JPH04102017A - Rotary encoder - Google Patents

Abstract

PURPOSE:To facilitate manufacture and also to attain reduction of the cost and improvement of precision by detecting a silhouette pattern generated by a reflected light from a scale part which is irradiated by a light from a light source device. CONSTITUTION:A conical scale 3 is fitted and fixed on a rotary shaft 7. A lattice pattern is formed on the scale 3 so that it surrounds the peripheral surface of the scale. When the lattice pattern on the scale 3 is irradiated by a linear light source 1a used as a light source device, a silhouette pattern is generated and it is detected by a photosensor 5 as a light-sensing means. The silhouette pattern is an expanded silhouette of the lattice pattern and it is so displaced as to rotate in the same direction and at the same angular velocity with the rotary shaft 7 as the shaft 7 rotates. Accordingly, the quantity of the light sensed by the photosensor 5 changes periodically with the rotation of the rotary shaft 7 and an output of the photosensor 5 becomes an encoder signal accompanying the rotation of the rotary shaft 7. The amount of rotation of the rotary shaft 7 is determined by the time differentiation thereof by this encoder signal and thereby the speed of rotation can be known.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a rotary encoder.

[Prior Art] A rotary encoder is known as a device for detecting and measuring rotation amount and rotation speed.

A disk-shaped scale is generally used as a scale for a rotary encoder.

On the other hand, a method for measuring the amount of movement using a shadow pattern is known from Japanese Patent Application Laid-Open Nos. 47616/1982 and 297513/1982, and this method of measuring the amount of movement can be used for rotary encoders. A shadow picture pattern is generated by irradiating a fine pitch grating pattern with light from a light source that satisfies predetermined conditions, and becomes a pattern that is an enlarged version of the grating pattern like a geometric optical shadow picture. Therefore, even if the pitch of the grating pattern is extremely fine, the movement of the grating due to the rotation of the scale can be optically detected easily and reliably.

[Problem to be solved by the invention] Therefore, in order to take advantage of the characteristics of a rotary encoder that uses a shadow pattern, the pitch of the grating pattern in the scale should be small. However, if the scale is made into a disk shape, the scale and rotation It is difficult to obtain accurate perpendicularity to the axis, and when using a shadow pattern, extremely high accuracy is required for the perpendicularity in order to improve accuracy by making the pitch finer.

For this reason, the encoder manufacturing process requires time, increases manufacturing cost, and also causes problems such as the perpendicularity occurring during use of the encoder, which tends to reduce rotation amount detection accuracy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel rotary encoder that can be realized at low cost and has high reliability.

[Means for Solving the Problems] A rotary encoder of the present invention includes a scale, a light source device, and a light receiving means.

The "scale" is formed into a cylindrical or conical shape, has a surface relief grating with a grating pattern at a minute pitch surrounding its circumference, and is fixed to a rotating shaft whose amount of rotation is to be measured. Note that the conical shape includes a truncated conical shape.

The "light source device" irradiates the scale with light for generating a silhouette pattern corresponding to the grid pattern.

The "light receiving means" detects a silhouette pattern generated by reflected light from the scale portion irradiated with light from the light source device.

The scale is "formed by plastic molding and is integrated or fitted into and fixed to the rotating shaft."

[For production] Here, the shadow picture pattern will be briefly explained.

There are two methods for generating a shadow pattern: a method using a point light source and a method using a linear light source. Since the mechanism of generating a shadow pattern using a point light source is disclosed in detail in Japanese Patent Application Laid-open No. 63-47616, here we will briefly explain how a shadow pattern is generated using a linear light source.

Regarding the silhouette pattern using a linear light source, please refer to Japanese Patent Application Laid-open No. 1983
-297513 publication has a detailed disclosure.

In FIG. 7, reference numeral 1 indicates a linear light source. Reference numeral 2 indicates a grating pattern with a pitch ξ whose grating repeating direction is in the vertical direction of the figure.

