JPH0466312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for automatically measuring the refractive index of transparent bodies such as optical glasses and transparent liquids.

(Prior Art) The following three types of conventional refractive index measuring devices are mainly known.

Spectrometer The refractive index of a sample is calculated by polishing a sample into a prism shape, allowing light to enter from one surface and emitting from the other surface, and measuring the deflection angle of the emitted light.

Prufrich refractometer A sample with an unknown refractive index (a surface polished so that the narrow angle between two adjacent surfaces is 90 degrees) is placed on a transparent body (base prism) with a known refractive index. Monochromatic light that is extremely close to and parallel to the base prism is incident on the sample side. Light is sequentially refracted and transmitted from the sample through the base prism and exits from the base prism side. The critical angle of this total reflection is measured and the refractive index is determined from this.

Although ordinary spectrometers and Pluffrich refractometers are both excellent measuring instruments, their disadvantages include the fact that they require optical polishing to process the sample, and furthermore, the adjustment of the measuring instruments and measurement operations are time-consuming.

V-block type refractometer In order to improve the above-mentioned drawbacks, this V-block type refractometer was developed. This is a 1937 Messrs Chance Brothers Co.
It is a refractometer developed by John Brothers & Co., Ltd., and has the configuration shown in Figure 7.
That is, the light rays emitted from the light source 31 pass through the filter 3.
2. The light beam passes through the slit 33, becomes a parallel beam by the collimator 34, and enters a V-block prism 35 made of a transparent material with a known refractive index. As the first step in the measurement process, a transparent sample 36 (hereinafter referred to as a standard piece) having exactly the same refractive index as the V-block is placed on the sample position using a contact liquid, and then placed on the scale provided in the eyepiece of the telescope 37. Measure the position of the slit image formed on the machine. In the next step, a sample with an unknown refractive index is placed in place of the standard piece 36 and the position of the slit image is measured in the same manner. The refractive index of the sample whose refractive index is unknown is calculated using a predetermined calculation formula by determining the amount of deviation (deflection angle) between the positions of the two imaging slit images. There are two methods for measuring this declination: a) fixed telescope type (differential type) and b) movable telescope type.
In the former case, the telescope 37 is always fixedly installed, as shown by the solid line in Fig. 7, but in the latter case, the telescope 37 is always fixedly installed.
The telescope is moved as shown by the dotted line in the figure.

The V-block refractometer constructed in this way is
Compared to spectrometers and Pulfritz refractometers, there is no need to polish the sample (because a contact liquid with a refractive index close to that of the sample is used), and measurements can be made in a sandy state, allowing for rapid measurement, and processing. There are advantages such as lower cost and easier measurement work.

Furthermore, in the fixed telescope type (differential type) mentioned above, compared to the movable telescope type, if the refractive index of the V block and the sample are significantly different, the slit image will be out of the field of view of the eyepiece.
Although there is the inconvenience of having to replace the block each time, the declination angle is kept within a small range and errors in declination measurement are suppressed to a small level.

(Problems to be Solved by the Invention) A conventional differential refractometer is constructed as shown in FIG. This was done by making visual measurements. For this reason, the following various problems occurred in the operation of adjusting the scale to the center of the slit image.

(1) Individual habits tend to emerge.

(2) The position of the slit image changes depending on the position of the observer's head (the angle at which the eyes look into the eyepiece).

(3) It is easy to misread the micrometer.

(4) People with severe astigmatism and presbyopia are particularly susceptible to eye strain.

(5) When the slit image becomes blurred due to the condition of the sample, it is difficult to locate the center of the image.

(6) After measuring the declination angle, mistakes and errors may occur during transcription or computer input during the refractive index calculation process.

(7) When measuring the declination angle, before measuring the sample, use as a reference the declination angle of a transparent sample (standard piece) that has exactly the same refractive index as the V block (theoretically, in this case the declination angle is 0°). However, depending on the assembly condition of the V block, a slight deviation angle will appear) must be measured in advance.

The present invention is intended to solve these problems, and the first purpose of the present invention is to simplify the measurement work by automating the refractive index measurement of transparent objects, and to eliminate individual errors. The second thing is to
The purpose of this is to improve measurement accuracy and reliability.

(Means for Solving the Problems) The above object of the present invention is to place a sensor instead of placing an eyepiece at the focal position of a telescope in the conventional differential refractometer shown in FIG. This was achieved by inserting the shutter immediately after the block, making the standard piece unnecessary.

Accordingly, the present invention provides a differential optical refractive index measuring device comprising a slit, a transparent V-block, and an imaging lens, which includes a first optical path that passes only through the V-block, and a second optical path that passes through the V-block and the sample. a shutter means for selectively switching between the first optical path and the second optical path; and a sensor for detecting the respective positions of the images of the slit formed through the first optical path and the second optical path. , means for controlling the driving of the shutter means and processing an output signal from the sensor.

