JP4953661B2 - Photoelectric encoder - Google Patents

Description

  The present invention relates to a photoelectric encoder. In particular, the present invention relates to an improvement in a photoelectric encoder having a telecentric optical system in which a lens and an aperture are inserted between a main scale and a light receiving element.

  As described in Patent Document 1, as shown in FIG. 1, a lens 42 and an aperture 44 serving as a telecentric optical diaphragm are disposed between a main scale 20 and, for example, a light receiving element array 34 constituting a light receiving unit 30. A lens optical system (telecentric optical system) 40 is inserted and the distances a and b between the lens 42 and the scale 21 of the main scale 20 and the light receiving elements 35 on the light receiving element array 34 are adjusted as shown in FIG. Thus, a photoelectric encoder that can set the magnification is considered. In FIG. 1, 10 is a light source, and f is a focal length of the lens 42.

  In the photoelectric encoder using the telecentric optical system 40, an image on the main scale 20 is projected onto the light receiving element array 34 through the lens optical system (42, 44). Here, by arranging the aperture 44 at the focal position of the lens 42, even if the distance (gap) between the main scale 20 and the lens 42 varies, the positional relationship between the lens 42, the aperture 44, and the light receiving element array 34 varies. Otherwise, the magnification fluctuation of the image formed on the light receiving element array 34 can be suppressed.

  Further, Patent Document 2 describes that the light is incident on the wafer through a narrow gap on the side of the reticle projection optical system using the Scheimpflug condition.

JP 2004-264295 A Japanese Patent Laid-Open No. 10-82611

  However, when a photoelectric encoder using a telecentric optical system as in Patent Document 1 is configured as a reflection type, when a half mirror 46 having an aperture 44 formed at the center is inserted as shown in FIG. If the amount of light that reaches the light receiving element 34 after passing through the light beam is reduced to (1/2) × (1/2) = (1/4), and the amount of light reaching the light source 10 is to be ensured, supply to the light source 10 Four times as much current is required. Further, since the optical axis is perpendicular to the surface of the main scale 20, the optical system cannot be reduced in size. In the figure, 12 is a collimating lens for collimating the light emitted from the light source 10.

  On the other hand, if the optical axis is inclined as shown in FIG. 4, the air gap is different between the center and the end as shown in FIG. There was a problem that the contrast could not be secured in the entire area, and the signal detection efficiency was lowered.

  It has not been considered to use the Shineproof condition for a photoelectric encoder using a telecentric optical system.

  The present invention has been made to solve the above-described conventional problems, and it is an object to prevent a decrease in contrast by focusing on the entire image plane even when the optical system is tilted and the optical system is downsized. And

According to the present invention, in a photoelectric encoder having a lens optical system between a main scale and a light receiving element , the lens optical system is a telecentric optical system including a lens and an aperture disposed at a focal position of the lens. In addition , the above problem has been solved by arranging the surface of the main scale , the main surface of the lens, and the image plane of the light receiving element so as to have a Shine proof relationship in which the three surfaces extend at one place. Is.

  The angle formed between the surface of the main scale and the main lens surface is the same as the angle formed between the main lens surface and the image plane of the light receiving element.

In the photoelectric encoder having a lens optical system between a main scale and a light receiving element, the lens optical system includes a lens and an aperture disposed at a focal position of the lens. In the lens optical system , at least the second lens is inserted between the first lens and the light receiving element so that the focal point thereof is at the focal position of the first lens. The surface, including the focal point of the first lens and the focal point of the second lens, and a plane extending from the three of the focal plane perpendicular to the optical axis and the image plane of the light receiving element, is formed in one place. The magnification can also be corrected so as to be in a shine-proof relationship.

  The angle formed between the surface of the main scale and the focal plane and the angle formed between the focal plane and the image plane of the light receiving element are the same.

  The lens optical system is a double-sided telecentric optical system.

  According to the present invention, as shown in FIG. 6, if the surface obtained by extending the subject surface, the lens main surface, and the image surface intersects at one place, the Sine proof condition that the entire image surface is in focus is satisfied. As a result, the entire image plane is in focus. Therefore, even if the optical axis is tilted to reduce the size of the optical system, it is possible to prevent a decrease in contrast.

  Note that the magnification of the A ′ point and the B ′ point in FIG. 6 is different, and the subject appears distorted, but the first lens and the second lens are connected to each other with their focal points coincided with each other. Can also correct the magnification to prevent distortion of the subject.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In the first reference embodiment, as shown in FIG. 7, the object surface on the scale 20, the main surface of the lens 42, and the image surface on the light receiving element 34 satisfy the Scheimpflug condition, and the angle theta ₁ of the lens main face, so that the lens principal plane and the image plane of the angle theta ₂ are identical, scale 20, a lens 42, and is obtained by arranging the light receiving elements 34.

In this reference embodiment, since θ ₁ = θ _2, the optical magnification of the image _{M = tanθ 2 / tanθ 1 =} 1
1 × optical system.

In particular, when θ ₁ = θ ₂ = 45 °, θ ₁ + θ ₂ = 90 °, and assembly is easy.

