Optical coding device and coding method

Abstract

Optical coding device (1; 1A), comprising: a light source (4) configured to emit collimated light; a scale (2) which contains a diffraction grating (S) configured to diffract light emitted from the light source (4) into a multitude of diffracted light rays; a light receiving unit (6) configured to receive diffracted signal light (10; 10A) and diffracted interference light (20; 20A) resulting from diffraction through the diffraction grating (S), wherein the diffracted signal light (10; 10A) propagates at a predetermined diffraction angle on both sides of an optical axis of the light emitted by the light source (4), and the diffracted interference light (20; 20A) propagates at a diffraction angle greater than a diffraction angle of the diffracted signal light (10; 10A) on both sides of the optical axis of the light emitted by the light source (4); and an optical element (5) which is located between the scale (2) and the light receiving unit (6), wherein the optical element (5) contains a section (8; 8A) with a periodic structure, which is periodically formed; and the periodic section (8; 8A) is a plurality of slot sections or comprises a plurality of slot sections which are substantially formed with a rectangular waveform or sinusoidal waveform in cross-section, wherein the periodic section (8; 8A) is configured to: to divide the diffracted signal light (10; 10A) into first split rays (11; 13), which propagate at a predetermined angle, and second split rays (12; 14), which propagate at a larger angle than that of the first split rays (11; 13); and to divide the diffracted interference light (20; 20A) into first split rays (21; 23), which propagate with a predetermined angle of propagation, and second split rays (22; 24), which propagate with a larger angle of propagation than that of the first split rays (21; 23), and to make the diffraction efficiency of the first split rays (21, 23) of the diffracted interference light (20; 20A) lower than the diffraction efficiency of the first split rays (11, 13) of the diffracted signal light (10; 10A); wherein the section (8; 8A) with periodic structure is periodically formed on a surface of the optical element (5; 5A) which faces the scale (2) or the light receiving unit (6); wherein the optical element (5) comprises the section (8; 8A) with periodic structure, which is formed on a surface of the optical element (5) facing the scale (2), and a smooth surface (9) which faces the light receiving unit (6) and is parallel to a direction in which the diffraction grating (S) is arranged; and wherein the smooth surface (9) is configured to completely reflect the second split rays (12,14; 22, 24).

Description

field of technology

[0001] This invention relates to an optical coding device and a method for coding an optical signal. Technical background

[0002] An optical coding device of the relevant technology is known. The optical coding device comprises a scale equipped with a diffraction grating arranged along a measuring direction, and a head containing a light receiver that receives light emitted by a light source through the diffraction grating. The head is configured to move relative to the scale along its measuring direction and to detect the magnitude of the relative movement with the scale.

[0003] US 2016 / 0 216 101 A1 describes a distance measuring device that uses doubly diffracted light of a single diffraction order for measurement. DE 10 2005 029 917 A1 describes a position measuring device for detecting the relative position of a scanning unit and a physical element movable in at least one measuring device for this purpose. WO 2014 / 096 764 A1 describes an optical element for generating diffraction orders for a coding device, wherein the optical element comprises an arrangement of diffraction features arranged such that the distance between the centers of adjacent diffraction features varies irregularly from one pair of adjacent features to the next.JP 2006 - 259 439 A describes a demultiplex element comprising a diffraction grating surface with a diffraction grating on which uneven structures extending in one direction are periodically formed, as well as a transmitted light projection surface and a demultiplexed light projection surface, wherein the demultiplex element is characterized in that the light incident on the diffraction grating surface is transmitted in a straight line and projected from the transmitted light projection surface, and a portion of the incident light is diffracted, completely reflected from the transmitted light projection surface in a transparent base body, and directed to the demultiplexed light projection surface to be projected from the demultiplexed light projection surface as demultiplexed light.DE 693 21 329 T2 describes a device for displacement detection comprising a light source (1), a first diffraction grating (G1) arranged on the same substrate as a second diffraction grating (G2) to diffract and split light emitted by the light source and to shine diffracted light rays of ±1st order onto the second diffraction grating (G2), a third diffraction grating (G3) for synthesizing a reflectively diffracted light ray of +1st order, which is produced by reflective diffraction of the diffracted light ray of +1st order through the second diffraction grating, and a reflectively diffracted light ray of -1st order, which is produced by reflective diffraction of the diffracted light ray of +1st order through the second diffraction grating. order is generated by the second diffraction grating to form interference light, and a light receiving element (3) to convert the interference light into a signal representing a displacement of the substrate.

[0004] In this optical coding device, the diffraction grating converts the light emitted by the light source into a multitude of beams of diffracted light. These many beams of diffracted light create an interference pattern with the same period as that of the diffraction grating, and the light receiver detects a signal from this interference pattern. The optical coding device calculates the magnitude of the relative motion between the scale and the head from the detection result (signal) from the light receiver.

[0005] The many rays of diffracted light contain diffracted light that travels in the same direction as the optical axis of the light emitted by the light source, diffracted light that travels with predetermined diffraction angles on both sides of the optical axis, and diffracted light that travels with diffraction angles greater than the predetermined diffraction angles on both sides of the optical axis.

[0006] Assuming that diffracted light traveling in the same direction as the optical axis is zero-order diffracted light, the multitude of diffracted light rays can be ordered as first-order diffracted light and second-order diffracted light, which travels from the zero-order diffracted light in the direction in which the diffraction angle increases.

