KR840002359B1 - Infared fays film tick measuring instrument - Google Patents

Abstract

Apparatus for measuring film thickness using infrared radiation, said apparatus comprising a radiation projector arranged to supply a beam of infrared radiation to a radiation diffusing member, the latter having an aperture arranged to provide passage for said beam through the diffusing member to a reflector arranged to intercept the beam and to direct the radiation from the beam back on to a concave non- specular reflecting surface of the diffusing member, said non- specular reflecting surface being arranged to direct diffuse radiation derived from the beam through a film position, through which an infrared transmissive film can extend when the apparatus is in used, a radiation receiver being arranged on the opposite side of the film position from the diffusing member.

Description

Infrared film thickness meter

1 is a schematic diagram of an infrared film thickness meter according to the prior art

2 is a schematic cross-sectional view of an infrared film thickness meter according to the present invention.

FIG. 3 is a graph comparing the measurement obtained in the prior art measuring device of FIG. 1 with the measurement example of the present invention according to FIG. 2, showing the measured output on the vertical axis and the film thickness on the horizontal axis.

4 is a cross-sectional view of the reflector in the embodiment of the present invention of FIG.

5 is a graph showing the output of the reflector of FIG. 4, showing the position measurement along the diameter of the concave reflector of FIG. 4 on the horizontal axis and the light intensity measurement on the vertical axis.

6 is a diagram showing the output of the lead sulfide element in the infrared detector, showing the output on the vertical axis and the projection light intensity on the horizontal axis.

7 is a cross-sectional overview of another embodiment of the present invention

FIG. 8A is a side view of the second reflecting mirror in the embodiment of the present invention of FIG.

8 (b) is a perspective view

Figure 9 (a) is a side view of another embodiment of the second reflecting mirror of the present foot

Figure 9 (b) is a perspective view

10 is a cross-sectional view of the reflector in the embodiment of the present invention of FIG.

FIG. 11 is a graph showing the light intensity distribution on the reflecting surface of the receiver when using the reflector of FIG.

12 is a graph of zero displacement caused by the deviation of the projection and the reception time for the measuring instrument according to the infrared thickness side wing of the Zoal and the present aspect.

The present invention relates to an infrared film thickness meter, and more particularly, to a measuring device capable of accurately and continuously measuring a transparent or translucent very thin plastic film and a film having a high-precision plane.

Transparent or translucent very thin plastic films and films with high strength planes are generally produced in continuous plate form. And sometimes film thickness was measured using a film thickness gauge continuously or at periodic intervals to ensure good production.

There are two types of film thickness gauges used to measure film thickness, namely contact and non-contact. In the contact gauge, the thickness was measured by direct contact with a dial or micrometa, and in the non-contact gauge, radiation such as beta or gamma rays was transmitted through the film. The amount of radiation absorbed by the film is then used to determine the film thickness.

However, the major drawback of non-contact film measuring devices by radiation is the costly and cumbersome measurement to protect the workers due to the excessive occurrence of radioisotopes. Thus, sufficient shielding for radiation has raised the price of the device.

In order to solve the drawback of such a non-contact thickness gauge by radiation, the non-contact thickness gauge using infrared radiation has been limited. These devices are based on the absorption difference of the infrared rays by the film due to the radiation wavelength of the infrared rays passing through the film.

Infrared light having a small light absorbing element and having a wavelength of lambda R (hereinafter referred to as R) and light having a large light absorbing element and having a wavelength of lambda M (hereinafter referred to as M) as the measurement wavelength are alternately applied to the film. Radiate about. After they pass through the film, the intensity of the light measured is converted to the common logarithm used to determine the thickness change of the film.

When the thickness distribution over the film width is to be measured, the infrared light source and the accompanying sensitizer are installed on the scanning frame reciprocating in the width direction on the film when the film is wound. The exact arrangement between the infrared radiation source and the sensitizer is important because the change in light received by the sensitizer affects the measurement of the film thickness.

Deviation of the alignment between the radiation source and the sensing period due to mechanical error in the manufacture of the scanning frame results in measurement errors. In addition, an effective method of controlling the manufacturing price of the scanning frame is to reduce the scanning error due to the deviation of the light side, and attempts to eliminate the difference in scanning as an infrared ray measuring device according to the prior art have not been successful.

