WO2007004367A1

WO2007004367A1 - Optical encoder

Info

Publication number: WO2007004367A1
Application number: PCT/JP2006/310348
Authority: WO
Inventors: Toru Oka; Yoichi Ohmura; Hajime Nakajima; Takashi Okamuro; Kosuke Shamoto
Original assignee: Mitsubishi Electric Corporation
Priority date: 2005-06-30
Filing date: 2006-05-24
Publication date: 2007-01-11
Also published as: TW200702636A; JP2008241243A

Abstract

An optical encoder which is very small in distortion of a signal output from a light reception element even when a non-uniform irradiation distribution is given by a light source. The optical encoder comprises a light source, a fist lattice having openings and receiving light from the light source, a second lattice having openings arranged on the same circumference and receiving light having a intensity distribution formed by the first lattice, a third lattice having openings arranged on the same circumference and receiving light passed through the second lattice, and a light reception element receiving light from the third lattice, wherein the opening of the first lattice are such that the centers of the openings are arranged at the intersections between concentric circles and equiangular-pitch line segments passing the center of the concentric circles, and the shape of an opening changes in a sinusoidal form symmetrically in an outward direction and an inward direction with an concentric circle as a symmetric axis.

Description

Specification

Optical encoder

Technical field

The present invention relates to an optical encoder that can optically detect a relative movement amount between gratings.

Background art

In the conventional optical encoder, the theory of a three-grid method (grating image) in an optical encoder using three gratings has been proposed. According to this theory, if a spatially incoherent light source is used, the first grating, the second grating, and the third grating are arranged in order along the light traveling direction, and specific conditions are adjusted, the first grating is formed. Predetermined spatial frequency components included can be mapped onto the third grating with a predetermined OTF (Optical Transfer Function). The specific conditions are determined by parameters such as the shape of the second lattice, the distance from the first lattice to the second lattice, and the second lattice force as well as the distance to the third lattice. These parameters determine the OTF up to the third lattice of each spatial frequency component contained in the first lattice.

[0003] The action of each of the three lattices in the theory of the three-grid method is as follows. 1) First grating: Determines the spatial frequency distribution on the entrance surface. 2) Second lattice: OTF for each spatial frequency from the first lattice force to the third lattice based on the shape of the second lattice, the distance from the first lattice to the second lattice, the distance from the second lattice to the third lattice, etc. To decide. 3) Third grating: Transmits only the desired component from the imaged intensity distribution. It plays the role of a so-called index slit (for example, see Non-Patent Document 1).

[0004] In addition, in an optical encoder that applies a geometric theory, a first grating is formed by arranging a plurality of shapes obtained by folding up and down a sine wave (for example, see Patent Document 1). ).

Patent Document 1: Japanese Patent Laid-Open No. 5-87592 (page 6, FIG. 1)

Special Reference 1: K. Hane and CPurover, Imaging with rectangular transmission gratins, "J. Opt. Soc. Am. A4, 706-711, 1987 Disclosure of the invention

Problems to be solved by the invention

[0006] In the conventional optical encoder, the first grating is formed by a single-stage slit in which a plurality of shapes obtained by folding up and down a sine wave are arranged, so that the distribution of illumination from the light source is uneven. In such a case, there was a problem that distortion occurred in the sinusoidal intensity distribution on the first grating, and distortion also occurred in the intensity distribution on the light receiving element array.

[0007] The present invention has been made to solve the above-mentioned problems, and even when nonuniformity occurs in the illumination distribution from the light source, the signal output distortion of the light receiving element force is extremely small. An optical encoder is obtained.

Means for solving the problem

[0008] An optical encoder according to the present invention is formed by a first grating having an opening and receiving light from a light source, and an opening or a reflection part arranged on the same circumference. A second grating that receives light having an intensity distribution, a third grating that has openings arranged on the same circumference and receives light from the second grating, and a light receiving element that receives light from the third grating; An optical encoder of the three-grid method with the center of the opening disposed at the intersection of the concentric circle and a line segment of equiangular pitch passing through the center of the concentric circle in the opening of the first grating, The shape of the opening is characterized in that it changes in a sine wave shape symmetrically in the outer and inner directions with a concentric circle as the axis of symmetry.

[0009] The optical encoder according to the present invention includes a first grating that has an opening and receives light from a light source, and a light having an intensity distribution formed by the first grating that has an opening or a reflection part. A three-grating optical encoder comprising: a second grating that receives light; a third grating that has an aperture and receives light of a second grating force; and a light receiving element that receives light from the third grating. The opening portion of the first grating is characterized in that a plurality of slit rows in which openings having a shape in which a sine wave is folded up and down are continuously arranged are provided in the same phase.

[0010] Further, the optical encoder according to the present invention is formed by a first grating having an opening and receiving light from a light source, and an opening or a reflection part arranged on the same circumference. A second grating that receives light having a specified intensity distribution, a third grating that has openings arranged on the same circumference and receives light of the second grating force, and a light receiving element that receives light of the third grating force With three In the optical encoder of the grating method, an opening pattern in which the duty ratio of the transmission part changes in a sine wave shape is continuously arranged radially on the same circumference with respect to the center of the circle. It is characterized by this.

[0011] Further, the optical encoder according to the present invention includes a first grating having an opening and receiving light from a light source, and light having an intensity distribution formed by the first grating having an opening or a reflection part. A three-grating optical encoder comprising: a second grating that receives light; a third grating that has an aperture and receives light of a second grating force; and a light receiving element that receives light from the third grating. The opening portion of the first grating is characterized in that an opening pattern in which the duty ratio of the transmission portion changes in a sine wave shape is continuously arranged in the direction in which the duty ratio changes.

The invention's effect

The optical encoder according to the present invention is formed by a first grating having an opening and receiving light from a light source, and an opening or a reflecting part arranged on the same circumference. A second grating that receives light having an intensity distribution, a third grating that has openings arranged on the same circumference and receives light from the second grating, and a light receiving element that receives light from the third grating; An optical encoder of the three-grid method with the center of the opening disposed at the intersection of the concentric circle and a line segment of equiangular pitch passing through the center of the concentric circle in the opening of the first grating, The shape of the aperture is a shape that changes in a sinusoidal shape symmetrically in the outer and inner directions with a concentric circle as the axis of symmetry, so even if the illumination distribution is uneven, the signal from the light receiving element An optical encoder with extremely low output distortion can be obtained.

[0013] Further, the optical encoder according to the present invention includes a first grating that has an opening and receives light from a light source, and light having an intensity distribution formed by the first grating that has an opening or a reflection part. A three-grating optical encoder comprising: a second grating that receives light; a third grating that has an aperture and receives light of a second grating force; and a light receiving element that receives light from the third grating. The opening of the first grating is provided with multiple rows of slits in the same phase, each of which has an opening with a sine wave folded back up and down. However, it is possible to obtain an optical encoder with extremely small distortion of signal output from the light receiving element.

