JPH04161819A - Measuring apparatus for amount of movement - Google Patents

Abstract

PURPOSE:To obtain the measuring accuracy of twice readily and positively in a movement amount measuring method utilizing a shadow pattern by generating the shadow pattern having the space frequency of twice the frequency of the conventional shadow pattern based on a grating pattern. CONSTITUTION:A 'shadow pattern' is generated by the interference between + or -1st order diffracted lights. In this method, the order of the interfering diffracted lights is made to be twice. In details, a linear scale is formed of a plate having the thin width. The longitudinal direction is made to be the grating arranging direction. Thus, the grating pattern is linearly formed. Here, the thickness of the grating pattern is set at 1/4 or less of the light emitting wavelength of a linear light ray 1, and the excellent shadow pattern is generated. In this constitution, the light is emitted from a light source 1 on the scale 2. A light sensor 3 is arranged at the generating position of the shadow pattern. The scale 2 is displaced, and the amount of the displacement of the scale 2 is magnified. This is detected with the sensor 3, and the movement amount of the scale 2 is measured. At this time, an oxide film 16 is deposited on a substrate 15 of the scale, and a grating pattern 17 is provided on the film. Thus, the scale is provided.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a movement amount measuring method.

[Prior art] A "shadow picture pattern" corresponding to the grid pattern is generated by irradiating a light flux from a linear light source onto the grid pattern, and a displacement of the shadow pattern due to the movement of the grid pattern is detected by an optical sensor to create the grid pattern. A method of measuring the amount of movement of a pattern is known (Japanese Patent Application Laid-Open No. 1-297513).
.

The phenomenon in which the shadow picture pattern occurs is referred to as a "diffraction shadow picture phenomenon", and since the present invention utilizes this diffraction shadow picture phenomenon,
First, the diffraction shadow picture phenomenon will be briefly explained below.

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

A grating pattern has transmittance changes or reflectance changes repeated in a single period in one direction, but the grating pattern 12 shown in FIG. 2 has transmittance changes repeated in a single period in the vertical direction of the figure. It is something that

Regarding the grating pattern, the "direction in which the change in transmittance or the change in reflectance is repeated in a single period" is referred to as "the grating arrangement direction". In FIG. 2, the vertical direction of the figure is the lattice arrangement direction of the lattice pattern 12. The grating pattern 12 has a grating pitch, ie, a period of transmittance change in the grating arrangement direction, ξ.

The linear light source 10 has a length d in the lattice arrangement direction of the lattice pattern 12. Examples of linear light sources include A I G
It is preferable to use a semiconductor laser such as aAs or GaAs whose longitudinal direction of the light emitting part is parallel to the lattice arrangement direction.

When the light beam from the linear light source 10 is irradiated onto the grating pattern 12, diffracted light L□,' is emitted from each irradiated portion of the grating pattern 12.
L2. L, etc. occur. Interference fringes as shown by reference numeral 20 appear in the region where these diffracted lights interfere with each other.

When the length d of the linear light source 10 and the grating pitch ξ of the grating pattern 12 satisfy the following condition (1/10)≦(d/ξ)≦2 (1), the interference fringes 20 are “like a linear light source”. This occurs as if an ideal point light source was placed at position 10 and the lattice pattern 12 was enlarged as a geometric optical silhouette. That is, the distance between the linear light source 1o and the grid pattern 12 and the distance between the grid pattern 12 and the screen 14 are set as b as shown in the figure.
Engineering.

If b2, the interference fringes 20 will be the lattice pattern 12 expanded by ((b x + b 2) / b x) times in the lattice arrangement direction. Therefore, such interference fringes are called "shadow patterns."

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

Therefore, the amount of movement of the lattice pattern can be expanded to ((b1+b2)/b,) by the shadow picture pattern 20, and by using the shadow picture pattern, extremely minute displacements of the lattice pattern itself can be measured with high precision.

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

Furthermore, while it is ideal for the light to be irradiated onto the lattice pattern from a linear light source to be coherent, even incoherent light from a light source such as an LED can be produced using an aperture with a slit of length d as shown in Figure 3. ((■) in the same figure), an aperture with an elliptical opening whose major or minor axis is d (I), or an aperture with a circular opening whose diameter is d (III). When the grating pattern is taken out and irradiated with the direction of d corresponding to the lattice arrangement direction of the lattice pattern, a shadow pattern can be generated if the relationship between d and the lattice pitch ξ satisfies the above equation (1). can.

Since the movement amount of the lattice pattern can be measured with high accuracy by using the shadow pattern as described above, it is possible to measure the movement amount with extremely high accuracy by using the shadow pattern.

[Problem to be solved by the invention] In measuring the amount of movement using the shadow picture pattern as described above,
The finer the pitch of the grid pattern formed on the scale,
Although measurement accuracy can be increased, there is a limit to how small the pitch of the grating pattern can be made when creating the grating pattern.