Since the film thickness is very thin (50 microns (μ) or less) (hereinafter, the unit is used as "mu") as an infrared ray sensitive device according to the prior art, it results in interference between infrared rays reflected on the front and rear surfaces of the film, These interferences increase the measurement error. One proposal to deal with this difference in interference has been to use distributed infrared light rather than parallel light. However, the use of this scattered ray results in a significant problem of large zero-point displacement resulting in axial deviation between the projector and the receiver, which has not significantly improved the measurement accuracy.

Japanese Patent Application No. 51-115850 discloses a means for preventing interference of an infrared ray meter by radiating light dispersed in a material to be measured. This light beam was used to project a light beam onto a light dispersion tube such as frosted glass to disperse the light beam and irradiate the film. Although the accuracy of the measurements has been increased by eliminating the interference of irradiated light with respect to smooth film surfaces and relatively rough film surfaces, this method is only valid for film thicknesses of 100 mu or less. In addition, other devices using high power infrared radiation sources have been proposed, but they have not been able to meet the industrial requirements due to their low efficiency.

It is therefore an object of the present invention to provide an infrared film thickness meter which can very accurately measure an extremely thin film, such as a film having a high precision surface, with an infrared detector, without any energy loss, of infrared light that will pass through the film to be measured.

Another object of the present invention includes an optical receiver including an optical projector including an infrared radiation source, a rotation ring having a band pass filter installed in a circular conversion, and an infrared detector disposed on the other side of the sound to be measured.

The first reflecting mirror is provided on the projector side of the penisum, and has a concave hemispherical reflecting surface having a hole in the center through which infrared rays will pass, and the concave reflecting surface is disposed toward the film. The second reflecting mirror is installed on the projector side of the film and forms a convex spherical or conical reflecting surface facing the first reflecting mirror.

The collecting guide is provided on the light receiving side of the film and forms a conical reflecting surface having an infrared detector located at its vertex. The infrared detector converts the light intensity into an electrical signal that is input to the electrical data processing and display unit to calculate the film thickness, which is displayed on the display unit.

This invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 denotes an infrared projector in which a beam of low high radiation is emitted, which includes a radiation source 12 such as a tungsten bulb and a glow bar lamp, which is the wavelength of the desired infrared ray. It is selected according to the, and comprises a suter constituting the disc 14 to be rotated by the synchronous motor (16). This rotating disk 14 has two holes in symmetrical positions around it. Band filters 18 and 20 are located in the holes on the rotating disc 14, and the band filters 18 pass through infrared rays having a reference wavelength lambda M. The lens 22 has an infrared radiation source 12 and a band filter 18, 20 located in the hole on the rotating disk 14, and the band filter 18 passes infrared light having a reference wavelength lambda R. On the other hand, the filter 20 is configured to pass infrared rays having a measurement wavelength λ M. The lens 22 is disposed between the infrared radiation source 12 and the bandpass filters 18 and 20 to condense the scattered beams of infrared radiation emitted from the radiation source 12 into parallel beams. In this way, the parallel beam of infrared radiation passing through the lens 22 is filtered by the band filters 18 and 20.

The light sensitizer 24 is arranged at a fixed distance from the light projector 10 and measures the thickness of the film 26 that is continuously moved between them. This photodetector 24 comprises a light flux lens 28 having their axes arranged on the axes of the lenses 22. The infrared detector 30 is disposed at the focal point of the light focusing lens and may include a photoelectric device such as a lead sulfide element or a lead selenide element. The infrared detector 30 is disposed at the focal point of the light focusing lens and may include a photoelectric element such as a lead sulfide element or a lead selenide element. The infrared detector 30 is connected to the electronic circuit 32 and in turn to the instrument 34 to indicate the thickness of the film 26.

According to the prior art, the lens 22 converts a beam of infrared rays from the radiation source 12 into a parallel beam and is filtered by the band filters 18 and 20, and has a reference wavelength λ R and a measurement wavelength λ M. Only turns are applied to the film 26 to be measured. The infrared detector 30 detects infrared rays that have passed through the film 26. The output of the infrared detector 30, which indicates the intensity of the received infrared rays of the reference wavelength and the measured wavelength, is sent to the electronic circuit 32 where it calculates a large yield between the onion fields to determine the thickness of the film 26. And displayed on instrument 34.

