JP2927145B2 - Method and apparatus for measuring retardation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a birefringence measuring apparatus, and more particularly to a method for measuring the retardation of a film or sheet made of a polymer material. It can be applied to the case where it has, and is suitable for inspection of a film for a transparent electrode substrate of a liquid crystal display and the like. Furthermore, the present invention is suitable for not only a case where a sample is cut out to a predetermined size and measurement is performed offline, but also an online measurement and control in a film or sheet manufacturing process, because measurement is performed in a short time.

[0002]

2. Description of the Related Art Birefringence measurement is often used as a method for determining the optical anisotropy of a transparent or translucent material. Online birefringence measuring the conventional sheet materials, for example, Japanese
As shown in JP-A-5-209823 , a sheet to be measured is passed between three or more pairs of polarizers arranged in a fixed polarization orientation relationship (parallel Nicol state) and an analyzer, and a single-wavelength light beam is polarized. There is a method of measuring the transmitted light intensity of each analyzer when irradiating the sheet to determine the retardation and the direction of the main refractive index of the sheet to be measured.

In this method, when the anisotropy of the sheet to be measured is small and the retardation is several tens nm or less,
Sufficient measurement accuracy cannot be obtained. For this reason, it has been proposed to superimpose a sample on a retardation plate with a known retardation and measure the combined retardation of both. However, in the case of this overlay measurement, it is necessary to align the main refractive index directions of the measurement sheet and the retardation plate so that they are overlapped. In practice, when the anisotropy of the measurement sheet is small, the main refractive index direction can be accurately determined. Thus, it was difficult to obtain an accurate retardation.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a retardation measuring apparatus which enables online measurement of retardation during a process of producing a polymer film or sheet having small anisotropy.

[0005]

According to the retardation measuring method of the present invention, three or more pairs of a polarizer and an analyzer placed in a parallel Nicols state are arranged with their polarization directions shifted from each other, and the polarizer and the analyzer are analyzed. A retardation plate having a known retardation (R ₀ ) is placed between the photon and the photon, and the sheet to be measured (unknown retardation (Rs) unknown) is placed between the retardation plate and the analyzer. And the intensity of light transmitted through a polarizer, a retardation plate, a sheet to be measured, and an analyzer with respect to light of a specific wavelength is detected, and the retardation plate and the sheet to be measured are interposed. , The apparent retardation (R) and the orientation angle (Ψ) are determined, and these apparent values are expressed by a relational expression: Rs = ｛ (Δ
R) ² + ( c / b ) ² · Ψ) ² ｝ ^1/2 ─ (1), φ =
(1/2) · cos ^-1 (ΔR / Rs) × [sign of {}] ─
(2) (where ΔR = R−R ₀ , where c / b is R
₀ and a constant determined by the wavelength of light used for measurement) to determine the retardation and the main refractive index direction of the sheet to be measured. here,
The above relational expressions (1) and (2) are equations obtained by optically solving the state of superposition of the two retardation plates and the sheet to be measured, and the specific wavelength and R ₀ used in the measurement are constant. Is an expression obtained from simulation results calculated by changing Rs and φ variously.

[0006] The retardation measuring apparatus according to the present invention comprises three or more pairs of flat plates arranged with their polarization directions shifted from each other.
A pair of polarizer and analyzer placed in a row Nicol state and its
Placed between polarizer and analyzer with known principal refractive index orientation
Retardation plate with a known retardation (R ₀ )
Interposed between the retarder and the analyzer (unknown letter date
(Rs) unknown orientation angle (φ))
And a polarizer, retarder,
Check the intensity of the light transmitted through the measurement sheet and the analyzer.
Means for exiting, value relation retardation (R) and the orientation angle of the apparent combined and detected phase difference plate and the measured sheet (Ψ): Rs = {( ΔR) 2 + (c /
b ) ²・ Ψ) ² ｝ ^1/2 ─ (1), φ = (1/2)・ co
s ⁻¹ (ΔR / Rs) × [sign of Ψ] ─ (2) (where Δ
R = R−R ₀ , where c / b is a constant determined by R ₀ and the wavelength of light used for measurement) to determine the retardation and principal refractive index direction of the sheet to be measured. characterized in that an arithmetic unit.

