JPH02254316A - Displacement measuring device - Google Patents

Abstract

PURPOSE:To measure the displacement of an optical scale highly accurately by forming a reflecting film on a relief type diffraction grating, and illuminating the optical scale from the side of the other surface of a transparent substrate. CONSTITUTION:Luminous flux is not inputted into the surface of a reflecting film 2 from the side of the surface of a substrate on which a relief type diffraction grading is formed. But the luminous flux is inputted from the side of the surface of the substrate that is the opposite side from the surface on which the relief type diffraction grating is formed. Namely, when reflection preventing treatment and reflection-reducing optical coating for incident light are applied on a light inputting surface 6 of the transparent substrate 1, the incident luminous flux 20 is not attenuated and reaches a boundary plane between the grooves of the relief type diffraction grating of the substrate 1 and the reflecting film 2. The light is reflected, and reflected light rays 21 and 22 are generated. Therefore, the specified amount of the diffracted light is generated regardless of the thickness of the reflecting film 2. Therefore, when the diffracted light is made to interfere, the change in brightness and darkness is detected and the displacement amount of a body to be checked is detected and the displacement amount of a body to be checked is measured; the stable output is obtained from a photodetector element, and the highly accurate measurement can be performed.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a displacement measuring device, and particularly to a displacement measuring device that measures the displacement of an optical scale in which a relief-type diffraction grating is formed on a transparent substrate using diffracted light generated by the relief-type diffraction grating. This invention relates to a displacement measuring device.

[Prior art]

Conventionally, as this type of displacement measuring device, for example,
A device as disclosed in Japanese Patent No. 1-39289 is known. This device forms periodic grooves on a glass substrate to form a relief-type diffraction grating, and the surface of the periodic grooves is made of Au.
An optical scale is constructed by depositing a reflective film such as 5Af. This optical scale is then illuminated from above the relief-type diffraction grating as shown in Figure 4, and the diffracted lights generated by the relief-type diffraction grating are made to interfere with each other to form interference fringes. Optical scale by converting
The displacement of

Such a relief type diffraction grating weakens the intensity of the zero-order reflected diffraction light (regularly reflected light) by appropriately setting the height of the grooves.
This is extremely effective because it can increase the intensity of high-order reflected diffraction light used for measurement.

However, as shown in FIG. 4, when the reflective film 2 is deposited on the groove surface, the shape and depth of the groove change due to variations in the thickness of the deposited film. As a result, in the conventional apparatus, the amount of diffracted light fluctuates, making highly accurate measurement impossible.

[Summary of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide a displacement measuring device capable of performing highly accurate measurements.

To achieve this objective, the displacement measuring device of the present invention includes:
An optical scale with a relief-type diffraction grating formed on one side of a transparent substrate is illuminated with light, and the diffracted light generated by the relief-type diffraction grating is used to form interference fringes, and the interference fringes are photoelectrically converted. The apparatus for measuring the displacement of the optical scale by forming a reflective film on the relief-type diffraction grating, and illuminating the optical scale from the other substrate surface side of the transparent substrate. .

In the present invention, light is irradiated from the substrate surface opposite to the substrate surface on which the relief-type diffraction grating with a reflective film is formed, and diffracted light is generated by the relief-type diffraction grating. There is no variation in the amount of diffracted light due to variation in the thickness of the reflective film. Therefore, the displacement of the optical scale can be measured with extremely high precision.

The displacement measurement device of the present invention can be used to read various optical scales, such as the displacement of a so-called linear scale that translates in a predetermined direction, or the displacement of a so-called rotary scale that rotates about a predetermined axis. However, in this application, various features of the present invention will be explained with reference to several examples.

〔Example〕

FIGS. 1(A) to CC') are explanatory diagrams showing the basic features of the present invention.

In the figure, l indicates a transparent substrate on which a relief-type diffraction grating is formed, 2 indicates a reflective film, 6 indicates a light incident surface of the transparent substrate 1, 20 indicates incident light, 2I indicates -1st-order diffracted light, and 22 indicates +1st-order diffracted light. .

Figure 1 (A) is an example of an optical scale that forms a relief-type diffraction grating with grooves having a rectangular cross-sectional shape, and Figure 1 (B).
Similarly, a sinusoidal diffraction grating is formed, as shown in Fig. 1 (
Similarly, C) also has a triangular wave-shaped blazed diffraction grating. In both optical scales, a reflective film 2 for increasing the intensity of reflected diffraction light is deposited on the groove surface of the relief type diffraction grating. The substrate l forming the relief type diffraction grating is made of a light-transmitting material such as glass or transparent resin.

In the present invention, the light beam is not incident on the surface of the reflective film 2 from the substrate surface side on which the relief type diffraction grating is formed, but is made incident on the substrate surface side opposite to the surface on which the relief type diffraction grating is formed. The light incident surface 6 of the transparent substrate I is subjected to anti-reflection and transmission enhancement treatment for the incident light (so that the incident light beam 20 is not attenuated and passes through the boundary between the grooves of the relief type diffraction grating of the substrate 1 and the reflective film 2). It reaches the surface, is reflected by the reflective film and becomes reflected diffracted light 2.
1.22 occurs.

Therefore, a constant amount of diffracted light is generated regardless of the thickness of the reflective film 2.

