JPS58200103A - Optical interference type length measuring device - Google Patents

Abstract

PURPOSE:To improve resolution readily, by multiplying the output of a light detector, comparing the phase of the output of the light detector and the phase of a reference frequency signal, and applying a constant speed servo action to a driving means of a material to be measured. CONSTITUTION:Laser light from a light source 8 becomes interference light L3 of light L1, which is reflected by a reference reflector 10 through a collimator lens 9, and light L2, which is reflected by a reflector 7. The intereference light L3 is inputted in a light detector 11. Its oputput is inputted in a comparator 13 through a preamplifier 12. The phase of its output rectangular waveform is compared with the phase of a reference signal from a reference frequency generating circuit 24 in a comparator 23. By its output, a constant servo action is applied to a moving stage 6 through a phase compensation circuit 25. Meanwhile, the output signal of a comparator 13 is multiplied by PLL, and the pulse output is inputted in a gate circuit 15 through a pulse generator 14. The reflected light from a ferrite block 3 is detected by the detector 3. A gate circuit 15 is opened through a comparator 20. The pulses are counted, and the width of a lap surface 5 is measured at high resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an optical interference sub-head device using a Michelnon interferometer.

Conventionally, when manufacturing a rotating magnetic head (head chip) for a VTR, an optical interference sub-head device using a 1-Michael non-interference needle is used. Figure 1 shows the rotating magnetic head, which is made of ferrite. (la) is the tape contacting surface of the magnetic head (1). This magnetic head (1) is constructed by bonding head bodies (IA) and (IB), and the joint is constricted, and a gap g is formed at the tape-to-m surface C1a). The narrow part is filled with glass (2) for mechanical reinforcement.

As shown in Fig. #I2, the K used to pierce such a magnetic head has many # (4) cross sections @U-shaped wrinkles formed in parallel on the negative surface, and an elongated ship at the groove (4). A pair of ferrite strips (3) with surfaces (5) formed thereon are provided, and these are pasted together using adhesive so that each lap surface (5) forms a ring, creating the one-point mackerel embroidery shown in Figure 3. Separate as shown,
The tube is then filled with glass to obtain a large number of rotating magnetic heads.

The width d of the lapped surface portion (5) of this ferrite block (3) is determined by the magnetic field of recent rotating magnetic heads! 2! Since the track width of the gap has become narrower, it is necessary to form the gap with an accuracy of %KAi, which is determined by the processing accuracy of the groove (4). For this reason, this lap surface (5
) must be accurately measured.

Therefore, an example of an interferometric side length device previously proposed by the present applicant for measuring the width of the lap surface (5) of a ferrite block (3) will be explained with reference to FIG. (6) is a moving stage, on which the above-mentioned ferrite block (3) is placed as a fixed object. It is assumed that this moving stage (6) moves in a direction perpendicular to the groove (4) of the block (3). A reflector (7) having reflective surfaces (7a) and (7b) orthogonal to each other is mounted on the moving stage (6). (8) is a light source, and in this example, for example, a helium neon laser f
t, source. The laser beam from this light source (8) is made incident on the reference reflector ′1: via the collimator lens (9). The reference reflector αQ is parallel to the mirror surface (lon), which forms an angle of 45 degrees with respect to the direction of the light Lo from the collimator lens (9), and the mirror surface (10a), respectively. Orthogonal reflective surfaces (1
0b) and (10c). Also, the reflective surface (7a) of the reflector (sword) is parallel to the no-fu 2-2 surface (10 m).

A part of the light L1 is reflected by the nof mirror surface (10a), the reflective surface (10b), and the reflective surface (IOC), and then enters the photodetector αB. In addition, some other party L2 of the former Lo passed through the half-built surface (10a) and reflected at the reflector (7).
Reflecting surface C7m>, C7b) -Reference reflector frame-
・A photodetector that overlaps reflections on one side of -7 mirror (10m) (
1m) K is incident. And these party L1. Lt interfere with each other and enter the photodetector tAIK as interference jtLs.

From the photodetector 叡υ, the fifth
A sine wave detection output as shown in FIG. λ is generated.

The light intensity I can be expressed as shown in the following equation.

I −Io(1+α(2)(two,'λ)) However, I
o is an initial value, α is a coefficient that determines the degree of modulation, and D is a moving distance of the moving stage (6). In this case, if the original wavelength of the colaser light fll(8) is λ, the period of this λ detection output is -. The detection output from the photodetector aυ is supplied to the comparator αJ via the preamplifier Q3, whereby the waveform is shaped and a rectangular wave as shown in FIG. 5BK is obtained. By supplying this rectangular wave to the pulse generator α, as shown in FIG.
When a pulse with a period of λ/4 corresponding to the rise and fall of the rectangular wave is output, this is supplied to the gate circuit o9.

On the other hand, an optical position detection device αD is provided, and the source of this, for example, from a helium/neon laser light source is an objective lens Q8.
The surface of the ferrite block (3) is irradiated with a spot diameter of 1 to 2 mli degrees on the surface of the ferrite block (3) and its lapped surface (5). is returned to the photodetector of the optical position detection device aη, and generates a position detection output corresponding to the lap surface (5). The detection output for the reflected light has a high level at the wrap surface (5) and a low level at 1111 (4). Thus, the optical position detection device 07)
From this, a position detection output as shown in FIG. εAK is obtained, which is supplied to the comparator (1) via the preamplifier a9 and is waveform-shaped, thereby obtaining a rectangular wave as shown in FIG. 6B.