[0014] Further, the optical encoder according to the present invention is formed by a first grating having an opening and receiving light from a light source, and an opening or a reflection part arranged on the same circumference. The A second grating that receives light having a predetermined intensity distribution, a third grating that has openings arranged on the same circumference and receives light of the second grating force, and a light receiving element that receives light of the third grating force The aperture of the first grating has an opening pattern in which the duty ratio of the transmission part changes in a sine wave pattern on the same circumference, radially with respect to the center of the circle. Therefore, even if the distribution of illumination from the light source is nonuniform, an optical encoder with extremely small signal output distortion can be obtained even if the light receiving element is strong.

[0015] The optical encoder according to the present invention includes a first grating that has an opening and receives light from a light source, and a light having an intensity distribution formed by the first grating that has an opening or a reflection part. A three-grating optical encoder comprising: a second grating that receives light; a third grating that has an aperture and receives light of a second grating force; and a light receiving element that receives light from the third grating. In the opening of the first grating, the aperture pattern in which the duty ratio of the transmission part changes in a sine wave pattern is continuously arranged in the direction in which the duty ratio changes. However, it is possible to obtain an optical encoder with extremely small signal output distortion due to light receiving element force.

Brief Description of Drawings

FIG. 1 is a configuration diagram of an optical encoder showing Embodiment 1 of the present invention.

FIG. 2 is an opening pattern of openings of the first lattice in the first embodiment of the present invention.

FIG. 3 is an example of an OTF calculation result in Embodiment 1 of the present invention.

FIG. 4 is a configuration diagram of an optical encoder showing Embodiment 2 of the present invention.

FIG. 5 shows an opening pattern of the opening of the first grating in the second embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical encoder showing Embodiment 3 of the present invention.

FIG. 7 shows an opening pattern of the opening of the first grating in the third embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical encoder showing Embodiment 4 of the present invention.

FIG. 9 shows an opening pattern of the opening of the first grating in the fourth embodiment of the present invention.

FIG. 10 is an example of the calculation result of OTF in Embodiment 4 of the present invention.

FIG. 11 is a configuration diagram of an optical encoder showing Embodiment 5 of the present invention.

FIG. 12 shows an example of the calculation result of OTF in the fifth embodiment of the present invention.

FIG. 13 is a configuration diagram of an optical encoder showing Embodiment 6 of the present invention. FIG. 14 is a configuration diagram of an optical encoder showing Embodiment 7 of the present invention.

FIG. 15 is a configuration diagram of an optical encoder showing Embodiment 8 of the present invention.

FIG. 16 is a configuration diagram of an optical encoder showing Embodiment 9 of the present invention.

Explanation of symbols

[0017] 1, 11, 21, 31 First grating, 2, 12, 42, 52 Second grating, 3, 13 Third grating, 4 Light source, 5, 15, 25, 35 First grating substrate, 6, 16, 46, 56 Substrate for second grating, 7, 17 Light receiving element, 8, 18, 28, 38 Transmitting part, 9, 19, 29, 39 Non-transmitting part, 101a to 101e Same circle, 102a to 102e line Min, 111 users.

BEST MODE FOR CARRYING OUT THE INVENTION

[0018] Embodiment 1.

FIG. 1 shows a configuration diagram of an optical encoder according to Embodiment 1 for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings, and is applied to a rotary encoder in which gratings having a predetermined angular pitch are arranged radially. In FIG. 1, along the light traveling direction, the light source 4, the first grating 1 that has an opening and receives light from the light source 4, and the first grating 1 that has openings arranged on the same circumference. The second grating 2 that receives light having the formed intensity distribution, the third grating 3 that has openings arranged on the same circumference and receives light from the second grating 2, and the third grating 3 A light receiving element 7 for receiving light is provided.

The second grid 2 is disposed between the first grid 1 and the third grid 3. The second lattice 2 is supported so as to be angularly displaceable around the central axis C of the second lattice substrate 6. The light source 4 is composed of an LED or the like and emits spatially incoherent light having a center wavelength. The optical axis Q of the light source 4 is parallel to the central axis C and is positioned at a radius Ra from the central axis C.

[0020] The first grating 1 is formed on a transparent first grating substrate 5 by patterning such as a metal thin film, and has a grating pitch P at a position where the optical axes Q intersect.

An aperture of an amplitude grating type with 1 and a tally scale opening is constructed to receive the light from the light source 4 to produce a sinusoidal intensity distribution.

FIG. 2 shows an opening pattern of the opening of the first grating 1 in the first embodiment. The opening pattern includes a light transmitting portion 8 and a non-transmitting portion 9. At the opening of the first grid 1 The center of the opening is arranged at the intersection of two or more concentric circles 101a to 101e and the equiangular pitch line segments 102a to 102e passing through the center of the concentric circle. The shape changes in a sine wave shape symmetrically in the direction and the inner direction. For this reason, the shape of the opening is a shape that is enlarged or reduced in the circumferential direction of the concentric circles 10 la to LOLO in proportion to the distance from the center of the concentric circles 101 a to 101 e. The openings are arranged so that they have the same phase in the circumferential direction. A concentric circle is two or more circles that share the center. The radii of the concentric circles 101a to 101e may be equally spaced or unequal. Moreover, each opening may contact in the radial direction of a concentric circle, and does not need to contact. Lattice pitch P

1 is defined as the pitch of the aperture arranged near the position intersecting the optical axis Q.

[0022] The second grating 2 is formed by patterning a metal thin film or the like on the surface of the transparent second grating substrate 6 formed in a disk shape rotatable around the central axis C, and the optical axis Q intersects. The rotary scale of the amplitude grating having the grating pitch P is formed at the position of the radius Ra, and is arranged at the position separated from the first grating 1 by the first distance Z. Second grid 2 is

1

The intensity distribution produced by the first grating 1 in response to the light from the first grating 1 is imaged on the third grating 3 arranged at a second distance Z from the second grating 2. . Rotary

2

The shape of the scale is such that at the radius Ra where the optical axis Q intersects, an transmissive part and a non-transmissive part are alternately arranged for every half of the grating pitch P (= PZ2) to form an amplitude grating with a duty ratio of 50%. It is better to form.

[0023] The third grating 3 is an amplitude grating type having a grating pitch P at a position where the optical axes Q intersect.

2

The rotary scale is configured and placed at a position 2 Z away from the 2nd grid 2

2

Has been. The shape of the rotary scale is such that at the position where the optical axis Q intersects, a transmissive part and a non-transmissive part are alternately arranged for every half of the grating pitch P (= P Z2).

twenty two

It is better to form a 50% amplitude grating. The light receiving element 7 is formed of a photodiode or the like, and converts light that has passed through the third grating 3 into an electrical signal. The third grating 3 is provided integrally on the light receiving surface of the light receiving element 7. The third grating 3 and the light receiving element 7 may be provided separately.

