JPH0519081B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application] The present invention relates to a film thickness measuring device that measures the thickness of a film based on the amount of light beams such as infrared rays absorbed by the film. The present invention relates to a film thickness measuring device suitable for measuring the thickness of film.

[Prior art]

In recent years, the fields of application of films, especially polymer films such as polyester films, have been expanding, and the requirements for their quality have become stricter. There is a strong demand for uniformity of film thickness as a quality factor, and therefore thickness control by on-line measurement has become necessary.

By the way, as a thickness measuring method capable of the above-mentioned online measurement, there have already been proposals such as Japanese Patent Laid-Open No. 53-31155. What is disclosed in JP-A No. 53-31155 is to measure infrared rays at the wavelength of the absorption peak of a film (absorption wavelength) and infrared rays at a wavelength that is hardly absorbed by the film (reference wavelength), which are measured by switching filters. This is an excellent two-color infrared thickness meter that alternately passes the same light path through the same optical path, and is expected to provide stable continuous measurement, but it has the following problems. In other words, when the film thickness changes significantly or the temperature changes, the transmittance of the absorption wavelength and the reference wavelength do not change in the same way, resulting in a film thickness measurement error.
As the thickness decreases, the amount of absorption by the film decreases, resulting in a decrease in measurement sensitivity and accuracy, and for this reason, there is a problem in that it is not sufficient to monitor changes in thickness.

[Purpose of the invention]

In response to this situation, the present inventor has previously filed a patent application in 1983.
In No. 201506, we proposed the following method shown in Figure 1 as a film thickness measuring method that can accurately and online measure films as thin as 10 μm or less to as thick as several 100 μm. In the figure, P is a target film to be measured, for example, a traveling polyethylene terephthalate (PET) film during production. S is a reference film, which has the same composition as the target film and has the same thickness t ₀ as the thickness set in the production conditions.

Reference numeral 1 denotes a light source that emits a light beam I ₀ of a wavelength suitable for the target film (for example, in the case of a PET film, an infrared beam with a wavelength of 5.8 μm whose absorption coefficient is approximately 1). 2 is a light projecting system that splits the light beam _I0 into a measurement beam Ip and a reference beam Is and guides it to a target film P and a reference film S;
This is a known optical system consisting of a mirror 2a, a half mirror 2b, and a reflecting mirror 2c.

3 is the reference beam transmitted through the reference film S
A light receiving system that guides I's and the measurement beam I'p that has passed through the target film P to a photoelectric conversion section 4, which will be described later.
It is composed of a and 3b.

The photoelectric conversion unit 4 described above is composed of photodetectors 4a and 4b with good responsiveness such as InSb semiconductors, and converts both received beams I′p and I′s into a measurement signal Ep, which is an electrical signal proportional to the amount of received light. Convert to reference signal Es.

5 processes both signals Ep and Es to produce the target film P.
A logarithmic ratio calculation circuit 5a that calculates the ratio Ep/Es of both signals Ep and Es, and also calculates and outputs the logarithm El of the ratio Ep/Es in a signal processing unit that obtains a thickness signal Et related to the thickness t of the signal. The thickness of the reference film S is t ₀ in the output El.
and an arithmetic circuit 5b that adds a predetermined value corresponding to the thickness signal Et to obtain a thickness signal Et.

That is, the target film P and the reference film S to be measured are irradiated with the light beam _I0 , and the respective transmittances I'p and I's are detected by the photodetectors 4a and 4b, and the light intensity ratio I' is determined. The ratio Ep/Es corresponding to /I's is measured, and the thickness of the target film P is measured based on this ratio. Therefore, P of the target film
Since the thickness of the film S is detected as a variation from the reference film S, measurement can be performed with high sensitivity and rapid response, and measurement can also be made resistant to environmental changes such as fluctuations in the light source 1.

Furthermore, in the present invention, since a film having the same composition and approximately the same thickness as the target film is used as the reference film, the transmitted light on the target film side
Looking at Ip′ and the transmitted light Is′ on the reference film side,
Since the light loss due to reflection on each film surface acts to the same extent, Ip' and Is' become approximately equal. As a result, the operating conditions of the photoelectric conversion element, the gain of the amplifier system, etc. can be made substantially the same, and stable and highly sensitive measurement is possible.

