JP2008241243A - Optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical encoder which does not generate distortion in a signal output from a light receiving element even when non-uniformity occurs in an irradiation distribution from a light source.
SOLUTION: Light having an intensity distribution formed by a light source 4, a first grating 1 having an opening and receiving light from the light source, and an opening arranged on the same circumference is formed. A second grating 2 for receiving, a third grating 3 having openings arranged on the same circumference and receiving light transmitted through the second grating 2, and a light receiving element 7 for receiving light from the third grating 3; In the opening of the first lattice, the center of the opening is arranged at the intersection of the concentric circle and the line segment of the equiangular pitch passing through the center of the concentric circle, and the shape of the opening is the outer direction and the inner direction with the concentric circle as the axis of symmetry. The shape is changed to a sine wave symmetrically.
[Selection] Figure 1

Description

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

  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 a specific condition is adjusted, it is included in the first grating. A predetermined spatial frequency component can be imaged on the third grating with a predetermined OTF (Optical Transfer Function). The specific condition is determined by parameters such as the shape of the second grating, the distance from the first grating to the second grating, and the distance from the second grating to the third grating. With these parameters, the OTF up to the third grating of the spatial frequency components included in the first grating is determined.

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

  Further, in an optical encoder applying a geometric theory, a first grating is configured by arranging a plurality of shapes obtained by folding up and down a sine wave (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 5-87592 (page 6, FIG. 1) K.Hane and C.P.Grover, "Imaging with rectangular transmission gratings," J.Opt.Soc.Am.A4, 706-711, 1987

  In the conventional optical encoder, since 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, if there is non-uniformity in the irradiation distribution from the light source There is a problem that distortion occurs in the sinusoidal intensity distribution on the first grating and distortion also occurs in the intensity distribution on the light receiving array.

  The present invention has been made to solve the above-described problems, and provides an optical encoder that does not generate distortion in the signal output from the light receiving element even when the irradiation distribution from the light source is uneven. Is.

  An optical encoder according to the present invention has an intensity distribution 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. Three gratings comprising: a second grating for receiving light; a third grating having openings arranged on the same circumference; for receiving light from the second grating; and a light receiving element for receiving light from the third grating The center of the opening 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 a concentric circle. Is a shape that is changed in a sine wave shape symmetrically in the outer direction and the inner direction with respect to the axis of symmetry.

  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 first grating that has an opening or a reflection part and has an intensity distribution formed by the first grating. A three-grating optical encoder comprising two gratings, a third grating having an opening and receiving light from the second grating, and a light receiving element receiving light from the third grating, This opening 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.

  The optical encoder according to the present invention has an intensity 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 distribution; a third grating that has openings arranged on the same circumference; that 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, in which the opening portion of the first lattice is continuously arranged in a radial pattern with respect to the center of the circle on the same circumference, the opening pattern in which the duty ratio of the transmission portion changes sinusoidally It is characterized by that.

  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 first grating that has an opening or a reflection part and has an intensity distribution formed by the first grating. A three-grating optical encoder comprising two gratings, a third grating having an opening and receiving light from the second grating, and a light receiving element receiving light from the third grating, The opening is characterized in that an opening pattern in which the duty ratio of the transmission part changes in a sine wave shape is continuously arranged in the direction in which the duty ratio changes.

  An optical encoder according to the present invention has an intensity distribution 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. Three gratings comprising: a second grating for receiving light; a third grating having openings arranged on the same circumference; for receiving light from the second grating; and a light receiving element for receiving light from the third grating The center of the opening 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 a concentric circle. The optical system does not generate distortion in the signal output from the light receiving element even if the illumination distribution from the light source is non-uniform, because it is a shape that changes symmetrically in the outer and inner directions about the axis of symmetry. An encoder can be obtained.

  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 first grating that has an opening or a reflection part and has an intensity distribution formed by the first grating. A three-grating optical encoder comprising two gratings, a third grating having an opening and receiving light from the second grating, and a light receiving element receiving light from the third grating, Since the apertures in this section are provided with multiple rows of slit rows in which the sine wave folds up and down are continuously arranged in the same phase, even if the illumination distribution from the light source is uneven, the light receiving element It is possible to obtain an optical encoder in which no distortion occurs in the signal output from the encoder.

  The optical encoder according to the present invention has an intensity 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 distribution; a third grating that has openings arranged on the same circumference; that 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, in which the opening portion of the first lattice is continuously arranged in a radial pattern with respect to the center of the circle on the same circumference, the opening pattern in which the duty ratio of the transmission portion changes sinusoidally Therefore, an optical encoder that does not generate distortion in the signal output from the light receiving element can be obtained even when the irradiation distribution from the light source is uneven.

  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 first grating that has an opening or a reflection part and has an intensity distribution formed by the first grating. A three-grating optical encoder comprising two gratings, a third grating having an opening and receiving light from the second grating, and a light receiving element receiving light from the third grating, Since the aperture pattern in which the duty ratio of the transmissive part changes in a sinusoidal pattern is continuously arranged in the direction in which the duty ratio changes, the aperture from the light-receiving element It is possible to obtain an optical encoder in which no distortion occurs in the signal output.