[0007] The light receiving unit primarily detects a signal from an interference pattern generated from diffracted light of ± first order. Consequently, diffracted light of ± first order becomes diffracted signal light, and diffracted light of a higher order than diffracted light of ± first order becomes diffracted interference light.

[0008] When the optical receiver is illuminated with diffracted signal light and diffracted interference light, the interference pattern produced by the diffracted signal light is distorted by the diffracted interference light, and noise appears in the signal detected by the optical receiver. Therefore, the accuracy of the magnitude of relative motion calculated from the signal by the optical receiver decreases, and the optical coding device becomes less reliable.

[0009] In response, the interference position measuring device (optical coding device) disclosed in JP 2619566 B includes a main scale (a scale) arranged along a transmission diffraction grating (a diffraction grating), a light source illuminating the main scale with light, and a photodetector (a light receiving unit) outputting a signal from an interference pattern produced by a plurality of beams of diffracted light passing through the transmission diffraction grating.

[0010] The interference position measuring device is configured such that the main scale is positioned between the light source and the photodetector. Furthermore, the interference position measuring device includes a diffraction grating beam splitter and an optical block between the light source and the main scale. This block illuminates the main scale with only the diffracted light of ± first order from the multitude of beams of diffracted light passing from the light source through the diffraction grating beam splitter.

[0011] The optical block contains an integrated prism that reflects the diffracted ± first-order light towards the principal scale, but deflects the diffracted light adjacent to the diffracted ± first-order light in a direction where the principal scale is not illuminated, and a zero-order diffracted light shielding device that physically shields zero-order diffracted light (i.e., a diffracted light shielding device that shields diffracted light except for diffracted ± first-order light). The integrated prism is configured as a rectangular parallelepiped with a longitudinal direction parallel to the optical axis of the light emitted to the diffraction grating beam splitter. The zero-order diffracted light shielding device is provided within the integrated prism and is located substantially in the central part of the integrated prism.

[0012] The interference position measuring device contains the optical block and thus removes diffracted interference light using the zero-order diffracted light shielding device, so that the main scale is illuminated only with the diffracted light ± first order (the diffracted signal light). Summary of the invention; Technical task

[0013] In this optical coding device, providing the integrated prism and the device for shielding diffracted light, which shields diffracted light in addition to the diffracted light of ± first order, requires providing space for reflecting and deflecting the multitude of rays of diffracted light between the light source and the scale. Therefore, a problem arises in that the structure of the optical coding device becomes large.

[0014] One object of the invention is to provide an optical coding device which can prevent a situation in which the light receiving unit is irradiated with diffracted interference light, while preventing an increase in the size of the optical coding device. Solution to the problem

[0015] This problem is solved according to the invention by the features of the independent claims. Specific embodiments are the subject of the dependent claims.

[0016] According to one aspect of the invention, an optical coding device is provided, comprising: a light source configured to emit collimated light; a scale containing a diffraction grating configured to diffract light emitted by the light source into a plurality of diffracted light beams; a light receiving unit configured to receive diffracted signal light and diffracted interference light resulting from diffraction through the diffraction grating, wherein the diffracted signal light travels at a predetermined diffraction angle on both sides of an optical axis of the light emitted by the light source, and the diffracted interference light travels at a diffraction angle greater than a diffraction angle of the diffracted signal light on both sides of the optical axis of the light emitted by the light source;and an optical element located between the scale and the light receiving unit, wherein the optical element includes a periodic section of structure which is periodically formed on a surface of the optical element facing the scale or the light receiving unit; and the periodic section of structure is configured to split the diffracted signal light and the diffracted interference light into first split rays which propagate at a predetermined angle of propagation, and second split rays which propagate at an angle of propagation greater than the angle of propagation of the first split rays, and to make the diffraction efficiency of the first split rays of the diffracted interference light lower than the diffraction efficiency of the first split rays of the diffracted signal light.

[0017] According to a special embodiment, the section with periodic structure is periodically formed on a surface of the optical element which faces the scale or the light receiving unit.

[0018] An optical coding device according to one embodiment of the invention comprises: a light source configured to emit collimated light; a scale comprising a diffraction grating configured to diffract light emitted by the light source into a plurality of diffracted light beams; a light receiving unit configured to receive diffracted signal light and diffracted interference light resulting from diffraction through the diffraction grating, wherein the diffracted signal light has a predetermined diffraction angle on both sides of an optical axis of the light emitted by the light source, and the diffracted interference light has a diffraction angle greater than a diffraction angle of the diffracted signal light on both sides of the optical axis of the light emitted by the light source; and an optical element located between the scale and the light receiving unit.The optical element contains a section with a periodic structure, which is periodically formed on a surface of the optical element facing the scale or the light receiving unit. The section with a periodic structure splits the diffracted signal light and the diffracted interference light into first split rays, which propagate at a predetermined angle of spread, and second split rays, which propagate at an angle of spread greater than the angle of spread of the first split rays, and makes the diffraction efficiency of the first split rays of the diffracted interference light lower than the diffraction efficiency of the second split rays of the diffracted signal light.

[0019] The multitude of diffracted light rays that travel from the diffraction grating of the scale to the optical element can be classified as diffracted light ± first order and diffracted light ± second order in the direction in which the diffraction angle increases, starting from the optical axis of the light emitted from the light source to the scale.