[0024] The first grid 1 and the third grid 3 are fixed to a housing or the like. The second grating 2 is the optical axis It is supported so that it can be angularly displaced in the circumferential direction perpendicular to Q. If the spatial frequency component included in the first grating 1 satisfies the condition that the image is formed on the third grating 3, and if the second grating 2 is angularly displaced by rotation, the intensity distribution on the third grating 3 is also the same. Move in the direction. Therefore, the transmitted light from the third grating 3 is photoelectrically converted by the light receiving element 7, and the relative angular displacement of the second index 2 can be detected by changing the signal output.

Here, a design method for conditions under which the spatial frequency component included in the first grating 1 is imaged on the third grating 3 based on the theory of the three-grid method will be described. In the configuration of the optical encoder shown in FIG. 1, the frequency characteristic of the image formed on the third grating 3 and its contrast can be obtained by obtaining the OTF. OTF can be expressed by the Fourier transform of the square of the Inners response in the optical system.

FIG. 3 shows an example of the OTF calculation result when the image magnification is an enlargement system. When the shape of the second grating 2 is an amplitude grating with a duty ratio of 50% in which transmissive parts and non-transmissive parts are alternately arranged for each half of the grating pitch P (= PZ2), it is shown in FIG. OTF calculation results are obtained. In Fig. 3, the vertical axis is the DC component and the OTF after the standardization, and the horizontal axis is the second distance Z as the light source 4

Using the wavelength λ of 2 and the grating pitch の of the second grating 2, it is standardized with で = Ρ ² / λ. As an example, the first distance Ζ is fixed at a position of 1.5 Τ. In Figure 3, Ν is a number

1

This corresponds to the imaging condition parameter 定義 defined in 1.

[0027] [Equation 1]

[0028] Only when this Ν becomes an integer, the spatial frequency included in the first grating 1 is imaged on the third grating 3 with a predetermined ΟΤ F. The grid pitch 、 is the number 1, the first distance Ζ, the second distance Ζ and

1 1 2 and 3rd grating 3 is determined by Equation 2 which is a relational expression of image magnification using the grating pitch 格子.

2

The

[0029] [Expression 2] = (2) Here, the numerical value of Ν represents the imaging condition of each spatial frequency component. For example, when Ν = is designed as a basic spatial frequency component, Ν = 2, 3 ... Several components, that is, harmonic components, cause distortion components on the third grating 3. In the present embodiment, since the first grating 1 has a sine wave shape, the first grating 1 does not include spatial frequency components other than the basic spatial frequency. Therefore, no matter how much OTF other than the basic spatial frequency is present, if the illumination distribution from the light source 4 is uniform and the intensity distribution on the first grating 1 is an ideal sine wave, Since harmonic components are not imaged on the third grid 3, in principle, no distortion occurs in the intensity distribution on the third grid 3. Therefore, a distortion component is not generated in the signal output obtained from the light receiving element 7 force, and an extremely accurate sine wave output can be obtained.

[0031] Each parameter such as P, P, P, Z, Z, and λ at the time of design is a parameter of Formula 1.

1 2 1 2

Any design can be made by focusing on the imaging conditions corresponding to Ν, the image magnification of Equation 2, and the OTF of the fundamental spatial frequency component.

[0032] As an example, a case where an m-pitch lattice is formed on the circumference of Ra = 9.55 mm (the number of slits per rotation is 2000) will be described. The OTF at the wavelength of light source 4 = 900nm and Z = 1.5T is the same as in Fig. 3. Therefore, Z = 3T position

At 1 2, an OTF absolute value of 0.637 can be obtained at an image magnification of 2 ×. OTF = 0.637 means that the image is formed on the third grating 3 with the image power amplitude 63.7 of the first grating 1 having the amplitude 100. When the OTF value is negative, an inverted image of the first grating 1 is formed on the third grating 3. When the second grating 2 is rotated by 360 ° 1Z2000 along with the rotation of the disk that is the second grating substrate 6, the image formed on the third grating 3 also moves one period, and the signal after photoelectric conversion Can detect the angular displacement of the disk.

In addition, a plurality of sinusoidal openings are arranged in the same phase at the opening of the first grating 1. For this reason, even if the irradiation distribution from the light source 4 becomes non-uniform due to contamination, variation in the radiation distribution, etc., the total intensity distribution on the first grating 1 is sinusoidal due to the averaging effect of each aperture. Therefore, the light receiving element output that is transmitted through the third grating 3 and photoelectrically converted is a highly accurate sine wave output in which distortion is suppressed.

[0034] In the present embodiment, the case where the image magnification is 2 has been described. However, as long as the image forming condition and the relational expression of the image magnification are satisfied, the image magnification can be any number. It may be an enlargement system or reduction system of other magnifications. Also, make the first distance Z equal to the second distance Z to make the image magnification equal. It is good also as a structure.

Further, in the present embodiment, a force configured to move the first lattice 1 and the third lattice 3 with respect to the second lattice 2 may be any relative movement between the lattices. The first lattice 1 may be moved with respect to the second lattice 2 and the third lattice 3. When the first grating 1 is moved, the image formed on the third grating 3 is opposite to the moving direction of the first grating 1.

[0036] In the present embodiment, the number of openings having a sinusoidal shape symmetrically about the outer direction and the inner direction with the concentric circle as the axis of symmetry is five in the circumferential direction and five in the radial direction. The example which arranged one by one was shown. Increase or decrease the number of apertures according to the irradiation area and design pitch.

[0037] As described above, the opening of the first lattice 1 has the center of the opening at the intersection of the concentric circle and the equiangular pitch line passing through the center of the concentric circle, and the shape of the opening is concentric. Therefore, even if the illumination distribution of four light sources is nonuniform, the signal output from the light receiving element 7 is extremely distorted. And small optical encoder can be obtained.

[0038] Embodiment 2.

FIG. 4 shows a configuration diagram of an optical encoder according to Embodiment 2 for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings. In FIG. 4, along the light traveling direction, the intensity distribution formed by the light source 4, the first grating 11 having an opening and receiving light from the light source 4, and the first grating 11 having an opening is shown. A second grating 12 for receiving light, a third grating 13 having an opening for receiving light from the second grating 12, and a light receiving element 17 for receiving light from the third grating 13. . XI and X2 are in the same direction as X.

The second lattice 12 is disposed between the first lattice 11 and the third lattice 13. The light source 4 includes a spatially incoherent light source 4 such as an LED, and emits spatially incoherent light having a center wavelength λ.

[0040] The first grating 11 is formed on a transparent first grating substrate 15 by patterning such as a metal thin film, has a grating pitch Ρ, receives light from the light source 4, and has a sinusoidal shape. Create intensity distribution Made.

FIG. 5 shows an opening pattern of the opening of the first grating 11 in the second embodiment. The opening pattern includes a light transmitting portion 18 and a non-transmitting portion 19. The opening portion of the first grating 11 has a configuration in which a plurality of slit rows in which openings having a shape in which a sine wave is folded up and down are continuously arranged are provided in the same phase. The slit row is configured by continuously arranging openings with a sine wave folded up and down at a lattice pitch P. In other words, the slit row changes with one period P.