On the other hand, the thickness measuring apparatus according to the prior art of FIG. 1 continuously measures the thickness of the film and can be handled safely and easily, but this causes a serious defect when the film is very thin, for example, 50 mu or less. That is, interference occurs that increases the error of measurement between the light rays reflected before and after the film. Furthermore, since the surfaces of films such as polyethylene, terephthalate film, polypropylene, and films are smooth and highly accurate, interference of multi-beams is likely to occur. And such interference causes a change in the amount of light transmitted and an increase in measurement error.

2 shows the basic elements of the embodiment of the present invention, in which the same elements as those of the conventional measuring device of FIG. 1 are denoted by the same reference numerals. The light projector 10 includes a shutter and an infrared light source 12 such as tungsten that emits infrared radiation in a predetermined wavelength range, that is, preferably 1.6 to 1.9 mu, or 2.0 to 2.6 mu. The shutter includes a rotating disc 14 made of an opaque material that does not pass infrared rays, and a synchronous motor 16 for driving the rotating disc 14. This disc 14 has two band filters 18, 20 having a half bandwidth of 200 to 400 nm. The band pass filter 18 passes infrared rays of the reference wavelength lambda R having various absorption coefficients, and a small portion of the infrared rays of this wavelength is absorbed by the film to be measured. The other thermal filter 20 on the rotating disc 14 passes only the infrared rays of the measurement wavelength lambda M, which has a larger absorption coefficient than the reference wavelength lambda R.

The lens 220 is positioned between the bandpass filters 18 and 20 and the infrared light source 12 of the rotating disc 14 to convert the radiated infrared rays into parallel beams.

The photosensitive member 24 detects the beam of infrared rays emitted by the light source 12. The film 26 to be measured is continuously moved in one direction between the light projector 10 and the light sensitizer 24.

The first reflecting mirror 36 is precisely arranged on one side of the film 26 together with the light source 12, and a rotating disc 14 having band filters 18 and 20 therebetween. The first reflecting mirror 36 is a rectangular block having a high reflectance, and the inner hemispherical concave reflecting surface 38 is coated or polished with a reflective material such as barium to have an uneven surface for separating reflection.

This reflector has a hole 40 of sufficient diameter formed in the hemispherical reflecting surface 38 so that the infrared beam emitted from the light projector 10 can sufficiently pass through the hole 40 in the single reflecting mirror 36.

The concave reflecting surface 38 is arranged so that infrared light is reflected toward the film 26, as shown in FIG. 2. The hole 40 has its center at the center of the lens 22 and the infrared light source 12; Are arranged to match. The second reflecting mirror 44 is disposed near the center of the concave reflecting mirror 38 and supported by appropriate means (not shown). The second reflecting mirror 44 is disposed near the center of the concave reflecting mirror 38 and supported by appropriate means (not shown). The second reflecting mirror 44 has a smooth reflecting surface 42 of convex hemisphere facing the concave reflecting mirror 38.

The light sensitizer 24 includes a condensing guide 48 with a conical reflecting surface 46, which provides a very smooth mirror surface. An infrared detector 30 comprising an optoelectronic device is preferably located on the axis of the conical reflective surface 46.

Next, the operation of the apparatus according to the present invention will be described. According to FIG. 2, the lens 22 alternately filters the beam of infrared light emitted by the light source 12 by the band filters 18 and 20 provided on the rotating disc 14 and converts the beam into parallel beams. The filters 18 and 20 pass only infrared rays of the reference wavelength lambda R and the measurement wavelength lambda M. The infrared beam passed at that time passes through the hole 40 formed in the first reflecting mirror 36.

The infrared beam is reflected by the convex reflecting surface 42 of the first reflecting mirror 44. This reflected beam is dispersed by the concave reflecting surface 38 of the first reflecting mirror 36, and this scattered infrared light is received by the photosensitive device 24 through the film 26 to be measured. This passed mine is reflected or guided toward the infrared detector 30 by the conical reflecting surface 46 of the condensing guide 48. Since the infrared rays of the reference wavelength lambda R and the measurement wavelength lambda M pass through the infrared detector 30 alternately, the detector alternately supplies an electrical output indicating the intensity of each wavelength. This output is then applied to an electronic circuit as in FIG. 1 to calculate the logarithm of the light intensity of the two wavelengths transmitted to determine the thickness of the film.

Most of the infrared rays distributed and reflected by the concave surface 38 of the first reflecting mirror 36 are projected onto the conical reflecting surface 46 of the condensing guide 48 to be condensed by the infrared detector 30, thereby providing a high signal to noise ratio. An electrical signal is obtained, thus resulting in high accuracy and reliability in measuring film thickness.