In the linear light source 1, the light emitting portion has a length d in the vertical direction of the drawing (the direction of repeating the lattice in the lattice pattern). This length d
satisfies the condition l/10≦(d/ξ)≦2(1), when the grating pattern 2 is irradiated with coherent light from the linear light source 1, the reflected light or transmitted light from the grating pattern 2 is reflected as shown in FIG. A distribution of light intensity as shown on the right side of the image appears. The arrangement of the maximum light intensity distribution behaves exactly the same as the geometrical optical shadow picture of the grid pattern 2 when a point light source is placed at the position of the linear light source 1, so this light intensity pattern is called a shadow picture pattern. be.

The light that generates the shadow pattern is not limited to coherent light, even incoherent light from LEDs etc.
Slits as shown in Figure 8 ((I)), elliptical or circular apertures ((u), (I)
II)) and irradiates the grating pattern with the direction of the length dA in FIG. 8 corresponding to the grating repetition direction, the length dA meets the condition 10≦(dA/ If ξ)≦2(2) is satisfied, a shadow pattern is generated.

There is no particular restriction on the length of the light emitting length in the direction perpendicular to the drawing in FIG. 7 in the linear light source 1, and the slit width and aperture width in the direction perpendicular to dA in the slit and aperture shown in FIG. There are no particular restrictions.

In the present invention, a point light source, a linear light source, or a combination of an LED and a slit as shown in FIG. 8 can be used as the light source device.

The scale is "formed by plastic molding," but a grid pattern mold is previously formed on the molding mold. The molded cylindrical or conical scale is fitted and fixed onto the rotating shaft, and is integrated with the rotating shaft during the molding stage.

The matrix having the above-mentioned lattice pattern can be produced, for example, as follows.

That is, a magnetic recording layer is formed in a thin layer on the circumferential surface of a cylindrical or conical base to form a magnetic recording medium having the same shape as the scale. A lattice pattern is written on the magnetic recording layer of this magnetic recording medium using a magnetic head to form a magnetization pattern that follows the lattice pattern. Subsequently, "a magnetic colloid fluid in which the particle size of colloid particles is sufficiently smaller than that of the magnetization pattern" is applied onto the magnetic recording layer to visualize the magnetization pattern.

A metal layer is laminated on the visualized lattice pattern, and then the metal layer is peeled off to obtain the above-mentioned matrix.

The above-mentioned "substrate" can be made of metal, glass, plastic, etc. The magnetic B layer formed in a thin layer on the substrate is made of Fe2
It may be an in-plane magnetized film such as O, etc., or a perpendicular magnetized film such as CoCr. If a perpendicular magnetization film is used, it is also possible to produce a lattice pattern with a pitch of 0.1 μm.

A "magnetic colloidal fluid" is one in which fine powder of a ferromagnetic material such as iron oxide is dispersed in a surfactant. The particle size of the fine powder is sufficiently smaller than the magnetization pattern to be visualized, for example, 50 to 200 particles.

[Example code] Specific examples will be described below.

In the embodiment shown in FIG. 1, reference numeral 7 indicates a rotation axis for measuring the amount of rotation. The rotating shaft 7 is supported by a bearing 6,
It is rotationally driven by a disturbance means such as a motor (not shown).

A scale 3 having a conical shape (more precisely, a truncated conical shape) is fitted and fixed onto the rotating shaft 7 . As shown in FIG. 5(I), the scale 3 has a fitting hole for the rotating shaft, and a lattice pattern is formed around the circumferential surface, and the rotating shaft 7 is inserted into the fitting hole. It is passed through and fixed to the rotating shaft 7 by fixing means such as adhesive.

Reference numeral 1a denotes a linear light source, specifically a semiconductor laser arranged so that the longitudinal direction of its light emitting part corresponds to the lattice repeating direction of the lattice pattern. When the linear light source 1a is used as a light source device to illuminate the grid pattern on the scale 3, a shadow pattern is generated, which is detected by the optical sensor 5 as a light receiving means. The silhouette pattern is a shadow-like enlargement of the lattice pattern, and as the rotation shaft 7 rotates, it is displaced so as to rotate in the same direction as the rotation shaft 7 at the same angular velocity. Therefore, as the rotation shaft 7 rotates, the amount of light received by the optical sensor 5 changes periodically, and the output of the optical sensor 5 becomes an encoder signal as the rotation shaft 7 rotates. The amount of rotation of the rotary shaft 7 can be determined by this encoder signal, and the rotation speed can be determined by differentiating it with respect to time.

