JPH03122507A - Measuring apparatus for minute gap - Google Patents

Abstract

PURPOSE:To enable measurement of the amount of a gap on a real time basis by a method wherein a plurality of measuring light beams are made to fall on an object of measurement, the respective interference light beams thereof are obtained therefrom and the amount of the gap is measured from the ratio of the interference light beams with reference to a table. CONSTITUTION:A light source 21 outputs measuring light beams LR, LG and LB of wavelengths lambdaR, lambdaG and lambdaB. These measuring light beams LR to LB are made to fall on a head 11 from the back through an optical system. Accordingly, interference fringes corresponding to the amount of a gap between a head 11 and a tape 12 are generated by the head and the tape, interference light beams caused by these interfer ence fringes are supplied to a color video camera 31, and a color video signal based on the interference light beams is taken out of the camera 31. This video signal is supplied to a color processing circuit 32 and color signals ER, EG and EB corresponding to the light beams LR to LB are separated and taken out. These signals ER to EB are supplied to a division circuit 35 via level correction circuits 33R to 33B and A/D converters 34R to 34B. Quotients U to W obtained in the circuit 35 are supplied to ROM 36, and the amount (d) of the gap is taken out from a data output of the ROM 36 and outputted to a terminal 37.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a micro gap measuring device.

[Summary of the invention]

The present invention is a micro-gap measuring device that can measure the amount of a gap in real time by measuring the amount of the gap from the ratio of interference light of at least two types of measurement light.

[Conventional technology]

For example, in a magnetic recording/reproducing device such as a VTR, if a gap is created between a magnetic head and a magnetic tape, this gap results in a spacing loss during recording and reproduction, resulting in deterioration of characteristics.

The gap between this head and the tape is, for example, 50 nm.
Although it is very small, there is a method that uses light interference to measure such minute gaps.

That is, measurement light is incident on a dummy magnetic head made of glass from behind to form interference fringes like Newton's rings, as shown by the solid line in Fig. 4.
A change in brightness (light intensity) in the direction X of the interference fringes is determined, and an envelope W connecting the white peaks of this brightness curve and an envelope B connecting the black peaks are determined. Then, the difference between the maximum value of the envelope W and the minimum value of the envelope B is the wavelength λ of the measurement light.
The difference ΔD between the brightness curve and the envelope B in the vicinity of x=O of the brightness curve corresponds to the amount of gap at the coordinate X.

Therefore, the distribution of the gap amount in the X direction can be determined from these values λ, D, and ΔD.

Document: JP-A-61-130807 [Problem to be Solved by the Invention] However, when using this method, the accuracy of the measurement result is determined by the accuracy of the envelopes W and B, so it is difficult to determine the envelope line from the white peak and the black peak. When determining W and B, it is necessary to estimate the envelope lines W and B using a high-order interpolation function such as a spline function.

For this reason, calculations become quite complicated, and real-time calculations and three-dimensional distribution calculations are extremely difficult.

Further, since the envelope B is obtained by interpolation or estimation, the envelope B may intersect with the brightness curve near X=O due to disturbances, and the amount of gap may not be measured correctly.

This invention attempts to solve these problems.

[Means to solve the problem]

Now, in a Newton ring as shown in Figure 3, ■=Intensity of incident light in the glass (1) a Reflectance on the glass (1) b Reflectance on the glass (2) x Reflectance on the glass (1) If the incidence rate is the intensity of light reflected at the interface between glass (1) and air - a
l Intensity of light reflected on the surface of glass (2) and incident on glass (1)=(1-a)bl.

therefore, α: Amplitude intensity λ1: Center wavelength Δλ1: Single: The intensity 11 of the interference light is as follows.

1, = α2(a t+ b2+ 2a b −co
s(4πH(x)/λ1)Xcos((ΔH/λ,)(
4πH(X)/λ, )) d=H(x): Amount of gap Similarly, β: Amplitude intensity □Degree λ2: Center wavelength Δλ2: Half 2: The intensity I2 of the interference light is as follows.

1+=β2(a 2+ b ”+2 a b −cos
(4z H(X)/λ2)xcos((Δλt/λ2)
(4πH(X)/λ2)) Therefore, the ratio R of the intensities 1t and Tz of these two interference lights is R=I+/1! becomes.

The formula for the ratio R is a periodic function of the clearance d, and indicates that the clearance d and the ratio R are in a one-to-hand relationship during one cycle.

That is, if the ratio R of the intensities of the two interference lights is known, the gap amount d can be uniquely known from the ratio R.

Next, it will be examined to what extent the clearance ld can be uniquely determined from the ratio R.

Here, λR: wavelength λ of the first interference light, : wavelength λll of the second interference light: wavelength I of the third interference light R(d): intensity IG(d) of the first interference light If the intensity of the second interference light In(d) is the intensity of the third interference light, I R(d) = 1-cos(4πd/λ7.)1 G
(d) = 1-cos(4tt d /λ,)I n(
d) = 1-co, s(4tt d /λ,).

Note that since the intensity of the incident light is arbitrary, the intensity of the interference light IR (
The intensity of the incident light is set so that the maximum value of d) to II(d) is 2 and the minimum value is O. However, the intensities of these incident lights are equal to each other.

Since each of the intensities L-1n is a periodic function, the range from when the ratio R reaches a certain value to the next value (that is, one period) is the range from which the gap Nd is calculated from the ratio R. This is within the range that is possible.

And the intensity ■8~In is IR=1 when d=o,
=1. =O, so the next time the ratios R become equal is when IR=Ia=Ig=O. For example, λg=640nm (red) λ. = 560 nm (green), λ richness = 440 nm (blue), then d = 49.28 μm.