The present invention is directed to an apparatus for carrying out the above-described method, and particularly to a film thickness measuring apparatus with excellent environmental resistance and suitable for on-line measurement during manufacturing processes.

[Structure and operation of the invention]

The present invention achieves the above object and is characterized by the following configuration.

That is, in the present invention, a light beam from the same light source is guided by a projection system to a target film to be measured and a reference film, and the transmitted light from both films is converted into an electrical signal by a photoelectric conversion section, and the ratio is calculated. In a film thickness measuring device that measures the thickness of a target film based on this ratio, a film having the same composition and approximately the same thickness as the target film is used as a reference film. A pair of heads are arranged facing each other with a gap for the film to pass through, and one head houses a reference conversion system that receives transmitted light from the light source, the light projection system, and the reference film and converts it photoelectrically. However, the other head houses a measurement conversion system for receiving and photoelectrically converting the transmitted light from the target film, and each head is divided into small chambers by partition walls for each of the light source and the heat source of the photoelectric conversion section. This is a film thickness measuring device characterized by being air purged with air at a constant temperature and humidity.

The above-mentioned predetermined reference film refers to a film that generates a reference signal that compensates for the influence of factors other than the thickness of the target film on the measurement, as is clear from the above-mentioned principle. The films have the same characteristics, especially the light transmission characteristics for the light beam used. Therefore, a film having the same composition as the target film can be applied. Further, films having the same surface characteristics such as flatness are also preferable because they have the same reflection characteristics. From these points of view, films of the same composition and approximately the same thickness manufactured under the same manufacturing conditions are preferred.

The details of the present invention described above will be explained based on an embodiment suitable for continuous measurement in the manufacturing process of PET film.

FIG. 2 is a front view of the above embodiment, and FIG. 3 is a side view thereof.

As shown in the figure, in this embodiment, the film P to be measured is
An upper head 200 is disposed on the upper side, and a lower head 300 is disposed on the lower side thereof, and these are held by an upper arm 101 and a lower arm 102 of a common frame 100. Therefore, the upper head 200 and the lower head 30
0 vibrates integrally in response to vibrations from the floor etc.
There is no occurrence of optical axis deviation.

The interiors of the upper head 200 and the lower head 300 are constructed as shown in FIGS. 4 and 5. FIG. 4 shows an upper head 200 and a lower head 30.
A front sectional view on the optical axis plane of 0, Fig. 5 is A of Fig. 4.
- It is an arrow view from the A line.

First, the configuration of the upper head 200 will be explained. 1 in the figure is a light source, which is attached to a predetermined position on the upper side of the upper case 201 as shown in the figure, and emits an infrared beam I ₀ vertically downward. The light source 1 includes a light collecting cover 13 having a jacket structure, which forms a light collecting path 12 having a truncated cone shape with a predetermined length and a predetermined apex angle and a mirror surface on the circumferential surface, the lower side of which is a small-diameter emission aperture 11; a reflective cover 15 having a jacket structure forming a reflective space 14 whose peripheral surface is a mirror surface such as a paraboloid of revolution or a spherical surface; It consists of. The heating element 16 is a sheathed electric heater coated with ceramic, and a thermocouple is embedded together with the heater wire so that the temperature can be controlled at a constant temperature. In addition, air at a constant temperature is supplied to the jacket to stabilize the temperatures of the condensing path 12 and the reflection space 14. Therefore, the target infrared beam I ₀ can be effectively and stably generated at low temperatures. In this example, when the temperature of the heating element 16 was set to 290°C, an infrared beam with a wavelength of 5.8 μm and a beam diameter of 8φ and an intensity equivalent to that of a tungsten lamp at 1500°C was obtained. Another advantage is that the beam diameter can be set freely, and even a thin beam can have high intensity as in the above example. Moreover, it has the practical advantage of being cheaper than other light sources.