[0020] Accordingly, of the multitude of diffracted light rays, diffracted light ± first order corresponds to the diffracted signal light, and diffracted light ± second and higher order corresponds to the diffracted interference light.

[0021] The "diffraction angles" are, in particular, angles originating from the optical axis of the light source, at which the diffracted signal light and the diffracted interference light, which have been diffracted by the diffraction grating of the scale, travel to the optical element. The "propagation angles" are angles originating from the optical axis of the light source, at which the first and second split rays of the diffracted signal light and the diffracted interference light, which have been split by the section with periodic structure of the optical element, travel within the optical element.

[0022] The “diffraction efficiency” is, in particular, a ratio between the diffracted signal light and the diffracted interference light falling on the optical element, and the first split rays and the second split rays of the diffracted signal light and the diffracted interference light passing inside the optical element.

[0023] Accordingly, with regard to the first and second split rays of the diffracted signal light and the first and second split rays of the optical interference light that have been split by the section with periodic structure, the optical element makes the diffraction efficiency of the first split rays of the diffracted interference light lower than the diffraction efficiency of the first split rays of the diffracted signal light. Consequently, the diffracted interference light irradiated by the light receiving unit can be suppressed, and the signal-to-noise ratio can be improved compared to a case where the section with periodic structure is not used.

[0024] Furthermore, the optical element can suppress the diffracted interference light illuminating the light-receiving unit by utilizing the periodic structure section formed in the surface of the optical element facing the scale or light-receiving unit. Thus, it is not necessary to provide a space between the scale and the light-receiving unit for reflecting and deflecting the multitude of diffracted light rays and for shielding them.

[0025] Consequently, the optical element can prevent an increase in the size of the optical coding device and can prevent a situation in which the light receiving unit is irradiated with the diffracted interference light.

[0026] It is preferable that the optical element includes a section with a periodic structure, which is formed on a surface of the optical element facing the scale, and a smooth surface, which faces the light-receiving unit and is parallel to the direction in which the diffraction grating is arranged. Furthermore, the smooth surface, in particular, perfectly reflects the second split rays.

[0027] Accordingly, the optical element includes, in particular, the section with a periodic structure, which is formed in a surface of the optical element facing the scale, and the smooth surface, which faces the light-receiving unit and is parallel to the direction in which the diffraction grating is arranged. Thus, the second split rays of the diffracted signal light and the diffracted interference light, which are generated by the section with a periodic structure, can be completely reflected, preventing a situation in which the light-receiving unit is illuminated by the second split rays.

[0028] Consequently, the optical element can also prevent a situation in which the light receiving unit is irradiated with the diffracted interference light.

[0029] It is preferable that the section with periodic structure is a plurality of slot sections or comprises a plurality of slot sections which are essentially formed with a square waveform in cross-section.

[0030] According to this configuration, the periodic section comprises a multitude of groove sections, essentially formed with a square waveform in cross-section. Consequently, the diffracted light rays illuminating the optical element can be diffracted with a higher diffraction efficiency than in a case where the periodic section has a different shape. The optical coding device can thus maintain a stable diffracted signal light.

[0031] Furthermore, it is preferable that the section with periodic structure is or comprises a multitude of slot sections which are essentially formed with a sinusoidal waveform in cross-section.

[0032] According to this configuration, the section with a periodic structure comprises a multitude of groove sections, which are essentially formed with a sinusoidal waveform in cross-section. Thus, the multitude of diffracted light rays illuminating the optical element can be diffracted with a higher diffraction efficiency than in a case where the section with a periodic structure has a different shape. The optical coding device can therefore maintain a stable diffracted signal light.

[0033] According to a further aspect of the invention, a method for encoding an optical signal is provided, comprising: emitting collimated light using a light source; diffracting the light into a plurality of diffracted light rays using a scale containing a diffraction grating; receiving diffracted signal light and diffracted interference light resulting from diffraction through the diffraction grating, wherein the diffracted signal light travels at a predetermined diffraction angle on both sides of an optical axis of the light emitted by the light source, and the diffracted interference light travels at a diffraction angle greater than a diffraction angle of the diffracted signal light on both sides of the optical axis of the light emitted by the light source.and arranging an optical element between the scale and the light receiving unit, wherein the optical element contains a section with a periodic structure, which is periodically designed, thereby splitting the diffracted signal light and the diffracted interference light into first split rays, which propagate with a predetermined angle of propagation, and second split rays, which propagate with an angle of propagation which is greater than the angle of propagation of the first split rays, and thereby making a diffraction efficiency of the first split rays of the diffracted interference light lower than a diffraction efficiency of the first split rays of the diffracted signal light.

[0034] According to a special embodiment, the section with periodic structure is periodically formed on a surface of the optical element and arranged so that it faces the scale or the light receiving unit.

[0035] In particular, the optical element is designed to include the section with periodic structure, which is formed on a surface of the optical element which faces the scale, and a smooth surface which faces the light receiving unit and is parallel to a direction in which the diffraction grating is arranged.

