JP3017516B2 - Optical encoder and index mask - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical encoder and an index mask.

[Prior art] In an optical encoder that detects a displacement amount and a rotation amount of a moving body, a scale is integrated with the moving body to be displaced or rotated, and the displacement or rotation of a grid pattern formed on the scale is optically detected. Is done.

In such an optical encoder, the smaller the grating pitch of the grating pattern formed on the scale, the finer the amount of displacement and rotation can be detected.

Conventionally, the fineness of the grating pitch that can be detected optically is several tens of microns
m has been the limit, but recently, a grid pattern with an extremely fine pitch is irradiated with light to generate a shadow pattern, and the displacement and rotation of the grid pattern itself are detected by detecting the movement of the shadow pattern. How to do it,
A grating pitch of up to about 0.1 μm has been allowed.

That is, coherent light from a linear light source or incoherent light extracted through an aperture having an extremely fine slit or an elliptical or circular fine opening is converted into a fine-pitch lattice pattern under predetermined conditions. When illuminated, the transmitted or reflected light of the grid pattern produces a shadow pattern enlarging the grid pattern like a shadow, and the displacement or rotation of the grid pattern itself is measured by detecting the displacement or rotation of the shadow pattern. You can.

[Problem to be Solved by the Invention] The above-described shadow picture pattern and the problem to be solved in the present invention will be described with reference to FIGS. 7 to 9.

In FIG. 7, reference numeral 1 denotes a light source, and reference numeral 2 denotes a lattice pattern. The light source 1 has a circular light emitting portion having a diameter d, and emits monochromatic coherent light. When the diameter d of the light emitting portion of the light source 1 and the grating pitch に in the grating pattern 2 satisfy the following condition: (1/10) ≦ (d / ξ) ≦ 2 (1) 2 irradiates a shadow pattern. That is, a virtual plane 3 is considered in parallel with the lattice pattern 2, and the light intensity distribution on the plane 3 is as shown on the right side of the figure. In FIG. 7, the grid pattern 2 and the plane 3 are orthogonal to the drawing, but the right side of the drawing is drawn with the plane 3 parallel to the drawing.

When the coherent light is emitted from the light source 1 to the grating pattern 2, diffracted light 10 is generated from each irradiated portion of the grating pattern 2, and a shadow pattern 11 is generated by interference at a portion where the diffracted lights overlap.

This shadow pattern 11 is called a shadow pattern because it behaves like "geometric optical shadow of the grid pattern 2 when a point light source is placed at the position of the light source 1". Assuming that the distance between the light source 1 and the grid pattern 2 is b1 and the distance between the grid pattern 2 and the plane 3 is b2, the pattern pitch in the shadow pattern 11 is (b1 +
The size of the shadow pattern can be arbitrarily changed by changing b1 and b2.

The light that generates the shadow pattern is not limited to coherent light. Although shadow patterns by irradiating conventional monochromatic incoherent light emitted from the light source directly in a grid pattern 2 does not occur, for example, as shown in FIG. 8, a slit having a slit length d _A is formed aperture (FIG. ( _A )), when incoherent light is extracted through an aperture having an elliptical or circular opening having a diameter of dA (FIGS. (B) and (c)) and irradiated on the grating pattern 2, Generating a shadow pattern when the direction of d _A corresponds to the lattice repetition direction in the lattice pattern and the condition (1/10) ≦ (d _A / ξ ≦ 2 (2) is satisfied) Can be.

In the case of the coherent light source, if the “length d of the light emitting portion in the direction corresponding to the grating repetition direction in the grating pattern” satisfies the above (1), a shadow pattern is generated, and the direction orthogonal to the grating repetition direction is generated. Does not affect the occurrence / non-occurrence of the shadow pattern. Therefore, the “length of the light emitting portion in the direction orthogonal to the grating repetition direction” in the grating pattern can be appropriately determined. The same applies to the aperture diameter of the aperture for incoherent light.

Therefore, in this specification, the term “linear light source” refers to a coherent light source (semiconductor laser or the like) in which the light emitting portion length d in the direction corresponding to the grating repetition direction in the grating pattern satisfies the above (1); the lattice repeat direction in opening diameter d _a in the direction corresponding to intended to refer to the combination of aperture and incoherent light source which satisfies the above (2) (LED or the like).

FIG. 9 (a) shows a part of a shadow picture pattern. When the grid pattern 2 moves in the vertical direction in FIG. 7, the shadow pattern moves in the horizontal direction in FIG. 9 (a).
At this time, in order to detect the displacement of the shadow pattern, a light sensor having a light receiving surface having a width smaller than the width Y ₀ of the dark portion of the shadow pattern (for simplicity, it is equal to the width of the light portion) is used. What is necessary is just to arrange fixedly in the position of. However, with this method, it is difficult to obtain a detection signal of sufficient intensity when the displacement of the shadow pattern is fast or when the contrast of the shadow pattern is low. Thus, for example, as shown in FIG. 9 (b), using the index mask 5 having an array of apertures 50 with an aperture width Y ₀ in pattern pitch X ₀ of shadow pattern,
If only the light passing through the opening 50 is made incident on the optical sensor 9 having a large light receiving area, a good detection signal can be obtained.

