Optical scale for encoder and optical encoder

Abstract

The present disclosure provides an optical scale for an encoder, the optical scale having a disk-shaped glass base material in which a center hole is formed, and having an optical pattern having two regions with different reflectances or transmittances, wherein: the glass base material is provided with a first surface, a second surface facing the first surface, and an outer peripheral side surface positioned between the first surface and the second surface; in a cross-sectional view in a thickness direction, when a point at which the glass base material separates from an extended surface of the first surface is defined as an end portion A, and a point at which the glass base material separates from an extended surface of the outer peripheral side surface on the first surface side is defined as an end portion B, the distance between the end portion A and the end portion B is 0.20 mm or less, and in an outer peripheral edge portion on the first surface side, the number of microcracks observed in a region having an outer peripheral length of 1 mm and a width of 0.5 mm is 30 or less.

Description

Optical scale for encoder and optical encoder

[0001] The present disclosure relates to an optical scale for an encoder and an optical encoder.

[0002] Conventionally, an optical encoder has been used in a servo motor or the like provided with a control mechanism. Optical encoders include transmissive encoders and reflective encoders. An optical encoder includes an optical scale, a light source such as an LED that irradiates the optical scale with light, and a light detector that detects transmitted light or reflected light from the optical scale.

[0003] Patent Document 1 discloses a reflective optical scale for an encoder in which high-reflection regions and low-reflection regions are alternately arranged on a substrate, the low-reflection region including a low-reflection portion having a metal chromium film disposed on one surface of the substrate and a chromium oxide film and a chromium nitride film disposed in any order on the surface of the metal chromium film opposite to the substrate, and the high-reflection region having a higher reflectance of light incident from the side opposite to the substrate of the reflective optical scale for an encoder than the low-reflection region.

[0004] Conventionally, an optical scale is manufactured by fragmenting a multi-sided body in which a plurality of optical scales are arranged side by side by machining such as drilling.

[0005] International Publication No. 2021 / 201024

[0006] When fragmenting by machining, it is necessary to chamfer the corners of the glass substrate after machining in order to prevent chipping or the like from occurring at the corners of the glass substrate. The chamfered glass substrate has fine microcracks in the chamfered portion, and there is a risk that the optical scale will crack starting from the microcracks.

[0007] The present invention has been made in view of the above circumstances, and the main object thereof is to provide an optical scale capable of suppressing cracking.

[0008] One embodiment of the present disclosure provides an optical scale for an encoder having a disc-shaped glass substrate with a central hole formed therein, and an optical pattern having two regions with different reflectivity or transmittance, wherein the glass substrate comprises a first surface, a second surface facing the first surface, and an outer peripheral surface located between the first surface and the second surface, and in a cross-sectional view in the thickness direction, when the point where the glass substrate separates from the extended surface of the first surface is defined as end A, and the point on the first surface side where the glass substrate separates from the extended surface of the outer peripheral surface is defined as end B, the distance between end A and end B is 0.20 mm or less, and the number of microcracks observed in a region with an outer peripheral length of 1 mm and a width of 0.5 mm on the outer peripheral edge on the first surface side is 30 or less.

[0009] One embodiment of the present disclosure provides an optical encoder comprising the above-described optical scale for encoders, a light source for irradiating the surface of the optical scale for encoders with measurement light, and a photodetector for detecting reflected or transmitted light from the optical scale for encoders.

[0010] This disclosure offers the advantage of providing an optical scale that can suppress cracking.

[0011] These are schematic perspective views, schematic plan views, and schematic cross-sectional views illustrating the optical scale for encoders in this disclosure. This is a cross-sectional view of the outer edge of the first face side of a conventional optical scale for encoders. This is a schematic diagram of SEM images of the outer edge of the first face side of the optical scale for encoders in this disclosure and a conventional optical scale for encoders. This is a schematic cross-sectional view illustrating the optical scale for encoders in this disclosure. This is a schematic perspective view and schematic front view illustrating a method for measuring the load at failure and the displacement at failure using a tensile-compression testing machine. This is a schematic plan view illustrating the transmissive optical scale for encoders in this disclosure. This is a schematic cross-sectional view illustrating the transmissive optical scale for encoders in this disclosure. This is a schematic plan view illustrating the reflective optical scale for encoders in this disclosure. This is a schematic cross-sectional view illustrating the reflective optical scale for encoders in this disclosure. This is a schematic plan view illustrating a multi-faceted optical scale for encoders in this disclosure. This is a schematic perspective view illustrating the optical encoder in this disclosure. This is a schematic perspective view illustrating the optical encoder in this disclosure.