[0036] Furthermore, the coding also includes the complete reflection of the second split rays by the smooth surface. Brief description of the drawings

[0037] These and other tasks, features, and advantages of this invention will become clearer upon reading the following detailed description of preferred embodiments and the accompanying drawings. It should be noted that although embodiments are described separately, individual features of them can be combined to form further embodiments. Fig. Figure 1 is a perspective view of an optical coding device according to a first embodiment. Fig. Figure 2 is a diagram showing diffracted signal light and diffracted interference light in the optical coding device. Fig. Figure 3 is a diagram that shows the first split rays of the diffracted signal light in the optical coding device. Fig. Figure 4 is a diagram showing the first split rays of the diffracted interference light in the optical coding device. Fig. Figure 5 is a diagram showing the second split rays of the diffracted signal light in the optical coding device. Fig. Figure 6 is a diagram showing the second split rays of the diffracted interference light in the optical coding device. Fig. Figure 7 is a diagram illustrating an optical coding device according to a second embodiment. Description of embodiments: First embodiment

[0038] A first specific embodiment of the invention is described below with reference to the drawings.

[0039] Fig. Figure 1 is a perspective view of an optical coding device according to the first embodiment.

[0040] As in Fig. Figure 1 shows an optical coding device, in particular a linear encoder or linear encoder, which includes an elongated scale 2 containing a diffraction grating S along a measuring direction, and a head 3 which moves along the scale 2 and obtains position information from an amount of the relative movement with respect to the scale 2.

[0041] In the following descriptions and drawings, the longitudinal direction of scale 2 (the measuring direction) can indicate the X direction, the transverse direction can indicate the Y direction, and the vertical direction can indicate the Z direction.

[0042] The head 3 contains a light source 4, which emits collimated light, an optical element 5, which allows the passage of a multitude of diffracted light rays from the diffraction grating S of the scale, and a light receiving unit 6, which detects an interference pattern generated by the scale 2 and the optical element 5 and outputs a signal. The head 3, which contains these elements, is arranged such that it is able to extend and retract in the X-direction as a single unit relative to the scale 2.

[0043] Scale 2 is formed from, or comprises, a transparent element, such as glass, which transmits light from the light source 4. The diffraction grating S, which is arranged, for example, with a period of 2 µm along the X-direction, is provided on a surface of scale 2. The diffraction grating S diffractes the light emitted by the light source 4 into a multitude of diffracted light rays.

[0044] Light source 4 emits collimated light perpendicular to one surface of scale 2 (in the -Z direction). The wavelength of the light emitted by light source 4 is, for example, 700 nm. A light-emitting diode (LED) is used as light source 4. However, light source 4 is not limited to an LED, and any desired light source can be used.

[0045] The optical element 5 is made of a transparent material, such as glass, which transmits the multitude of diffracted light rays from the diffraction grating S of the scale 2. The optical element 5 is specifically designed to have a thickness (in the Z direction) of 1 mm. The optical element 5 is arranged between the scale 2 and the light receiving unit 6. The optical element 5 is positioned at a distance of 1 mm from the scale 2 and from the light receiving unit 6. The light receiving unit 6 contains a light-receiving part 7, which receives the multitude of diffracted light rays passing through the scale 2 and the optical element 5, and detects a signal from an interference pattern generated by the diffracted light.

[0046] The light-receiving part 7 is configured to have a width of, in particular, 2 mm in the measuring direction (X-direction). For the light-receiving part 7, a photodiode array (a PDA) is used, which is arranged essentially on the side facing the optical element 5 in the -Z direction such that it overlaps, at least partially, with the optical element 5. In other words, the scale 2 and the light-receiving part 7 are arranged essentially such that they face each other and overlap, at least partially, with the optical element 5 positioned between them.

[0047] A PDA is a detector capable of measuring a multitude of interference patterns simultaneously. However, the light-receiving part (7) is not limited to a PDA, and any suitable detector can be used, such as a position-sensitive detector (PSD) or a CCD sensor.

[0048] Fig. Figure 2 is a diagram showing diffracted signal light and diffracted interference light in the optical coding device.

[0049] As in Fig. As shown in Figure 2, the optical element 5 contains several groove sections 8, which represent a section with a periodic structure formed in the surface of the optical element 5 which is substantially facing the scale 2, and a smooth surface 9 which is substantially facing the light receiving unit 6 and is parallel to the direction in which the diffraction grating S is arranged (the X-direction).

[0050] The multiple slot sections 8 are configured such that they have a rectangular waveform in cross-section. In particular, the many slot sections 8 are configured such that they have a width of 160 nm, a depth of 480 nm and / or a period of 400 nm.

[0051] The many diffracted light rays are diffracted by the diffraction grating S of the scale to diffracted signal light 10, which travels with a predetermined diffraction angle on both sides of an optical axis L of the light emitted by the light source 4, and diffracted disturbance light 20, which travels with a diffraction angle greater than that of the diffracted signal light 10 on both sides of the optical axis L of the light emitted by the light source 4.

[0052] Here, the “diffraction angles” are angles, based on the optical axis L of the light from the light source 4, at which the diffracted signal light 10 and the diffracted disturbance light 20 pass through the diffraction grating S of scale 2 towards the optical element 5.

[0053] The multiple groove sections 8 divide the diffracted signal light 10 into first split beams 11, which propagate at a predetermined angle (solid line arrows), and second split beams 12, which propagate at a larger angle than the first split beams 11 (dashed line arrows). Furthermore, the multiple groove sections 8 divide the diffracted interference light 20 into first split beams 21, which propagate at a predetermined angle (dashed line arrows), and second split beams 22, which propagate at a larger angle than the first split beams 21 (solid line arrows).

