value difference ΔV1 and the second output value difference ΔV2 are used to determine whether or not the refractive index measurement is accurate. Therefore, if the emission intensity of the fluorescent lamp is different when the output values v1, v2, and v3 are input to the calculation means 104, the output value differences ΔV1 and ΔV2 are caused by external light incident on the refractive index measuring device. Without the light source 103, the output value of the light receiving sensor 104 when the light source 103 emits light at the time of refractive index measurement or weak light emission does not accurately indicate the value. Therefore, when the refractive index measurement device is used in an environment where light from a fluorescent lamp may be incident, the intervals at which the output values v1, v2, and v3 are measured are matched with the cycle of turning on / off the fluorescent lamp. It is preferable.

  In addition, the external light incident on the refractive index measuring apparatus may be not only the fluorescent lamp described above but also light having a non-constant intensity such as natural light. However, since the output values v1, v2, and v3 are measured in a relatively short time, it is not a big problem when the external light does not change rapidly. On the other hand, when external light that cannot be considered constant during the measurement period is incident, even if the external light quantity is within the linearity range of the light receiving sensor 104, the calculation means 204 has an accurate external light quantity. Canceling is not possible and an error occurs in measurement. In the conventional method of determining whether or not to issue a warning based only on the magnitude of the output value v3 (external light quantity) at the time of extinction, when external light that cannot be considered constant is incident during the measurement period. Even when the external light quantity happens to be small, the warning is not issued if the output value v3 when the light is turned off is measured. However, in the present invention, if the external light amount at the time of measuring each of the output values v1, v2, and v3 is different, even if each of the output values v1, v2, and v3 is within the range showing the linearity of the light receiving sensor 104, ΔV1 and ΔV2 /0.8 does not match and the refractive index measuring device can issue a warning.

  In the above, the output value v1 at the time of refractive index measurement of all the light receiving elements of the light receiving sensor 104, the output value v2 at the time of weak light emission, and the output value v3 at the time of extinction are input to the calculation means 204, Although the case where the element is set as the evaluation target of linearity is described, only the light receiving element in the limited region of the light receiving sensor 104 may be set as the evaluation target of linearity.

  As shown in FIG. 4, the amount of light reflected on the measurement surface 102 received by the light receiving sensor 104 is larger or smaller than the incident angle θ on the measurement surface 102 (hereinafter referred to as “critical angle”). There is a big difference. Therefore, there is a large difference in output value between a light receiving element that receives light having an incident angle θ smaller than the critical angle and a light receiving element that receives light having a larger incident angle. The measuring means 207 obtains a critical angle based on the first output value difference ΔV1 of each light receiving element, and measures the refractive index based on the critical angle. Therefore, if the output values of the light receiving element that receives light incident on the measurement surface 102 at a critical angle and the light receiving elements around the light receiving element are linearly related to the amount of light received, the refractive index can be accurately measured. .

  When the measurement unit 207 obtains the critical angle as described above, the measurement unit 207 determines a light receiving element to be evaluated for linearity based on the obtained critical angle. The light receiving elements to be evaluated here are, for example, a light receiving element that receives light incident on the measurement surface 102 at a critical angle obtained by the measuring unit 207 and a light receiving element in the vicinity thereof.

  When the light receiving element to be evaluated is determined, the measuring unit 207 inputs the position information of the light receiving element determined as the evaluation target to the calculating unit 204.

  The calculation means 204 acquires only the output value v1 at the time of refractive index measurement, the output value v2 at the time of weak light emission, and the output value v3 at the time of extinction that are output from the light receiving element specified by the input position information. The calculation means 204 includes the first output value difference ΔV1 corresponding to the light receiving element that has acquired the output value v1 during refractive index measurement, the output value v2 during weak light emission, and the output value v3 during extinction, and the second Output value difference ΔV2. The determination unit 205 determines whether or not the measurement of the refractive index is accurately measured based on the first output value difference ΔV1 obtained by the calculation unit 204 and the second output value difference ΔV2. judge.

  FIG. 2 is a schematic diagram of a refractive index measuring apparatus that employs a total reflection method in which light reflected by the measurement surface 102 is directly received by the light receiving sensor 104. Some refractive index measuring apparatuses that employ the total reflection method employ a configuration in which light reflected by the measurement surface 102 and emitted from a prism is received by the light receiving sensor 104 via a convex lens.

  When the light receiving sensor 104 receives light via the convex lens, the amount of light received by the light receiving sensor 104 other than light reflected by the measurement surface 102 such as external light can be reduced. However, providing a convex lens in the refractive index measuring device has disadvantages such as a measurement error due to optical aberration of the lens and a complicated configuration of the refractive index measuring device. On the other hand, when the convex lens as shown in FIG. 2 is not provided, there is a disadvantage in that the amount of received light such as external light received by the light receiving sensor 104 is larger than that of the refractive index measuring device provided with the convex lens.

  In the present invention, even if the light receiving sensor 104 receives external light, whether or not the refractive index is accurately measured can be accurately determined. Therefore, when the present invention is applied to a refractive index measuring apparatus that does not include a convex lens. Thus, it is possible to realize a refractive index measuring apparatus that has a simple configuration and can accurately determine whether or not the refractive index is accurately measured.

It is a functional block diagram of the refractive index measuring apparatus of this invention. It is a schematic diagram of a refractive index measuring apparatus employing a total reflection method. It is a graph showing the relationship between the amount of light received by the light receiving sensor and the output value. It is a graph showing intensity distribution of reflected light from a measurement surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 102 Measurement surface 103 Light source 104 Light receiving sensor 200 Refractive index measuring apparatus 201 Light emission control means 204 Arithmetic means 205 Judgment means 206 Notification means

Claims (2)

Refraction that measures the refractive index of the object to be measured based on the output value of a light receiving sensor that emits a light source toward the measurement surface of the prism on which the object to be measured is placed and receives the light reflected by the measurement surface In the rate measuring device,
Light emission control means for controlling the light emission intensity of the light source;
The first output value difference of the light receiving sensor when the light source emits light with the light emission intensity at the time of measurement and when the light source is turned off, and the light receiving sensor when the light source emits weak light that is weaker than that at the time of measurement. Computing means for obtaining the second output value difference of
Whether the refractive index is accurately measured based on the ratio between the first output value difference and the emission intensity at the time of measurement, and the ratio between the second output value difference and the emission intensity of the weak emission. A refractive index measuring apparatus comprising a determining means for determining whether or not. The refractive index measuring apparatus according to claim 1, further comprising a notifying unit that notifies a warning when it is determined that the measurement is not accurately performed by the determining unit.

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