[0012] Embodiments of this disclosure will be described below with reference to the drawings and other figures. However, this disclosure can be implemented in many different ways and should not be interpreted as being limited to the embodiments described below. In addition, the drawings may be schematically represented in terms of width, thickness, shape, etc. of each part compared to the actual form in order to make the explanation clearer, but these are merely examples and should not limit the interpretation of this disclosure. Furthermore, in this specification and in each figure, elements similar to those described above with respect to previously shown figures will be denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0013] In this specification, when describing a configuration in which one member is placed on top of another member, unless otherwise specified, the terms "on top" or "below" include both cases: one in which the other member is placed directly above or below the other member so as to be in contact with it, and another in which the other member is placed above or below the other member via yet another member. Similarly, when describing a configuration in this specification in which one member is placed on the surface of another member, unless otherwise specified, the terms "on the surface" or "on the surface" include both cases: one in which the other member is placed directly above or below the other member so as to be in contact with it, and another in which the other member is placed above or below the other member via yet another member.

[0014] The optical scale for encoders and optical encoders described herein will be explained in detail below.

[0015] A. Optical scale for encoder Figure 1(a) is a schematic perspective view showing an example of an optical scale for encoder in this disclosure. Figure 1(b) is a schematic plan view of the optical scale in Figure 1(a), and Figure 1(c) is a schematic cross-sectional view taken along line A-A in Figure 1(b).

[0016] As shown in Figures 1(a) to 1(c), the encoder optical scale 10 has a disc-shaped glass substrate 1 having a first surface 1a, a second surface 1b facing the first surface 1a, and an outer peripheral surface 1c located between the first surface 1a and the second surface 1b, with a central hole 1h formed therein. The encoder optical scale 10 has an optical pattern having two regions with different reflectance or transmittance, although it is not specifically shown in Figure 1. The glass substrate 1 has a thickness direction D Ｔ In a cross-sectional view (Figure 1(c)), when the point where the glass substrate 1 separates from the extended surface of the first surface 1a is defined as end A, and the point where the glass substrate 1 separates from the extended surface of the outer peripheral surface 1c is defined as end B, the distance L1 between end A and end B is 0.20 mm or less, and the number of microcracks observed in a region with an outer peripheral length of 1 mm and a width of 0.5 mm on the outer peripheral edge E1 on the first surface side is 30 or less. Such an encoder optical scale 10 is usually manufactured by etching a multi-faceted encoder optical scale into individual pieces.

[0017] Figure 2 is a schematic cross-sectional view showing an example of a glass substrate in a conventional optical scale for encoders. Conventional optical scales for encoders are usually manufactured by machining a multi-faceted optical scale for encoders into individual pieces. The glass substrate 11, which has been machined by drilling or other machining, is usually chamfered at the corners with a file or the like to prevent chipping or cracking, and a chamfered portion 11d is formed. Therefore, if the point where the glass substrate 11 separates from the extended surface of the first surface 11a is defined as end A, and the point where the glass substrate 1 separates from the extended surface of the outer peripheral surface 11c is defined as end B, the distance L11 between end A and end B becomes somewhat long.

[0018] On the other hand, in the optical scale of this disclosure, as shown in Figure 1(c), the distance L1 between end A and end B in a cross-sectional view of the glass substrate 1 is small compared to the above range. Hereinafter, the shape of the outer peripheral edge E1 of the first surface side 1a is also referred to as the specific shape.