Embodiment 1 FIG.
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, a light source 4, a first grating 1 having an opening and receiving light from the light source 4, and an opening arranged on the same circumference and the first grating 1. The second grating 2 that receives the light having the formed intensity distribution, the third grating 3 that has openings arranged on the same circumference and receives the light from the second grating 2, and the light from the third grating 3 And a light receiving element 7 for receiving the light.

  The second grating 2 is disposed between the first grating 1 and the third grating 3. The second grating 2 is supported so as to be angularly displaceable around the central axis C of the second grating substrate 6. The light source 4 is composed of an LED or the like, and emits spatially incoherent light having a center wavelength λ. 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.

The first grating 1 is formed by patterning a metal thin film or the like on a transparent first grating substrate 5 and has an opening of an amplitude grating type rotary scale having a grating pitch P ₁ at a position where the optical axis Q intersects. In this configuration, the light from the light source 4 is received to produce a sinusoidal intensity distribution.

FIG. 2 shows an opening pattern of the openings of the first grating 1 in the first embodiment. The opening pattern includes a light transmitting portion 8 and a non-transmitting portion 9. In 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 line segments 102a to 102e having an equiangular pitch passing through the center of the concentric circle. 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. For this reason, the shape of the opening is a shape enlarged or reduced in the circumferential direction of the concentric circles 101a to 101e in proportion to the distance from the center of the concentric circles 101a to 101e. The openings are arranged so as to have the same phase in the circumferential direction. The radii of the concentric circles 101a to 101e may be equidistant or unequal. Moreover, each opening may contact in the radial direction of a concentric circle, and does not need to contact. The grating pitch P ₁ is defined as the pitch of the openings arranged in the vicinity of the position intersecting the optical axis Q.

The second grating 2 is formed by patterning a metal thin film or the like on the surface of a transparent second grating substrate 6 formed in a disk shape rotatable around the central axis C, and has a radius Ra where the optical axis Q intersects. In this position, a rotary scale of an amplitude grating having a grating pitch P is formed and arranged at a position separated from the first grating 1 by the first distance Z ₁ . The second grating 2 receives the light from the first grating 1 on the third grating 3 in which the intensity distribution produced by the first grating 1 is arranged at a position separated from the second grating 2 by the second distance Z _2. Is imaged. The shape of the rotary scale is such that a transmissive portion and a non-transmissive portion are alternately arranged for each half of the grating pitch P (= P / 2) at the position of the radius Ra where the optical axis Q intersects, and the duty ratio is 50%. It is better to form an amplitude grating.

The third grating 3 constitutes an amplitude grating type rotary scale having a grating pitch P ₂ at a position where the optical axes Q intersect, and is arranged at a position separated from the second grating 2 by a second distance Z ₂ . . The shape of the rotary scale, in a position where the optical axis Q intersects, half of the grating pitch _{P 2 (= P 2/2} ) and a transmissive portion and a non-transmissive portion disposed alternately for each, a duty ratio of 50% amplitude It is better to form a lattice. 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 integrally provided on the light receiving surface of the light receiving element 7. Note that the third grating 3 and the light receiving element 7 may be provided separately.

  The first grid 1 is fixed to a housing or the like. The second grating 2 is supported so as to be angularly displaceable in the circumferential direction orthogonal to the optical axis Q. When the spatial frequency component included in the first grating 1 satisfies the condition that an image is formed on the third grating 3, 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. Thus, the transmitted light from the third grating 3 is photoelectrically converted by the light receiving element 7, and the relative angular displacement amount of the second grating 2 can be detected from the change in 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 the contrast thereof are obtained by obtaining the OTF. OTF can be expressed by the square Fourier transform of the impulse response in the optical system.

FIG. 3 shows an example of an 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 a transmission part and a non-transmission part are alternately arranged every half of the grating pitch P (= P / 2), it is shown in FIG. OTF calculation results are obtained. In FIG. 3, the vertical axis represents the OTF normalized with the DC component, and the horizontal axis represents the second distance Z ₂ using the wavelength λ of the light source 4 and the grating pitch P of the second grating 2, and T = P ² This is normalized by / λ. As an example, the first distance Z ₁ is fixed at a position of 1.5T. In FIG. 3, N corresponds to the imaging condition parameter N defined by Equation (1).

Only when N becomes an integer, the spatial frequency included in the first grating 1 is imaged on the third grating 3 by a predetermined OTF. The grating pitch P ₁ is determined by Expression 1 and Expression 2, which is a relational expression of image magnifications using the first distance Z ₁ , the second distance Z _2, and the grating pitch P ₂ of the third grating 3.