The present invention was made in view of the above-mentioned circumstances, and
The object of the present invention is to provide a novel method for measuring the amount of movement that can further increase the limit of the measurement accuracy of the conventional method of measuring the amount of movement using a shadow pattern.

[Means for Solving the Problems] The movement amount measuring method of the present invention is based on the method of ``irradiating a grating pattern formed on a scale with a light beam from a linear light source, and creating a shadow-like pattern by interference of diffracted light by the grating pattern. This method uses an optical sensor to detect the displacement of a shadow-like pattern as the scale moves in the direction of the lattice arrangement, thereby measuring the amount of movement of the scale, and is characterized by the following points.

That is, ``a grating pattern is formed such that the thickness D of the grating in the grating pattern is 1/4 or less of the emission wavelength of the linear light source, and a shadow-like pattern is generated by interference of the ±1st-order diffracted light by the grating pattern. ” point.

The scale may be a so-called linear scale in which the scale is formed in a narrow plate shape and a lattice pattern is formed linearly in the elongated direction, or it may be in the shape of a disk and the lattice pattern is formed in an annular shape on the periphery. (Claim 3) It is also possible to have a cylindrical shape [with a lattice pattern formed on the circumferential surface so as to surround the cylinder axis with the lattice arrangement direction perpendicular to the generatrix of the circumferential surface" (Claim 4) .

[Function] The "shadow picture pattern" used in conventional movement measurement is caused by interference between diffracted lights generated by the grating pattern as described above, but more precisely, it is caused by interference between the 0th-order diffracted light and the 0th-order diffracted light. , is generated due to interference with first-order or 11th-order diffracted light. The shadow pattern is an enlarged version of the grid pattern.

However, in the present invention, r
A silhouette pattern J is generated. As described above, the conventional "shadow picture pattern" and the "shadow picture pattern" of the present invention differ in the order of the diffracted light that interferes with them.

In a "shadow-like pattern," the intersecting angle between the interfering diffracted lights is twice the intersecting angle between the diffracted lights in the shadow-like pattern, so if you compare them at the same position, the spatial frequency of the shadow-like pattern is equal to the spatial frequency of the shadow-like pattern. It will be twice as much.

Therefore, the spatial frequency of the shadow-like pattern generated in the present invention is twice the spatial frequency of the shadow-like pattern generated from the same grid pattern. This is equivalent to ``reducing the lattice pitch of the lattice pattern itself, which is the source of the silhouette pattern, to 1/2''.

To generate a shadow-like pattern, it is sufficient to cause the ±1st-order diffracted lights to interfere with each other, but to generate a good shadow-like pattern, the ±1st-order diffracted light beams generated from the grating pattern must be caused to interfere with each other.
It is necessary that the intensity of diffracted light other than the first order 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 thickness D of the grating of the grating pattern is 174 or less of the emission wavelength λ of the linear light source.

±1 of the diffracted light generated in the actual grating pattern
To determine whether the intensity of the next-order diffracted light is sufficiently greater than the intensity of the diffracted lights of other orders, it is sufficient to examine the Fraunhofer diffraction of the grating pattern.

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

The intensity distribution of the diffracted light of each order of Fraunhofer diffraction using a grating pattern that satisfies the condition D≦λ/4 is as shown in Figure 1 (B). It turns out that patterns can be generated. It goes without saying that the grating pitch ξ shown in FIG. 1(A) should satisfy the above-mentioned condition (1).

[Example code] Specific examples will be described below.

FIG. 4 shows an example in which the present invention is implemented using Linhasgale as scale 2. Scale 2 is thin.

It has a plate shape with a wide width, and a lattice pattern is formed linearly with the long plane direction as the lattice arrangement direction.

Of course, the thickness of the grating pattern is 1 of the emission wavelength of the linear light source 1.
/4 or less, so that a good silhouette-like pattern can be generated.

A scale 2 is irradiated with a linear light source 1, and a light sensor 3 is placed at a position where a shadow-like pattern is generated.

When the scale 2 is displaced in the direction of the arrow, the silhouette pattern is also displaced in the same direction so as to enlarge the displacement of the scale 2. This is detected by the optical sensor 3 and the displacement of the scale 2 is detected. Measure. A two-pitch displacement of the silhouette pattern with respect to the optical sensor 3 corresponds to a one-pitch displacement of the scale grating pattern.

FIG. 5 shows an example in which the present invention is implemented using a scale 2A having a disk shape.

The scale 2A formed in the shape of a disk is transparent and has a circular grating pattern formed on its periphery with the rotation direction as the grating arrangement direction, so that the scale 2A, which is formed in the shape of a disk, is transparent and has a circular grating pattern with the rotation direction as the grating arrangement direction. Optical sensors 3 are arranged at the positions of the patterns.