In the retardation measuring apparatus according to the present invention, the polarizer, the analyzer and the light receiving means constituting the transmittance detecting means are substantially concentric with each other.
They may be arranged on the same circumference having one diameter .
An optical path for a monitor light beam may be provided substantially at the center of the circumference. A means for detecting the transmittance for three or more types of polarized light having different polarization directions; a means for sampling detection outputs of these detection means in accordance with a predetermined program; a means for storing sampled data; Means for calculating the retardation and the main refractive index direction from the data.

[0008]

As an embodiment of the present invention, a case will be described in which three or more pairs of polarizers and analyzers are used in a parallel Nicol state and having different polarization directions. At this time,
The analyzer transmitted light intensity I (θi) is represented by the following equation.

[0009]

[Number 1] _{I (θi) = I 0 {} 1+ (C-1) / 2} sin 2 2 (θi-Ψ) ·· (1) C≡cos (2πR / λ) ··· (2)

Here, I ₀ : the intensity of the linearly polarized wave incident on the sheet to be measured R: the state where the phase difference plate and the sheet to be measured are superposed
Apparent retardation λ: wavelength of measurement light θi: azimuthal angle of polarizer and analyzer with respect to reference direction (MD direction) ：: with retardation plate and sheet to be measured superimposed
Apparent orientation angle i: number of pairs of polarizer and analyzer. At this time, R and Ψ are obtained by numerical operations in the same manner as in JP-A-209823 .

In the present invention, it is assumed that measurement is performed in a state in which a sheet to be measured and a retardation plate fixed to a measurement system having a known retardation are superimposed between a polarizer and an analyzer. Retardation Rs of measurement sheet
And the orientation angle φ are variously changed, and the apparent retardation R and the orientation angle の when superimposed on the retardation plate of the retardation R ₀ are found, and Rs, Ψ,
Find the relationship between R ₀ and φ. First, a method of measuring low retardation (30 nm or less) using an on-line phase difference meter will be discussed. At this time, the condition is that a retardation plate with a known retardation is used, and the overlay measurement with the sheet to be measured is performed while the retardation plate is fixed.

The apparent retardation and the orientation angle by the parallel Nicol rotation method when the retardation plate and the sheet to be measured are overlapped with each other with the principal refractive index directions forming an arbitrary angle are obtained by simulation. , will be directing the relationship between the retardation and the orientation angle of the retardation and the orientation angle and the measured sheet apparent from the result.

FIG. 5 is a diagram for explaining the amplitude of a linearly polarized wave in the arrangement state of each optical element of the present invention and a sheet to be measured. In the figure, it is defined as follows. OX, OY: Main refractive index direction of retardation plate aa ', bb': Main refractive index direction of sheet to be measured PP ': Transmission axis direction of polarizer and analyzer φ: Orientation angle θ of sheet to be measured : Polarizer , Analyzer rotation angle R ₀ : retardation of retardation plate Rs: retardation of sheet to be measured

Now, let the amplitude of the linearly polarized light after passing through the polarizer be A
The amplitudes of the two linearly polarized waves after passing through the phase difference plate are A ₁ and A ₂ , and the amplitudes of the four linearly polarized waves after passing through the sheet to be measured are A ₁ ′ and A ₁ ”,
If A ₂ ′, A ₂ ″, each amplitude is represented as follows: A ₁ = A cos θ A ₂ = A sin θ A ₁ ′ = A cos θ cos φ (3) A ₁ ″ = A cos θ sin φ (4) A ₂ ′ = Asin θ sin φ (5) A ₂ ″ = Asin θ cos φ (6)

The amplitudes of A ₁ ′, A ₁ ″, A ₂ ′, and A ₂ ″ after passing through the analyzer are represented by A _1P ′, A _1P ″,
A _2P ', "If you is as _{follows. A 1P A 2P' = Acosθcosφcos} (θ-φ) ·· (7) A 1P" = Acosθsinφsin (θ-φ) ·· (8) A 2P '= Asinθsinφcos (θ-φ) ·· (9 ) a 2P "= Asinθcosφsin (θ-φ) ·· (10) a 1P ' and a _1P", a _2P' and a _2P "the amplitude of each of the composite wave a _1P, If _A2P, it will be as follows.