[0054] Here, the "propagation angles" are angles based on the optical axis L of the light from the light source 4, with which the first split rays 11 and 21 and the second split rays 12 and 22 of the diffracted signal light 10 and the diffracted disturbance light 20, which have been split by the several groove sections 8 of the optical element 5, travel within the optical element 5.

[0055] The arrows with solid lines and the arrows with dashed lines, which are in Fig. Figure 2 indicates the directions in which the first split rays 11 and 21 and the second split rays 12 and 22 of the diffracted signal light 10 and the diffracted interference light 20 propagate, as well as their respective diffraction efficiencies. The "diffraction efficiency" is a ratio between the diffracted signal light 10 and the diffracted interference light 20 incident on the optical element 5, and the first split rays 11 and 21 and the second split rays 12 and 22 of the diffracted signal light 10 and the diffracted interference light 20.

[0056] The arrows with solid lines indicate a higher diffraction efficiency than the arrows with dashed lines, while the arrows with dashed lines indicate a lower diffraction efficiency than the arrows with solid lines.

[0057] The smooth surface 9 is formed on the surface which faces the light receiving unit 6 and reflects the second split rays 12 and 22 essentially completely.

[0058] With the configuration of the optical coding device 1 as described above, the following results are obtained when the diffraction efficiencies of the first split beams 11 and the second split beams 12 of the diffracted signal light 10 and the first split beams 21 and the second split beams 22 of the diffracted disturbance light 20 are calculated by the RCWA (Rigorous Coupled Wave Analysis) method.

[0059] The diffracted signal light 10 travels at a diffraction angle of 20.48 degrees from the scale 2 to the optical element 5. The diffracted signal light 10, which is diffracted by the several groove sections 8, is split into the first split rays 11 and the second split rays 12.

[0060] The diffraction efficiency of the first split rays 11 of the diffracted signal light 10 is 94.0%, and the diffraction efficiency of the second split rays 12 of the diffracted signal light 10 is 5.0%. The second split rays 12 of the diffracted signal light 10 propagate within the optical element 5 at a propagation angle of 69.0 degrees.

[0061] Here, the diffracted light, which travels within the optical element 5 (made of glass) at a propagation angle greater than or equal to 41.8 degrees, is reflected by the smooth surface 9, which is the interface between the glass (the optical element 5) and the air, and is therefore not emitted to the light-receiving element 6. In other words, diffracted light traveling within the optical element 5 at a propagation angle greater than or equal to 41.8 degrees is completely reflected by the smooth surface 9.

[0062] The second split rays 12 of the diffracted signal light 10 propagate at an angle of 69.0 degrees within the optical element 5 and are therefore completely reflected by the smooth surface 9.

[0063] The diffracted interference light 20 travels at a diffraction angle of 44.43 degrees from the scale 2 to the optical element 5. The diffracted interference light 20, which is diffracted by the several groove sections 8, is split into the first split rays 21 and the second split rays 22.

[0064] The diffraction efficiency of the first split rays 21 of the diffracted interference light 20 is 14.7%, and the diffraction efficiency of the second split rays 22 of the diffracted interference light 20 is 85.1%. The second split rays 22 of the diffracted interference light 20 propagate at an angle of 44.4 degrees within the optical element 5. Diffracted light, which propagates at an angle of propagation greater than or equal to 41.8 degrees within the optical element 5, is completely reflected by the smooth surface 9, and thus the second split rays 22 of the diffracted interference light 20 are completely reflected by the smooth surface 9.

[0065] As a result, the optical element 5 can reduce the influence of the diffracted interference light 20, with which the light receiving element 6 is irradiated, to 15.6%.

[0066] By using the optical element 5 in which the multiple groove sections 8 are formed, the optical coding device 1 can therefore improve the signal-to-noise ratio compared to a case in which the optical element 5 is not used.

[0067] The Fig. Figures 3 to 6 are diagrams that depict the diffracted signal light and the diffracted interference light in the optical coding device. Fig. Figure 3 is a diagram that represents the first split rays 11 of the diffracted signal light 10, Fig. Figure 4 is a diagram showing the first split rays 21 of the diffracted disturbance light 20, Fig. Figure 5 is a diagram that represents the second split rays 12 of the diffracted signal light 10, and Fig. Figure 6 is a diagram showing the second split rays 22 of the diffracted disturbance light 20.

[0068] The light paths of the diffracted signal light 10 and the diffracted interference light 20, which arise due to the optical element 5, are described.

[0069] As in Fig. As shown in Figure 3, the light-receiving part 7 is illuminated by the first split rays of the diffracted signal light 10 through the several groove sections 8 of the optical element 5. As shown in Figure 3, the light-receiving part 7 is illuminated by the diffracted signal light 10 through the several groove sections 8 of the optical element 5. Fig. As shown in Figure 4, although the first split rays 21 of the diffracted interference light 20 reach the light receiving unit 6, the light-receiving part 7 is almost entirely unilluminated by these first split rays 21 of the diffracted interference light 20. The diffraction efficiency of the first split rays 21 of the diffracted interference light 20 has a greater rate of decay than the diffraction efficiency of the first split rays 11 of the diffracted signal light 10. Thus, the optical element 5 can reduce the influence of the first split rays 21 of the diffracted interference light 20, with which the light receiving element 6 is irradiated, by using the multiple groove sections 8.