Also, as in the first embodiment of the present invention shown in FIG. 8, it may be telecentric optical system 40 which is disposed an aperture 44 at the focal position of the lens 42.

Further, as in the second embodiment shown in FIG. 9, it is possible to make an M-fold optical system with θ ₁ ≠ θ ₂ .

Next, the second reference embodiment will be described in detail with reference to FIG.

In this reference embodiment, a second lens 48 that is the same as the lens 42 (also referred to as a first lens) is inserted in the opposite direction on the opposite side of the focal plane 46 so that the focal point comes to the focal point of the first lens 42. The lens optical system 50 includes a subject surface, a surface that includes the focal points of the first lens 42 and the second lens 48, and a surface (referred to as a focal plane) perpendicular to the optical axis, and an image surface. The scale 20, the lens optical system 50, and the light receiving element 34 are set so that the angle θ ₁ formed by the object plane and the aperture plane and the angle θ ₂ formed by the aperture plane and the image plane coincide with each other while satisfying the proof condition.
Is arranged.

In this reference embodiment, since the second lens 48 of the first lens 42 and the outlet side of the inlet side are the same ones, the reverse almost completely aberration produced by the first lens 42 in the second lens 48 Correction can be made, and aberrations can be canceled almost completely, and the signal detection efficiency can be greatly improved.

Further, since the second lens 48 is inserted so that the focal point of the second lens 48 comes to the focal point of the first lens 42, the light exiting the second lens 48 becomes parallel light, which is an image as compared with the first reference embodiment. The keystone distortion (magnification) is corrected.

In particular, when θ ₁ = θ ₂ = 45 °, θ ₁ + θ ₂ = 90 °, and assembly is easy.

Further, as in the third embodiment of the present invention shown in FIG. 11, the lens optical system 50 is replaced with a double-sided telecentric optical system 51 in which an aperture 44 is disposed at the focal position of the first lens 42 and the second lens 48. You can also

Further, as in the fourth embodiment shown in FIG. 12, it is possible to make an M-magnification optical system with θ ₁ ≠ θ ₂ . In this case, since the entrance lens 42 and the exit lens 48 are different from each other, there is a possibility that the aberration cannot be completely removed, but the assembly allowable range in the gap direction can be expanded.

Here, in a lens optical system in which two lenses are connected so that their focal points coincide with each other, the shine proof includes the focal points of the two lenses and the focal plane perpendicular to the optical axis is the main surface of the lens system. The reason for applying the principle of is described. Consider a focus position s ₂ ′ when an object is tilted in a lens optical system 50 in which the focal length of the entrance lens 42 is f ₁ and the focal length of the exit lens 48 is f ₂ as shown in FIG.

(I) When s ₁ = −f ₁ (on the optical axis):
s ₂ '= f ₂
(Ii) When s ₁ ≠ −f ₁ (outside optical axis):
(1 / s ₁ ') = (1 / s ₁ ) + (1 / f ₁ )
Than,
s ₁ '= s ₁ f ₁ / (s ₁ + f ₁ )
Thus, the object position for the exit lens 48 is
s ₂ = − (f ₁ + f ₂ −s ₁ ′) = − (s ₁ f ₂ + f ₁ ² + f ₁ f ₂ ) / (s ₁ + f ₁ )

Therefore,
From (1 / s ₂ ′) = (1 / s ₂ ) + (1 / f ₂ ), s ₂ ′ = {f ₂ (s ₁ f ₂ + f ₁ ² + f ₁ f ₂ )} / f ₁ ²
= (F ₂ ² / f ₁ ² ) · s ₁ + f ₂ + (f ₂ ² / f ₁ ² ) · f ₁
s ₂ '−f ₂ = (f ₂ ² / f ₁ ² ) (s ₁ + f ₁ )

From FIG.
Δx ′ = (f ₂ ² / f ₁ ² ) · Δx (1)

Here, if the height of the object is y and the height of the image is y ′,
y ′ = βy = − (f ₂ / f ₁ ) · y

Now, if y = θ ₁ Δx, y ′ = βy = − (f ₂ / f ₁ ) · y from the equation (1)
=-(F ₂ / f ₁ ) · θ ₁ Δx
= − (F ₂ / f ₁ ) · θ ₁ · (f ₁ ² / f ₂ ² ) · Δx ′
= −θ ₁ · (f ₁ / f ₂ ) · Δx ′

Therefore, when the object plane is tilted by θ ₁ , if the image plane is tilted by θ ₁ · (f ₁ / f ₂ ), the entire surface will be in focus. From this, the intersection of the extension line of the object plane and the image plane comes to the focal plane 46.

In any of the above-described embodiments, the light receiving element 34 must be tilted with respect to the scale 20 and assembly is required. A third reference embodiment in which the scale 20 and the light receiving element 34 can be configured in parallel will be described in detail with reference to FIG.

