JPS58173454A - Optical detector utilizing polarized light - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical detection using polarized light, and in particular to optical detection of transparent bodies and thin paper.

BACKGROUND OF THE INVENTION Apparatus for sensing properties of material surfaces are well known in the art. For example, U.S. Pat. No. 3, lI3j. ,2
In No. 4tO, the % character of the material is determined by the quotient of the output signal from the 2III photomultiplier tube. The magnitude of these signals from the photomultiplier tube is determined by the energy κ from a single light source that simultaneously penetrates a small area and a large area of the material being studied. U.S. Patent No. O
In λ,oH, surface properties are determined by pointing a single light source at a material surface and comparing the amount of light reflected from the surface at λ different angles with a pair of detectors.

Another US Pat. No. J, U7J, 036, No. 3.
No. 623.91.9, No. 3.7 Hiroshi 1.3/0, and No. Hiroshi. θl Hiromu. No. 0θ describes various methods for detecting the presence or absence of a copy sheet or document in a xerograph copying machine. A common method for detecting originals and covey sheets is to place a light source on one side of the sheet path and a detector on the other side of the path.
tt or 7-t exists. but,
It is very difficult to detect transparent objects or thin paper using such a method. Within that ring, at the wavelength used for detection,
This is because the attenuation constant is small. To solve this difficulty, an attempt was made to make the optical path oblique to the plane of the paper and use a complex signal processing circuit to detect slight changes in the transmitted light. Also,
Another way to overcome this difficulty is to manually apply a white strip onto the transparent body in order to provide the transparent body with a detectable portion. However, these methods are time consuming and wasteful of costs.

Therefore, a simple and reliable method for detecting various types of transparent materials and thin papers with the same detector is provided, without the need for complex and expensive detector circuits or special markings. is desirable.

Purpose of the Invention From the above, what is the purpose of the present invention? Iil! simple and 1
It is an object of the present invention to provide a device for detecting transparent materials and thin paper, which is economical and does not have a center wall to adjust for various types of paper. Other objects and advantages of the invention will become apparent upon reading the following description. Also, if the invention
The new special purpose characterized by P is the fI &
The details are specified in the box.

Structure of the Invention The present invention relates to an apparatus for detecting the presence or absence of a transparent object or thin paper using a light source and a photodetector.

A polarizing filter is placed in front of the light source and photodetector P;1. When the polarization planes of both filters are parallel to each other,
Place a thin paper or AII body between the light source and the detector.
The resulting attenuation is so large that transparent objects or Fi thin paper can be detected. In another $voice example,
By aligning the polarization planes of the portrait filters to each other, it is possible to determine whether the front side of the transparent body is up or down. In the book 91 dormitory example, - the polarization planes of the filters are mutually! ! -1n. Transparent bodies made from optically active substances have increased transmission.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To assist in understanding the invention, reference is made to the accompanying drawings, in which like parts are designated by like reference numerals.

It is known that transparent materials such as Mylar exhibit birefringence. That is, the refractive index for light (L wave) K whose polarization plane is parallel to the optical axis of the transparent body is different from the refractive index for light (0 wave) K whose polarization plane is perpendicular to the optical axis K11l. Generally, light that enters a transparent body is linearly polarized, and if the plane of polarization is neither exactly parallel nor perpendicular to the optical axis, the light that emerges is elliptically polarized. Therefore, if a polarizing element is attached to the light source and the detector, the plane of polarization of the light wave passing through the light wave will change in this way, resulting in a very large attenuation.

In the case of plain paper, the western plane is scattered by the paper, resulting in a large attenuation of polarized light.

Referring to FIG. 7, a thin paper bag (transparent body 14) is inserted between the light source lO and the photodetector 12, and #E/ A second polarizer P is inserted between the transparent body 14 and the photodetector 12, and the polarizers P and P are parallel to each other at a distance Kt. In this case, due to the presence of the parallel polarizing filters, the attenuation of light from the light source to the photodetector is greater than the attenuation when no polarizing filters are present.