1 It is composed by folding up and down sine waves for multiple periods. In FIG. 5, the XI direction is the same as the XI direction shown in FIG. 4, and the traveling direction of the sine wave is the XI direction. A plurality of slit rows are provided in the amplitude direction of the sine wave so that the sine waves constituting the slit row have the same phase. The size of the opening in the amplitude direction of the sine wave arranged in each slit row may be the same or different as long as the openings are arranged so as to have the same phase. Moreover, each opening may contact and does not need to contact.

[0042] The second grating 12 is formed on the transparent second grating substrate 16 by patterning such as a metal thin film, and constitutes an amplitude grating having a grating pitch P. 1 distance Z

The intensity distribution created by the first grating 11 by receiving the light from the first grating 11 is placed at a position separated by 1 and the third distance is placed at a position away from the second grating 12 by the second distance Z. Lattice 13

2

The image is formed on the top. For the grating shape, it is better to form an amplitude grating with a duty ratio of 50% by alternately arranging transmissive parts and non-transmissive parts for each half of the grating pitch P (= PZ2).

[0043] The third grating 13 constitutes an amplitude grating having a grating pitch P, and the second distance from the second grating 12 is the second distance.

2

It is located at a position separated by Z. The lattice shape is half of the lattice pitch P (= P / 2)

It is better to form an amplitude grating with a duty ratio of 50% by arranging transmissive parts and non-transmissive parts alternately every 2 2 2. The light receiving element 17 is formed of a photodiode or the like, and converts light that has passed through the third grating 13 into an electrical signal. The third grating 13 is integrally provided on the light receiving surface of the light receiving element 17. The third grating 13 and the light receiving element 17 may be provided separately.

[0044] The first grid 11 and the third grid 13 are fixed to a housing or the like. On the other hand, the second grating 12 is supported so as to be movable relative to the first grating 11 and the third grating 13 along the X direction intersecting the light traveling direction. If the spatial frequency component included in the first grating 11 satisfies the condition for forming an image on the third grating 13, the second grating 12 moves on the X axis, 3 The light intensity distribution on the grating 13 also moves in the same direction. Therefore, the transmitted light from the third grating 13 is photoelectrically converted by the light receiving element 17, and the signal output changing force can also detect the relative movement amount of the second grating 12.

[0045] The air equivalent distance from the first grid 11 to the second grid 12 is Z, and the second grid 12 to the third grid 13

1

OTF can be calculated using the lattice pitch P, P, P as Z

2 1 2

The three-grid method theory as shown in Embodiment Mode 1 can be applied.

[0046] As an example, for the first distance Z = 1.5T and N = l as the basic spatial frequency

1

This will be described in detail. If the wavelength of the light source 4 is 900nm and the grating pitch P of the second grating 12 is P = 30m, then T = lmm, and Z = 1.5T (= 1.5mm), Z = 3T (= 3mm)

1 2

The absolute value of OTF for N = l is the maximum 0.637 at position. 1st distance Z and 2nd distance Z

Since the ratio of 1 2 is 2, in the configuration as in the present embodiment, an inverted image twice that of the first grating 11 is formed on the third grating 13 with OTF 0.637. The grating pitch P of the third grating 13 is 90 m from the imaging condition formula at N = l, and the grating pitch P of the first grating 11 is the image

2 1 The relational force of magnification is also 45 m. In this configuration, when the second grating 12 moves by one period in the X-axis direction, the image formed on the third grating 13 also moves by one period in the same direction, and the signal power after photoelectric conversion is also the second grating 12. Can be detected.

[0047] At the position of Z = 3T, OTF is also applied to frequency components of N = 2 or more at the same time as N = l.

2

Is present. However, since the first grating 11 is sinusoidal and has only basic spatial frequency components, higher-order components of N = 2 or higher do not appear on the third grating 13. Therefore, if the irradiation distribution from the light source 4 is uniform and the intensity distribution on the first grating 11 is an ideal sine wave, in principle, no distortion occurs in the intensity distribution on the third grating 13. Therefore, extremely accurate sine wave output can be obtained.

[0048] Further, since the opening of the first grating 11 has a plurality of rows of slit rows in which the openings having a shape in which a sine wave is folded up and down are continuously arranged in the same phase, dirt and radiation distribution Even if the irradiation distribution from the light source 4 is nonuniform due to variations in the light intensity, etc., the total intensity distribution on the first grating 11 becomes sinusoidal due to the averaging effect of each aperture. The light receiving element output that is transmitted and photoelectrically converted is a highly accurate sine wave output with suppressed distortion. [0049] In the present embodiment, as described above, when the image magnification is two times, any image magnification can be used as long as the image forming condition and the relational expression of the image magnification are satisfied. It may be an enlargement system or reduction system of other magnifications. Also, make the first distance Z equal to the second distance Z to make the image magnification equal.

1 2

It is good also as composition to make. Even if the relationship between the imaging condition and the image magnification does not completely satisfy Equations 1 and 2, the same operation as described above can be performed as long as it is substantially satisfied.

[0050] In the present embodiment, the second grating 12 is moved with respect to the first grating 11 and the third grating 13. However, since the relative movement between the gratings is sufficient, 1 lattice 11 may be moved relative to the second lattice 12 and the third lattice 13, or the third lattice 13 may be moved relative to the first lattice 11 and the second lattice 12. . When the first grating 11 is moved, the image formed on the third grating 13 is opposite to the moving direction of the first grating 11.

[0051] Further, in the present embodiment, an example is shown in which five rows of slit rows are arranged, each having several openings each of which has a sine wave folded up and down. The number of openings may be increased or decreased depending on the irradiation area, the design pitch, and the like.

[0052] As described above, the opening of the first grating 11 is provided with a plurality of slit rows in the same phase in which openings having a shape in which a sine wave is folded up and down are continuously provided. Even when the irradiation distribution is non-uniform, an optical encoder with extremely small distortion of the signal output from the light receiving element 17 can be obtained.

[0053] Embodiment 3.

FIG. 6 shows a configuration diagram of an optical encoder according to Embodiment 3 for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings, and has a predetermined angular pitch using a duty modulation pattern in which the transmittance changes in a sine wave shape as the first grating. It is applied to a rotary encoder that has a grid with a radial grid. In FIG. 6, the configuration other than the first lattice 21 and the first lattice substrate 25 is the same as that of the first embodiment. In FIG. 6, the same reference numerals as those in FIG. 1 denote the same or equivalent parts, and this is common throughout the entire specification. In addition, the description of the constituent elements appearing in the entire specification is merely an example, and is not limited to these descriptions. [0054] The first grating 21 is formed on the transparent first grating substrate 25 by patterning such as a metal thin film, and at the position where the optical axes Q intersect, the grating pitch P

An aperture of an amplitude grid type rotary scale with 1 is constructed to receive light from the light source 4 to produce a sinusoidal intensity distribution.