[0070] As in Fig. As shown in Figure 5, the second split rays 12 of the diffracted signal light 10 are deflected by the multiple groove sections 8 of the optical element 5 at a larger angle than that of the first split rays 11 of the diffracted signal light 10, and the propagation angles of the second split rays 12 of the diffracted signal light 10 are greater than or equal to 41.8 degrees. As a result, the second split rays 12 of the diffracted signal light 10 are completely reflected by the smooth surface 9. As shown in Fig. As shown in Figure 6, the second split rays 22 of the diffracted interference light 20 are also deflected by the multiple groove sections 8 of the optical element 5 at a larger angle than that of the first split rays 21 of the diffracted interference light 20, and the propagation angles of the second split rays 22 of the diffracted interference light 20 are greater than or equal to 41.8 degrees. As a result, the second split rays 22 of the diffracted interference light 20 are thus completely reflected by the smooth surface 9. The second split rays 22 of the diffracted interference light, which have a higher diffraction efficiency than that of the first split rays 21 of the diffracted interference light 20, are completely reflected by the smooth surface 9, and thus the smooth surface 9 of the optical element 5 can suppress the diffracted interference light 20 with which the light-receiving element 6 is irradiated.

[0071] According to this embodiment, the following effects in particular can be achieved.

[0072] (1) With respect to the first split rays 11 and the second split rays 12 of the diffracted signal light 10 and the first split rays 21 and the second split rays 22 of the diffracted interference light 20, which are split by the multiple slot sections 8, which constitute a section with a periodic structure, the optical element 5 makes the diffraction efficiency of the first split rays 21 of the diffracted interference light 20 lower than the diffraction efficiency of the first split rays 11 of the diffracted signal light 10. Consequently, the diffracted interference light 20, with which the light receiving unit 6 is irradiated, can be suppressed and / or the signal-to-noise ratio can be improved compared to a case in which the multiple slot sections 8, which constitute a section with a periodic structure, are not used.

[0073] (2) The optical element 5 can suppress the diffracted interference light 20, with which the light receiving unit 6 is illuminated, by using the multiple groove sections 8, which form a section with a periodic structure in the one surface of the optical element 5 that faces the scale 2. Thus, it is not necessary to provide a space between the scale 2 and the light receiving unit 6 for reflecting and deflecting the diffracted light and for shielding the diffracted light.

[0074] Consequently, the optical element 5 can avoid an enlargement of the optical coding device 1 and can suppress a situation in which the light receiving unit 6 is irradiated with the diffracted interference light 20.

[0075] (3) The optical element 5 contains the multiple groove sections 8, which form a section with a periodic structure, in one surface of the optical element 5 facing the scale 2, and the smooth surface 9, which faces substantially towards the light receiving unit 6 and is parallel to the direction in which the diffraction grating S is arranged (the X-direction). Thus, the second split rays 12 and 22 of the diffracted signal light 10 and the diffracted disturbance light 20, which have been generated by the multiple groove sections 8, can be completely reflected, making it possible to suppress a situation in which the light receiving unit 6 is illuminated by the second split rays 12 and 22.

[0076] Consequently, the optical element 5 can also suppress a situation in which the light receiving unit 6 is irradiated with the diffracted interference light 20.

[0077] (4) The multiple slot sections 8, which constitute a section with a periodic structure, are in particular designed with a cross-sectional area essentially of a rectangular waveform, and thus the multitude of light rays with which the optical element 5 is illuminated can be diffracted with a higher diffraction efficiency than if the multiple slot sections 8 were designed with a different shape. The optical coding device 1 can thus obtain the diffracted signal light in a stable manner.

[0078] Accordingly, an optical coding device is described which can suppress a situation in which a light receiving unit is irradiated with diffracted interference light, while preventing an increase in the size of the optical coding device. In particular, an optical coding device 1 comprises a scale 2 containing a diffraction grating S, a light receiving unit 6 configured to receive light from a light source 4, and an optical element 5 arranged between the scale 2 and the light receiving unit 6. The optical element 5 includes several groove sections 8, which form a section with a periodic structure in a surface of the optical element 5.The multiple groove sections 8 are configured to split diffracted signal light 10 and diffracted interference light 20 into first split rays 11, 21, which propagate with a predetermined angle of propagation, and second split rays 12, 22, which propagate with an angle of propagation greater than the angle of propagation of the first split rays 11, 21, and to make the diffraction efficiency of the first split rays 21 of the diffracted interference light 20 lower than the diffraction efficiency of the first split rays 12 of the diffracted signal light 10. Second embodiment

[0079] A second specific embodiment of the invention is described below with reference to the drawings. It should be noted that in the following description, parts that have already been described are designated with the same reference numerals, and their descriptions are omitted.

[0080] The head 3 of the optical coding device 1 according to the first special embodiment contains the optical element 5. As in Fig. However, as shown in Figure 7, a head 3A of an optical coding device 1A according to this embodiment differs from the head 3 according to the first embodiment in that the head 3A contains an optical element 5A.