Referring to Figure 1b, a light source 10 and a photodetector! 2, a parallel polarizer P%P is similarly shown, but in this case the transparent body 14 is at an angle K to the light beam or optical path. As a result, the attenuation increases, and the attenuation varies with the relative tilt of the transparent body with respect to the path of light from the light source 1G. In the case of FIG. 1C, the transparent body 14Fi first
As shown in Figure 1, in this case KFi, polarizer P and pFi are placed directly in front of each other.

In this case, there is no attenuation, and conversely, the detector 1
The transmission of light to 2 increases. The same result can be obtained even if one transparent body 14 is tilted as shown in FIG.

Broom/--Referring to the figure, a transparent body 14 is shown for polarizers P, P, and K arranged at Kl'' from each other.The arrow on the transparent body 14 indicates the direction of its ff plane. 1st
In the case of figure f, polarizers P and P, K arranged in lily
On the other hand, the transparent body 14 is placed diagonally. In the case of FIG. 1e, the light from the light source 10 is generally attenuated or small.

On the other hand, in the case of the first diagram, the attenuation may become larger or smaller depending on the relative tilt of the optical axis of the transparent body 14 with respect to the polarization plane of the light from the light source IO.

Table 7 shows typical results of the attenuation of light from the light source 10 for various woodcutter transparencies, different polarizer placements, and transparency poses.

Polarizer P, P2, and mylar sea in between) 1
The arrangement of polarizer-transparent body-polarizer with 4' is shown in Fig. 2, and the relationship between the 1 optical axis and the polarization plane is shown in Fig. 2.
The angle between the polarization plane of the first polarizing filter P and the optical axis I of the transparent body is -, and the angle between the first polarizing filter P and the second polarizing filter P (analyzer) is -. The intensity of the light coming out of the second polarizing filter P can be expressed by the following formula (F, ^, J@nklns and H,E
, Whit@-Fundam@ntalsof 0p
tics', 3rd edition, Chapter 27, /rij7).

1 (branch) ^ (cosφ+44slnJcos#*5in
(φ-#) cos (φ-') sin a/co] Here,
^ is the amplitude of the linearly polarized light coming out from Pl, and 1 is the ordinary ray (0) and extraordinary ray (0) after passing through the transparent sheet 14t.
E) and the place! It is the difference (non-polarization effect, absorption effect, Oku ignored the attenuation effect).

The three states can be considered as follows. That is, parallel polarizers (φ=0 or π), perpendicular polarizers (φ=π/co or 3π/co), and diagonal polarizers (φ=π/co).
≠, 3π/≠, ...).

The intensity of the emitted light is given by the following equation:

Boo＾(/ -IIsln"@cos"#sIn"
a/λ]1 Attenuation is selected as O when a=Q, π/, 2, -... θ
It can be seen that the maximum pressure is reached when =π/li, 3π/11... In addition, the maximum attenuation is determined by the value of 1-1, and is 100% for l-, Jπ, jπ, ... os.
, and is O when -=θ, λπ, · fist...

The intensity of the emitted light is given by the following equation:

l oc, ^” 44sln”#co-〇sIn” J
/, 2 Therefore, the maximum attenuation (100%) if, −=
When 01π/ko,...-, the minimum attenuation is #=
Occurs when π/≠,... When O<#<π/2, the attenuation setting is determined not only by 0 but also by the value of -121.
If 'a=π/≠, I=π, 3π,...
When..., go to I^, and δ=01λK,...
When , the value is 1. Orthogonal polarizer arrangement is −=π/
When ≠, .

≠! Polarizer that forms @ (φ=π/Hiroshi, 3π/Hiroshi, fist...
・) The intensity of the emitted light can be found in the following equation.