[0016]

[Number 2] _{^{A 1P 2 = A 1P '2}} + A 1P "2 + 2A 1P' A 1P" cosδs ·· (11) A 2P 2 = A 2P '2 + A 2P "2 + 2A 2P' A 2P" cosδs ·· ( 12) where δs = 2πRs / λ, λ: measurement wavelength

Further, _{assuming that} the phases of the combined waves A _1P and A _2P are η ₁ and η ₂ respectively, they are expressed as follows.

[0018]

Tanη ₁ = A _1P ”sin δs / (A _1P ′ + A _1P ” cos δs)... (13) tanη ₂ = A _2P ”sin δs / (A _2P ′ + A _2P ” cos δs). The analyzer transmitted light intensity I (θ) is A _1P and A _2P
Therefore, it is as follows.

[0019]

I (θ) = A _1P ² + A _2P ² + 2A _1P A _2P cosη (15) where η = δ ₀ −η ₁ + η ₂ −π (0 ≦ θ <π /
2) η = δ ₀ −η ₁ + η ₂ (π / 2 ≦ θ ≦ π) δ ₀ = 2πR ₀ / λ

Since the transmitted light intensity distribution can be found from equation (15), if R ₀ and the value of Rs and φ are variously changed while R ₀ is constant, the apparent retardation R and the orientation angle Ψ of the superimposed state can be obtained. Can be requested. For example, calculation is performed with R ₀ = 150 nm and λ = 590 nm,
When expressed as ΔR = R−R ₀ , the results shown in Table 1 are obtained.

[0021]

[Table 1]

Next, when each numerical value in Table 1 is three-dimensionally represented by ΔR as the X axis, Ψ as the Y axis, and Rs as the Z axis, a secondary conical surface as shown in FIG. 6 is obtained. Generally, a quadratic cone is represented by the following equation. X ² / a ² + Y ² / b ² -Z ² / c ² = 0 (16)

The intersection of the secondary conical surface with the ZX plane and the YZ plane is a straight line, and is represented by the following equations. Z = ± (c / a) X Z = ± (c / b) Y From the relationship between ΔR and Rs when Ψ = 0, c / a = 1, and Ψ and Rs when ΔR = 0. When the relationship was examined, c / b was found to be 6.71738. By substituting these numerical values into equation (16) and rearranging, Rs is represented by the following equation.

[0024]

Rs = ｛ΔR ² + (6.771738 · Ψ) ² ｝ ^1/2 (17)

Next, FIG. 8 shows the relationship between ΔR, φ, and Rs. When Rs is fixed, the relationship between φ and ΔR can be approximated by the following equation. ΔR = Rscos2φ (18) Accordingly, φ is obtained by the following equation. φ = (1/2) · cos ⁻¹ (ΔR / Rs) × [sign of Ψ] · (19)

[0026]

1 is a schematic structural view of an embodiment of an orientation measuring apparatus according to the present invention, wherein (S) is a sheet to be measured, (1) is a sample portion through which a measurement sample passes, and (2) is a sample section. Light source unit, (3) wavelength selection unit (filter unit), (4) polarization unit, (5) retardation plate, (6) analyzer unit, (7) photoelectric conversion of analyzer transmitted light intensity Photodetector.

The light source unit (2) includes a required number of small light sources (21). (2
2) ... (26) are provided at substantially equal angular intervals on the same circumference, and the parallel light beams (21), (22), ... ) Is irradiated downward in FIG. Instead of an individual light source, a disk-shaped light source or an annular light source is used, and a plurality of parallel light beams as described above are extracted by a light-gathering system such as a light-gathering lens (or light-gathering mirror) and an aperture (or slit). It may be. Further, after the light from one light source is converted into a light beam having an appropriate diameter by a light condensing system, a required number of the parallel light beams may be extracted by an appropriate number of optical fibers. The filter section (3) may be constituted by one filter plate, or may be constituted by incorporating a filter element at a position corresponding to each light beam on the holding plate.