The infrared beam I ₀ emitted from the radiation aperture 11 is controlled by the chopper device 60 at a predetermined period (in this example,
500Hz) is converted into pulsed light. The chopper device 60 has a known configuration in which a motor 63 rotates a rotary disk 62 having predetermined through holes 61 arranged at appropriate intervals on the same circumference at a constant speed. In addition,
The motor 63 is attached to the upper case 2 together with the light shielding cover 64.
It is attached and positioned by an attachment member 65 to a surface plate 202 provided on the rear wall 201a of 01.

The infrared beam I ₀ leaving the chopper device 60 is
The beam enters the light projection system 2 and is split into a measurement beam I _P and a reference beam Is. That is, the light projecting system 2 includes a lens barrel block 21 that forms a vertical optical path with a cylindrical peripheral surface that penetrates in the vertical direction and has a mirror surface, and a horizontal optical path that is also cylindrical and has a mirror surface that is orthogonal to the vertical optical path. A filter unit 22 is removably screwed onto the entrance of the vertical optical path, and a holding unit 23 is removably fitted from the left side of the horizontal optical path, so that the filter unit 22 is arranged to intersect the vertical optical path at an angle of 45 degrees. The beam is divided into a vertical measurement beam Ip and a horizontal reference beam Is by the half mirror 2b. In this example, the filter of the filter unit 22 is a bandpass filter with a transmission center wavelength of 5.8 μm. Also, 24 in the figure is
A beam diameter setting unit for setting the diameter of the measurement beam Is, consisting of a ring of a suitable diameter, is screwed onto the exit of the vertical optical path. The lens barrel block 21 is positioned by being fixed to a surface plate 203 on the rear wall 201a of the upper case 201 via a sizing block 204 by aligning knobs and pins. Therefore, assembly is very simple, and the main optical path is covered by the lens barrel to eliminate the influence of environmental conditions such as external light.

A reference system for generating the aforementioned reference signal Es is connected to the horizontal optical path of the lens barrel block 21. That is, a holder _S1 in which a predetermined reference film S is set is screwed onto the exit of the horizontal optical path. As the reference film S, a film having the same composition and the same thickness as the target film under the same manufacturing conditions, specifically, a PET film, can be used.

The reference beam I's transmitted through the reference film S is converted into a reference signal Es by the following reference conversion system.
That is, at the exit of the horizontal optical path of the lens barrel block 21, a lens holder 31 consisting of a cylindrical body with a mirror surface and a predetermined length is removably set by notch pin alignment, and a condensing lens 3b consisting of a germanium convex lens is fixed. It is fixed to the lens holder 31 by screwing the ring 32 to constitute the above-mentioned light receiving system.

Then, the reference beam focused by lens 3b
I's enters an infrared photodetector 4b placed at the focal point of the lens 3b, and is converted into a reference signal Es. The optical path from the lens 3b to the photodetector 4b is surrounded by a cylindrical cover 41b whose inner surface is mirror-finished so as not to be affected by environmental conditions such as external light. The photodetector 4b is IRS manufactured by Fujitsu Limited.
-311S was used. 42b in the figure is a photodetector 4b
43b is a heat sink used for the photodetector 4b.
This is a circuit unit that houses the temperature control circuit and preamplifier of IRS-311S. The positioning of the photodetector 4b is exactly the same as that of the lens barrel block 21, and the explanation thereof will be omitted.

Reference numeral 205 in the figure denotes a partition plate that is a partition wall that divides the upper head 200 into small chambers for each heat source, and is provided to separate the light source device 1 and the components related to the photodetector 4b.
As mentioned above, the jacket built into the light source device is air-purged so that the light collection path and reflection space are at a predetermined temperature. Each chamber is individually purged with air controlled at a constant temperature and humidity, and the same air is used to purge the lens barrel block 21.
The lower opening and the optical path before and after the reference film S are air purged to stabilize the measurement conditions, especially the temperature and humidity. Note that 206 in the figure is the upper head 200.
This is the front cover plate.

