JPS629207A - Measuring instrument for film thickness - Google Patents

Abstract

PURPOSE:To measure film thickness accurately by applying a constant AC magnetic field to a film to be measured at right angles, converting the rotation of a plane of polarization due to Faraday effect into light intensity, and intermitting light incident on a photodetector and performing signal processing. CONSTITUTION:Light from a light source 3 is polarized by a polarizer 4 into linear polarized light, which is transmitted through a magnetic tape 1 which is arranged between coils 2a and 2b of a magnetic field producing device 2 and runs at right angles to the traveling direction of the light to enter an analyzer 5. This magnetic field is produced perpendicularly to the film 1b of the tape 1 at a frequency which is sufficiently high for the run. Further, the film 1b is made of a magnetic material, so the plane of polarization of the linear polarized light rotates. The angle of the rotation is found and the thickness of the film is processed from the angle. At this time,the rotation of the plane of rotation is converted by the analyzer 5, etc., into the light intensity and the light incident on the photodetector 6 is intermitted 9 to perform the signal processing, so the film thickness is measured accurately under no influence of the dark current of the photodetector 6 under non-contacting state nor any shift in the position of the object film.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a film thickness measuring device for measuring the film thickness of a coating film for controlling and monitoring a coating machine in a manufacturing line for, for example, magnetic tape. It is.

[Conventional technology]

Figure 3 is a configuration diagram of a conventional eddy current type film thickness measuring device.
) is a magnetic tape in which a coating film (1b) of a magnetic material is attached on a base material (1a) such as polyester. αD is the detector;
The excitation winding (11b) is wound around the core (11a), and the oscillator +
It is excited at 1s6゛.

Next, the operation fζ will be explained. An excitation magnetic field is generated between the open ends of the core (11a), but the excitation impedance changes if a magnetic body is located close to the core (11a).

Since this change varies depending on the characteristics, size, position, etc. of the magnetic body, by detecting this change in impedance, the thickness of the magnetic body can be detected under conditions of constant characteristics, constant position, and constant width.

[Problem that the invention seeks to solve]

Conventional film thickness measurement equipment maintains a constant distance Cζ between the film to be measured and the detector, and is sensitive unless they are close together, usually in contact.
It could not be measured stably and could not be incorporated into the production line.

The present invention has been developed to solve the above-mentioned problems, and provides a film thickness measuring device that is non-contact and unaffected by changes in the position of the film to be measured.

[Means for solving problems]

The film thickness measuring device according to the present invention emits linearly polarized light into space and transmits the film to be measured placed in a magnetic field.
The rotation of the plane of polarization caused by the Faraday effect is detected as a change in light intensity using an analyzer using blinking light.

[Effect]

The film thickness measuring device according to the present invention, while the film to be measured is running, -
A main alternating current magnetic field is applied in a direction perpendicular to the film to be measured, the rotation of the plane of polarization due to the Faraday effect of the film to be measured is converted to light intensity, and the light entering the receiver is blinked to perform signal processing and calculate the film thickness. .

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
The figure is a configuration diagram, and the same numbers as in FIG. 3 indicate the same parts. In the figure, (2) is a magnetic field generator, and the coil (
2a) (2b) and a driving power source (2C). (3
) is a light source with a wavelength that passes through the magnetic coating (1b),
(4) is a polarizer, (5) is an analyzer, (6) is a light receiver, (
7) is an A/D converter, (8) is a digital processing circuit, (
9) is a drive circuit for driving the light source (3) in pulses.

Next, the operation will be explained.