Since the azimuth angle of the conical reflecting surface 46 increases, the light rays reaching the infrared detector 30 by this surface tend to reflect toward the film 26 opposite to the axis of the infrared detector 30 at the minimum. do. Experimental results show that the preferred peak angle is between 20 ° and 60 °. At the peak angle of 40 °, the output signal from the detector 30 was 2.5 times larger than the output signal at the peak angle of 100 °.

Another advantage of the present invention is that the scattered light beam reflects the infrared beam at the concave reflecting surface 38 before passing through the film 26, so that the scattered light beam is projected at various angles in the film. And the interference between light rays reflected by the front and rear surfaces of the film to be generated in the parallel beam can be eliminated, and the error that can occur in the measurement can be minimized.

3 shows the film thickness measurement results according to the present invention. To create this graph, a bandpass filter with a half amplification level of 200 to 400 nm was used to measure polyethylene terephthalate film, which has a high degree of surface treatment. If such a film is measured by the parallel ratio of the device according to the conventional example, interference will occur even at approximately 100 mu thickness, thus reducing the accuracy of the measurement.

It can be determined from FIG. 3 that the device of the present invention can limit the measurement error to less than 1 mu even for very thin films in the thickness range from 1 to 10 mu. The error causing interference between the adjacent infrared rays is also greatly reduced, and the accuracy has been lined up compared to the conventional apparatus using the parallel beam of infrared rays. The light condensing guide 48 is configured to reflect almost the infrared rays of the reference wavelength λ R and the measurement wavelength λ M reflected by the concave surface 38 of the first reflector 36 to be reflected and collected by the infrared detector 30. The conical reflective surface 46 of is reached. This ensures a safe output and does not require the use of light sources that require high power, thus enabling the use of small light sources of about 10 to 30 watts.

Therefore, the present invention can measure plastic films such as polyethylene-terephthalate or polypropylene with an accuracy of less than 1 mu. In addition, the present invention can be used to measure very thin films such as 10mu to 20mu, as well as films with high accuracy, without causing interference by multiple reflections.

In addition, the present invention is effective for quality control of the film. In comparison with a conventional measuring instrument using radioactivity, the head measuring apparatus of the present invention is safe to handle and operate. In addition, since the projector and the receiver are substantially simpler and smaller than the radiation farm meter, the overall production cost is also substantially reduced.

The present invention was tested with a condensing guide 48 formed of conical and semicircular surfaces. The light sensitivity obtained on the hemispherical surface was about 1/3 or 1/4 of the light intensity reflected by the conical surface. Therefore, the hemispherical reflecting surface is clearly dropped.

The cross-sectional views of the first and second reflectors 36 and 44 in FIG. 4 show how the emitted infrared light is generated. This infrared ray passes through the hole 40 formed in the bottom surface of the concave reflection surface 38 of the first reflection mirror 36, and the light beam is reflected by the smooth convex reflection surface 42 to enter the dispersed radiation region. It is reflected by the dispersing means at point P on the concave reflecting surface 38 to go straight toward the film to be measured (not shown). The beam of infrared light reflected at point P towards the film is in the portion having a vertex angle [theta] limited to lines PQ and lines PR.

Light intensity distributions such as lead sulfide elements or lead selenide elements located within the light receiver 48 are shown in FIG. It can be concluded that a drop in light intensity occurs behind the second reflecting mirror 44, as indicated by the symbol S from the figure.

As shown by the optoelectronic device 30 such as lead sulfide element or lead selenide element located in the optical receiver 48, the output characteristic or resistance change due to the projection light intensity changes depending on the wavelength of the projection light. The lead sulfide element has a characteristic curve shown in FIG. Since the output characteristics indicated by the infrared photoelectric element of the reference wavelength (λR) are different from those of the measurement wavelength (λM), even if the infrared intensity of onion fields (λR) and (λM) changes at the same ratio, The output ratio of the optoelectronic device is changed.

In addition, as indicated by S in FIG. 5, since the light intensity falls behind the second reflecting mirror 44, the intensity variation of the projection infrared rays caused by slight side deviation between the projector and the receiver occurs at zero point transition. Is enlarged.

7 is an embodiment of the invention similar to the second embodiment, except that the second reflecting mirror 44 of FIG. 2 is of another shape with a convex reflecting surface 42 'as indicated by reference numeral 44'. It is shown.