Next, the lower head 300 will be explained. The lower head 300 houses a measurement conversion system that receives the measurement beam I'p that has passed through the film P to be measured and converts it into an electrical signal Ep. The light receiving system consists of a block body 33 made of a cylindrical body, a condensing lens 3a made of a germanium convex lens built into a receiving part that enlarges the optical path of the block body 33, and a screw thread attached to the end of the optical path of the block body 33. A condensing unit 34 having a conical condensing path with a mirrored peripheral surface.
and a mask unit 3 for adjusting the size of the measurement beam I'p attached to the entrance side of the condensing unit 34.
5, the rear wall 301a of the lower case 301
The measurement beam from the upper head 200 is attached via a sizing block 303 to a surface plate 302 provided at
The optical axis of the light receiving system is arranged so that it coincides with the optical axis of Ip.

The light receiving aperture of the condensing unit 34 is 1.5 to 3 times larger than the projection aperture of the measurement beam Ip, that is, the aperture of the beam system setting unit 24. A mask unit 35 shown in FIG. 6 is attached to the light receiving port. As shown in the figure, the mask unit 35 has a slit 35 having a predetermined width orthogonal to the running direction of the target film P.
a, a mask plate 35b with a predetermined width and a predetermined transmittance provided on both sides thereof, and a shielding plate 35c that blocks light. As the mask plate 35b, a PTE film having a predetermined thickness, specifically, approximately the same thickness as the target film, was used.

Note that all optical paths of the block main body 33 directly hit by the measurement beam I'p are mirror surfaces.

The measurement beam I′p from the light receiving system described above is converted into an electrical signal.
The photoelectric conversion section for converting into Ep has exactly the same configuration as the photoelectric conversion section for the reference beam I's described above.
That is, the lens 3a is placed at the focal position of the lens 3a.
A photoelectric detector 4a using IRS-311S, a cylindrical cover 41a, a radiator 42a, and a circuit unit 43
a, and a sizing block 304 is placed on the surface plate 302.
It is attached and positioned by.

305 in the figure is the aforementioned partition plate, and each chamber divided by the partition plate 305 is air purged with air under the same conditions as the air used for air purging of the upper head 200. Furthermore, the optical path of the light receiving system for the aforementioned measurement beam I'p is similarly air purged. 306 in the figure is a front cover plate.

By the way, the upper head 200 and the lower head 30
In front of the measurement beam Ip, that is, upstream in the film running direction, there is an air curtain block 1 provided with two air outlets 111 that are sufficiently longer than the diameter of the measurement beam Ip in the width direction of the film P to be measured.
10 is provided to blow air under the same conditions as the air purge described above onto both sides of the film P to be measured, thereby blocking the accompanying airflow.

From the above configuration, this embodiment has the following effects.

It is divided into two parts: an upper head 200 and a lower head 300. The upper head 200 houses the light source 1, the light projection system 2, and the reference system, and the lower head 300 houses the measurement conversion system. It is compact, and it is very easy to adjust the optical axis of the optical system. Furthermore, since both heads are held on the same pedestal, vibration resistance is excellent.

In addition, both the upper head 200 and the lower head 300 were divided into small chambers for each heat source and air purged with air whose temperature and humidity were controlled to a constant level, making it possible to largely eliminate the influence of the measurement atmosphere. Furthermore, an air curtain unit 11 is installed upstream of the measurement section.
0, the air flow accompanying the film P to be measured was blocked, and air under a certain condition was allowed to accompany the film, so that the measurement conditions were stabilized. In this example, which uses infrared rays that are sensitive to the atmosphere, stability of the measurement atmosphere is very important.

If both the upper head 200 and the lower head 300 have a sealed structure, the insides of both are all blackened by black coating, etc., so that the influence of ambient light such as external light is almost eliminated.

Furthermore, since the main part of the optical path is entirely constituted by the lens barrel, there is little light loss due to the optical path and there is little influence from the above-mentioned disturbance light.

The rod-shaped heating element 17 is provided so that the light source 1 passes laterally through the focal point of the reflecting surface in the cavity, which is a combination of a reflecting surface made of a paraboloid of revolution and a condensing surface made of a conical surface. Similar to body cavity radiation, infrared radiation can be effectively generated as described above. Since the obtained infrared rays are mixed lights with random directions and phases, the measuring beam of the target film P is
This has the advantage that even if the angle with respect to Ip changes, the scattered light is averaged and the influence is small. Note that since a thermocouple or the like is embedded in the heating element 17 to control the temperature, the obtained infrared rays are stabilized.