1 ＾/, 2(/+5ln4'#sln J/, 2) The maximum transmission is a proverb π/1%jπ/I, ...e, the minimum o1i excess u, # = 3w /I, 7w/I
, *-s... occurs. a,,,Q, Ni/Hiroshi,
When /2, there is no change in the intensity. Therefore, when a transparent body is inserted between the optical polarizers and rotated, the intensity is /+sln J/- to / -sin'' with respect to the intensity when the transparent body is not present. Similarly, the degree of attenuation is determined by the phase angle -.This arrangement changes the sign of the term containing sin's/- when the transparent body is turned over, so '
There is a possibility that it will be connected to the front/back 1 detection device.

Table 2 summarizes the results for the nine three polarizer arrangements described above.

If the transparent body is oblique to the light beam, the value of J will change somewhat, as an expert in the six-body field will easily understand.

The relative attenuation produced by placing a thin piece of paper between parallel polarizing filters is much greater than when observed without a filter. It is clear that the higher attenuation is due to the scattering of the plane of polarization by the paper.

While we have shown and described what is thus far considered to be the preferred embodiment of the invention, it is likely that numerous changes and modifications will readily occur to those skilled in the art.
It is intended that the following claims cover all such changes and modifications that come within the true spirit and scope of the invention.

[Brief explanation of drawings]

Figures 1a to 1f show the combinations of angles [00, θ- and ≠j0] between the polarizers and cases where the paper or transparent sheet is perpendicular or inclined with respect to a beam of light. FIG. 2 is a layout diagram showing the polarizer-transparent body-polarizer power distribution in more detail. P, P...E photon, 10...II @ light source, 2 12-...photodetector, 14... Thin paper or transparent material.

Claims (9)

[Claims] (1) A light source that is placed near the material path and emits light in the direction of the material, and a first light source that is placed near the material path and detects the first light intensity when there is no material in the path and when there is material in the path. a second detector for detecting the amount of light, and at least two side photons are arranged near the material path between the light source and the first detector. A device that detects the presence or absence of material inside. (2) The apparatus according to claim 1, further comprising a polarizer between the light source and the material, and an analyzer between the detector and the material. (3) The device according to claim 2, wherein the material is transparent. (4) The device according to claim 2, wherein the material is thin paper. (5) The polarizing plane of the polarizer is parallel to the polarizing plane of the analyzer, and the material is a sheet placed perpendicular to the direction of the light emitted from the light source. Device in range 2nd present. (6) The sheet is placed obliquely to the optical path.
The device according to claim 1, characterized in that: (7) The light surface of the polarizer #i is perpendicular to the polarization plane of the analyzer, and the sheet is perpendicular to the direction of the light emitted from the light source. Claims No. 2, 2tIA memory device. (8) The device according to claim 7, wherein the sheet is placed in a direction oblique to the optical path. (9) The polarization plane of the polarizer is ≠5 with respect to the polarization plane of the analyzer.
0 seconds, the material is a sheet placed perpendicular to the direction of the light emitted from the light source. Device. Q□ The device according to item 1 of the patent application, characterized in that the sheet is placed in a direction oblique to the optical path. A light source that is placed near the sheet path and emits a constant amount of light; when the light source is placed near the sheet path and there is no sheet in the sheet path, a first amount of light emitted from the light source is detected; a light detector for detecting a second amount of light emitted from the light source when a sheet is present in the sheet path; and a polarizing filter disposed between the light source and the sheet path to detect the presence or absence of a sheet in the sheet path. and an analyzer filter disposed between the sheet passage and the photodetector, a sheet detection device for detecting the presence or absence of a sheet in the seed passage. (121 The detection device according to claim 1, wherein the polarization plane of the polarizer is parallel to the polarization plane of the analyzer. 03 The polarization plane of the polarizer is perpendicular to the polarization plane of the analyzer. Detection f! snow according to claim 2. I. The polarization plane of the polarizer is Vjo with respect to the light plane of the analyzer. Claim ii. detection device.