FIG. 7 shows an opening pattern of the openings of the first grating 21 in the third embodiment. The opening pattern includes a light transmitting portion 28 and a non-transmitting portion 29. The opening portion of the first grating 21 has a duty modulation pattern in which the transmittance changes in a sine wave shape, that is, an opening pattern in which the duty ratio of the transmission portion changes in a sine wave shape is radial with respect to the circle center on the same circumference Are arranged continuously. FIG. 7 shows a duty modulation pattern for one period, and this pattern is continuously arranged on the same circumference in the opening of the first grating 21. As shown in Fig. 7, the grating pitch P at the position intersecting the optical axis Q

1 and the pitch P is divided into 8 periods, and the period S is 1 period.

1

H P

It consists of a duty modulation pattern that changes in a sine wave shape at 1. Since the duty ratio changes sinusoidally at period S, the grating pitch P

The transmittance changes in a sinusoidal pattern every 1 and a sinusoidal light intensity distribution is created.

[0056] The air equivalent distance from the first grid 21 to the second grid 2 is Z, and from the second grid 2 to the third grid 3

1

By using the lattice pitch at a position perpendicular to the optical axis Q as Z

2

Therefore, the OTF in the rotary encoder can be calculated, and the theory of the three-grid method can be applied.

[0057] Since the first grating 21 has a duty modulation pattern in which the transmittance changes in a sine wave shape, the intensity distribution produced by the first grating 21 has a basic spatial frequency. When the irradiation distribution from the light source 4 is uniform and the intensity distribution on the first grating 21 is sinusoidal, the intensity distribution on the third grating 3 is also sinusoidal, and thus the signal output obtained from the light receiving element 7 is However, no distortion component is generated. In addition, by setting the OTF in the division period constituting the duty modulation to zero, the generation of higher-order components due to the division period can be suppressed. In addition, since the first grating 21 has a duty modulation pattern in which the transmittance changes in a sine wave shape, even if the irradiation distribution from the light source 4 is uneven due to variations in the radiation distribution, the first grating 21 is 1 Since the intensity distribution on grid 21 is sinusoidal, it passes through third grid 3 and The light receiving element output obtained by the conversion is a highly accurate sine wave output with suppressed distortion.

[0058] Each parameter such as P, P, P, Z, Z, and E at the time of design corresponds to the parameter N in Equation 1.

1 2 1 2

Any combination is possible if the design is focused on the corresponding imaging conditions, the image magnification of Equation 2, and the OTF of the fundamental spatial frequency component.

[0059] As an example, the case where a lattice with a pitch of 30 μm is formed on the circumference of Ra = 9.55 mm (the number of slits per rotation is 2000) will be specifically described. The OTF at the wavelength of the light source 4 = 90 Onm, Z = 1.5T is the same as that shown in Fig. 3 in the first embodiment.

1

Therefore, at the position of Z = 3T, an OTF absolute value of 0.637 can be obtained at an image magnification of 2x.

2

The In this case, if the second grating 2 is rotated by 1Z2000 of 360 ° along with the rotation of the disk that is the second grating substrate 6, the image formed on the third grating 3 also moves by one period, Signal force after photoelectric conversion The angular displacement of the disc can be detected.

[0060] OTF exists for higher frequency components at the same time as N = l at Ζ = 3Τ

2

. The first grating 21 is a sinusoidal duedy modulation pattern, which is a basic spatial frequency component, and for 分割 = 8, which is the division period of the duty modulation pattern, the OTF is less than 0.01. Higher order components do not appear substantially above. Therefore, the intensity distribution on the third grating 3 is also sinusoidal, and an extremely accurate sine wave output can be obtained.

[0061] In the present embodiment, the case where the image magnification is 2 has been described. As long as the image forming condition and the relational expression of image magnification are satisfied, the image magnification may be any amount, and an enlargement system or a reduction system with other magnifications may be used. Also, make the first distance Ζ equal to the second distance Ζ to make the image magnification equal.

1 2

It is good as a configuration.

Further, in the present embodiment, the second grating 2 is moved with respect to the first grating 21 and the third grating 3. For example, the first lattice 21 may be moved relative to the second lattice 2 and the third lattice 3 as long as the relative movement is between the lattices. When the first grating 21 is moved, the image formed on the third grating 3 is in the opposite direction to the moving direction of the first grating 21.

[0063] In the present embodiment, the lattice pitch Ρ of the first lattice 21 is divided into eight and A key modulation pattern was constructed. As long as the duty ratio changes in a sine wave pattern, it can be divided into any number of divisions. For example, if the number of divisions is increased, a smoother sine wave intensity distribution can be obtained.

[0064] As described above, the opening portion of the first grating 21 has the opening pattern in which the duty ratio of the transmission portion changes in a sine wave shape continuously arranged on the same circumference in the radial direction of the center force of the circle. Even when the irradiation distribution from the light source 4 is nonuniform, an optical encoder with extremely small distortion of the signal output from the light receiving element 7 can be obtained.

Embodiment 4.

FIG. 8 shows a configuration diagram of an optical encoder according to the fourth embodiment for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings, and uses a duty modulation pattern whose transmittance changes in a sine wave shape as the first grating. In FIG. 8, the configuration other than the first grating 31 and the first grating substrate 35 is the same as that of the second embodiment.

[0066] The first grating 31 is formed on the transparent first grating substrate 35 by patterning such as a metal thin film, has a grating pitch P, receives light from the light source 4, and has a sinusoidal shape. Create intensity distribution

1

Made.

FIG. 9 shows an opening pattern of the opening of first grating 31 in the fourth embodiment for carrying out the present invention. The opening pattern is composed of a light transmitting portion 38 and a non-transmitting portion 39. In the opening of the first grating 31, a duty modulation pattern in which the transmittance changes in a sine wave form, that is, an opening pattern in which the duty ratio of the transmission part changes in a sine wave form is continuously arranged in the direction in which the duty ratio changes. Is. Lattice pitch P is the length of the aperture pattern whose transmittance changes sinusoidally for one period.

1. The aperture pattern shown in Fig. 9 has a grating pitch P, and a period S obtained by dividing the grating pitch P by eight is defined as one period.

1 1

Consists of a duty modulation pattern in which the tee ratio changes sinusoidally at a grating pitch P

1

Has been. Since the duty ratio changes sinusoidally at period S, every grating pitch P

1, the transmittance changes in a sine wave shape, and a sinusoidal intensity distribution is produced.

[0068] Further, the air equivalent distance from the first grid 31 to the second grid 12 is the first distance Z, and the second grid 12

1

For the force, the air equivalent distance to the third grid 13 is the second distance Z. At this time, Z and Z It is better to set the OTF at the division period S of the tee modulation pattern as close to zero as possible.