  Here, the numerical value of N represents the imaging condition of each spatial frequency component. For example, when N = 1 is designed as a basic spatial frequency component, N = 2, 3,... Become higher-order spatial frequency components, that is, harmonic components, and causes distortion components on the third grating 3. Become. In the present embodiment, since the first grating 1 has a sine wave shape, the first grating 1 does not include a spatial frequency component other than the basic spatial frequency. Therefore, no matter how many OTFs other than the basic spatial frequency are present, if the irradiation distribution from the light source 4 is uniform and the intensity distribution on the first grating 1 is an ideal sine wave, the third Since no harmonic component is imaged on the grating 3, no distortion occurs in the intensity distribution on the third grating 3 in principle. Therefore, no distortion component is generated in the signal output obtained from the light receiving element 7, and an extremely accurate sine wave output can be obtained.

The parameters such as P ₁ , P, P ₂ , Z ₁ , Z _2, and λ at the time of design are the imaging conditions corresponding to the parameter N in Equation 1, the image magnification in Equation 2, and the OTF of the fundamental spatial frequency component. Any design can be made by paying attention to the design.

As an example, a 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 described. The OTF at the wavelength λ = 900 nm and Z ₁ = 1.5T of the light source 4 is the same as that shown in FIG. Accordingly, an OTF absolute value of 0.637 can be obtained at a position of Z ₂ = 3T at an image magnification of 2 ×. OTF = 0.637 means that an image of the first grating 1 having an amplitude of 100 is formed on the third grating 3 with an amplitude of 63.7. 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 1/2000 of 360 ° in accordance with the rotation of the disk as the second grating substrate 6, the image formed on the third grating 3 is also moved by one period, and after photoelectric conversion The angular displacement of the disc can be detected from the signal.

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

In the present embodiment, the case where the image magnification is 2 times has been described. However, the image magnification may be any number as long as the image forming condition and the relational expression of the image magnification are satisfied. System may be used. Alternatively, the first distance Z ₁ and the second distance Z ₂ may be made equal to make the image magnification equal.

  In the present embodiment, the first grating 1 and the third grating 3 are moved with respect to the second grating 2. However, any relative movement between the gratings may be used. The grating 1 may be moved with respect to the second grating 2 and the third grating 3. When the first grating 1 is moved, the image formed on the third grating 3 is in the opposite direction to the moving direction of the first grating 1.

  Further, in the present embodiment, the number of openings having a sine wave shape symmetrically changed in the outer direction and the inner direction with the concentric circle as the axis of symmetry is arranged in the circumferential direction by 5 pieces and in the radial direction by 5 pieces, respectively. An example is shown. The number of openings may be increased or decreased depending on the irradiation area, the design pitch, and the like.

  As described above, the center of the opening is arranged at the intersection of the concentric circle and the equiangular pitch line segment passing through the center of the concentric circle in the opening of the first lattice 1, and the shape of the opening has the concentric circle as an axis of symmetry. An optical encoder that does not generate distortion in the signal output from the light receiving element 7 even when the distribution of illumination from the light source 4 is non-uniform because it has a sine wave shape that is symmetrical in the outer direction and the inner direction. Obtainable.

Embodiment 2. FIG.
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 light source 4, the first grating 11 having an opening to receive light from the light source 4, and the intensity distribution formed by the first grating 11 having an opening. A second grating 12 that receives light, a third grating 13 that has an opening and receives light from the second grating 12, and a light receiving element 17 that receives light from the third grating 13 are provided. X1 and X2 are in the same direction as X.

  The second grating 12 is disposed between the first grating 11 and the third grating 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.

The first grating 11 is formed by patterning a metal thin film or the like on the transparent first grating substrate 15, has a grating pitch P ₁ , and receives a light from the light source 4 to produce a sinusoidal intensity distribution. Yes.

FIG. 5 shows an opening pattern of the openings of the first grating 11 in the first embodiment. The opening pattern includes a light transmitting portion 18 and a non-transmitting portion 19. The opening 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 having a shape in which a sine wave is folded up and down at a lattice pitch P ₁ . That is, slit matrix is constructed by folding the sine wave of multiple cycles that vary in one period P ₁ vertically. In FIG. 5, the direction of X1 is the same as the direction of X1 shown in FIG. 4, and the traveling direction of the sine wave is the direction of X1. 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.

The second grating 12 is formed on the transparent second grating substrate 16 by patterning a metal thin film or the like, constitutes an amplitude grating having a grating pitch P, and is separated from the first grating 11 by the first distance Z ₁ . The intensity distribution produced by the first grating 11 by receiving the light from the first grating 11 is placed on the third grating 13 arranged at a position away from the second grating 12 by the second distance Z _2. The image is formed. As for the lattice shape, it is preferable to form an amplitude lattice with a duty ratio of 50% by alternately arranging transmissive portions and non-transmissive portions every half of the lattice pitch P (= P / 2).

The third grating 13 constitutes an amplitude grating having a grating pitch P ₂ and is arranged at a position separated from the second grating 12 by a second distance Z ₂ . Lattice shape, a half of the grating pitch _{P 2 (= P 2/2} ) and a transmissive portion and a non-transmissive portion disposed alternately for each, it is better to form a duty ratio of 50% of the amplitude grating. 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. Note that the third grating 13 and the light receiving element 17 may be provided separately.