FIG. 2 shows another embodiment. In order to avoid clutter, the same symbols as in Figure 1 have been omitted for items that are thought to pose no risk of confusion.

In this example, scale 4 is as shown in Figure 5 (II).
It has a cylindrical shape with a fitting hole for the rotating shaft 7, and a lattice pattern is formed on the circumferential surface so as to surround it. A grid pattern is irradiated by a linear light source 1a, and a generated shadow pattern is detected by an optical sensor 5.

The embodiment shown in FIG. 3 is a modification of the embodiment shown in FIG. In this embodiment, the light source device is composed of an LED lb and a slit plate 1c. The slit plate 1c has slits as shown in FIG. 8(I), and the incoherent light from the LED 1b is taken out through the slits of the slit plate 1c and is irradiated onto a grating pattern.

The example shown in FIG. 4 is also a modification of the embodiment shown in FIG. The light from the semiconductor laser 1a' is converted into a parallel beam 2 by the lens 2.
It is converted into a person and irradiated to scale 4.

The semiconductor laser 1a' has a light emitting part whose longitudinal direction is in the vertical direction in the figure, and the curvature of the surface of the scale 4 forms a linear light source as a virtual image. The light beam reflected by the scale behaves like light transmitted through a grid pattern by a linear light source as a virtual image, and generates a shadow pattern. This silhouette pattern is detected by the optical sensor 5.

FIG. 6 shows a method for manufacturing the scale.

In FIG. 6(I), reference numeral 12 indicates a cylindrical base. This base body 12 is made of metal such as AI, Fe, ~i, etc. A thin magnetic recording layer 14 with a thickness of several thousand layers is formed on the circumferential surface of the base 12 by vapor deposition, sputtering, electrodeposition, etc. of a magnetic material such as Fe403. The cylindrical base 12 and the magnetic recording layer 14 constitute a magnetic recording medium.

When a signal 10 of a constant frequency is applied to the magnetic head 16 while rotating the magnetic recording medium at a constant speed with high precision in the direction of the arrow by a rotating means (not shown), the in-plane magnetization direction alternates as shown in FIG. 6(I). A magnetic pattern is formed by the arrangement of the reversed magnetic domains.

Once the magnetic pattern as described above is formed over the entire circumference of the magnetic recording layer 14, grain sizes of 50 to 20 mm are formed on the magnetic recording layer 14.
Apply 0 magnetic colloid fluid.

Then, as shown in FIG. 6 (II), the colloidal particles of the magnetic colloidal fluid gather at the boundaries of the magnetic domains forming the magnetization pattern formed in the magnetic recording layer, so that they form patterns 11 with the same pitch as the magnetization pattern, for example, 1 μm pitch. is formed by colloidal particles.

Note that if a layer of soft magnetic material such as permalloy or Ni--Zn ferrite is provided between the cylindrical substrate 12 and the magnetic recording layer 14, writing of the magnetic pattern is facilitated and the density of the magnetic pattern can be increased.

When the magnetization pattern is visualized as pattern 11 by colloidal particles in this way, a sixth pattern is created on top of pattern 11.
As shown in Figure (III), a metal thin layer 11A is formed.

The metal thin layer 11A can be produced by, for example, depositing Ni, Au, or other metal onto the pattern 11 by sputtering, vacuum evaporation, or the like.

Subsequently, the entire magnetic recording medium with the metal thin layer 11A formed on the circumferential surface is soaked in a metal electrolyte (for example, Ni sulfamate).
The thin metal layer 11A is used as a negative electrode, a positive electrode is placed in the electrolytic solution, and a DC voltage is applied between both electrodes. Then, metal ions in the electrolyte (N in the case of Ni sulfamate mentioned above)
i ions) are deposited on the metal thin layer 11A serving as a negative electrode to form a metal layer 13 as shown in FIG. 6(Iv).