The sensor is preferably a charge-coupled device sensor (CCD sensor), and the CCD sensor is preferably placed in a plane perpendicular to the optical axis.
Also, the CCD sensor is one-dimensional (line sensor),
Regardless of the type of 2D (area sensor).
The output signal from the CCD sensor is amplified by an amplifier and analyzed by a processing unit (CPU).

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an optical layout diagram showing a first embodiment of the present invention, in which a light source 1, condenser lens 2, slit 3, collimator lens 4, V block 5, sample 6, shutter 7, imaging lens 8, CCD It is composed of a sensor 9 and a control unit 10. The light source 1 is a discharge tube that emits a single wavelength, for example, a helium discharge tube that emits light with a wavelength of 587.6 nm.
Hydrogen discharge tubes that emit light at 486.1 nm and 656.3 nm are used. Instead of a discharge tube, a He-Ne laser or the like may be used. condenser lens 2
is for forming a light source image onto the slit 3, and a large aperture ratio is desirable because it brightens the image. The light coming out from slit 3 is sent to collimator lens 4
The light is made into parallel light, passes through the V block 5 and the sample 6 (the optical path is slightly bent at this time), passes through the shutter 7, and is focused by the imaging lens 8.
An image is formed on a CCD sensor 9 placed at the focal plane.

FIG. 2 shows the transparent V-block 5, sample 6, and shutter 7 in detail. The V block 5 is made of a transparent body with a known refractive index, and each has a vertical angle.
90°, -45°, its size is approximately 40 mm square, and its thickness is
It is machined to a diameter of 15 to 25 mm, and the surfaces where the light beam enters and exits are polished. Sample 6 is a transparent material with an unknown refractive index processed to have an apex angle of 90°. The shutter 7 is for passing the light beams A and B separately, and is driven by a light shielding plate 7a. That is,
The shutter 7 is provided with apertures independently from each other through which the light beams A and B can pass, and these apertures are closed by selectively moving the light shielding plate 7a under the control of the control unit. Selectively shaded. Here, the light beam A has passed through the V block 5 and the sample 6, and is bent at the interface between them according to the difference in refractive index between the two. On the other hand, the light beam B passes only through the V block 5 and does not pass through the sample 6, so it travels straight as it is. Therefore, by detecting the positions of the slit image of the light beam A and the slit image of the light beam B formed on the CCD sensor 9, and electrically measuring the distance △x between the two positions as described in detail later, from the measured values, The refractive index can be determined using a predetermined calculation formula. Shutter drive, position detection, analysis, and display are all performed by a central processing unit (CPU) and peripheral circuits within the control unit 10. In other words, by providing the shutter 7, there is no need to use a standard piece, and the operator has to perform the same operation twice as in the past: first placing the standard piece and determining the imaging position, and then performing the same operation on the sample. There is no need to do
Automation has become possible as measurement can be done in one step.

The CCD sensor 9 used in this embodiment has, for example, 3648 pixels each having a size of 8 μm×8 μm arranged in a straight line. When the slit image is projected here, the output signal from the CCD sensor 9 becomes as shown in FIG. Here, 90% of the peak level
If only the above signals are taken out and the position half the width is taken as the center position of the image (x _A , x _B , respectively), the position detection accuracy will be as high as 8 μm or less.

In the graph of FIG. 3, two peaks indicate the output signal distribution of each pixel 9A, 9B, . The distance Δx between the two peaks (x _A , x _B ) changes in accordance with the difference in rate. That is, if the refractive index of the sample 6 is exactly equal to that of the V block 5, both peaks in FIG. 3 will coincide and show a single peak distribution.

Now, the calculation formula for determining the refractive index is as shown in the following formula (1) in the case of a differential refractometer.

Here, n: refractive index of sample 6 n ₀ : refractive index of V block 5 f: focal length of imaging lens 8 (mm) △x: imaging position x of luminous flux A and luminous flux B (in Fig. 2) Distance between _A and x _B (mm) In the case of this example, △x = (x _B - x _A )・8/1000 mm Therefore, in terms of resolution in refractive index measurement, 1
In order to achieve ×10 ^-5 , the focal length of the imaging lens must be 400 mm or more. In this embodiment, this is set to 1000 mm, so the theoretical resolution is 4×10 ^-6 .

In this embodiment, the operator first applies V to the measuring instrument.
Enter the refractive index of the block, then place a sample with an unknown refractive index on the V block (at this time, make sure that the contact liquid enters between the V block and the sample),
Press the start switch (not shown) provided on the control unit. Then, this device immediately activates the slit image forming device (x _A ,
x _B ) are sequentially measured, analyzed, and the resulting refractive index is displayed. Switching between the shutters of the luminous flux A and the luminous flux B is automatically performed immediately after the measurement on one side is completed. The time required for one measurement is approximately 5 seconds from pressing the start switch to displaying the resulting refractive index.

FIG. 4 shows the accuracy of the refractive index measurement values measured by the refractive index measuring device of this example, and FIG. 5 shows the reproducibility of data with the refractive index measuring device of this example.