  The first grid 11 is fixed to a housing or the like. On the other hand, the 2nd grating | lattice 12 is supported so that a movement is possible along the X direction which cross | intersects a light advancing direction. When the spatial frequency component included in the first grating 11 satisfies the condition that an image is formed on the third grating 13, if the second grating 12 moves on the X axis, the light intensity distribution on the third grating 13 also changes. Move in the same direction. Therefore, the transmitted light from the third grating 13 is photoelectrically converted by the light receiving element 17, and the relative movement amount of the second grating 12 can be detected from the change in the signal output.

The air equivalent distance from the first lattice 11 to the second lattice 12 is Z ₁ , the air equivalent distance from the second lattice 12 to the third lattice 13 is Z ₂ , and the lattice pitches P ₁ , P, and P ₂ are used for OTF. And the theory of the three-grid method as shown in Embodiment Mode 1 can be applied.

As an example, a case where the first distance Z ₁ = 1.5T and N = 1 as a basic spatial frequency will be specifically described. When the wavelength λ of the light source 4 is 900 nm and the grating pitch P of the second grating 12 is 30 μm, T = 1 mm. When Z ₁ = 1.5T (= 1.5 mm), Z ₂ = 3T (= 3 mm). The absolute value of OTF with N = 1 becomes 0.637 at the maximum. Since the ratio of the first distance Z ₁ and the second distance Z ₂ is 2, in the configuration as in the present embodiment, a double inverted image of the first grating 11 is the third OTF of 0.637. An image is formed on the grating 13. The grating pitch P ₂ of the third grating 13 is 90 μm from the imaging condition formula at N = 1, and the grating pitch P ₁ of the first grating 11 is 45 μm from the relational expression of image magnification. 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 from the signal after photoelectric conversion, the second grating 12 The amount of movement can be detected.

At the position of Z ₂ = 3T, OTF exists for frequency components of N = 1 or more at the same time as N = 1. 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, when 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. An extremely accurate sine wave output can be obtained.

  In addition, the opening of the first grating 11 is provided with a plurality 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. Even if the irradiation distribution from the light source 4 is non-uniform due to the above, the total intensity distribution on the first grating 11 becomes sinusoidal due to the averaging effect of each aperture, so that the third grating 13 is transmitted. The light receiving element output obtained by the photoelectric conversion is a highly accurate sine wave output in which distortion is suppressed.

In the present embodiment, the case where the image magnification is 2 times has been described. However, the image magnification may be any number as long as the image forming condition and the relational expression of the image magnification are satisfied. System may be used. Alternatively, the first distance Z ₁ and the second distance Z ₂ may be set equal to make the image magnification equal.

  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, the first grating 11 is used. May be configured to be moved with respect to the second lattice 12 and the third lattice 13, or the third lattice 13 may be moved with respect 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 in the opposite direction to the moving direction of the first grating 11.

  In the present embodiment, an example is shown in which five rows of slit rows each having four openings each of which sine waves are folded up and down are arranged. The number of openings may be increased or decreased depending on the irradiation area, the design pitch, and the like.

  As described above, the opening portion of the first grating 11 is provided with a plurality of rows of slit rows in which openings having a shape in which a sine wave is folded up and down are continuously arranged in the same phase. Even when nonuniformity occurs, it is possible to obtain an optical encoder that does not generate distortion in the signal output from the light receiving element 17.

Embodiment 3 FIG.
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 whose transmittance changes in a sine wave shape as the first grating. Is applied to a rotary encoder arranged radially. In FIG. 6, the configuration other than the first grating 21 and the first grating 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 corresponding parts, and this is common throughout the entire specification. Further, the description of the constituent elements appearing in the whole specification is merely an example and is not limited to these descriptions.

The first grating 21 is formed by patterning a metal thin film or the like on the transparent first grating substrate 25, and has an opening of an amplitude grating type rotary scale having a grating pitch P ₁ at a position where the optical axis Q intersects. In this configuration, the light from the light source 4 is received 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 radially with respect to the center of the circle on the same circumference. It is 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, with the grating pitch P ₁ at the position intersecting the optical axis Q, a period S obtained by dividing the grating pitch P ₁ into eight periods is defined as one period, and the duty ratio changes sinusoidally at the grating pitch P _1. It consists of a duty modulation pattern. Since the duty ratio changes in a sine wave shape at the period S, the transmittance changes in a sine wave shape for each grating pitch P ₁ , and a sinusoidal light intensity distribution is produced.

The air equivalent distance from the first grating 21 to the second grating 2 is Z ₁ , the air equivalent distance from the second grating 2 to the third grating 3 is Z _2, and the grating pitch at a position orthogonal to the optical axis Q is used. By doing so, the OTF in the rotary encoder can be calculated, and the theory of the three-grid method can be applied.

  Since the first grating 21 has a duty modulation pattern whose 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, so that the signal output obtained from the light receiving element 7 is as follows. However, no distortion component is generated. Further, by setting the OTF in the division period constituting the duty modulation to zero, generation of higher-order components due to the division period can be suppressed. Furthermore, 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 nonuniform due to dirt or variations in the radiation distribution, the first grating 21 is used. Since the intensity distribution on 21 is sinusoidal, the light receiving element output obtained through photoelectric conversion through the third grating 3 is an extremely accurate sine wave output in which distortion is suppressed.