The optical sensor 3 detects the rotational displacement of the silhouette pattern as the scale 2A rotates, and the amount of rotation of the scale 2 is measured as the amount of movement.

In both the examples shown in FIG. 4 and FIG.
It may be arranged not only on the optical axis but also at a position away from the optical axis as shown by the broken line.

In the embodiment shown in FIG. 6, a grating pattern 8 is formed on the circumferential surface of the cylindrical shaft 7 of the motor 6 so as to surround the cylindrical shaft, and a shadow pattern is generated by the light from the linear light source 1. The amount of rotation of the shaft 7 is measured as the amount of movement by detecting the rotational displacement of the silhouette pattern with the rotation of the shaft 7, which is a scale, using the optical sensor 5.

The embodiment shown in FIG. 7 is a modification of the embodiment shown in FIG. 6, and is an example in which a grating pattern 8 formed on an axis 7 serving as a scale is irradiated with incoherent light. That is, L
The light from EDI' is irradiated onto the grating pattern 8 through the aperture LA as described with reference to FIG. Even in this case, a shadow pattern is generated, so the optical sensor 5 detects the rotational displacement of the shadow pattern as the shaft 7 rotates, and the amount of rotation of the shaft 7 is measured as the amount of movement.

In each of the embodiments described above, it goes without saying that the displacement speed and displacement acceleration can be measured by subjecting the detected movement amount to time differentiation processing.

Finally, a method for forming a lattice pattern on the scale will be explained. The grating pattern used to carry out the present invention is a so-called phase grating, which is a grating pattern in which the thickness of the grating is 174 times or less than the emission wavelength of the linear light source, as described above. Various manufacturing methods are conventionally known. Here, the Bitter method will be explained as one such method.

A magnetized film made of CoCr, Fe, or O with a thickness of several thousand layers is formed on the part of the scale where the lattice pattern is to be formed, and a lattice pattern is written on this magnetized film using a magnetic head to create a magnetized pattern corresponding to the lattice pattern. form. A magnetic colloid fluid is applied to this magnetized pattern to visualize it. The magnetic colloidal fluid is made by dispersing fine iron oxide powder with a particle size of 50 to 200 in a surfactant.
When this is applied to the magnetization pattern, the fine iron oxide powder is attracted to the boundaries of magnetic domains in the magnetization pattern, making the magnetization pattern visible. Once visualized in this manner, the surfactant is evaporated, and then an appropriate resin is coated to fix the visualized lattice pattern on the magnetized film. When visualizing a magnetization pattern using a magnetic colloidal fluid, a -like magnetic field is applied so as to overlap the magnetization pattern, and the thickness of the lattice pattern made of fine iron oxide powder is controlled by adjusting the strength of this magnetic field. , to form the desired grating pattern necessary for practicing the invention.

FIG. 1(A) shows the scale thus formed. Reference numeral 15 indicates a scale base, and reference numeral 16 indicates a magnetized film. Arrows in the magnetized film 16 indicate the direction of magnetization in the magnetization pattern written by the magnetic head, and reference numeral 17 indicates the formed lattice pattern.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a novel method for measuring the amount of movement using a silhouette pattern. In this method, a shadow pattern with twice the spatial frequency of a conventional shadow pattern can be generated from a grid pattern, so it is easy to achieve double the measurement accuracy compared to a method using a conventional shadow pattern. It can definitely be achieved.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the characteristic parts of the present invention, Figures 2 and 3 are diagrams for explaining the diffraction shadow picture phenomenon, Figure 4 is a perspective view showing an embodiment, and Figure 5 is a separate diagram. 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 Chi J Figure (A) Shiku B) Jyo 2 Figure 3b Figure (A) (5) (C> Horse 4 Mouth muscle D Figure

Claims (1)

[Claims] 1. A light beam from a linear light source is irradiated onto a grating pattern formed on a scale, and a shadow-like pattern is generated by interference of diffracted light by the grating pattern, and a shadow pattern is generated in the grating arrangement direction of the scale. A method for measuring the amount of movement of a scale by detecting the displacement of a shadow-like pattern due to movement using an optical sensor, and in which the thickness D of the lattice in the lattice pattern is 1/4 or less of the emission wavelength of a linear light source. A method for measuring the amount of movement, characterized in that a grating pattern is formed in a certain manner, and a silhouette-like pattern is generated by interference of ±1st-order diffracted light by the grating pattern. 2. The movement amount measuring method according to claim 1, wherein the scale is in the form of a narrow plate, and the lattice pattern is formed linearly in the longitudinal direction. 3. The movement amount measuring method according to claim 1, wherein the scale is disk-shaped, and the lattice pattern is formed in an annular shape on the periphery. 4. Claim 1, characterized in that the scale is cylindrical, and a lattice pattern is formed on the circumferential surface so as to surround the cylinder axis with the lattice arrangement direction being perpendicular to the generatrix of the circumferential surface. , a method for measuring the amount of movement.