In FIG. 4, each data is the difference between the refractive index measurement value measured with the measuring device of this example and the value measured with a precision spectrometer (Shimadzu GM-1 or GMR-1). It has a frequency distribution on the order of 10 ^-5 . Refractive index measurement accuracy is approximately ±1~
It can be said to be 2×10 ^-5 . In FIG. 5, each data is a frequency distribution of the difference between the average value and the individual data when the same sample was measured 5 to 6 times, also on the order of x10 ^-5 . The result was ±1×10 ⁻⁵ . Since the refractive index measured using a precision spectrometer is ±1 to 2×10 ⁻⁵ , it is considered that the refractive index measuring device of this example is superior to a precision spectrometer in terms of reproducibility.

The V block used in this example had a glass type LF2 (n _d =
1.59041), and the contact liquid was a mixture of α-bromonaphthalene and liquid paraffin (JIS100, viscosity calibration liquid) with n _d =1.59054. Sample 6 is glass type SK5 (n _d =1.58800 to 1.59000).

FIG. 6 is a schematic optical layout diagram showing a second embodiment of the present invention. The refractive index measuring device of the second embodiment is
Light source 11, condenser lens 12, slit 1
3. Collimator lens 14, V block and sample 15, shutter 17, imaging lens 18, CCD
sensor 19, control unit 20,
RS232C interface 21, eyepiece 2
2, and mirrors 23-28.

This second embodiment becomes clear from FIG. 6, and is characterized by using a plurality of mirrors 23, 24, 25, and 26 to bend the optical path, and the refractive index measurement operation is the same as in the first embodiment. It is.

The refractive index measuring device of the second embodiment has the following features: the size of the entire system is made compact by bending the optical path; the optical path is divided by a driving mirror 28 to enable conventional visual measurement; and the RS232C interface It is characterized in that the addition of 21 enables communication with external devices. This mirror 28 can also be fixed and replaced with a half mirror. However, it is inevitable that the light intensity will decrease slightly.

In the second embodiment, "B10E", which is a Burroughs online terminal/offline personal computer, was connected to the external device. Then, register the refractive index of many V blocks on the B10E side,
The measuring device only measures the declination angle.
That is, the refractive index calculation using equation (1) is processed and displayed in B10E.

This allows for more V-block refractive index files and facilitates maintenance when replacing V-blocks.

(Effects of the Invention) As described above, according to the refractive index measuring device of the present invention, the measurement work is automated, so it is possible to eliminate all human errors related to the measurement work, and to obtain accurate data. can be obtained, and the working time can be significantly reduced compared to that of conventional differential refractometers. Furthermore, since the operator is freed from the act of looking through a conventional eyepiece, it is possible to significantly reduce the labor of the operator. Furthermore, in conventional differential refractometers, there was a risk that the standard piece would be lost or damaged, but according to the present invention, such a risk can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an optical layout diagram showing one embodiment of the present invention, FIG. 2 is an enlarged layout diagram showing the V block and shutter portion in the embodiment of FIG. 1, and FIG. 3 is an enlarged layout diagram of the embodiment of FIG. A characteristic diagram showing the output of the CCD sensor, FIGS. 4 and 5 are graphs for explaining the accuracy of refractive index measurement values, FIG. 6 is an optical layout diagram showing another embodiment of the present invention, and FIG. The figure is an optical layout diagram showing a conventional differential refractive index measuring device. 1, 11... Light source, 2, 12... Condenser lens, 3, 13... Slit, 4, 14... Collimator lens, 5... V block, 15... V block and sample, 6... Sample, 7, 17... Shutter, 8, 1
8...Imaging lens, 9, 19...CCD sensor, 1
0, 20...Control unit, 21...Interface, 22...Eyepiece, 23-28...Mirror.

Claims (1)

[Scope of Claims] 1. A differential optical refractive index measurement device comprising a slit, a transparent V block, and an imaging lens, comprising: a first optical path that transmits only the V block;
a second optical path that passes through the V block and the sample; a shutter means that selectively switches between the first optical path and the second optical path; and the slit that forms an image through each of the first optical path and the second optical path. 1. A differential automatic measuring device for optical refractive index, comprising: a sensor for detecting each position of an image; and means for controlling driving of the shutter means and processing an output signal from the sensor. 2. The shutter means is driven by the control means to selectively block light from two apertures for passing each of the light beams of the first optical path and the light beam of the second optical path, and the apertures. The differential automatic measuring device for optical refractive index according to claim 1, which comprises a light shielding plate. 3. The differential automatic measuring device for optical refractive index according to claim 1 or 2, wherein the sensor is a charge-coupled device sensor formed by linearly arranging a large number of micropixels. 4. The differential automatic measuring device for optical refractive index according to claim 1 or 2, wherein the sensor is a charge-coupled device sensor formed by two-dimensionally arranging a large number of micropixels. 5. The differential automatic measuring device for optical refractive index according to claim 1, wherein the optical path from the slit to the sensor is bent by a plurality of mirrors.