Each parameter such as P ₁ , P, P ₂ , Z ₁ , Z _2, and λ at the time of design focuses on the imaging conditions corresponding to the parameter N in Equation 1, the image magnification in Equation 2, and the OTF of the fundamental spatial frequency component. All the combinations are possible.

As an example, a 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 λ = 900 nm and Z ₁ = 1.5T of the light source 4 is the same as that shown in FIG. 3 shown in the first embodiment. Therefore, the OTF is doubled at the image magnification of Z ₂ = 3T. An absolute value of 0.637 can be obtained. In this case, when the second grating 2 is rotated by 1/2000 of 360 ° with the rotation of the disk which is the second grating substrate 6, the image formed on the third grating 3 is also moved by one period. Thus, the angular displacement of the disk can be detected from the signal after photoelectric conversion.

At the position of Z ₂ = 3T, OTF exists for higher-order frequency components simultaneously with N = 1. Since the first grating 21 is a basic spatial frequency component with a sinusoidal duty modulation pattern, and N = 8, which is the division period of the duty modulation pattern, the OTF is 0.01 or less. 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.

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 the image magnification are satisfied, any image magnification may be used, and an enlargement system or a reduction system having other magnifications may be used. Alternatively, the first distance Z ₁ and the second distance Z ₂ may be made equal to make the image magnification equal.

  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 grating 21 may be moved relative to the second grating 2 and the third grating 3 as long as the movement is relative between the gratings. When moving the first grating 21, the image formed on the third grating 3 is in the opposite direction to the moving direction of the first grating 21.

Further, in the present embodiment, the duty modulation pattern is configured by dividing the grating pitch P ₁ of the first grating 21 into eight. Any number of divisions may be used as long as the duty ratio changes in a sinusoidal pattern. For example, when the number of divisions is increased, a smoother sinusoidal intensity distribution can be obtained.

  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 radially from the center of the circle on the same circumference. An optical encoder in which distortion does not occur in the signal output from the light receiving element 7 can be obtained even when the irradiation distribution is nonuniform.

Embodiment 4 FIG.
FIG. 8 shows a configuration diagram of an optical encoder according to Embodiment 4 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.

The first grating 31 is formed by patterning a thin metal film on the first grating substrate 35 transparent, has a grating pitch P _1, and making the intensity distribution of the sinusoidal receives light from the light source 4 Yes.

FIG. 9 shows an opening pattern of openings of the first grating 31 in the fourth embodiment for carrying out the present invention. The opening pattern includes a light transmitting portion 38 and a non-transmitting portion 39. The opening portion of the first grating 31 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 continuously arranged in the direction in which the duty ratio changes. It is. The length of the opening pattern whose transmittance changes sinusoidally for one period is the grating pitch P ₁ . Opening pattern shown in FIG. 9 is a grating pitch P _1, the period S where the grating pitch P ₁ divided into eight as one period, composed of a duty modulation pattern that duty ratio varies sinusoidally with the grating pitch P ₁ Has been. Since the duty ratio at a period S changes sinusoidally, the transmittance for each grating pitch P ₁ is changed sinusoidally, sinusoidal intensity distribution is produced.

Further, an air equivalent distance from the first grating 31 to the second grating 12 is a first distance Z ₁ , and an air equivalent distance from the second grating 12 to the third grating 13 is a second distance Z ₂ . At this time, it is better to set Z ₁ and Z ₂ so that the OTF in the division period S of the duty modulation pattern is as close to zero as possible.

  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 2nd grating | lattice 12 is supported so that a movement is possible along the X direction which cross | intersects a light advancing 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 on the third grating 13 is reflected. The 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 relative movement amount of the second grating 12 can be detected from the change in the signal output. 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 whose transmittance changes in a sine wave shape, the intensity distribution produced by the first grating 31 has 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. Further, by setting the OTF in the division period constituting the duty modulation to zero, generation of higher-order components due to the division period can be suppressed. Furthermore, 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 nonuniform 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 through photoelectric conversion through the third grating 13 is a highly accurate sine wave output with suppressed distortion.

Each parameter such as P ₁ , P, P ₂ , Z ₁ , Z _2, and λ at the time of design focuses on the imaging conditions corresponding to the parameter N in Equation 1, the image magnification in Equation 2, and the OTF of the fundamental spatial frequency component. All the combinations are possible.

FIG. 10 shows an example of an OTF calculation result when the image magnification is an enlargement system. In FIG. 10, the vertical axis represents the OTF normalized by the DC component, and the horizontal axis represents the second distance Z ₂ using the wavelength λ of the light source 4 and the grating pitch P of the second grating 12, and T = P ² This is normalized by / λ. Here, the case where the first distance Z ₁ = 1.5T, N = 1 is a basic spatial frequency, and the duty modulation pattern of the first grating 31 is configured by eight divisions as shown in FIG. Explained. As shown in FIG. 10, when the wavelength λ of the light source 4 is 900 nm and the grating pitch P of the second grating 12 is 30 μm, T = 1 mm. Therefore, when Z ₁ = 1.5T (= 1.5 mm) and the image magnification is double, the OTF absolute value of N = 1 is 0.637 at the position of Z ₂ = 3T (= 3 mm). It becomes.