FIG. 2 is a schematic diagram showing an embodiment of the displacement measuring device of the present invention, and shows a so-called optical sonia encoder that reads an optical scale that is displaced in the direction of the arrow in the figure.

In the same figure, ll is the optical scale shown in FIG. 1(A), and a relief type diffraction grating with periodic grooves carved on one substrate surface of the transparent substrate I is formed, and Au, A
A reflective film is applied by vapor-depositing 1st grade. Further, an antireflection film (not shown) is formed on the substrate surface opposite to the substrate surface on which the relief type diffraction grating is formed.

31 is a semiconductor laser which is a coherent light source, 32 is a collimator lens, 33 is a reflecting mirror, and 34 is a half mirror 13.
5 is a light receiving element.

The light beam emitted from the laser 31 passes through the collimator lens 32
As a result, the optical scale 11 is irradiated with a substantially parallel beam of light. As shown in FIG. 2, when a light beam is irradiated from a direction perpendicular to the surface on which the diffraction grating is formed, first-order diffracted light is generated in the angle ±θ force direction given by the following equation.

θ=sin-'(λ/p) ・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・ (1)(λ
: wavelength of the laser 31, p: pitch of the diffraction grating) The ±1st-order diffracted lights 21 and 22 are each reflected by the reflecting mirror 33 and superimposed via the half mirror 34 to become interference light and enter the light receiving element 35. .

When the optical scale 11 moves by X in the direction of the arrow in FIG. 2, the phase of the +1st-order diffracted light 22 becomes 2πx/p, -1
The phase of the next diffracted light 21 changes by -2πx/p. As a result, the light receiving element 35 obtains an output signal 1 (x) expressed by the following equation.

1 (X) = 1exp[i(ωt+2πx/p)l
+exp(i(ωt-2πx/p)]=2 (1+c
os (4yr x/p)1 Therefore, the output signal from the light receiving element 35 is a sine wave signal with one period of x=p/2. For example, if the pitch p of the diffraction grating is 1.6 μm, A sine wave signal with a period of .8 μm is obtained. In this way, from the output signal of the light receiving element 35, the optical scale 11
The amount of movement can be measured. If the optical scale 11 is attached to an object to be measured (not shown), such as a movable stage, the amount of movement of this stage can be measured with high precision and a resolution of 1 μm or less.

According to this displacement measuring device, the substrate forming the diffraction grating is made of a light-transmissive material, and the light beam is incident on the surface of the substrate opposite to the surface on which the diffraction grating is formed. Even if the thickness of the reflective film changes, the amount of diffracted light does not decrease or fluctuate. Therefore, when measuring the displacement of an object by interfering the diffracted light and detecting the change in brightness of the interference light, a stable output signal is obtained from the light receiving element, making highly accurate measurement possible. There is an effect.

FIG. 3 is a schematic diagram showing another embodiment of the present invention. In the same figure, 7 is the same light-transmissive substrate as the substrate 1 shown in FIGS. 1(A) to (C). Glass or the like is processed into a disc shape, and periodic grooves are formed on one substrate surface at equal angular pitches. A relief-type diffraction grating is formed by carving. Then, a reflective film 2 is deposited on the groove surface.

As in the first sections (A) to (C), the rotation angle can also be measured by inputting a light beam from the side of the substrate surface 6 opposite to the surface on which the relief-type diffraction grating of the light-transmissive substrate 7 is formed. Effects equivalent to those of the embodiment can be obtained.

In the embodiments described above, a device for measuring the amount of movement or rotation (rotation angle) of an optical scale was exemplified, but the present invention can also be applied to a device that measures the speed of movement or rotation of an optical scale. be.

Furthermore, the optical system for reading the optical scale is not limited to the form shown in FIG.
No. 61-212728, JP-A-62
The optical system disclosed in Publication No. 6119, U.S. Pat.
629,886 and US Pat. No. 4,676.645.

〔Effect of the invention〕

As described above, in the present invention, light is irradiated onto the optical scale from the substrate surface opposite to the substrate surface on which the relief-type diffraction grating with a reflective film is formed, and the relief-type diffraction grating causes the diffraction light to be emitted. is generated and used for geodetic measurements, so there is no variation in the amount of diffracted light due to variations in the thickness of the reflective film. Therefore, it is possible to provide a displacement measuring device that can measure the displacement of an optical scale with extremely high precision.

[Brief explanation of drawings]

FIGS. 1(A) to 1(C) are explanatory diagrams for showing the basic features of the present invention. FIG. 2 is a schematic diagram showing an embodiment of the displacement measuring device of the present invention. FIG. 3 is a schematic diagram showing another embodiment of the present invention. FIG. 4 is an explanatory diagram showing a conventional displacement measuring device. 1... Transparent substrate 2... Reflective film 11... φ... Optical scale 20... Incident light 21.22... Diffracted light 31... ... Semiconductor laser 32 ... Collimator lens 33 ... Reflector 34.1] ... Half mirror 35 ... Light receiving element Fig. 1 (A)

Claims (1)

[Claims] An optical scale with a relief-type diffraction grating formed on one side of a transparent substrate is illuminated with light, and the diffracted light generated by the relief-type diffraction grating is used to form interference fringes, and the interference fringes are photoelectrically converted. In the apparatus for measuring the displacement of the optical scale, a reflective film is formed on the relief-type diffraction grating, and the optical scale is illuminated from the other substrate surface side of the transparent substrate. Displacement measuring device.