Therefore, the amount of minute clearance required for boat fishing, i.e., several μm.
Within a certain range, the gap d can be uniquely determined from the ratio R of the intensity of the interference light.

And all of the above holds true not only for Newton's rings, but also for, for example, the minute gap between the dummy glass head and the tape.

Focusing on the above points, the present invention supplies at least two types of measurement light to a measurement target to obtain two interference lights, determines the ratio R of the intensity of these two interference lights, and calculates the ratio R of the intensity of these two interference lights. The amount of clearance is measured by drawing a table using as a variable (input).

[Effect]

The amount of clearance can be measured in real time without the need for complex calculations.

〔Example〕

In the example shown in Figure 1, the gap d between the magnetic head and the magnetic tape is to be measured, where (11) is a dummy magnetic head made of glass, and (12) is the magnetic tape. .

Furthermore, (21) indicates the light source of the measurement light, and this light source (2
1) is composed of a laser oscillator, a strobe light emitter, etc., and outputs multiple measurement lights with sharp spectra (high Q). In this example, the above-mentioned wavelength λ
□ λ6. λ, measurement light LII+Lr,tL8 is output.

Then, this measurement light LII-Lll passes through the optical system to the half mirror (22) of the microscope (22) in this example.
23) and enters the head (11) from behind.

Therefore, the head (11) and the tape (12) produce interference fringes corresponding to the amount of gap between them, and the interference light of these interference fringes passes through the half mirror (22) to a color image sensor, such as a color video camera (31). A color video signal based on the interference light is extracted from the camera (31).

This video signal is then supplied to the color processing circuit (32), where the color signal corresponding to -Lm, in this example, the three primary color signals ER+EG+Ea of red, green, and blue, is separated and extracted. . In addition, at this time, the signal E R-E
For example, as shown in FIG. 2, the level of s changes depending on the interference light from the head (11).

These signals E*-Eg are then applied to the level correction circuit (3
A/D converter (34R) through (33B)
) to (34B). In this case, the correction circuit (3
3R) to (33B) are the signals E R"' at the time of measurement.
This is for white balance of Ea.

That is, prior to measurement, the head (11) is, for example, temporarily removed so that no interference light occurs, and
The correction circuit (33
R) to (33B), the level of the signal E*""EB is corrected.

Therefore, during measurement, converters (34R) to (34B)
), the intensity difference between the output light Lm-Ls of the light source (21),
A digital signal E R-E m that is not affected by the wavelength sensitivity characteristics of the camera (31) is output.

Then, this signal E*−Es is sent to the division circuit (35)
For example, U=EG/ER, V −Ea/ER, W=Eel/EG
is performed and the quotient U-W is supplied to the ROM (36). In this case, the quotient U-W is nothing but the ratio R of interference light, so the ROM (36) has a table for converting the quotients U-W into the gap amount d, and the quotient U
~W is supplied to the ROM (36) as its address input, the gap id is taken from the data output, and this gap id is output to the terminal (37).

In this way, according to the present invention, it is possible to measure minute gaps such as the gap between a magnetic head and a tape. Since each incident interference light is obtained and the amount of gap is measured by referring to a table based on the ratio of the interference lights, calculations only require division when determining the ratio.

Therefore, the amount of clearance can be measured in real time, and the three-dimensional distribution can also be easily determined.

Furthermore, since the envelope line is not used or the envelope is interpolated or estimated, measurement errors due to intersections between the envelope and the brightness curve do not occur. Furthermore, only simple signal processing is required and no complicated optical system is required.

In addition, in the above, all of the quotient U-W is ROM (3
6), but it is also possible to supply only one of them for simplicity. Similarly, the measurement light from the light source (21) can also be of two types.

Furthermore, the measurement light LR"'LR from the light source (21) can be outputted sequentially rather than simultaneously, and the ratio R can be obtained by synchronizing the signal ER%E8.

Furthermore, the measurement light, ~L, can be set to a wavelength such that the bright and dark positions of the interference fringes are complementary and the ratio R takes a clear value, depending on the amount of gap to be measured. Further, the color imaging method of the camera (31) and the method of separating the color signal corresponding to the interference light from the obtained color video signal are also arbitrary. For example, the camera (31) may be a line sensor.

〔Effect of the invention〕

According to this invention, a plurality of measurement beams are incident on the object to be measured to obtain respective interference beams, and the gap amount is measured by referring to a table based on the ratio of the interference beams, so calculation is performed when calculating the ratio. It only requires the division of . Therefore, it is possible to measure the amount of clearance in real time, and
A three-dimensional distribution can also be easily obtained.

Furthermore, since no envelope is used or no interpolation or estimation of the envelope is performed, measurement errors due to intersections between the envelope and the brightness curve do not occur. Furthermore, only simple signal processing is required and no complicated optical system is required.

BRIEF DESCRIPTION OF THE 3rd DRAWING FIG. 1 is a system diagram of an example of the present invention, and FIGS. 2 to 4 are diagrams for explaining the same.

(21) is a light source, (22) is a microscope, (3rd grade) is a color video camera, (32) is a color processing circuit, (33R) ~ (
33B) is a level correction circuit, (34R) to (34B) are A/D converters, (35) is a division circuit, and (36) is a table ROM.

χ；O Characteristic diagram Figure 4

Claims (1)

[Scope of Claims] A light source that outputs at least two measurement lights having different wavelengths; an optical means for supplying the measurement light to the measurement object; and interference light obtained by supplying the measurement light to the measurement object. color imaging means to which is supplied, a division circuit for determining the ratio of color signals of the interference light outputted from the color imaging means, and a table for converting the ratio from the division circuit into the gap amount of the object to be measured. A device for measuring minute gaps.