[0081] Furthermore, the optical element 5 according to the first embodiment includes the several groove sections 8, which represent a section with a periodic structure, in particular having a substantially rectangular waveform in cross-section. However, the optical element 5A according to this embodiment differs from the optical element 5 according to the first embodiment in that the optical element 5A contains several groove sections 8A, which represent a section with a periodic structure, in particular having a sinusoidal waveform in cross-section.

[0082] The multiple slot sections 8A are specifically designed with a sinusoidal waveform in cross-section. In particular, the slot sections 8A have a depth of 640 nm and / or a period of 400 nm.

[0083] With the configuration of the optical coding device 1A according to this embodiment, the following effects are achieved when the diffraction efficiencies of the first split beams 13 (arrows with solid line) and the second split beams 14 (arrows with dashed line) of the diffracted signal light 10A and the first split beams 23 (arrows with dashed line) and the second split beams 24 (arrows with solid line) of the diffracted interference light 20A are calculated by the RCWA method (Rigorous Coupled Wave Analysis).

[0084] The diffracted signal light 10A travels at a diffraction angle of 20.48 degrees from the scale 2 to the optical element 5A. The diffracted signal light 10A, which has been diffracted by the several groove sections 8A, is split into the first split rays 13 and the second split rays 14.

[0085] The diffraction efficiency of the first split rays 13 of the diffracted signal light 10A is 96.3%, and the diffraction efficiency of the second split rays 14 of the diffracted signal light 10A is 3.2%. The second split rays 14 of the diffracted signal light 10A propagate within the optical element 5A at a propagation angle of 69.0 degrees. Diffracted light propagating within the optical element 5A at a propagation angle greater than or equal to 41.8 degrees is completely reflected by the smooth surface 9, and thus the second split rays 14 of the diffracted signal light 10A are completely reflected by the smooth surface 9.

[0086] The diffracted interference light 20A travels at a diffraction angle of 44.43 degrees from the scale 2 to the optical element 5A. The diffracted interference light 20A, which is diffracted by the several slot sections 8A, is split into the first split rays 23 and the second split rays 24.

[0087] The diffraction efficiency of the first split rays 23 of the diffracted interference light 20A is 38.5%, and the diffraction efficiency of the second split rays 24 of the diffracted interference light 20A is 61.0%. The second split rays 24 of the diffracted interference light 20A propagate at an angle of 44.4 degrees within the optical element 5A. Diffracted light propagating at an angle of 41.8 degrees or greater than or equal to 41.8 degrees within the optical element 5A is completely reflected by the smooth surface 9, and thus the second split rays 24 of the diffracted interference light 20A are completely reflected by the smooth surface 9.

[0088] As a result, the optical element 5A can reduce the influence of the diffracted interference light 20A, with which the light receiving element 6 is irradiated, to 40.0%.

[0089] By using the optical element 5A, in which the multiple slot sections 8A are formed, the optical coding device 1A can therefore improve the signal-to-noise ratio compared to a case in which the optical element 5A is not used.

[0090] According to this embodiment, in addition to the same effects as described in (1) to (3) in the first embodiment, the following effects can be achieved.

[0091] (4) The multiple slot sections 8A, which represent a section with a periodic structure, are designed with a sinusoidal waveform in cross-section, and thus the multitude of diffracted light rays with which the optical element 5A is illuminated can be diffracted with a higher diffraction efficiency than in a case where the multiple slot sections 8A are designed with a different shape. The optical coding device 1A can thus obtain the diffracted signal light stably. Variations in the design

[0092] It should be noted that the invention is not limited to the foregoing embodiments; variations, improvements and the like, which are within the scope to which the object of this invention can be fulfilled, are likewise included in the invention.

[0093] For example, although the foregoing embodiments describe the application of the invention in the optical coding device 1 or 1A, which is a linear encoder, the coding device can instead be a rotary encoder; the shape of the detector, the detection method and the like are not subject to any special restrictions as long as the coding device is an optical coding device.

[0094] Although the optical element 5 or 5A is made of glass in the preceding embodiments, it can be made of a transparent material other than glass and can be of any desired thickness. Furthermore, while the groove width, groove depth, and period for the multiple groove sections 8 or 8A, which represent sections with a periodic structure, are defined, these dimensions can be set to any numerical values. Additionally, while the multiple groove sections 8 or 8A are primarily formed with a rectangular waveform or a sinusoidal waveform in cross-section, respectively, they can be formed with a different shape. Finally, the multiple groove sections 8 or 8A can be formed in the single surface facing the light-receiving unit 6.

[0095] In other words, it is sufficient for the optical element to contain a section with a periodic structure, which is periodically formed in a surface facing the scale or the light receiving unit, as long as the section with a periodic structure essentially divides the diffracted signal light and the diffracted interference light into first split rays, which propagate at a predetermined angle of propagation, and second split rays, which propagate at an angle of propagation greater than the angle of propagation of the first split rays, and makes the diffraction efficiency of the first split rays of the diffracted interference light lower than the diffraction efficiency of the first split rays of the diffracted signal light.

[0096] Although in the above embodiments the optical element 5 or 5A contains in particular the smooth surface 9 on the one surface which faces the light receiving unit 6 (the light receiving part 7), the smooth surface 9 can be formed on the one surface which faces the scale 2.

[0097] Furthermore, although in the foregoing embodiments the light-receiving part 7 is fixed at a width of 2 mm along the X-direction, the light-receiving part 7 can have any desired width. Moreover, although the scale 2 and the light-receiving unit 6 are each arranged at a position 1 mm away from the optical element 5 or 5A, the scale 2 and the light-receiving unit 6 can be arranged at any desired distance from the optical element 5 or 5A, respectively.