[0069] The first lattice 31 is fixed to a housing or the like. The third grating 13 is fixed to the light receiving element 17 and the like. The second grating 12 is supported so as to be movable along the X direction intersecting the light traveling direction. As an example, when the spatial frequency component included in the first grating 31 satisfies the condition for forming an image on the third grating 13, if the second grating 12 moves on the X axis, The light intensity distribution also moves in the same direction. Therefore, the transmitted light from the third grating 13 is photoelectrically converted by the light receiving element 17, and the signal output changing force can also detect the relative movement amount of the second grating 12. Even in such a configuration, the theory of the three-grid method is similarly applied.

Since the first grating 31 has a duty modulation pattern in which the transmittance changes in a sine wave shape, the intensity distribution produced by the first grating 31 becomes a basic spatial frequency. The intensity distribution on the third grating 13 is also sinusoidal, so that no distortion component is generated in the signal output obtained from the light receiving element 17. In addition, by setting the OTF in the division period constituting the duty modulation to zero, the generation of higher-order components due to the division period can be suppressed. In addition, since the first grating 31 has a duty modulation pattern in which the transmittance changes in a sine wave shape, even if the irradiation distribution from the light source 4 is uneven due to dirt or variations in the radiation distribution, the first grating 31 Since the intensity distribution on 31 is sinusoidal, the light receiving element output obtained by photoelectric conversion through the third grating 13 is an extremely accurate sine wave output with suppressed distortion.

[0071] Each parameter such as P, P, P, Z, Z, and E at the time of design corresponds to the parameter N in Equation 1.

1 2 1 2

FIG. 10 shows an example of the OTF calculation result when the image magnification is an enlargement system. In Fig. 10, the vertical axis is the DC component and the OTF after standardization, and the horizontal axis is the second distance Z and the wavelength λ of the light source 4 and the second

2

Using the lattice pitch の of the lattice 12, it is standardized by Τ = Ρ ² / e. Where the first distance Ζ = 1.5Τ, N = l as the basic spatial frequency, and the duty modulation of the first grating 31

1

A specific description will be given of the case where the non-turn is composed of eight divisions as shown in FIG. As shown in FIG. 10, when the wavelength of the light source 4 is 900 nm and the grating pitch P of the second grating 12 is P = 30 m, T = lmm. Therefore, if Z = 1.5T (= 1.5mm) and the image magnification is 2x

1

In this case, the absolute value of OTF for N = l is the maximum 0.637 at the position of Z = 3T (= 3mm).

2

[0073] Since the ratio of the first distance Z and the second distance Z is 2, the inverted image twice that of the first grating 31 is

1 2

The image is formed on the third grating 13 by OTFO. 637. The lattice pitch P of the third lattice 13 is N = l

2

From the imaging condition formula in this case, it is 90 m, and the grating pitch P of the first grating 31 is a relational expression of image magnification.

1

The force is 45 / z m. With this configuration, when the second grating 12 moves by one period in the X-axis direction, the image formed on the third grating 13 also moves by one period in the same direction, and the second grating 12 Can be detected.

[0074] As shown in Fig. 10, considering the case where the duty modulation pattern of the first grating 31 is configured by 8 divisions, when calculating the OTF at N = 8, its absolute value is less than 0.01. . Z

2

At the position of 3T, OTF exists for higher frequency components at the same time as N = l. For this reason, higher-order components do not substantially appear on the third lattice 13. Therefore, the intensity distribution on the third grating 13 is also sinusoidal, and an extremely accurate sine wave output can be obtained.

[0075] In the present embodiment, the case where the image magnification is 2 has been described. As long as the image forming condition and the relational expression of image magnification are satisfied, the image magnification may be any amount, and an enlargement system or a reduction system with other magnifications may be used. Also, make the first distance Ζ equal to the second distance Ζ to make the image magnification equal.

1 2

It is good as a configuration.

[0076] In the present embodiment, the second grating 12 is moved with respect to the first grating 31 and the third grating 13. However, since the relative movement between the gratings is sufficient, A configuration in which one lattice 31 is moved with respect to the second lattice 12 and the third lattice 13 or a configuration in which the third lattice 13 is moved with respect to the first lattice 31 and the second lattice 12 may be employed. . When the first grating 31 is moved, the image formed on the third grating 13 is opposite to the moving direction of the first grating 31.

[0077] In the present embodiment, the lattice pitch の of the first lattice 31 is divided into eight and

1

However, if the duty ratio is a sine wave pattern, it can be divided into any number of divisions.For example, if the number of divisions is increased, the sine wave intensity becomes smoother. Distribution can be obtained.

As described above, the opening portion of the first grating 31 has the opening pattern in which the duty ratio of the transmission portion changes in a sine wave shape continuously arranged in the direction in which the duty ratio changes. Even if the irradiation distribution is uneven, it is possible to obtain an optical encoder in which the distortion of the signal output from the light receiving element 17 is extremely small.

[0079] Embodiment 5.

FIG. 11 shows a configuration diagram of an optical encoder according to the fifth embodiment for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings, and includes a reflective amplitude grating as the second grating. In FIG. 11, a spatially incoherent light source 4, a first grating 11 that has an aperture and receives light from the light source 4, and a light having an intensity distribution formed by the first grating 11 that has a reflection part. A second grating 52 for receiving light, a third grating 13 having an opening for receiving light from the second grating 52, and a light receiving element 17 for receiving light from the third grating 13. As shown in the second embodiment, the opening portion of the first grating 11 is provided with a plurality of stages of slit rows in the same phase in which openings having a shape in which a sine wave is folded up and down are continuously arranged. The lattice pitch of the first lattice 11 is P, the lattice pitch of the second lattice 52 is P, and the lattice pitch of the third lattice 13 is P. light source

1 2

4 consists of a spatially incoherent light source such as an LED, and emits spatially incoherent light with a central wavelength.

The third grating 13 is arranged on the same side as the first grating 11 with respect to the second grating 52. The slit direction of each of the first lattice 11, the second lattice 52, and the third lattice 13 is set to the vertical direction on the paper surface, and the moving direction of the second lattice 52 is set to the vertical direction parallel to the paper surface. The second grating 52 is provided on the second grating substrate 56, and the second grating 52 is moved by the movement of the second grating substrate 56. Light from the light source 4 passes through the first grating 11 obliquely, is reflected obliquely by the second grating 52, passes obliquely through the third grating 13, and reaches the light receiving element 17. 1st distance Z, 2nd distance

1

Z is the distance between the first grating 11 and the second grating 52, and between the second grating 52 and the third grating 13, respectively.

2

Indicates a gap. It is defined by the distance along the light traveling direction. Z and Z are the same distance

1 2

In addition, the first grating 11, the second grating 52, and the third grating 13 are arranged, and the image magnification is equal. Note that Z and Z are different by changing the arrangement of the first lattice 11 and the third lattice 13. You may make it become a distance. Any enlargement system or reduction system may be used as long as it satisfies the imaging condition and the relational expression of image magnification.