Since the ratio of the first distance Z ₁ and the second distance Z ₂ is 2, an inverted image twice that of the first grating 31 is formed on the third grating 13 with OTF 0.637. The grating pitch P ₂ of the third grating 13 is 90 μm from the imaging condition formula at N = 1, and the grating pitch P ₁ of the first grating 31 is 45 μm from the relational expression of image magnification. With such a 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 is obtained from the signal after photoelectric conversion. Can be detected.

As shown in FIG. 10, in consideration of the case where the duty modulation pattern of the first grating 31 is configured by 8 divisions, when calculating the OTF at N = 8, the absolute value becomes 0.01 or less. At the position of Z ₂ = 3T, OTF exists for higher-order frequency components simultaneously with N = 1. For this reason, a high-order component does not substantially appear on the third grating 13. Therefore, the intensity distribution on the third grating 13 is also sinusoidal, and an extremely accurate sine wave output can be obtained.

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 the image magnification are satisfied, any image magnification may be used, and an enlargement system or a reduction system having other magnifications may be used. Alternatively, the first distance Z ₁ and the second distance Z ₂ may be made equal to make the image magnification equal.

  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, the first grating 31 is used. May be configured to move relative to the second lattice 12 and the third lattice 13, or the third lattice 13 may be moved relative to the first lattice 31 and the second lattice 12. When the first grating 31 is moved, the image formed on the third grating 13 is in the opposite direction to the moving direction of the first grating 31.

Further, in the present embodiment, the grating pitch P ₁ of the first grating 31 is divided into eight to form a duty modulation pattern, but any number of divisions may be used as long as the duty ratio changes in a sine wave shape, for example, As the number of divisions is increased, a smoother sinusoidal intensity distribution can be obtained.

  As described above, the opening portion of the first grating 31 has an opening pattern in which the duty ratio of the transmissive portion changes in a sine wave shape continuously arranged in the direction in which the duty ratio changes, so that the irradiation distribution from the light source 4 is not affected. Even when uniformity occurs, an optical encoder that does not generate distortion in the signal output from the light receiving element 17 can be obtained.

Embodiment 5. FIG.
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-grating 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 having an opening and receiving light from the light source 4, and a light having an intensity distribution formed by the first grating 11 having a reflection part. The second grating 52 for receiving light, the third grating 13 having an opening for receiving light from the second grating 52, and the light receiving element 17 for receiving light from the third grating 13 are provided. As shown in the second embodiment, the opening portion of the first grating 11 is provided with a plurality of rows 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 grating pitch of the first grating 11 is P ₁ , the grating pitch of the second grating 52 is P, and the grating pitch of the third grating 13 is P ₂ . The light source 4 is a spatially incoherent light source such as an LED, and emits spatially incoherent light having a center wavelength λ.

The third grating 13 is disposed on the same side as the first grating 11 with respect to the second grating 52. The slit direction of each of the first grating 11, the second grating 52, and the third grating 13 is set to a direction perpendicular to the paper surface, and the moving direction of the second grating 52 is set to a 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. In the present embodiment, the first distance Z ₁ and the second distance Z ₂ are defined as distances along the light traveling direction. The first grating 11, the second grating 52, and the third grating 13 are arranged so that Z ₁ and Z ₂ are equal in distance, and the image magnification is equal. It should be noted that the arrangement of the first grating 11 and the third grating 13 may be changed so that Z ₁ and Z ₂ have different distances. As long as the image forming condition and the relational expression of image magnification are satisfied, any image magnification may be used, and an enlargement system or a reduction system may be used.

FIG. 12 shows the calculation result of the OTF in this configuration. In FIG. 12, the vertical axis represents the OTF normalized with the DC component, and the horizontal axis represents the values of the first distance Z ₁ and the second distance Z ₂ . It can be seen that the maximum value or the minimum value of the OTF can be obtained at a position that is an integral multiple of 2T in the basic spatial frequency component of N = 1. For example, under the condition of Z ₁ = Z ₂ = 2T, the OTF absolute value is 0.637, and each pitch between 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, so the overall configuration is compact. Can be. In addition, 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 provided in the same phase. Thus, even when the irradiation distribution from the light source 4 is non-uniform, a highly accurate sine wave output in which distortion is suppressed in the light receiving element 17 can be obtained.

  Note that the opening of the first grating 11 has a duty modulation pattern in which the transmittance changes in a sine wave shape as shown in the fourth embodiment, that is, the opening pattern in which the duty ratio of the transmissive portion changes in a sine wave shape. It may be arranged continuously in the direction in which the ratio changes.

  As described above, the opening portion of the first grating 11 is provided with a plurality of rows of slit rows in which openings having a shape in which a sine wave is folded up and down are continuously arranged in the same phase. Even when nonuniformity occurs, it is possible to obtain an optical encoder that does not generate distortion in the signal output from the light receiving element 17. Further, since the third grating 13 is disposed 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.