The polarizing section (4) and the analyzing section (6) are shown in FIG.
As shown in plan views in (b) and (c), the polarizers (41), (42),... At positions corresponding to the optical axes of the holding plates (40) and (60), respectively. 46), the analyzers (61), (62),...
The polarization directions of the polarization elements of the polarization section (4) are shifted by 30 degrees. For example, if the polarizer (41) is oriented at 0 °,
Each of the polarizers (42) and (46) has a +
30 °, + 60 °, + 90 °, + 120 °, + 150 °
Are arranged. The polarizers of the analyzer (6) are arranged such that the polarizers of the polarizer (4) have a polarization direction such that those on the same optical axis have a predetermined polarization direction relationship, for example, a parallel Nicol relationship. Is given.

The retardation (5) has a known retardation and principal refractive index direction.

Although not shown, the sample section (1) is provided with a measurement space having a relatively narrow gap through which a sheet-like sample continuously fed from a production line passes. This measurement space may be closed at both ends in the width direction for a narrow width measurement sheet, but the work of setting the photometry section on the measurement sheet, setting the photometry section to an arbitrary position in the width direction of the measurement sheet, It is preferable to form one side in the width direction of the measurement space in an open shape in scanning of the light measuring unit (measurement point) at the other point. For this purpose, when the light measuring unit is formed as one unit, the light projecting unit from the light source unit to the polarizing unit and the light receiving unit of the light detecting unit and the detecting unit are arranged outside one side end of the sample sheet. It is preferable to provide a cantilevered (“U-shaped”) type holding mechanism for supporting with a. Alternatively, the measurement can be performed while the light emitting unit and the light receiving unit are synchronously scanned in the width direction of the measurement sheet.

The sample portion is provided at a position corresponding to a measurement point on the measurement sheet (corresponding to the measurement point) at every fixed distance movement of the measurement sheet, at predetermined time intervals, or in synchronization with the sampling timing of the measurement data. An ink-jet or other appropriate marking mechanism that attaches a measurement position identification mark is provided at the side edge of the sheet to be measured, or on the measurement point, etc., and the sampling data of the detection signal is also identified according to the code attached to the sheet. Data processing may be performed by attaching a code. It can be used as appropriate for tabulation of measurement results, extraction and processing of arbitrary data from measurement / storage data, rechecking of measurement data, and the like.

The detecting section (7) includes a detecting element (71),
, (76) are arranged on the holding plate (70) corresponding to each optical axis position. As the detection element,
Photoelectric conversion elements such as solar cells, photodiodes,
A CCD element or the like is used. The multiple light beam measuring units including the light source unit, the filter unit, the polarizing unit, the phase difference plate, the sample unit, the analyzing unit, and the detecting unit are provided as a single unit with the space for passing the measurement sheet. Can be formed. This makes it possible to reduce the size of the entire photometric unit, standardize the design and manufacture of each element of each unit of the photometric unit, assemble, adjust, and inspect the photometric unit, and improve the accuracy and production efficiency. In addition, since the photometric unit can be handled as one detection end by unitization, it can be installed in the production line, especially for instrumentation work, scanning of the measuring point (and therefore the photometric unit) in the width direction of the measuring sheet, It is possible to improve efficiency such as the exterior and other protection instrumentation of the photometric unit against environmental temperature and atmosphere, installation work, and installation of a scanning mechanism for measuring points in the width direction of the measurement sheet.

The size of the measuring point of the photometric unit (the whole polarized light beam in each required direction) is, for example, several mm to 10 m.
It can be formed in a circle having a diameter (φ) of about m or a square of the same degree, but for rough online measurement of a long sheet, for example, a diameter (or square) of about 2 to 3 cm may be used. The following parts are the data processing part and the control part, and the main part can be installed separately from the site environment separately from the photometric part. The transmission of measurement data and control commands between the photometric part and In addition to a wired or wireless electric signal, a means such as optical communication using an optical fiber can be used.