[0019] Figure 3(a) is a schematic diagram of a scanning electron microscope (SEM) image of the outer peripheral edge E1 on the first surface 1a side of the glass substrate 1 of the encoder optical scale of the present disclosure shown in Figure 1. Figure 3(b) is a schematic diagram of a scanning electron microscope (SEM) image of the outer peripheral edge on the first surface 11a side of the glass substrate 11 of a conventional encoder optical scale. As shown in Figure 3(b), the glass substrate 11 after machining has microcracks C in the chamfered portion 11d, and the number of microcracks C is greater than the range shown above. Therefore, cracks are likely to occur starting from the microcracks C. On the other hand, as shown in Figure 3(a), the outer peripheral edge on the first surface 1a side of the encoder optical scale of the present disclosure has a number of microcracks C observed in a region with an outer peripheral length of 1 mm and a width of 0.5 mm that is less than or equal to a predetermined number. Therefore, microcracks are suppressed, and cracks in the encoder optical scale can be suppressed.

[0020] Furthermore, since the optical scale in this disclosure is manufactured by etching to create individual pieces, it is assumed that the outer peripheral edge E2 on the second surface, the inner peripheral edge E3 on the first surface, and the outer peripheral edge E4 on the second surface, as illustrated in Figure 1(a), have the same specific shape as the outer peripheral edge E1 on the first surface 1a. Moreover, it is assumed that the number of microcracks in the outer peripheral edge E2 on the second surface, the inner peripheral edge E3 on the first surface, and the outer peripheral edge E4 on the second surface are about the same as the number of microcracks in the outer peripheral edge E1 on the first surface 1a.

[0021] The optical scale for encoders of this disclosure will be described in detail below.

[0022] 1. Glass Substrate As shown in Figure 1(a), the glass substrate 1 in this disclosure has a disc shape in which a central hole 1h is formed, and comprises a first surface 1a, a second surface 1b opposite to the first surface, and an outer peripheral surface 1c located between the first surface 1a and the second surface 1b. The first surface 1a and the second surface 1b are each flat surfaces and are parallel to each other. The outer peripheral surface 1c is a surface that extends substantially perpendicular to the first surface 1a and the second surface 1b.

[0023] (1) Distance L The glass substrate in this disclosure has a specific shape at the outer peripheral edge E1 on the first surface 1a side. That is, as illustrated in Figure 1(c), the glass substrate 1 has a specific shape in the thickness direction D Ｔ In a cross-sectional view, when the point where the glass substrate 1 separates from the extended surface of the first surface 1a is defined as end A, and the point where the glass substrate 1 separates from the extended surface of the outer peripheral surface 1c is defined as end B, the distance L1 between end A and end B is 0.20 mm or less. That is, the glass substrate in this disclosure does not have a chamfered portion on the outer peripheral edge E1 on the first surface 1a side. The above distance L1 is preferably 0.15 mm or less, more preferably 0.10 mm or less, and particularly preferably 0 mm. On the other hand, the above distance L1 is, for example, 0 mm or more, may be 0.01 mm or more, or 0.02 mm or more. Specifically, the above distance L1 in this disclosure is, for example, preferably 0 mm or more and 0.20 mm or less, may be 0.01 mm or more and 0.15 mm or less, or 0.02 mm or more and 0.10 mm or less.

[0024] The method for measuring the distance L1 described above is as follows: First, the glass substrate is cut perpendicular to the first surface using a glass cutter. Next, the cut surface is polished to a flat surface using a polishing machine to obtain a cross-sectional measurement sample. The cut surface of the cross-sectional measurement sample is observed at a magnification of 20x using a scanning electron microscope from a direction perpendicular to the cut surface, and the distance L1 is measured. The distance L1 described above is the average value of observations and measurements taken at a total of 12 points, with the circumference of the scale marked in 30° increments. Note that a distance L1 of 0 mm means that when the cut surface of the cross-sectional measurement sample is observed at a magnification of 20x using a scanning electron microscope from a direction perpendicular to the cut surface, the positions of end A and end B coincide, as shown in Figure 4.

