JP3034586B2 - Movement amount measurement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a movement amount measuring method.

[Prior Art] A grid pattern is generated by irradiating a light beam from a linear light source onto a grid pattern to generate a "shadow pattern" corresponding to the grid pattern, and detecting the displacement of the shadow pattern accompanying the movement of the grid pattern by an optical sensor. A method for measuring the amount of movement of a pattern is known (Japanese Patent Laid-Open No. 1-297513).

The phenomenon that the shadow pattern described above occurs is called "diffraction shadow phenomenon".
Since the present invention utilizes this diffraction shadow phenomenon, the diffraction shadow phenomenon will first be briefly described below.

In FIG. 2, reference numeral 10 denotes a linear light source, reference numeral 12 denotes a grid pattern, and reference numeral 14 denotes a screen.

The grating pattern is a pattern in which a change in transmittance or a change in reflectance is repeated in one direction in a single cycle, whereas the grating pattern 12 shown in FIG. 2 is a pattern in which a change in transmittance is vertically repeated in a vertical direction in the figure. It is a thing. Regarding the grating pattern, the “direction in which the transmittance change or the reflectance change is repeated in a single cycle” is referred to as a “grating arrangement direction”. In FIG. 2, the vertical direction in the figure is the grid arrangement direction of the grid pattern 12. The grating pattern 12 has ξ as the grating pitch, that is, the period of transmittance change in the grating arrangement direction.

The linear light source 10 has a length d in the grid arrangement direction of the grid pattern 12. As the linear light source, for example, a light source in which the longitudinal direction of the light emitting portion of a semiconductor laser such as AlGaAs or GaAs is parallel to the lattice arrangement direction is preferable.

When the light beam from the linear light source 10 is irradiated to the grating pattern 12, the diffracted light L ₁ from each of the irradiated portion of the grating pattern 12, L _2, L _3, etc. are generated. Then, interference fringes indicated by reference numeral 20 appear in the region where these diffracted lights interfere with each other.

Length d of linear light source 10 and grating pitch of grating pattern 12 ξ
However, when the condition of (1/10) ≦ (d / ξ) ≦ 4 (1) is satisfied, the interference fringe 20 is “like a linear light source.
An ideal point light source was placed at the position of 10, and the grid pattern 12 was enlarged as a geometric optical shadow picture. "
That is, the distance between the linear light source 10 and the grid pattern 12 and the distance between the grid pattern 12 and the screen 14 are respectively represented by b ₁ , b
Assuming that ₂ , the interference fringes 20 are obtained by enlarging the lattice pattern 12 by {(b ₁ + b ₂ ) / b ₁ } times in the lattice arrangement direction. Therefore, such interference fringes are referred to as "shadow pattern".

When the linear light source 10 is fixed and the grid pattern 12 is moved in the grid arrangement direction, the shadow pattern 20 is also displaced in the same direction as the grid pattern 12 while maintaining the shadow pattern relationship with the grid pattern 12.

Therefore, the amount of movement of the grid pattern can be expanded to {(b ₁ + b ₂ ) / b ₁ } by the shadow pattern 20, and the use of the shadow pattern enables highly minute displacement of the grid pattern itself to be measured with high accuracy. is there.

The dimension of the linear light source 10 in the direction orthogonal to the drawing of FIG. 2 is not particularly limited.

Ideally, the light emitted from the linear light source to the grating pattern is coherent light. However, even an incoherent light flux from a light source such as an LED may have an aperture having a slit of length d as shown in FIG. (Fig. 1 (I)), an aperture (II) having an elliptical opening whose major or minor diameter is d, or an aperture (III) having a circular opening whose diameter is d. Irradiating the lattice pattern such that the direction of d corresponds to the lattice arrangement direction of the lattice pattern, d and the lattice pitch ξ
If the relationship with satisfies the above equation (1), a shadow pattern can be generated.

When the shadow pattern is used, the amount of movement of the lattice pattern can be measured with high accuracy as described above. Therefore, the extremely accurate movement amount can be measured using the shadow pattern.

[Problem to be Solved by the Invention] In the movement amount measurement using the shadow pattern as described above, the smaller the pitch of the grid pattern formed on the scale, the higher the measurement accuracy can be. There is a limit to the pitch of the pattern that can be reduced naturally.

The present invention has been made in view of the above-described circumstances, and has as its object to provide a novel movement amount measurement method that can further increase the limit of measurement accuracy of a movement amount measurement using a conventional shadow pattern.

[Means for Solving the Problems] The moving amount measuring method according to the present invention provides a method of “irradiating a grid pattern formed on a scale with a light beam from a linear light source and generating a shadow pattern by interference of diffracted light due to the grid pattern. At least, a method of measuring the displacement of the scale by detecting the displacement of the shadow-like pattern accompanying the movement of the scale in the grid array direction by an optical sensor, and is characterized by the following points.