An input signal processing unit (8) performs amplification, A / D conversion, and the like of each detection output of the detection unit (7), and introduces them into the data processing unit. These elements and the transmitter
Depending on the system configuration of the entire measuring device, it may be provided at the detection end as appropriate. (B) is a data bus line of the data processing / control unit, and (9) is a CPU. (10) is RO
A program storage unit which is configured by a fixed (or semi-fixed) memory such as an M or EPROM and stores various control / arithmetic programs. A storage area (101) is a storage area of a control program for controlling the operation of the entire apparatus. In addition to the overall control program, an individual program for providing a measurement position identification mark on the measurement sheet, operating a filter exchange, or the like may be provided. , (102) are a storage area of a sampling program for instructing sampling of data from the detection output, and (103) performs various necessary calculations as described above from measurement data stored in a memory (10) described later. (104) is a CRT (12) and a printer (13)
Storage area of the output program for outputting to
Reference numeral 5) denotes a storage area for a monitoring program for automatically checking the operation of the apparatus.

The above-mentioned sampling program is a method of sampling data at a predetermined moving distance or a predetermined time of a continuous sheet-like sample coming out of a production line, or a specific point on the sample (regardless of whether the sample is stationary or moving, for example, Various methods are conceivable, such as a method of sampling the data of the marking points, etc., and the detection output of each detection element is input to the input processing unit (8) according to the selected sampling program.
Are stored in the memory (11) together with information on the number of the detection element (accordingly, the polarization direction) and information on the measurement position on the sample.

The above-mentioned calculation program performs various necessary calculations including calculation of retardation and calculation of the main refractive index direction from basic data and measurement data stored in the memory (11). The output program processes the CRT display of measurement results, print output, and other general output control. The output of the detection unit is sampled and stored in the memory (1).
Displaying the angle distribution diagram of the polarized light transmission intensity every time stored in 1), and performing processing such as continuous online display of changes in the orientation characteristics (or birefringence characteristics) in the flow direction of the sheet to be measured. Can also.

The monitoring program will be described later in detail.

The memory (11) is a memory having a variable storage content formed of, for example, a RAM, and an input buffer memory (111) for temporarily storing the above-described measurement data and the like introduced from the input processing unit (8). , An arithmetic processing data storage area (112) for storing processed data, basic data necessary for data processing, a basic data storage area (113) for storing formulas, etc., data for CRT display, printout, etc. Is stored in the output buffer memory (114). (14) is a keyboard input device.

FIG. 2 is a schematic system configuration diagram of a retardation measuring apparatus according to another embodiment of the present invention. Basically, the configuration is the same as that of FIG. Have been. 3 is different from the configuration of FIG. 1 in that each optical axis (L1), (L2),... For measuring the transmittance by polarized light beams having different polarization directions.
The point is that an optical path for monitoring (this optical axis is L7) is provided at the center of the aggregate of (L6).

That is, in the light source section (2), a light source (27) is newly provided, and in the polarizing section (4) and the analyzing section (6), a through-hole () is formed at the center of the holding disks (40) and (60). 47 '), (6
7 ′) are provided, and in the detection section (7), a light detection element (77) is provided at the center of the holding disk (70). Each of these elements (27), (47 '), (6)
7 ') and (77) are located on the optical axis. The position of the optical axis (L7) is preferably the center of each of the optical axes (L1) to (L6). However, the position is not strict and there is no problem even if the position is slightly shifted.

The light projected from the light source unit (2) does not need to be a split light beam, but may be a surface light source that generates a parallel light beam with a wide cross section. The detection unit (6) also transmits light through each optical path. For example, two-dimensional CC
It may be configured by a surface detector such as a D detection element, and the detection output of the portion corresponding to each optical path may be read.

The detection output of the detection element (77) is introduced into the data processing control section via the input processing section (8) in the same manner as the polarization transmittance detection output of the detection elements (71) to (76), and the control program is stored. The monitoring program (1
05) is used for monitoring various device operating states. For example, the detection element (7
Based on the output in 7), it is possible to determine whether the light amount of the light source lamp is equal to or more than the reference value and determine the lamp life. This confirmation may be performed automatically at a fixed time of use of the apparatus, or may be performed at any time.