[0025] As shown in Figure 1(c), the distance X between the end A of the glass substrate 1 and the extended surface of the outer peripheral side surface 1c is, for example, 0 mm or more and 0.20 mm or less, and may be 0.01 mm or more and 0.15 mm or less. As shown in Figure 1(c), the distance Y between the end B of the glass substrate 1 and the extended surface of the first surface 1a is, for example, 0 mm or more and 0.20 mm or less, and may be 0.01 mm or more and 0.15 mm or less.

[0026] The above distances X and Y are measured by preparing a cross-sectional measurement sample in the same manner as the measurement method for distance L1 described above, and then taking the measurement. Furthermore, distances X and Y are the average values ​​obtained by observing and measuring at a total of 12 points, with the circumference of the scale marked in 30° increments.

[0027] The glass substrate of this disclosure is obtained by etching a multi-faceted optical scale for an encoder into individual pieces and processing them into a disc shape with a central hole. Therefore, as shown in Figure 1(a), it is assumed that the outer peripheral edge E2 on the second surface side, the inner peripheral edge E3 on the first surface side, and the outer peripheral edge E4 on the second surface side of the glass substrate 1 of this disclosure have the same specific shape as the outer peripheral edge E1 on the first surface side.

[0028] (2) Microcracks The glass substrate in this disclosure has 30 or fewer microcracks C observed in an area with an outer circumference of 1 mm and a width of 0.5 mm on the outer peripheral edge of the first surface. The fewer the number of microcracks, the better; for example, 20 or fewer is preferred, and 0 is more preferred.

[0029] The method for measuring the number of microcracks in a region of outer circumference length 1 mm and width 0.5 mm on the outer edge side of the first surface 1a of the glass substrate is to observe the region of outer circumference side 1c with a width of 0.5 mm (indicated as P in Figures 1(b) and (c)) from the outer edge side 1c of the outer edge side of the first surface 1a of the glass substrate at a magnification of 20x using a scanning electron microscope and count the number of microcracks. The number of microcracks per 1 mm of outer circumference length is then calculated. A microcrack is defined as a crack with a maximum length of 1 μm or more and 100 μm or less in the SEM image.

[0030] (3) Thickness The thickness of the glass substrate in this disclosure is, for example, 0.1 mm or more, preferably 0.2 mm or more, and more preferably 0.4 mm or more. If the thickness of the glass substrate is within the above range, the strength as an optical scale for an encoder will be sufficient. On the other hand, the thickness of the glass substrate is, for example, 2.0 mm or less, preferably 1.5 mm or less, and more preferably 1.2 mm or less. The thickness of the glass substrate refers to the distance between the first surface and the second surface. Specifically, the thickness of the glass substrate in this disclosure is, for example, 0.1 mm or more and 2.0 mm or less, preferably 0.2 mm or more and 1.5 mm or less, and more preferably 0.4 mm or more and 1.2 mm or less.

[0031] (4) Shape The glass substrate in this disclosure has a perforated disc shape with a central hole. The outer diameter of the glass substrate is, for example, 15 mm or more, and may be 20 mm or more. On the other hand, the outer diameter of the glass substrate is, for example, 70 mm or less, and may be 60 mm or less. Specifically, the outer diameter of the glass substrate is, for example, 15 mm or more, 70 mm or less, and may be 20 mm or more, 60 mm or less. The inner diameter of the glass substrate is, for example, 5 mm or more, and 10 mm or less. The difference between the outer diameter and the inner diameter (outer-to-inner diameter difference) is, for example, 10 mm or more, and 30 mm or less.

[0032] (5) Maximum Height Sz In this disclosure, the maximum height Sz of the outer peripheral surface of the glass substrate is preferably 7.0 μm or less, more preferably 6.0 μm or less, and even more preferably 5.5 μm or less. The fewer areas with large height differences on the outer peripheral surface of the glass substrate, the less likely cracks are to occur originating from those areas. Therefore, by keeping Sz within the above range, cracking of the glass substrate can be suppressed. This makes it possible to suppress cracking of the optical scale. On the other hand, a smaller Sz is preferable, and the lower limit of Sz is not particularly limited, but may be, for example, 0.1 μm or more.