Embodiment 6 FIG.
FIG. 13 shows a block diagram of an optical encoder according to the sixth 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. 13, the configuration except that the slit direction of the first grating 11, the second grating 52, and the third grating 13 is set to the vertical direction parallel to the paper surface, and the moving direction of the second grating 52 is set to the vertical direction of the paper surface. This is the same as the fifth embodiment. 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.

Even in such a configuration, the theory of the three-grid method is applied. As shown in FIG. 13, the first distance Z ₁ from the first grating 11 to the second grating 52 and the second distance Z ₂ from the second grating 52 to the third grating 13 are distances along the light traveling direction. Defined. In the present embodiment, the first distance Z ₁ and the second distance Z ₂ are defined as distances along the light traveling direction. The first grating 11, the second grating 52, and the third grating 13 are arranged so that Z ₁ and Z ₂ are equal in distance, and the image magnification is equal. It should be noted that the arrangement of the first grating 11 and the third grating 13 may be changed so that Z ₁ and Z ₂ have different distances. As long as the image forming condition and the relational expression of image magnification are satisfied, any image magnification may be used, and an enlargement system or a reduction system may be used.

  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, so the overall configuration is compact. Can be. In addition, 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 provided in the same phase. Thus, even when the irradiation distribution from the light source 4 is non-uniform, a highly accurate sine wave output in which distortion is suppressed in the light receiving element 17 can be obtained.

  Note that the opening of the first grating 11 has a duty modulation pattern in which the transmittance changes in a sine wave shape as shown in the fourth embodiment, that is, the opening pattern in which the duty ratio of the transmissive portion changes in a sine wave shape. It may be arranged continuously in the direction in which the ratio changes.

  As described above, the opening portion of the first grating 11 is provided with a plurality of rows of slit rows in which openings having a shape in which a sine wave is folded up and down are continuously arranged in the same phase. Even when nonuniformity occurs, it is possible to obtain an optical encoder that does not generate distortion in the signal output from the light receiving element 17. Further, since the third grating 13 is disposed 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.

Embodiment 7 FIG.
FIG. 14 shows a configuration diagram of an optical encoder according to Embodiment 7 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 along the light traveling direction, a first grating 1 having an opening and receiving light from the light source 4, and a reflecting portion arranged on the same circumference are provided. A second grating 42 that receives light having an intensity distribution formed by the first grating 1; a third grating 3 that has openings arranged on the same circumference and receives light from the second grating 42; A light receiving element 7 that receives light from the three gratings 3 is provided.

In the opening of the first lattice 1, the center of the opening is disposed 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 is a shape that is changed in a sine wave shape symmetrically in the outer direction and the inner direction with a concentric circle as a symmetry axis. The grating pitch of the first grating 11 is P ₁ , the grating pitch of the second grating 52 is P, and the grating pitch of the third grating 13 is P ₂ . The light source 4 is a spatially incoherent light source such as an LED, and emits spatially incoherent light having a center wavelength λ.

The third grating 3 is disposed on the same side as the first grating 1 with respect to the second grating 42. The slit direction of each of the first grating 1, the second grating 42, and the third grating 3 is set so as to be perpendicular to the paper surface, and the moving direction of the second grating 42 is set so as to be the vertical direction parallel to the paper surface. . 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. The first distance Z ₁ and the second distance Z ₂ are defined as distances along the light traveling direction. The first grating 1, the second grating 42, and the third grating 3 may be arranged so that Z ₁ and Z ₂ have the same distance. Further, as shown in FIG. 14, the arrangement of the first grating 1 and the third grating 3 may be changed so that Z ₁ and Z ₂ have different distances. As long as the image forming condition and the relational expression of image magnification are satisfied, any image magnification may be used, and an enlargement system or a reduction system may be used.

  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. Can be. Further, the shape of the opening of the first grating 1 is a shape that is changed in a sine wave shape symmetrically in the outer direction and the inner direction with the 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 portion of the first grating has the same circular shape as the duty modulation pattern in which the transmittance changes in a sine wave shape as shown in the third embodiment, that is, the opening pattern in which the duty ratio of the transmissive portion changes in a sine wave shape. It may be arranged on the circumference continuously and radially with respect to the center of the circle.

  As described above, the opening center of the opening is arranged at the intersection of the concentric circle and the equiangular pitch line segment passing through the center of the concentric circle in the opening portion of the first lattice 1, and the shape of the opening is the axis of symmetry about the concentric circle. As a result, the optical output is such that the signal output from the light receiving element 7 is not distorted even when the irradiation distribution from the light source 4 is uneven. Can be obtained. Further, since the third grating 3 is arranged 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.