FIG. 12 shows the calculation result of OTF in this configuration. In Fig. 12, the vertical axis is the DC component and the normalized OTF, and the horizontal axis shows the values of the first distance Z and the second distance Z. N =

1 2

It can be seen that a maximum or minimum value of OTF can be obtained at a position that is an integral multiple of 2T for the fundamental spatial frequency component of 1. For example, the absolute value of OTF is 0.6 when Z = Z = 2T.

1 2

Therefore, the pitches of the first grating 11 and the third grating 13 may be determined so as to satisfy the imaging condition at this position.

By providing a reflection type amplitude grating as the second grating 52, the light source 4, the first grating 11, the third grating 13, and the light receiving element 17 can be arranged on the same side with respect to the second grating 52. The body configuration can be made compact. In addition, the openings of the first grating 11 are provided with a plurality of rows of slits in the same phase in which openings having a shape in which a sine wave is folded up and down are provided in the same phase. Even if the irradiation distribution from the light source 4 is non-uniform due to the cause, it is possible to obtain a highly accurate sine wave output in which distortion is suppressed in the light receiving element 17.

Note that the opening of the first grating 11 is a duty modulation pattern in which the transmittance changes in a sine wave shape as shown in Embodiment 4, that is, an opening in which the duty ratio of the transmissive portion changes in a sine wave shape. The pattern is arranged continuously in the direction in which the duty ratio changes.

[0084] As described above, the openings of the first grating 11 are provided with a plurality of slit rows in the same phase in which openings having a shape in which a sine wave is folded up and down are continuously arranged. Even when the irradiation distribution is non-uniform, an optical encoder with extremely small distortion of the signal output from the light receiving element 17 can be obtained. Further, since the third grating 13 is arranged on the same side as the first grating 11 with respect to the second grating 52, an optical encoder having a compact overall configuration can be obtained.

[0085] Embodiment 6.

FIG. 13 shows a configuration diagram of an optical encoder according to the sixth embodiment for carrying out the present invention. The optical encoder in this embodiment is composed of three gratings. This is a three-grid optical encoder. In FIG. 13, the configuration other than setting the slit direction of the first grating 11, the second grating 52, and the third grating 13 in the vertical direction parallel to the paper surface and setting the moving direction of the second grating 52 in the vertical direction on the paper surface is as follows. This is the same as the fifth embodiment. The light from the light source 4 passes through the first grating 11 obliquely, is reflected obliquely by the second grating 52, passes obliquely through the third grating 13, and reaches the light receiving element 17.

[0086] Even in such a configuration, the theory of the three-grid method is applied. As shown in Fig. 13, the first grid 11 force is also the first distance Z from the second grid 52, and the second distance from the second grid 52 to the third grid 13.

1

The separation Z is defined as the distance along the light traveling direction. Z and Z are equal distance

2 1 2

The first grating 11, the second grating 52, and the third grating 13 are arranged, and the image magnification is equal. Note that Z and Z have different distances by changing the arrangement of the first grating 11 and the third grating 13.

1 2

Let ’s get away. As long as the image forming condition and the relational expression of the image magnification are satisfied, an enlargement system or a reduction system may be used regardless of the image magnification.

[0089] As described above, the opening of the first grating 11 is provided with a plurality of slit rows in the same phase in which openings having a shape in which a sine wave is folded up and down are continuously arranged. Even when the irradiation distribution is non-uniform, an optical encoder with extremely small distortion of the signal output from the light receiving element 17 can be obtained. Further, since the third grating 13 is arranged on the same side as the first grating 11 with respect to the second grating 52, an optical encoder having a compact overall configuration is obtained. It can be done.

[0090] Embodiment 7.

FIG. 14 shows a configuration diagram of an optical encoder according to the seventh embodiment for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings, and is applied to a rotary encoder in which gratings having a predetermined angular pitch are arranged radially. A reflection type amplitude grating is provided as the second grating. In FIG. 14, a spatially incoherent light source 4, a first grating 1 that has an opening and receives light from the light source 4, and a reflective part arranged on the same circumference along the light traveling direction are shown. A second grating 42 for receiving light having an intensity distribution formed by the first grating 1; a third grating 3 having openings arranged on the same circumference and receiving light from the second grating 42; A light receiving element 7 for receiving light from the third grating 3 is provided.

[0091] The opening of the first grid 1 has the center of the opening at the intersection of two or more concentric circles and an equiangular pitch line segment passing through the center of the concentric circle as shown in FIG. The shape of the opening is a shape that changes in a sine wave shape symmetrically in the outer and inner directions with a concentric circle as the axis of symmetry. The lattice pitch of the first lattice 11 is P, the lattice pitch of the second lattice 52 is P, and the third lattice 13

1

The lattice pitch is P. Light source 4 is a spatially incoherent light source such as an LED.

2

It emits spatially incoherent light with a center wavelength λ.

The third grid 3 is arranged on the same side as the first grid 1 with respect to the second grid 42. Set the slit direction of the 1st grid 1, 2nd grid 42, and 3rd grid 3 so that each slit direction is perpendicular to the page, and set the movement direction of the 2nd grid 42 to be the vertical direction parallel to the page. To do. The second lattice 42 is provided on the second lattice substrate 46, and the second lattice 42 is moved by the rotation of the second lattice substrate 46. Light from the light source 4 passes through the first grating 1 obliquely, is reflected obliquely by the second grating 42, passes obliquely through the third grating 3, and reaches the light receiving element 7. Ζ and Ζ etc.

The first grid 1, the second grid 42, and the third grid 3 may be arranged so that the distance is 1 2. Also, as shown in Fig. 14, the arrangement of the first lattice 1 and the third lattice 3 is changed so that Ζ and Ζ

1 2 may be at different distances. If the configuration satisfies the imaging conditions and the relational expression of the image magnification, the image magnification can be an enlargement system or a reduction system.

[0093] By providing a reflective amplitude grating as the second grating 42, the light source 4 and the first grating 1, Since the third grating 3 and the light receiving element 7 can be arranged on the same side with respect to the second grating 42, the overall configuration can be made compact. In addition, the shape of the opening of the first grid 1 is a shape that changes in a sine wave shape symmetrically in the outer and inner directions with a concentric circle as the axis of symmetry. Even when the irradiation distribution is non-uniform, it is possible to obtain a highly accurate sine wave output in which distortion is suppressed in the light receiving element 7.

Note that the opening of the first grating has a duty modulation pattern in which the transmittance changes in a sine wave shape as shown in Embodiment 3, that is, the duty ratio of the transmissive portion changes in a sine wave shape. The opening pattern may be arranged radially continuously with respect to the center of the circle on the same circumference.

[0095] As described above, the opening center of the first lattice 1 is arranged at the intersection of the concentric circle and the equiangular pitch line segment passing through the center of the concentric circle, and the shape of the opening is The shape is a sinusoidal shape that changes symmetrically in the outer and inner directions with the concentric circle as the axis of symmetry.Therefore, even if the irradiation distribution from the light source 4 is uneven, the signal output from the light receiving element 7 is extremely distorted. A small optical encoder can be obtained. Further, since the third grating 3 is disposed on the same side as the first grating 1 with respect to the second grating 42, an optical encoder having a compact overall configuration can be obtained.