[0033] As described above, the optical scale in this disclosure is manufactured by separating it into individual pieces through etching. This allows the Sz to be within the above range. Furthermore, the etched surface tends to have a smooth, rounded shape rather than a sharp, angular shape. Therefore, etching is considered to have a positive effect on crack resistance.

[0034] Sz is measured using a laser microscope in accordance with ISO 25178-2:2021. A Keyence VK-X1000 laser microscope can be used. The objective lens should be 50x, and the measurement area should be 100 μm x 100 μm. Sz is the average of measurements taken at five arbitrary locations.

[0035] (6) Other glass substrates in this disclosure include, for example, soda glass substrates, alkali-free glass substrates, quartz glass substrates, and the like.

[0036] The glass substrate has high transmittance. The total light transmittance of the glass substrate is, for example, 80% or more, may be 85% or more, or may be 90% or more. The total light transmittance is measured in accordance with JIS K7361-1:1997.

[0037] 2. Optical Scales for Encoders The optical scales for encoders in this disclosure are optical scales for encoders having an optical pattern having two regions with different reflectivity or transmittance. The optical scales for encoders in this disclosure may also be transmissive optical scales for encoders having an optical pattern having two regions with different transmittance, namely a transmissive region and an opaque region (light-shielding region). Alternatively, they may be reflective optical scales for encoders having an optical pattern having two regions with different reflectivity, namely a reflective region (high reflectivity region) and an anti-reflective region (low reflectivity region).

[0038] (1) Bending stress The optical scale for encoders in this disclosure is designed to suppress cracking for the reasons described above. The optical scale for encoders in this disclosure preferably has a bending stress σ at fracture obtained by a three-point bending test of 200 MPa or more, and more preferably 300 MPa or more. On the other hand, the bending stress σ at fracture may be, for example, 500 MPa or less, and may also be 400 MPa or less. Specifically, the bending stress σ at fracture is preferably 200 MPa or more and 500 MPa or less, and more preferably 300 MPa or more and 400 MPa or less.

[0039] The optical scale for encoders in this disclosure may have a bending strain ε at fracture obtained by a three-point bending test that is, for example, 0.40% or more, or 0.50% or more. On the other hand, the bending strain ε at fracture may be, for example, 1.00% or less, or 0.80% or less. Specifically, the bending strain ε at fracture may be, for example, 0.40% or more, 1.00% or less, or 0.50% or more, or 0.80% or less.

[0040] The bending stress σ and bending strain ε at the time of fracture are measured using a tensile-compression testing machine. Figures 5(a) and 5(b) are schematic perspective and front views illustrating the method for measuring the load and displacement at the time of fracture using a tensile-compression testing machine. As shown in Figures 5(a) and 5(b), the tensile-compression testing machine 30 is equipped with a pair of spaced-apart support bases 31 and an indenter 32. A sample S is placed on the pair of support bases 31. Next, the indenter 32 is pressed against the sample S at a pressing speed of 0.5 mm / min. From the moment the load is applied to the sample S, the load and displacement are measured to determine the load and displacement at the time of fracture in the optical scale for the encoder. This measurement is performed five times, and the arithmetic mean of the load and displacement at the time of fracture is calculated. Using the obtained load and displacement at the time of fracture, the bending stress σ is calculated by the following formula (1), and the bending strain ε is calculated by the following formula (2). For the tensile-compression testing machine, an SDW-F tensile-compression testing machine (manufactured by IMADA) can be used. In the above measurement, the distance d between the centers of the pair of support bases 31 is 15 mm, the distance between the center of the support base and the center of the indenter is 7.5 mm, and the distance between the pair of support bases 31 is 10 mm. Furthermore, the support base 31 used has a semicircular upper end shape with a radius of 2.5 mm in cross-section, and the indenter 32 used has a semicircular tip shape with a radius of 2 mm in cross-section. Bending stress σ = (3 × P × d) / (2 × b × h) ２ (Equation 1) Bending strain ε = (6 × h × w) / d ２ (Equation 2) (In the equation, P is the load at failure [N], b is the sample width [mm], h is the sample thickness [mm], w is the displacement at failure [mm], and d is the distance between the centers of the support bases [mm]. Note that the sample width b is the width of the sample placed on the support base 31, as shown in Figure 5(b).)