The light emitted from the light source (3) is linearly polarized by the polarizer (4), passes through the coil (2a) of the magnetic field generator (2),
Transmits the magnetic tape (1). Since the base material (1a) of the magnetic tape (1) is transparent, most of the light passes through it, and the coating film (1b) passes through it with a certain transmittance. This transmitted light passes through the coil (2b) again and enters the analyzer (5). By the way, in the magnetic field generating device (2), a magnetic field is generated in the coils (2a) (2b) by the driving power source (2C). This magnetic field is generated in a direction perpendicular to the coating film (1b) and at a frequency sufficiently fast for the running of the magnetic tape (1). Since the coating film αb) is a magnetic material, the plane of polarization of the linearly polarized light rotates due to the Faraday effect. The magnitude of this rotation angle θ is expressed as θ=VrI−1L, where Vr is the Berb constant t of the magnetic material, H is the strength of the magnetic field, and L is the length of the magnetic material in the direction of light propagation, i.e. It is thick. Since Vr is a constant determined by the magnetic material and H is a constant magnetic field, θ=KL (K is a constant), and the thickness can be determined by determining the rotation angle θ. Therefore, an analyzer (5) is placed in a polarization direction that makes an angle of 46° with the polarization direction of the polarizer (4).
A light intensity of I = I□ (1+5 in2θ) is obtained from the analyzer +5]. Here, IO is the light intensity when the magnetic field is zero.

Since the light source (3) is pulse-driven by the drive circuit (9), it is turned on in synchronization with the driving of the light source (3).

The processing circuit (8) converts the AC signal of the rotation angle due to the Faraday effect of the output of the light receiver (6) into a digital value using the N converter (7) when the light is off and when the light is off, and its mean value. Calculate the ratio. In this case, by making the light source blink at a sufficiently fast cycle compared to the cycle of the alternating magnetic field,
It can be processed so as not to be affected by the dark current of the light receiver (6). That is, the true light value is determined by subtracting the output value of the A/D converter (7) when the light source (3) is turned off from the output value of the Aρ converter (7) when the light source (3) is turned on. can be found.

In addition, in the above embodiment, the light source (3) is blinked to compensate for the influence of the dark current of the light receiver (6), but the same effect can also be obtained by using the configuration shown in FIG. play.

In Figure 2, C1ω is a rotary plate with slits attached to the motor shaft, and by setting the slit to match the optical path, the blinking light can be input to the light receiver (6). . Components with the same numbers as in FIG. 1 indicate the same components, and are processed in the same manner as in FIG.

〔Effect of the invention〕

As described above, according to the present invention, the rotation of the plane of polarization depending on the thickness of the coating film due to the Faraday effect is converted into light intensity, and the light entering the receiver is processed by blinking, so it is non-contact and Film thickness can be accurately measured without being affected by changes in the position of the film to be measured or by the dark current of the photoreceiver.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a film thickness measuring device in one embodiment fζ of the present invention, Fig. 2 is a block diagram of another embodiment of the present invention, and Fig. 3 is a block diagram of a conventional film thickness measuring device. . In the figure, (1b) is a magnetic coating film as a film to be measured, (2) is a magnetic field generator, (3) is a light source, (4) is a polarizer, (5) is an analyzer, and (6) is a The light receiver (9) is a drive circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (4)

[Claims] (1) A light source, a polarizer, a film to be measured, an analyzer, and a light receiver having a wavelength that passes through a film to be measured that has a Faraday effect are arranged in sequence, and the film to be measured is oriented perpendicularly to the direction in which the light travels. A magnetic field generating device is provided to apply a constant alternating magnetic field to the light path between the polarizer and the analyzer, and the film to be measured runs across the generated magnetic field. A film thickness measuring device characterized in that the film thickness is measured by calculating the output of the light receiver while blinking the incident light. (2) The film thickness measuring device according to claim 1, wherein the light source is driven in pulses as means for blinking the amount of received light. (3) As a means for blinking the amount of received light, a light blocking plate is provided somewhere in the optical system, and the light path is intermittently interrupted by moving this light blocking plate. The film thickness measuring device described. (4) A/D conversion of the light receiver output is performed in synchronization with the flickering of the amount of received light, an alternating current component and an average value are determined, and a division operation is digitally processed. The film thickness measuring device according to any one of Item 3.