By the way, optical encoders are sometimes used in rather severe situations. It is not unusual to receive vibration or shock depending on the usage condition.

In the case of an optical encoder using a shadow pattern, the pitch of the grid pattern is extremely fine, and the grid pattern is greatly enlarged in the shadow pattern, but the shadow pattern is relatively insensitive to vibration and impact. This is considered because the shadow pattern is formed by interference between diffracted lights. However, even if the vibrations and shocks become large to some extent, it is inevitable that they affect the shadow pattern.

When an index mask as shown in FIG. 9 (b) is used, the amplitude of the detection signal may be extremely reduced due to the large impact or vibration as described above.

Hereinafter, the vibration / shock refers to a large vibration / shock that affects the shadow picture pattern.

The present invention has been made in view of the above circumstances, and has as its object to provide an optical encoder that is hardly affected by vibration and impact, and a novel index mask for realizing the optical encoder.

[Means for Solving the Problems] The index mask according to claims 1 to 3 is “irradiating a scale having a grid pattern with light from a linear light source and generating a shadow pattern of the grid pattern by transmitted light or reflected light from the scale. Optical encoder that detects the movement (displacement and rotation) of the shadow pattern accompanying the movement of the scale with an optical sensor and detects the amount of movement of the scale. Or an index mask provided near the light receiving surface.

In the index mask according to the present invention, when the pattern pitch of an ideal shadow pattern at the index mask arrangement position is X and the width of a bright portion is Y, n (n ≧ 2) openings have a pitch X. provided so as to be arranged into a pattern moving direction, n-number of "in the shadow pattern moving direction" of the opening opening width Di (i = 1~n) is 0 around the width Y of the bright portion <D _i It is characterized by having a distribution in the range of <X. That is, the opening width Di (i = 1 to n) in the moving direction of the n openings is
Using the width Y of the bright portion as a reference width, the light portion has various sizes in the range of 0 <Di <X.

The index mask according to claim 2 is provided so that n (n> 2) openings are arranged in the shadow pattern moving direction, and the arrangement pitch of the n openings is distributed around the pattern pitch X. It is characterized by having. That is,
The arrangement pitch of the n openings has various sizes with the pattern pitch X as a reference pitch.

The index mask of claim 3 is provided such that n (n ≧ 2) openings are arranged in the moving direction of the shadow pattern, and the arrangement pitch of the n openings has a distribution centered on the pattern pitch X. And that the opening widths Di (i = 1 to n) of the n openings in the shadow pattern moving direction have a distribution in the range of 0 <D _i <X around the width Y of the bright portion. Features. That is, the arrangement pitch of the n openings has various sizes with the pattern pitch X as a reference pitch, and the n opening widths Di (i =
1 to n) have various sizes in the range of 0 <Di <X, using the width Y of the bright portion as a reference width.

The optical encoder according to claim 4 "irradiates light from a linear light source to a scale having a grid pattern, generates a shadow pattern of the grid pattern by transmitted light or reflected light from the scale, and generates a shadow pattern of the grid pattern accompanying the movement of the scale. The optical encoder detects the movement with an optical sensor to detect the amount of movement of the scale, and has the index mask according to claim 1 or 2 or 3.

The optical encoder according to claim 5, wherein "a scale having a grid pattern is irradiated with light from a linear light source, and a shadow pattern of the grid pattern is generated by transmitted light or reflected light from the scale. An optical encoder for detecting movement by a pair of optical sensors and detecting an amount of movement of the scale, comprising the index mask of claim 1 in combination with one of the pair of optical sensors,
It is characterized by having the index mask of claim 2 in combination with the other.

[Operation] The inventors examined the effects of vibration and impact on the optical encoder using the shadow pattern, and found that the vibration and impact had the following effects on the shadow pattern.

Referring again to FIG. 9 (a), the pattern pitch in the shadow picture pattern is X ₀ , and the width of the bright portion is Y ₀ , but when vibration or impact acts, these X ₀ and Y ₀ act on It varies within a range determined by the magnitude of the impact. Therefore, an index mask 5 having openings arranged at a constant opening width and a constant pitch.
When using, when the X ₀ is changed reduces the degree of overlap with one another shift pattern pitch of the arrangement pitch and shadow patterns of a plurality of openings, the amplitude of the detection signal is to decrease. The Y ₀ is or overlapping at the same time the bright portion and dark portion in one of the openings if changed, or the amplitude of the detection signal light intensity or decreased entering the opening is reduced.