Then, the rectangular wave is supplied to the above-mentioned gate circuit a9,
The pulses shown in FIGS. 5C and 6C are gated with a period of λ/4. Thus, from K, the output terminal ae is shown as C in FIG.
And a gate output as shown in the aS diagram Cic is obtained. Then, by counting the number of pulses gated by this gate circuit 05, the width of the lap surface (5) of the ferrite block (3) is measured.

Now, the minimum resolution of such an original interferometric fog length device is determined by the counting error of the pulses whose period is λ/4 from the pulse generator 04, and therefore the accuracy is λ/4. Light III (8
When using a helium-neon laser light source as 1, λ
/4 corresponds to 0.15 μmFC. By the way, 1iiK
As mentioned above, the track width of the magnetic gap in the rotating magnetic head of recent VTRs has become significantly smaller, and it is necessary to further improve the processing precision when it comes to the amount i11.
A resolution of Ii degrees was insufficient.

As a means to improve this resolution, jt+1(81
Riffref the original source! (7) can be reflected back and forth many times to substantially increase the optical path length, but as the optical path length of the optical system becomes longer, the light # (laser light source) has a highly stable wavelength of the source. have to use something,
Further, there is a drawback that even higher precision is required for the arrangement of each optical element.

In view of this point, the present invention proposes an interferometric type device that can easily improve the resolution.

The optical interferometric length measuring device according to the present invention uses a reflector that moves integrally with a non-scooping object, and an interference light between a reference light from a nine birch tree that generates a source of wavelength λ and a reflected light from the reflector. K includes a detector for detection and a pulse generator that is supplied with the detection output from the photodetector and generates a pulse output with a period of λ/4, and counts the pulse output from the pulse generator. In the original interferometric side length measuring device designed to elongate the object to be measured, there is a multiplier that multiplies the detection output of the photodetector or the pulse output from the pulse generator, and the detection output from the photodetector and the standard. A constant speed servo is applied to the drive means that drives the object to be measured by comparing the phase with the frequency signal.
This is provided with a bot circuit.

Next, an embodiment of the present invention will be explained with reference to FIG. 7! Although it is clear,
Components corresponding to those in FIG. 4 described above are given the same reference numerals, redundant explanation will be omitted, and only the portions different from FIG. 4 will be explained with reference to FIG. 7. Conno (rater 03 and pulse generator a)
Insert a PLL capacitor as a multiplier between 4 and 4. This PLL Q2J may be inserted between the pulse generator I and the gate circuit a5 (・, the multiplication rate of this PLL (2) is 2, 3.4, etc. (is -1 is 2.4°8,...
...) can take any value, and by introducing that value, the resolution improves accordingly.

(3) is the detection output from the photodetector αυ and the reference jIH number signal from the reference frequency signal generator (2) (moving stage (
This is a servo circuit that compares the phase of the measuring object (6) with the feeding speed (determining the Liu's number) and applies constant speed servo to the driving means Qυ that drives the object to be measured. That is, the output of the comparator and the reference signal from the reference frequency signal generation circuit Q41 are compared by the phase comparator (C) K, and the comparison output is supplied to the drive amplifier (C) K via the phase compensation circuit (C). The output of the drive amplifier (E) is supplied to the drive means 0IJK. As this driving means Q11, a linear motor without a dead section or a static pressure air bearing without friction can be used. The moving speed of the moving stage (6) is, for example, 5 to lQmm/l1alC.

For example, if the PLL multiplication rate is chosen to be 8, the resolution will be 0.0.
It becomes 19871m.

According to the present invention described above, it is possible to obtain an optical interference type length measuring device that can improve resolution to a level J11.

Incidentally, if a multiplier circuit is provided but a servo circuit is not provided, there is a limit to the lock range of the multiplier circuit such as a PLL, so the tracking cannot be completed, but according to the present invention, there is no such possibility.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a rotating magnetic head suitable for use in manufacturing the optical interferometric length measuring device of the present invention, FIG. 2 is a perspective view showing a ferrite block that is a material forming the rotating magnetic head, and FIG. Figure 3 is a side view of the ferrite block.
FIG. 4 is a block diagram showing the principle of the optical interference type sub-head device previously proposed by the present applicant, a waveform diagram accompanying the explanation of the device in FIGS. 5 and 6, and FIG. FIG. 7 is a block diagram showing an embodiment of the optical interference type length measuring device according to the present invention. (3) is the object to be measured, (6) is the moving stage, (force is 1
reflector, (8) is a light source, Q (I is a reference reflector,
Ql) + head detector, a4 is the pulse generator, 09 is the gate circuit, a? ) is an optical position detection device, υ is a driving means, and PLL% α is a servo circuit as a kt multiplier. Hide Mori Matsukuma)

Claims (1)

[Scope of Claims] A reflector that moves integrally with the object to be measured, and a photodetector that detects interference light between a reference source from an f source that generates an element of wavelength λ and the reflected light from the reflector. , and a pulse generator that is supplied with the detection output from the photodetector and generates a pulse output with a period of λ/4, and by counting the pulse output from the pulse generator, it is possible to measure the object to be measured by counting the pulse output from the pulse generator. In the optical interference type sub-head device which is configured to have an edge length, a multiplier that multiplies the detection output of the photodetector or the pulse output from the pulse generator, and a multiplier that multiplies the detection output of the photodetector and the reference frequency signal. and a servo circuit that compares the phases of the signals and applies a constant load to a driving means for driving the object to be measured.