This reference embodiment is the same photoelectric encoder as the second reference embodiment shown in FIG. 10, in addition to the lens optical system 50 (also referred to as the first lens optical system) on the main scale 20 side, as shown in FIG. Thus, a second lens optical system 60 composed of third and fourth lenses 62 and 68 is also added to the light receiving element 34 side, and the surface of the main scale 20, the focal plane 46 of the first lens optical system 50, The three surfaces (referred to as virtual surfaces) on which the light receiving element 34 was present in the third embodiment, the virtual surface, the focal plane 66 of the second lens optical system 60, and the image surface of the light receiving element 34. The three members satisfy the Scheinproof relationship.

In this reference embodiment, especially when the _{θ 1 = θ 2 = θ 3} = θ 4 = 45 ° , the scale 20 and can be configured in parallel receiving element 34, the assembly is facilitated, the scale 20 Since the light receiving element 34 is offset, the space of the light source 10 is easily taken.

Further, as in the fifth embodiment of the present invention shown in FIG. 15, an aperture 44 is disposed at a position where the optical axis and the focal plane 46 intersect, and an aperture 64 is disposed at a position where the optical axis and the focal plane 66 intersect. Thus, both-side telecentric optical systems 51 and 61 can be used.

  Since the numerical aperture NA is defined by the first aperture 44, the second aperture 64 can be omitted.

  The lenses 42, 48, 62, and 68 are high-precision but expensive plano-convex lenses and biconvex lenses, a spherical ball lens that has a large distortion but is inexpensive, and a light beam that is parabolic in the lens medium. Aberration can also be canceled by using a pair of refractive index distribution type cylindrical GRIN lenses (also referred to as selfoc lenses) or drum lenses.

  The present invention can be applied to both an index grating and a light receiving element that are separated, and a light receiving element array in which both are integrated.

The perspective view which shows the principal part structure of the photoelectric encoder using a telecentric optical system Same top view Optical path diagram showing prior art using a half mirror Optical path diagram showing prior art with optical axis A diagram showing the problem of FIG. Diagram showing the principle of the present invention Optical path diagram showing a main configuration of a first reference embodiment FIG. 1 is an optical path diagram showing the main configuration of the first embodiment of the present invention. Optical path diagram showing main components of the second embodiment of the present invention. Optical path diagram showing main configuration of second reference form Optical path diagram showing the configuration of the main part of the third embodiment of the present invention. Optical path diagram showing main components of the fourth embodiment of the present invention. Optical path diagram showing the application of the Scheinproof principle to bilateral telecentric optics Optical path diagram showing main configuration of third reference embodiment Optical path diagram showing main configuration of fifth embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Light source 20 ... Main scale 30 ... Light-receiving part 34 ... Light receiving element 40 ... Telecentric optical system 42, 48, 62, 68 ... Lens 44, 64 ... Aperture 46, 66 ... Focal plane 50, 60 ... Lens optical system 51, 61 ... Both-side telecentric optics

Claims (10)

In a photoelectric encoder with a lens optical system between the main scale and the light receiving element,
The lens optical system is a telecentric optical system including a lens and an aperture disposed at a focal position of the lens, and
A photoelectric encoder, wherein the surface of the main scale, the main surface of the lens, and the image plane of the light receiving element are arranged so as to have a Shine proof relationship in which the three surfaces extend at one place.   2. The photoelectric encoder according to claim 1, wherein an angle formed between the surface of the main scale and the lens main surface is the same as an angle formed between the lens main surface and the image plane of the light receiving element.   3. The photoelectric encoder according to claim 2, wherein an angle formed by the surface of the main scale and the lens main surface and an angle formed by the lens main surface and the image plane of the light receiving element are 45 °. In a photoelectric encoder with a lens optical system between the main scale and the light receiving element,
The lens optical system is a telecentric optical system including a lens and an aperture disposed at a focal position of the lens, and at least a second lens is disposed between the first lens and the light receiving element. A lens optical system inserted so as to come to the focal point of the first lens;
The main scale surface, the focal point of the first lens and the focal point of the second lens, and the focal plane perpendicular to the optical axis and the image plane of the light receiving element are extended. A photoelectric encoder characterized in that the surfaces are in a shine-proof relationship where the surfaces meet at one place. 5. The photoelectric encoder according to claim 4 , wherein an angle formed by the surface of the main scale and the focal plane is the same as an angle formed by the focal plane and the image plane of the light receiving element. 6. The photoelectric encoder according to claim 5 , wherein an angle formed by the surface of the main scale and the focal plane and an angle formed by the focal plane and the image plane of the light receiving element are 45 degrees. A photoelectric encoder in which a plurality of lens optical systems are inserted between a main scale and a light receiving element,
The lens optical system is a telecentric optical system including a lens and an aperture disposed at a focal position of the lens, and
A photoelectric encoder characterized in that the lens optical system on the main scale side and the lens optical system on the light receiving element side satisfy the Scheinproof relationship, respectively. The photoelectric encoder according to claim 7 , wherein a surface of the main scale and an image plane of the light receiving element are parallel to each other. The lens optical system, photoelectric encoder according to any one of claims 4 to 8 characterized in that it is a bilateral telecentric optical system. Said lens lens constituting the optical system, the same ball lens, a photoelectric encoder according to any one of claims 4 to 9, characterized in that a pair of the GRIN lens or drum lens.

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