Embodiment 8 FIG.
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. The second grating 42 includes a reflection type amplitude grating. 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 in the vertical direction parallel to the paper surface, and the moving direction of the second grating 42 is set in the vertical direction on 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. The first distance Z ₁ and the second distance Z ₂ are defined as distances along the light traveling direction. The first grating 1, the second grating 42, and the third grating 3 may be arranged so that Z ₁ and Z ₂ have the same distance. Further, as shown in FIG. 14, the arrangement of the first grating 1 and the third grating may be changed so that Z ₁ and Z ₂ have different distances. As long as the image forming condition and the relational expression of image magnification are satisfied, any image magnification may be used, and an enlargement system or a reduction system may be used.

  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. Can be. Further, the shape of the opening of the first grating 1 is a shape that is changed in a sine wave shape symmetrically in the outer direction and the inner direction with the 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 has the same duty modulation pattern in which the transmittance changes in a sine wave shape as shown in the third embodiment, that is, the opening pattern in which the duty ratio of the transmissive portion changes in a sine wave shape. It may be arranged on the circumference continuously and radially with respect to the center of the circle.

  As described above, the center of the opening is arranged at the intersection of the concentric circle and the equiangular pitch line segment passing through the center of the concentric circle in the opening portion of the first lattice 1, and the shape of the opening is the axis of symmetry about the concentric circle. As a result, the optical output is such that the signal output from the light receiving element 7 is not distorted even when the irradiation distribution from the light source 4 is uneven. 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.

  In all the embodiments, the first grating may be used as the second grating, instead of the amplitude grating, for example, a grating in which optical feature quantities other than amplitude such as phase are periodically formed. The upper intensity distribution can be imaged on the third grating. Also in this case, if a sinusoidal intensity distribution is produced by 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 the fundamental frequency. For example, the pitch of each grating is set according to the imaging condition and the image magnification of N = 2. It may be determined and designed as a basic spatial frequency. In this case, the second harmonic component for N = 2 is N = 4, and the third harmonic component is N = 6.

It is a block diagram of the optical encoder which shows Embodiment 1 of this invention. It is an opening pattern of the opening part of the 1st grating | lattice in Embodiment 1 of this invention. It is an example of the calculation result of OTF in Embodiment 1 of this invention. It is a block diagram of the optical encoder which shows Embodiment 2 of this invention. It is an opening pattern of the opening part of the 1st grating | lattice in Embodiment 2 of this invention. It is a block diagram of the optical encoder which shows Embodiment 3 of this invention. It is an opening pattern of the opening part of the 1st grating | lattice in Embodiment 3 of this invention. It is a block diagram of the optical encoder which shows Embodiment 4 of this invention. It is an opening pattern of the opening part of the 1st grating | lattice in Embodiment 4 of this invention. It is an example of the calculation result of OTF in Embodiment 4 of this invention. It is a block diagram of the optical encoder which shows Embodiment 5 of this invention. It is an example of the calculation result of OTF in Embodiment 5 of this invention. It is a block diagram of the optical encoder which shows Embodiment 6 of this invention. It is a block diagram of the optical encoder which shows Embodiment 7 of this invention. It is a block diagram of the optical encoder which shows Embodiment 8 of this invention.

Explanation of symbols

  1, 11, 21, 31 1st grating, 2, 12, 42, 52 2nd grating, 3, 13 3rd grating, 4 Light source, 5, 15, 25, 35 1st grating substrate, 6, 16, 46 56, second grating substrate, 7, 17 light-receiving element, 8, 18, 28, 38 transmissive part, 9, 19, 29, 39 non-transmissive part, 101a to 101e same circle, 102a to 102e line segment.

Claims (4)

A first grating having an opening and receiving light from a light source;
A second grating that receives light having an intensity distribution formed by the first grating and having openings or reflecting portions arranged on the same circumference;
A third grating having openings arranged on the same circumference and receiving light from the second grating;
A three-grating optical encoder comprising a light receiving element for receiving light from the third grating,
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 having an equiangular pitch passing through the center of the concentric circle,
The optical encoder is characterized in that the shape of the opening changes in a sine wave shape symmetrically in the outer direction and the inner direction with the concentric circle as an axis of symmetry. A first grating having an opening and receiving light from a light source;
A second grating receiving light having an opening or a reflection part and having an intensity distribution formed by the first grating;
A third grating having an opening for receiving light from the second grating;
A three-grating optical encoder comprising a light receiving element for receiving 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. A first grating having an opening and receiving light from a light source;
A second grating that receives light having an intensity distribution formed by the first grating and having openings or reflectors arranged on the same circumference;
A third grating having openings arranged on the same circumference and receiving light from the second grating;
A three-grating optical encoder comprising a light receiving element for receiving light from the third grating,
The opening of the first grating is an optical encoder in which an opening pattern in which a duty ratio of a transmission portion changes in a sine wave shape is continuously arranged radially on the same circumference with respect to the center of the circle. A first grating having an opening and receiving light from a light source;
A second grating receiving light having an opening or a reflection part and having an intensity distribution formed by the first grating;
A third grating having an opening for receiving light from the second grating;
A three-grating optical encoder comprising a light receiving element for receiving light from the third grating,
An optical encoder characterized in that the opening portion of the first grating has an opening pattern in which a duty ratio of a transmission portion changes in a sine wave shape continuously arranged in a direction in which the duty ratio changes.

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