That is, "the thickness D of the grid in the grid pattern (> 0)
However, a grid pattern is formed so as to be 1/4 or less of the emission wavelength of the linear light source, and a shadow-like pattern is generated by interference of ± 1st-order diffracted light by the grid pattern.

The scale may be a so-called linear scale in which the grid pattern is formed linearly in the longitudinal direction by forming the grid pattern linearly in the longitudinal direction (claim 2), or the grid pattern is formed in an annular shape in the peripheral portion as a disk shape. (Claim 3), and may be formed as a columnar shape "a grid pattern is formed on a peripheral surface portion so as to surround a cylindrical axis with a direction perpendicular to the generatrix of the peripheral surface being a grid arrangement direction" (Claim 4). ).

[Effect] “Shadow pattern” used in conventional movement measurement
Is generated by interference between diffracted lights generated by the grating pattern as described above. More precisely, it is generated by interference between the 0th-order diffracted light and the 1st or -1st order diffracted light. Then, the shadow pattern is a grid pattern that is enlarged like a shadow.

However, in the present invention, a "shadow pattern" is generated by interference between ± 1st-order diffracted lights. As described above, the order of the diffracted light that interferes between the conventional “shadow pattern” and the “shadow pattern” of the present invention is different.

In the "shadow-shape pattern", the crossing angle of the diffracted light beams that interfere with each other is twice the crossing angle of the diffracted light beams in the shadow-shape pattern. Twice as large as

Therefore, the spatial frequency of the shadow pattern generated in the present invention is twice the spatial frequency of the shadow pattern generated from the same grid pattern. In other words, the generation of the shadow pattern is the same as the conventional one. The grid pitch of the grid pattern itself as the shadow pattern generation source has been reduced to half. "

In order to generate a shadow pattern, interference between ± 1st-order diffracted light beams is sufficient, but to generate a good shadow pattern, it is necessary to generate non- ± 1st-order diffracted light beams generated from the grating pattern. It is necessary that the intensity of the diffracted light is sufficiently smaller than the intensity of the ± 1st-order diffracted light.

As shown in FIG. 1 (A), the above condition can be satisfied if the grating thickness D (> 0) of the grating pattern is 1/4 or less of the emission wavelength λ of the linear light source. In order to check whether or not the intensity of the ± 1st-order diffracted light of the diffracted light generated in the actual grating pattern is sufficiently higher than the intensity of the other order diffracted light, it is sufficient to examine the Fraunhofer diffraction of the grating pattern.

This is because the relative magnitude relationship between the diffracted light intensities of each order in the Fraunhofer diffraction corresponds to the magnitude relationship between the intensities of the diffracted light beams of each order generated by the linear light source.

The distribution of the intensity of the diffracted light of each order of the Fraunhofer diffraction by the grating pattern satisfying the condition 0 <D ≦ λ / 4 depends on the magnitude of D, but as a general tendency, FIG. It is like.

In the Fraunhofer diffraction, the light beam incident on the diffraction grating is a parallel light beam, and the condition is different from the case where a divergent light beam from a linear light source is incident. However, even when a linear light source is used, the above 0 <D ≦ λ As a general tendency, the relative intensity of the diffracted light beams of each order generated from the grating pattern satisfying the condition of / 4, as shown in FIG. It is clear from the experimental fact that when a lattice pattern satisfying the above conditions is used, a shadow-like pattern with high contrast can be obtained. Needless to say, the grating pitch 示 す shown in FIG. 1A should satisfy the above condition (1).

[Example] Hereinafter, a specific example will be described.

FIG. 4 shows an embodiment in which the present invention is implemented using the scale 2 as a linear scale. The scale 2 has a narrow plate shape, and a lattice pattern is formed linearly with its longitudinal direction as a lattice arrangement direction. Of course, the thickness of the grating pattern is set to 1/4 or less of the emission wavelength of the linear light source 1, so that a good shadow-like pattern can be generated.

A scale 2 is irradiated by a linear light source 1 and an optical sensor 3 is arranged at a position where a shadow pattern is generated.

When the scale 2 is changed in the direction of the arrow, the shadow-like pattern also changes in the same direction so as to increase the displacement of the scale 2, and this is detected by the optical sensor 3 to measure the movement of the scale 2. I do. The displacement of the shadow pattern for two pitches with respect to the optical sensor 3 corresponds to the displacement of one pitch of the scale grid pattern.

FIG. 5 shows an example in which the present invention is implemented by making the scale 2A into a disk shape.

The scale 2A formed in a disk shape is light-transmissive, and a grid pattern is formed in an annular shape on the periphery with the rotation direction being a grid arrangement direction, and a shadow pattern generated by irradiation light from the linear light source 1 is formed. The optical sensor 3 is provided at the position of the pattern.

The rotational displacement of the shadow pattern accompanying the rotation of the scale 2A is detected by the optical sensor 3, and the amount of rotation of the scale 2 is measured as the amount of movement.

4 and 5, the optical sensor 3 for detecting the displacement of the generated shadow-like pattern is located not only on the optical axes AX and AX1 of the irradiation light beam but also at a position distant from the optical axis as shown by a broken line. May be deployed.