When the measurement is performed by scanning in the width direction of the measurement sheet, the edge of the sheet can be detected based on the fluctuation of the detection output of the detection element (77), and for example, it can be used for controlling the scanning in the width direction. Further, when there is a seam or dirt on the sheet to be measured, the change in the light amount of (77) becomes large in the vicinity of this portion. By detecting this, the direction of the retardation and the main refractive index is calculated from the sampling data. In this case, it is possible to prevent the value from greatly changing and adversely affecting subsequent measurements.

The polarizers (41) to (46) and the analyzers ((61) to (61)) are provided in the through holes (47 ') and (67'), respectively.
The same polarizer (47) and analyzer (67) as in (66) are provided, and both (47) and (67) have a parallel Nicol relationship,
If a polarization direction different from that of another polarizer / analyzer pair is given, the detection output of the detector (77) at this time is output together with the outputs of the detectors (71) to (76) in the main refractive index direction, It can also be used to calculate retardation.

In this case, as shown in FIGS. 3 and 4, the optical axis (L) including the polarizer (47) and the analyzer (67) is used.
The light flux of 7) is, for example, L1-L7-L4, L2-L7-
Three measurement light beams like L5, L3-L7-L6 are arranged in a straight line on the sample surface. Therefore, if the direction of these linear arrangements is made to coincide with the flow direction or the sheet width direction of the measurement sheet, if the retardation and the main refractive index direction are calculated from the detection output for the light flux arranged in one line, these are obtained. The width of the measurement point in the direction can be reduced.

FIG. 4 shows another example of the specific configuration of a part of the photometric unit, the light source unit (2), the polarizing unit (4), the light analyzing unit (6), and the detecting unit (7) of the apparatus shown in FIG. Shown, rectangular holding board (20A),
At (40A), (60A), and (70A), the respective elements are arranged on the circumference and at the center thereof, and through holes (h1) for positioning each optical axis are provided at four corners of each holding board. Is provided. Furthermore, the holding boards (60A) and (70A)
Through holes (h2) for assembling the two together are provided at the four corners, so that the two can be easily and compactly combined and separated.

A retardation calculation program using the above-mentioned retardation plate so that the above-mentioned retardation plate can be inserted into and separated from the optical path and a case where a retardation plate as described in JP-A-5-209823 is not required. It is also possible to provide a retardation calculation program for online measurement, so that both measurement methods can be switched according to the sheet to be measured.

(Measurement Example) FIG. 8 shows the results of measuring the retardation and the main refractive index direction by running the low retardation film at a speed of 3 m / min by the measuring method of the present invention. The horizontal axis of the graph is the time axis, one division 20
At 0 seconds, the vertical axis indicates the main refractive index direction at the top and the retardation at the bottom.

The number of data points was 550, and the maximum value of the retardation was 13.2 nm, the minimum value was 7.1 nm, and the average value was 10.0 nm.

[0050]

【The invention's effect】

1) Even in the case of a sample having a small anisotropy, for example, a polymer film having a retardation of several tens nm or less, the retardation and the main refractive index direction can be effectively obtained in a short calculation time. 2) Measurement data necessary for calculating the retardation can be obtained immediately at any time, and the on-line measurement of the retardation becomes possible. Therefore, in the film production line or the like, a change in the characteristics of the sheet to be measured in the flow direction can be known in detail. 3) The retardation and the main refractive index direction can be obtained simultaneously. 4) By providing the monitor optical path, it is possible to easily monitor various operation states of the apparatus. 5) The system can be configured by only adding a certain amount of software to the conventional system. 6) The method of measuring the retardation and the main refractive index direction of a polymer film or sheet having large anisotropy and the method of measuring as described above using a retardation plate can be switched.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a retardation measuring device according to one embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a retardation measuring device according to one embodiment of the present invention.

FIG. 3 is a detailed view of a polarizer and an analyzer in the configuration of FIG.

FIG. 4 is a diagram illustrating a specific configuration example of a part of a photometric unit of the apparatus in FIG. 1;

FIG. 5 is a diagram for explaining the operation principle of the present invention.