When the electrolyte is Ni sulfamate, the metal layer 13 formed by electroforming is a Ni layer. A cut 15 is made in the thin metal layer 11A and the metal layer 13 laminated in this way.
．． 15'(15' is not shown in FIG. 6(Iv)), and the thin metal layer 11A and the metal layer 13 are peeled off as one from the magnetic recording medium.

Then, the pattern 11 formed by the colloidal particles remains on the magnetic recording medium, and the same pattern as the magnetization pattern is formed by unevenness on the surface of the peeled metal thin layer 11A.

FIG. 6(V) shows the peeled metal thin layer 11A and the metal layer 13.
As shown in the figure, the mold is reinforced with a reinforcing member 17, the separated parts are joined together to form a matrix, and a cylindrical mold 7A corresponding to a rotating shaft is provided in the internal space. Then, plastic is injected into the hollow portion 18 using a plastic injection molding method or the like to obtain a plastic cylinder. This plastic cylinder is shown at 19 in FIG. 6 (Vl). The outer circumferential surface of the plastic cylinder 19 has unevenness 2 with the same pitch as the pattern 11.
0 is designed as a surface relief grating.

The plastic cylinder 19 can be used as the scale 4 as it is, but a metal reflective film is coated on the outer circumferential surface of A1, Au, C.
It may be formed by vapor deposition or sputtering of u, Cr, etc. to increase the reflectance.

By repeating the steps described in FIGS. 6(V) and 6(m), as many cylindrical scales as desired can be obtained.

In the above example, the magnetization pattern written by the magnetic head is formed by magnetization in the in-plane direction of the magnetic recording layer, so
The above method is suitable for producing a grating pattern with a pitch of 1 μm or more. If a perpendicularly magnetized film such as CoCr is used as the magnetic recording layer and a scale is formed in the same manner as described above, the pitch of the lattice pattern can be made fine to the order of 0.1 μm.

Furthermore, in the above example, the fitting hole for the rotating shaft was formed using the cylindrical mold 7A, but if the rotating shaft 7 itself is used instead of the cylindrical mold 7A, the scale can be integrated into the rotating shaft at the same time as injection molding of the scale. It can be performed.

In this case, "the scale molded from plastic is integrated with the rotating shaft".

In the above scale manufacturing method, the case of a cylindrical scale has been explained, but it goes without saying that the above method can be used as is for manufacturing a conical scale. In the case of a conical scale, the conical surface acts as a cutting taper during die cutting, making die cutting easy.

[Effects of the Invention] As described above, according to the present invention, a novel rotary encoder can be provided. Although this encoder has a grating pattern with an extremely fine pitch as described above, it is easy to manufacture, and it can be easily and precisely integrated or fitted into the rotating shaft, so it can be constructed at low cost and with high precision. Furthermore, there is no fear that the accuracy will decrease due to use.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining one embodiment, Fig. 2 is a diagram for explaining another embodiment, Fig. 3 is a diagram for explaining another embodiment, and Fig. 4 is a diagram for explaining another embodiment. FIG. 5 is a diagram for explaining the example, FIG. 5 is a diagram showing two types of scales, FIG. 6 is a diagram for explaining the scale manufacturing method, FIG. 7 is a diagram for explaining the silhouette pattern, FIG. FIG. 8 is a diagram for explaining slits and the like for converting incoherent light into light capable of generating a silhouette pattern. la, , linear light source as a light source device, 3, 4. , ,Scale, 510. Optical sensor as light receiving means, 601
, Bearing (I) Wood? Place 6 (I) (I) ] Danbato ( ＼

Claims (1)

[Scope of Claims] A scale that is formed in a cylindrical or conical shape and has a grating pattern with a fine pitch surrounding the circumferential surface as a surface relief grating, and is fixed to a rotating shaft whose amount of rotation is to be measured; A light source device that irradiates the scale with light to generate a shadow pattern corresponding to the lattice pattern, and a light receiving device that detects the shadow pattern generated by the reflected light from the scale portion irradiated with the light from the light source device. A rotary encoder, characterized in that the scale is formed by plastic molding and is integrated or fitted into and fixed to the rotating shaft.