Furthermore, the measurement beam transmitted through the target film P
Since I'p is received by the condensing unit 34 in the shape of an inverted cone with an aperture 1.5 to 3 times the beam diameter, the influence of the waving phenomenon of the target film P mentioned above can be reduced and the measurement stabilized. did.

In addition, since the mask unit 35 having a mask plate 35b with an appropriate light transmittance and a slit 35a is provided in front of the condensing unit 34, the level of the amount of light received by the photodetector 4a is maintained at a level that does not significantly reduce the S/N ratio. At the same time, we were able to improve the detection resolution due to the slit effect. Also, regarding the dynamic characteristics, the mask unit 35 acted as a spatial filter to detect thickness changes of several tens of Hz or more, which is required for online measurement, with a good S/N ratio. Specifically, the width of the slit 35a is 2 mm,
The mask unit 35 has a width of 5 mm on both sides of the mask plate 35b including the slit 35a, and a length of 15 mm.
Thickness changes of several tens of Hz could be detected effectively.
Note that the mask plate 35b at this time has the same thickness as the target film as described above, and therefore the mask plate 35b has the same thickness as the target film.
The amount of light transmitted through the slit 5b is about half that of the slit 35a.

Although the present invention has been described above based on examples, the present invention is not limited to these examples.

If it is necessary to detect the thickness of the film in the width direction, the upper head and the lower head may be synchronized and transferred in the width direction, and this can be easily achieved using a known configuration for an X-ray thickness meter. . In this case, because of the above-mentioned configuration, it is only necessary to pay attention to the optical axis deviation of the measurement system when moving, and since the aforementioned waving phenomenon of the target film and the optical axis deviation have equivalent effects on measurement errors, the optical axis This has the advantage that the influence of deviation is small.

In addition, when there is a high temperature heater etc. near the measurement point during the manufacturing process and the measurement atmosphere fluctuates greatly,
If it is difficult to stabilize the temperature conditions using only the air purge described in the embodiment, it is preferable to use a jacket structure for the partition walls, side walls, etc. and stabilize the temperature using a refrigerant such as water.

As described above, the present invention is suitable for on-line measurement of film thickness during the manufacturing process, and is very useful as it can be implemented in various ways.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the principle of the present invention, Fig. 2 is an overall front view of the embodiment, Fig. 3 is an overall side view thereof, Fig. 4 is a front sectional view of the main parts, and Fig. 5 4 is a cross-sectional view taken along line A-A in FIG. 4, and FIG. 6 is an explanatory diagram of the mask unit. DESCRIPTION OF SYMBOLS 1... Light source, 2... Light projecting system, 3... Light receiving system, 4... Photoelectric conversion part, 5... Signal processing part, 100... Frame, 200
...upper head, 300...lower head.

Claims (1)

[Claims] 1. A light beam from the same light source is guided to a target film to be measured and a reference film by a light projection system, and the transmitted light from both films is converted into an electrical signal by a photoelectric exchange unit and the ratio is calculated. In a film thickness measuring device which determines the ratio and measures the thickness of the target film based on this ratio, a film having the same composition and approximately the same thickness as the target film is used as a reference film; A pair of heads are arranged facing each other with an interval for the target film to pass therethrough, and one head is provided with a reference conversion system for receiving and photoelectrically converting transmitted light from the light source, the light projecting system, and the reference film. The other head houses a measurement conversion system for receiving and photoelectrically converting the transmitted light from the target film, and furthermore, the light source and each heat source of the photoelectric conversion section are separated by a jacket and a partition wall. , a film thickness measuring device characterized by being air purged with air at a constant temperature. 2. The film thickness measuring device according to claim 1, wherein the set of heads are disposed facing each other on a common pedestal. 3. The film thickness measuring device according to claim 1 or 2, wherein the light receiving aperture of the measurement conversion system is 1.5 to 3 times the projection aperture of the light projection system onto the target film. 4. Claim 1, wherein an air curtain block is provided on the upstream side in the running direction of the target film of the light receiving port of the measurement conversion system and the projection port for the target film of the light projecting system, for blocking the accompanying airflow of the target film. The film thickness measuring device according to item 1, 2 or 3.