FIG. 6 is a relationship diagram of ΔR, Ψ, and Rs.

FIG. 7 is a relationship diagram of ΔR, φ, and Rs.

FIG. 8 is a diagram illustrating an example of measurement by the apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sample part 2 Light source part 3 Filter part 4 Polarization part 5 Phase difference plate 6 Analysis part 7 Detection part 8 Input processing part 9 CPU 10 Program storage part 11 Data storage part 12 CRT display device 13 Printer 14 Keyboard input device 20, 40 , 60, 70 Holding board 21-26 Light source 41-47 Polarizer 47 'Through hole 61-67 Analyzer 67' Through hole 71-77 Detection element 101 Control program storage unit 102 Sampling program storage unit 103 Operation program storage unit 104 Output Program storage unit 105 Monitoring program storage unit 111 Input buffer memory 112 Operation processing data storage area 113 Basic data storage area 114 Output buffer memory B Data bus lines L1 to L7 Optical axis S Measurement sample

Claims (5)

(57) [Claims] 1. A set of three or more pairs of a polarizer and an analyzer placed in a parallel Nicols state are arranged with their polarization directions shifted from each other, and a position having a known retardation (R ₀ ) is placed between the polarizer and the analyzer. The retardation plate is placed in a state where the main refractive index direction is known, and a sheet to be measured (having unknown retardation (Rs) and unknown orientation angle (φ)) is interposed between the retardation plate and the analyzer,
The intensities of the light transmitted through the polarizer, the retardation plate, the sheet to be measured, and the analyzer with respect to the light having the specific wavelength are detected, respectively, and the apparent retardation (R) obtained by combining the retardation plate and the sheet to be measured and The orientation angle (Ψ) is obtained, and these apparent values are expressed by a relational expression: Rs = ｛ (ΔR) ² + ( c / b )
^{2 · Ψ) 2} 1/2 ─} (1), φ = (1/2) · cos -1
(ΔR / Rs) × [sign of Ψ] ─ (2) (where ΔR =
Is defined as R-R _0, c / b is substituted into a is) constant determined by the wavelength of light used for R ₀ and measurement,
A method for measuring retardation, comprising determining a retardation and a main refractive index direction of a sheet to be measured. 2. The three pairs arranged with their polarization directions shifted from each other.
A set of polarizer and analyzer placed in the above-mentioned parallel Nicol state
And the polarizer and analyzer with their principal refractive index orientations known
Between the retardation (R ₀ ) and the known phase difference
Between the plate and the phase difference plate and the analyzer (unknown
Retardation (Rs) with unknown orientation angle (φ)
Sheet to be measured, polarizer and phase for light of specific wavelength
Check the intensity of light transmitted through the difference plate, the sheet to be measured, and the analyzer.
A relational expression: Rs = ｛ (ΔR) ² + The value of the apparent retardation (R) and the orientation angle (Ψ) obtained by combining the detection means and the detected retardation plate and the sheet to be measured.
( C / b ) ² · Ψ) ² ｝ ^1/2 ─ (1), φ = (1 /
2) · cos ^-1 (ΔR / Rs) × [sign of Ψ] ─ (2)
(Where ΔR = R−R ₀ , where c / b is a constant determined by R ₀ and the wavelength of the light used for the measurement), and the retardation and principal refractive index of the sheet to be measured are substituted. retardation measuring apparatus characterized by comprising a calculating means for calculating a direction. 3. A polarizer, an analyzer and a light receiving means constituting the transmittance detecting means are substantially concentric with each other.
3. The retardation measuring device according to claim 2, wherein the retardation measuring devices are arranged on the same circumference having the same diameter . 4. The retardation measuring device according to claim 3, wherein a monitor light beam optical path is provided substantially at the center of each circumference . 5. A means for detecting transmittances for three or more types of polarized light having different polarization directions, a means for sampling detection outputs of these detection means according to a predetermined program, and a means for storing sampled data. 5. The retardation measuring apparatus according to claim 2, further comprising: means for calculating a retardation and a main refractive index direction from sampling data.