Therefore, in the index mask according to claim 1, array pitch of the openings as shown in FIG. 2 (a) is to have a distribution in the opening width D _{i (i} = 1~n) and constant. Although take it gradually becomes smaller in this figure opening width D _i is directed from the left side of FIG. To the right, may be determined independently of the size of the opening width to the arrangement of openings. Ideal for placement of index mask 5A (not affected by vibration / shock)
Assuming that the pattern pitch of the shadow pattern is X and the width of the bright portion is Y, the opening width Di (i = 1 to n) is centered around Y, that is, the standard width is Y, and is suitable in the range of 0 <D _i <X. It is determined to have an appropriate distribution.

Assuming that the magnification of the shadow pattern at the index mask arrangement position is K, the grid pitch of the grid pattern is ξ, and the width of the light pattern corresponding portion of the grid pattern is δ, K
= Kξ and Y = Kδ.

When such an index mask 5A is used, vibration and vibration
And bright region width Y ₀ of shadow pattern under the influence of impact is changed can be reduced the amplitude change in the detection signal also. That deviated toward the bright portion width is smaller the higher the detection efficiency of the "opening smaller than the opening width D _i is Y", if the bright region width is shifted to the large direction "opening width D _i This is because the detection efficiency at the “opening larger than Y” becomes higher.

As shown in FIG. 2 (b), in the index mask of claim 2, the opening width is set to Y and the arrangement pitch P _{i of the} openings is set.
Have a distribution centered on the pattern pitch X of the shadow pattern. Distribution of the pitch P _i in the index mask 5B is gradually decreases from the left to the right pitch may be at random.

In this manner, when the pattern pitch of the shadow pattern has a normal pitch X, for example, the symbol shown in FIG.
Appropriate detection is performed by the opening of the portion indicated by II, and when the pattern pitch is X + ΔX,
When the pattern pitch is X-ΔX, an appropriate detection is performed by the opening of the portion III.

As the index mask according to claim 3 shown in FIG. 2 (C), the width of the opening D _i is has a distribution in the range 0 <D _i <X around the Y, the arrangement pitch P _i of the opening It has a distribution centered on X.

In the case of the index mask 5C, the fluctuation of the detection signal can be suppressed to be small regardless of which of X and Y changes.

Although the index mask may be arranged near the light receiving surface of the optical sensor and separated from the light receiving surface, the index masks 5A, 5B, and 5C are provided in close contact with the light receiving surface of the optical sensor 9 as shown in FIG. Is also good.

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

FIG. 1 shows an embodiment in which the optical encoder according to claim 5 is implemented as a linear encoder. Reference numeral 1 is a linear light source described with reference to FIG. 7, reference numeral 20 is a linear scale displaced in the vertical direction in the drawing, reference numerals 9A and 9B are optical sensors, and reference numerals 5A and 5B are FIGS. Fig. 3B shows the index mask shown in Fig. 3B. The figure on the right side shows the state of the shadow pattern at the position where the index masks 5A and 5B are arranged. Light sensor 9
The outputs of A and 9B are compared by an appropriate comparator, and the one with the larger amplitude of the detection signal is used as the detection signal.

FIG. 4 shows an embodiment in which the optical encoder of claim 4 is implemented as a rotary encoder. Reference numeral 1A denotes a linear light source, and more specifically, the longitudinal direction of the light emitting portion of the semiconductor laser is set parallel to the lattice repetition direction in the lattice pattern of the disk-shaped scale 2A. Reference numeral 9A denotes an optical sensor, and reference numeral 5C denotes an index mask as shown in FIG. 2 (C).

FIG. 5 also shows an embodiment of the optical encoder according to claim 4. In this embodiment, the scale is “the lattice pattern 8 is formed on the peripheral surface of the rotating shaft 7 supported by the bearing 6”. The scale is driven to rotate by driving means such as a motor (not shown).

The linear light source 1A, index mask 5C, and optical sensor 9A are the same as those in the embodiment of FIG.

FIG. 6 is a modification of the embodiment of FIG. That is, in this embodiment, a linear light source is constituted by an aperture 1A 'having a slit-like opening and an LED 1' as shown in FIG. 8 (a).

In each of the embodiments shown in FIGS. 4 to 6, even if the pattern pitch and the bright portion width of the shadow pattern fluctuate due to the action of vibration and impact, the fluctuation of the detection signal can be suppressed to a small level and good detection can be performed.

The pitch of the grid pattern in the scale used in the optical encoder of the present invention can be as fine as about 0.1 μm. A magnetized film or an in-plane magnetized film is formed, a lattice pattern is written as a magnetized pattern on the magnetized film with a magnetic head, and the magnetized pattern is visualized and fixed with a magnetic fluid. "
The method is suitable. As the magnetic fluid, a magnetic colloid fluid, a photocurable magnetic fluid, or a thermosetting magnetic fluid can be used.