[0096] Embodiment 8.

FIG. 15 shows a configuration diagram of an optical encoder according to the eighth embodiment for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings, and is applied to a rotary encoder in which gratings having a predetermined angular pitch are arranged radially. In addition, a reflection type amplitude grating is provided as the second grating 42. In FIG. 15, the configuration except that the slit direction of the first grating 1, the second grating 42 and the third grating 3 is set to the vertical direction parallel to the paper surface, and the moving direction of the second grating 42 is set to the vertical direction of the paper surface. The same as in the seventh embodiment.

The second grating 42 is provided on the second grating substrate 46, and the second grating 42 is moved by the rotation of the second grating substrate 46. Light from the light source 4 passes through the first grating 1 obliquely, is reflected obliquely by the second grating 42, passes obliquely through the third grating 3, and reaches the light receiving element 7. 1st distance The separation Z and the second distance Z are defined by the distance along the light traveling direction. Z is equal to Z

1 2 1 2

The first grid 1, the second grid 42, and the third grid 3 may be arranged so that In addition, as shown in Fig. 15, the distance between Z and Z is changed by changing the arrangement of the first grid 1 and the third grid.

1 2

[0098] By providing a reflection-type amplitude grating as the second grating 42, the light source 4, the first grating 1, the third grating 3, and the light receiving element 7 can be arranged on the same side with respect to the second grating 42. The configuration can be made compact. In addition, the shape of the opening of the first grid 1 is a shape that changes in a sine wave shape symmetrically in the outer and inner directions with a concentric circle as the axis of symmetry. Even when the irradiation distribution is non-uniform, it is possible to obtain a highly accurate sine wave output in which distortion is suppressed in the light receiving element 7.

Note that the opening of the first grating 1 is a duty modulation pattern in which the transmittance changes in a sine wave shape as shown in Embodiment 3, that is, an opening in which the duty ratio of the transmissive portion changes in a sine wave shape. It is also possible to arrange the patterns continuously in a radial pattern with respect to the center of the circle on the same circumference.

[0100] As described above, the opening center of the first lattice 1 is arranged at the intersection of the concentric circle and the equiangular pitch line passing through the center of the concentric circle, and the shape of the opening is Since it has a sine wave shape symmetrically about the concentric circle in the outer and inner directions, the light source

Even if the irradiation distribution from 4 is non-uniform, an optical encoder with a very small distortion of the signal output from the light receiving element 7 can be obtained. Further, since the third grating 3 is disposed on the same side as the first grating 1 with respect to the second grating 42, an optical encoder having a compact overall configuration can be obtained.

[0101] Embodiment 9.

FIG. 16 shows a configuration diagram of an optical encoder according to the ninth embodiment for carrying out the present invention. The optical encoder in the present embodiment is a three-grid optical encoder composed of three gratings. In FIG. 16, the configuration other than the Dich user 111 is the same as that of the second embodiment. The Dich user 111 has a function of scattering light rays from the light source 4, and the scattered light rays irradiate the first grating 11. The above-mentioned scattering direction is an in-plane direction in order to improve the light detection efficiency or to suppress crosstalk when another scale pattern is provided on the first grating substrate 15. However, it is desirable to design so that it does not scatter in the vertical direction of the paper.

[0103] Diffraction of the light beam from the light source 4 is substantially parallel light and the pitch P of the first grating 11 is large.

1

Even if the angle is small, the diffusion angle from each sinusoidal opening of the first grating 11 can irradiate 4 or more apertures of the second grating 12, preferably 10 or more. What is necessary is just to design a scattering angle. The Dich user 111 can be manufactured by, for example, a resin molding technique (embossing) using an ultraviolet ray curing resin.

[0104] In FIG. 16, the Dich user 111 has the force provided on the light source 4 side on the first grid substrate 15 on the first grid 11 after the first grid 11 is formed by patterning such as a metal thin film. May be. The present embodiment can also be applied to the first to eighth embodiments.

[0105] In this way, the diffusion angle from each sinusoidal opening of the first grating 11 can be controlled by the Dich user 111, so the pitch P of the first grating 11

Even if the diffraction angle of a light beam with a large 1 is small, a sinusoidal light distribution based on the three-grid method can be imaged on the third grating 13, and the distortion of the signal output from the light receiving element 17 is extremely small. It is possible to obtain an optical encoder.

In all the embodiments, instead of the amplitude grating, for example, a grating in which optical features other than amplitude such as phase are periodically formed may be used as the second grating. The intensity distribution on the first grating can be imaged on the third grating. In this case as well, if a sinusoidal intensity distribution is produced on the first grating, distortion does not occur in the intensity distribution on the third grating, and an extremely accurate sine wave output can be obtained.

In all the embodiments, the basic spatial frequency may be designed with a frequency other than N = 1 as a basic frequency. For example, according to the imaging condition of N = 2 and the image magnification. The pitch of the grating may be determined and designed as a basic spatial frequency. In this case, the second-order harmonic component for N = 2 is N = 4, and the third-order harmonic component is N = 6.

Claims

The scope of the claims

[1] a first grating having an opening and receiving light from a light source;

A second grating for receiving light having an intensity distribution formed by the first grating and having openings or reflecting portions arranged on the same circumference;

A three-grid optical encoder comprising a third grating having openings arranged on the same circumference and receiving light from the second grating, and a light receiving element receiving light from the third grating. And

In the opening of the first lattice, the center of the opening is disposed at the intersection of a concentric circle and a line segment of equiangular pitch passing through the center of the concentric circle,

2. The optical encoder according to claim 1, wherein the shape of the opening is a shape that changes in a sine wave shape symmetrically in an outer direction and an inner direction with the concentric circle as an axis of symmetry.

[2] a first grating having an opening and receiving light of a light source power;

A second grating having an opening or a reflection part and receiving light having an intensity distribution formed by the first grating;

A third grating having an opening and receiving light from the second grating;

A three-grating optical encoder comprising a light-receiving element that receives light from the third grating,

The optical encoder according to claim 1, wherein the opening portion of the first grating is provided with a plurality of slit rows in the same phase in which slits having a shape in which a sine wave is folded up and down are continuously arranged.

[3] a first grating having an opening and receiving light of a light source power;

The opening portion of the first grating has an optical pattern in which an opening pattern in which the duty ratio of the transmission portion changes sinusoidally is continuously arranged radially on the same circumference with respect to the center of the circle. Encoder. A first grating having an opening to receive light from a light source;

A third grating having an opening and receiving light from the second grating;

The optical encoder is characterized in that an opening pattern in which the duty ratio of the transmission part changes in a sinusoidal manner is continuously arranged in the direction in which the duty ratio changes in the opening part of the first grating.