In FIG. 8, the second reflector 44 'includes a truncated cone portion 45 and a spherical portion 42' formed on the bottom surface of the truncated cone. This convex reflection surface 42 'is treated with a very smooth surface.

9, a second reflecting mirror 44 'is shown, in which a disconnected cone-shaped convex reflecting surface 42' is formed at the bottom of the united cone 45. As shown in FIG.

As in the FIG. 8 embodiment, the convex reflecting surface 42 "is treated with a smooth surface.

7, the diameter P ₁ of the conical reflecting surface 46 at the bottom is smaller than the diameter D ₂ of the conical reflecting surface 38 of the first reflecting mirror 36 at the open end.

According to FIG. 7, the lens 22 collects the infrared rays emitted from the light source 12 into parallel beams, which are filtered by the band filters 18 and 20 formed on the original plate 14, and the reference wavelength? The infrared ray of the measurement wavelength lambda M is symmetrically passed through the hole 40 of the first reflecting mirror 36. These infrared rays are reflected by the convex reflecting surface 42 'of the second reflecting mirror 44'. The light rays reflected by this surface 42 'are further reflected and scattered toward the film 26 by the concave reflecting surface 38 of the first reflecting mirror 36. After the light passes through the film 26, they are reflected by the conical cone reflecting surface 46 of the condensing guide 48 to focus into the infrared detector 30.

As described above, the infrared rays of the reference wavelength lambda R and the measurement wavelength lambda M alternately enter the detector 30, which converts the intensity of the light into a novel signal. These signals are applied to a suitable electronic circuit where the intensity ratio transmitted between the two magnetic fields (not shown) is converted into logarithmic yield.

Shielding of the light scattered by the second reflector 44 'is shown in FIG. This second reflecting mirror 44 'includes a truncated cone 45 and a convex reflecting surface 42', which may be formed as a spherical portion rather than a hemisphere.

A portion of the light beam is reflected at the point P on the convex reflection surface 38 of the first reflecting mirror 36 and spread as indicated by the line PR. Since the second reflecting mirror 44 'is formed as a truncated cone at the bottom thereof, the ratio of the scattered light shielded by the second reflecting mirror 44' is very small, and the scattering angle of the beam toward the film 26 is very small. (θ) is larger than that shown in FIG.

Therefore, the light intensity distribution in the sensitizer 24 is as shown in FIG. 11, where the light intensity near the optical axis of the sensitizer 24 is almost constant.

Since the opening diameter D ₁ of the conical reflecting surface of the condensing guide 48 is smaller than the opening diameter D ₂ of the concave reflecting surface 38 of the first reflecting mirror 36, the projector 21 and the receiver 24 When the axes of) are separated from each other, the amount of light entering the condensing guide 48 is at a level that minimizes the amount of almost zero transition.

FIG. 12 shows a measurement result of the zero point transition caused by the deviation of the axis between the conventional infrared film thickness meter and the sensor and the projector according to the present invention. This can be concluded that for the same amount of side departure, the zero point transition of the present invention is 1/4 smaller than that of the conventional device. Therefore, the present invention can tolerate a large mechanical error in manufacturing a scanning frame to install a projector or a sensitizer than a conventional apparatus. This substantially reduces the manufacturing cost of the scanning frame. As an example, in order to limit the scanning error to 0.1 mu, the scanning frame should be manufactured to within ± 1 mm of the off axis of the projector and the receiver.

According to the present invention, this zero point transition can be minimized even if there is a slight deviation from the projector and the receiver, so that the fixed thickness measurement of the film thickness can be performed. The present invention can sufficiently reduce the production cost since it can vanish a larger mechanical error in manufacturing the scanning frame.

Embodiments of the present invention, in addition to those described above and shown in the accompanying drawings, can be made a variety of other film thickness meter without departing from the spirit and scope of the present invention.

Claims (1)

A measuring device for measuring film thickness, comprising: an infrared source located on one side of the film, a disk having at least two holes rotatably installed between the infrared source and the film, and holes on the disk for filtering the infrared rays A concave hemispherical reflector having a bandpass filter disposed above, a reflecting surface facing the film, a hole therein, disposed between the infrared source and the film, whereby the infrared light passes through the hole; A light condensing guide disposed between the film and the concave reflector, the convex reflector having a convex reflecting surface facing the concave reflector, and a means for sensing the infrared light and disposed on an opposite side of the film from the infrared source; Infrared film thickness meter characterized in that it comprises a.

Images