"Magnetic colloid fluid" is obtained by dispersing a ferromagnetic substance into a fine powder having a particle size of 50 to 200 ° in a surfactant.
"Photocurable magnetic fluid" is a dispersion of the fine powder in a photocurable resin together with a surfactant, and "thermosetting magnetic fluid" is a dispersion of the fine powder in a thermosetting resin together with a surfactant. is there. Iron, Mn ferrite,
Ba ferrite or the like can be used. As the “photo-curable resin”, N′-vinyl carbazole, polyvinyl chloride, polystyrene and the like can be used. As the “thermosetting resin”, an epoxy resin, a silicone resin, a melamine resin, or the like can be used.

Since the photocurable resin is cured by light irradiation, when the magnetization pattern is visualized with a photocurable magnetic fluid, the code pattern can be fixed to the magnetized film simply by irradiating the visualized code pattern with light. Since the thermosetting resin is cured by heat, when the magnetization pattern is visualized with a thermosetting magnetic fluid, the code pattern can be fixed to the magnetic film only by heating the visualized code pattern.

[Effects of the Invention] Hereinafter, according to the present invention, a novel optical encoder and index mask can be provided. Since the index mask is configured as described above, the use of the index mask can effectively reduce the influence of vibration and impact on the optical encoder.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an example in which the optical encoder of the present invention is applied to a linear encoder, FIG. 2 is a diagram for explaining an index mask of the present invention, and FIG. FIG. 4 is a view for explaining a positional relationship, FIG. 4 is a view showing an example in which the optical encoder of the present invention is applied to a rotary encoder, and FIG. 5 is another example in which the optical encoder of the present invention is applied to a rotary encoder. FIG. 6 is a diagram showing another example in which the optical encoder of the present invention is applied to a rotary encoder, and FIGS. 7 to 9 are diagrams for explaining a shadow pattern and a problem to be solved by the present invention. . 1 Linear light source, 20 Linear scale, 5A, 5B Index mask, 9A, 9B Optical sensor

──────────────────────────────────────────────────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-63-47616 (JP, A) JP-A-1-297513 (JP, A) JP-A-2-57913 (JP, A) JP-A-1-216210 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01D 5/38 G01D 5/36

Claims (5)

(57) [Claims] A scale having a grid pattern is irradiated with light from a linear light source to generate a shadow pattern of the grid pattern by transmitted light or reflected light from the scale, and the shadow pattern of the shadow pattern accompanying the movement of the scale is generated. In an optical encoder that detects movement by an optical sensor and detects the amount of movement of the scale, an index mask disposed close to or near the single light receiving surface of the optical sensor. Assuming that the pattern pitch of the ideal shadow pattern at the index mask arrangement position is X and the width of the bright portion is Y, n (n ≧ 2) openings have a pitch X of the shadow pattern. An opening width Di (i) in the moving direction of the n openings in the moving direction.
= 1 to n) have various sizes in the range of O <Di <X, using the width Y of the bright portion as a reference width. 2. A scale having a grid pattern is irradiated with light from a linear light source to generate a shadow pattern of the grid pattern by transmitted light or reflected light from the scale. In an optical encoder that detects movement by an optical sensor and detects the amount of movement of the scale, an index mask disposed close to or near the single light receiving surface of the optical sensor. When a pattern pitch in an ideal shadow pattern at the index mask arrangement position is X, n (n> 2) openings are provided so as to be arranged in the moving direction of the shadow pattern. The arrangement pitch of the n openings is the pattern pitch X.
An index mask having various sizes with reference to a reference pitch. 3. The index mask according to claim 2, wherein the width of the bright portion in the ideal shadow pattern is Y, and the opening width Di of the n openings in the shadow pattern moving direction is Di. An index mask, wherein (i = 1 to n) has various sizes in a range of O <Di <X, using the width Y of the bright portion as a reference width. 4. A scale having a grid pattern is irradiated with light from a linear light source to generate a shadow pattern of the grid pattern by transmitted light or reflected light from the scale, and the shadow pattern of the shadow pattern accompanying the movement of the scale is generated. An optical encoder that detects movement by an optical sensor and detects the amount of movement of the scale, comprising the index mask according to claim 1, 2, or 3. 5. A scale having a grid pattern is irradiated with light from a linear light source to generate a shadow pattern of the grid pattern by transmitted light or reflected light from the scale, and the shadow pattern of the shadow pattern accompanying the movement of the scale is generated. An optical encoder that detects movement by a pair of optical sensors and detects the amount of movement of the scale, comprising: the index mask according to claim 1 in combination with one of the pair of optical sensors; An optical encoder comprising an index mask according to claim 2 in combination.