[0098] It should be noted that any dimensions or spatial relationships disclosed above are purely exemplary and other dimensions are possible, and in particular, exact agreement with the disclosed values ​​is not considered necessary. Industrial applicability

[0099] As described above, the invention can be advantageously applied to an optical coding device which can suppress a situation in which a light receiving unit is irradiated with diffracted interference light, while preventing an increase in the size of the optical coding device. Reference symbol list 1, 1A optical coding device 2 scale 4 light sources 5.5A optical element 6 Light receiving unit 8, 8A multiple slot sections (section with periodic structure) 9 smooth surface 10, 10A diffracted signal light 11, 13 first split rays 12, 14 second split rays 20, 20A diffracted interference light 21, 23 first split rays 22, 24 second split rays S diffraction grating

Claims

[1] Optical coding device (1; 1A), comprising: a light source (4) configured to emit collimated light; a scale (2) which contains a diffraction grating (S) configured to diffract light emitted from the light source (4) into a multitude of diffracted light rays; a light receiving unit (6) configured to receive diffracted signal light (10; 10A) and diffracted interference light (20; 20A) resulting from diffraction through the diffraction grating (S), wherein the diffracted signal light (10; 10A) propagates at a predetermined diffraction angle on both sides of an optical axis of the light emitted by the light source (4), and the diffracted interference light (20; 20A) propagates at a diffraction angle greater than a diffraction angle of the diffracted signal light (10; 10A) on both sides of the optical axis of the light emitted by the light source (4); and an optical element (5) which is located between the scale (2) and the light receiving unit (6), wherein the optical element (5) contains a section (8; 8A) with a periodic structure, which is periodically formed; and the periodic section (8; 8A) is a plurality of slot sections or comprises a plurality of slot sections which are substantially formed with a rectangular waveform or sinusoidal waveform in cross-section, wherein the periodic section (8; 8A) is configured to: to divide the diffracted signal light (10; 10A) into first split rays (11; 13), which propagate at a predetermined angle, and second split rays (12; 14), which propagate at a larger angle than that of the first split rays (11; 13); and to divide the diffracted interference light (20; 20A) into first split rays (21; 23), which propagate with a predetermined angle of propagation, and second split rays (22; 24), which propagate with a larger angle of propagation than that of the first split rays (21; 23), and to make the diffraction efficiency of the first split rays (21, 23) of the diffracted interference light (20; 20A) lower than the diffraction efficiency of the first split rays (11, 13) of the diffracted signal light (10; 10A); wherein the section (8; 8A) with periodic structure is periodically formed on a surface of the optical element (5; 5A) which faces the scale (2) or the light receiving unit (6); wherein the optical element (5) comprises the section (8; 8A) with periodic structure, which is formed on a surface of the optical element (5) facing the scale (2), and a smooth surface (9) which faces the light receiving unit (6) and is parallel to a direction in which the diffraction grating (S) is arranged; and wherein the smooth surface (9) is configured to completely reflect the second split rays (12,14; 22, 24). [2] Method for encoding an optical signal, comprising: Emitting collimated light using a light source (4); Diffraction of the light using a scale (2) which contains a diffraction grating (S) into a plurality of diffracted light rays; Receiving diffracted signal light (10; 10A) and diffracted interference light (20; 20A) resulting from diffraction through the diffraction grating (S), wherein the diffracted signal light (10; 10A) propagates at a predetermined diffraction angle on both sides of an optical axis of the light emitted by the light source (4), and the diffracted interference light (20; 20A) propagates at a diffraction angle greater than a diffraction angle of the diffracted signal light (10; 10A) on both sides of the optical axis of the light emitted by the light source (4); and Arranging an optical element (5) between the scale (2) and the light receiving unit (6), wherein the optical element (5) includes a section (8; 8A) with a periodic structure, which is periodically designed, wherein the section (8; 8A) with a periodic structure is a plurality of slot sections or comprises a plurality of slot sections which are essentially designed with a rectangular waveform or sinusoidal waveform in cross-section, thereby Dividing the diffracted signal light (10; 10A) into first split rays (11; 13), which propagate at a predetermined angle of propagation, and second split rays (12; 14), which propagate at a larger angle of propagation than that of the first split rays (11; 13); and Splitting the diffracted interference light (20; 20A) into first split rays (21; 23), which propagate at a predetermined angle, and second split rays (22; 24), which propagate at a larger angle than that of the first split rays (21; 23), causes the diffraction efficiency of the first split rays (21, 23) of the diffracted interference light (20; 20A) to be lower than the diffraction efficiency of the first split rays (11, 13) of the diffracted signal light (10; 10A); wherein the section (8; 8A) with periodic structure is periodically formed on a surface of the optical element (5; 5A) and is arranged such that it faces the scale (2) or the light receiving unit (6); wherein the optical element (5) is configured to include the section (8; 8A) with periodic structure, which is formed on a surface of the optical element (5) facing the scale (2), and a smooth surface (9) which faces the light receiving unit (6) and is parallel to a direction in which the diffraction grating (S) is arranged; and Complete reflection of the second split rays (12, 14; 22, 24) by means of the smooth surface (9).

Images