In the embodiment shown in FIG. 6, a lattice pattern 8 is formed on a peripheral surface of a cylindrical shaft 7 supported by a bearing 6 so as to surround the cylindrical shaft. A pattern is generated, and the rotational displacement of the shadow pattern accompanying the rotation of the shaft 7 serving as a scale is detected by the optical sensor 5 to measure the rotation amount of the shaft 7 as a movement amount.

The embodiment of FIG. 7 is a modification of the embodiment of FIG.
This is an example in which a grating pattern 8 formed on a shaft 7 as a scale is irradiated with incoherent light. That is
The light from the LED 1 'is applied to the grating pattern 8 via the aperture 1A as described with reference to FIG. Even in this case, since a shadow pattern is generated, the rotational displacement of the shadow pattern accompanying the rotation of the shaft 7 is detected by the optical sensor 5, and the rotation amount of the shaft 7 is measured as the movement amount.

In each of the above embodiments, it is needless to say that the displacement speed and the displacement acceleration can be measured by subjecting the detected movement amount to time differentiation processing.

Finally, a method of forming a lattice pattern on a scale will be described. The grating pattern used in the embodiment of the present invention is a so-called phase grating in which the thickness of the grating is 1/4 or less of the emission wavelength of the linear light source as described above. Various methods have been known for producing a pattern. Here, the bitter method will be described as one of such methods.

CoCr or Fe in the scale, where the grid pattern is formed
A magnetic film having a thickness of several thousand degrees is formed by ₃ O _{4, and} a lattice pattern is written on the magnetic film by a magnetic head to form a magnetic pattern corresponding to the lattice pattern. The magnetized pattern is coated with a magnetic colloid fluid to visualize it.
The magnetic colloid fluid is obtained by dispersing iron oxide fine powder having a particle size of 50 to 200 mm in a surfactant. When this is applied to a magnetic pattern, the iron oxide fine powder is adsorbed to the boundary of magnetic domains in the magnetic pattern. Visualize the magnetization pattern.
When the visualization is performed in this way, the surfactant is evaporated,
Thereafter, the visualized lattice pattern is fixed to the magnetic film by, for example, depositing a transparent oxide. When visualizing a magnetized pattern with a magnetic colloid fluid, a uniform magnetic field is applied so as to overlap the magnetized pattern, and the intensity of this magnetic field is adjusted to control the thickness of the lattice pattern made of iron oxide fine powder. It is also possible to form a desired lattice pattern required for implementing the present invention.

FIG. 1A shows a scale formed in this manner. Reference numeral 15 denotes a scale base, and reference numeral 16 denotes a magnetic film. The arrow in the magnetic film 16 indicates the direction of magnetization in the magnetic pattern written by the magnetic head. Symbol 17
Indicates a formed lattice pattern.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a novel movement amount measuring method using a shadow pattern. According to this method, a shadow pattern having a spatial frequency twice that of the conventional shadow pattern can be generated from the lattice pattern. Can be reliably realized.

[Brief description of the drawings]

FIG. 1 is a view for explaining a characteristic portion of the present invention, FIGS. 2 and 3 are views for explaining a diffraction shadow phenomenon, FIG. 4 is a perspective view showing an embodiment, and FIG. FIG. 6 is a perspective view showing another embodiment, and FIG. 7 is a perspective view showing still another embodiment. 1 ... linear light source, 2 ... linear scale, 3 ... optical sensor, 17 ... lattice pattern

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Akito 3-18-1 Waseda, Shinjuku-ku, Tokyo 203 Maru Shigeru Heights 203 (72) Inventor Tomoyuki Yamaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo (56) References JP-A-1-297513 (JP, A) Jikken 61-39289 (JP, Y2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01D 5/38

Claims (4)

(57) [Claims] 1. A grid pattern formed on a scale is irradiated with a light beam from a linear light source to generate a shadow-like pattern due to interference of diffracted light by the grid pattern, which is accompanied by movement of the scale in the grid array direction. In this method, the displacement of the shadow pattern is detected by an optical sensor to measure the amount of movement of the scale, wherein the thickness D (> 0) of the grid in the grid pattern is 1/4 or less of the emission wavelength of the linear light source. A moving amount measuring method, wherein a grating pattern is formed as described in (1), and a shadow-like pattern is generated by interference of ± 1st-order diffracted light by the grating pattern. 2. The moving amount measuring method according to claim 1, wherein the scale has a narrow plate shape and the lattice pattern is formed linearly in the longitudinal direction. 3. The moving amount measuring method according to claim 1, wherein the scale has a disk shape and the lattice pattern is formed in an annular shape at a peripheral portion. 4. The method according to claim 1, wherein the scale is cylindrical, and the grid pattern is formed on the peripheral surface so as to surround the cylindrical axis with a direction perpendicular to the generatrix of the peripheral surface being a grid arrangement direction. Characterized by the amount of movement measurement.