[0041] (2) Through-beam optical scale for encoder Figure 6 is a schematic plan view showing an example of a through-beam optical scale for encoder in this disclosure. As illustrated in Figure 6, the through-beam optical scale 10A for encoder has an optical pattern 53 having two regions with different transmittances, namely a transmission region 51 and a light-shielding region 52.

[0042] The structure of the transmissive optical scale preferably includes the above-described glass substrate and a patterned light-shielding layer disposed on the first surface side of the glass substrate.

[0043] FIG. 7 is an enlarged cross-sectional view taken along line A-A of the portion within the dotted frame a in FIG. 6. As illustrated in FIGS. 6 and 7, the transmissive optical scale 10A for an encoder includes the above-described glass substrate 1 and a light-shielding layer 54 disposed in a pattern along the circumferential direction of the glass substrate 1 on the first surface 1a side of the glass substrate 1. In the transmissive optical scale 10A for an encoder, a light-shielding region 52 where the light-shielding layer 54 is disposed and a transmissive region 51 where the light-shielding layer 54 is not disposed are alternately arranged in the circumferential direction. The light-shielding region 52 includes the glass substrate 1 and the light-shielding layer 54 in the thickness direction of the transmissive optical scale 10A for an encoder. The transmissive region 51 includes the glass substrate 1. The transmittance in the transmissive region 51 is higher than the transmittance in the light-shielding region 52. Note that the transmittance in the transmissive region 51 and the transmittance in the light-shielding region 52 indicate the transmittance at the same wavelength.

[0044] The transmittance in the light-shielding region may be lower than the transmittance in the transmissive region. The optical density of the light-shielding region is, for example, 2.5 or more, and may be 3.0 or more, 3.5 or more, or 4.0 or more.

[0045] In this specification, the optical density is the transmission density. The optical density is measured using an optical densitometer. An optical densitometer is a measuring instrument having a mechanism for irradiating a sample (the object to be measured) with light and measuring the intensity of the transmitted light. Specifically, measurement is performed by irradiating the sample with light in a direction perpendicular to the sample using a Takano OD reflectance measuring machine manufactured by Takano Co., Ltd.

[0046] The configuration of the light-shielding layer is not particularly limited as long as it satisfies the above optical density. The light-shielding layer may have the same configuration as the low-reflection layer described below.

[0047] (3) Reflective optical scale for encoder Figure 8 is a schematic plan view showing an example of a reflective optical scale for encoder in this disclosure. As illustrated in Figure 8, the reflective optical scale 10B for encoder has an optical pattern 63 having two regions with different reflectivity, namely a high-reflectivity region 61 and a low-reflectivity region 62.

[0048] The reflective optical scale for encoders in this disclosure has an optical pattern having two regions with different reflectivity, namely a high-reflectivity region and a low-reflectivity region. The configuration of the reflective optical scale for encoders is not particularly limited as long as it has an optical pattern having a high-reflectivity region and a low-reflectivity region. The reflective optical scale for encoders may have a high-reflectivity substrate having a glass substrate and a metal layer disposed on the first surface side of the glass substrate, and a patterned low-reflectivity layer disposed on the metal layer side of the high-reflectivity substrate. Alternatively, the reflective optical scale for encoders may have a low-reflectivity substrate and a patterned high-reflectivity layer disposed on one surface side of the low-reflectivity substrate. Each embodiment will be described below.

[0049] (i) First embodiment of a reflective optical scale for an encoder The first embodiment of a reflective optical scale for an encoder in this disclosure comprises a highly reflective substrate having a glass substrate and a metal layer disposed on the first surface side of the glass substrate, and a patterned low-reflective layer disposed on the metal layer side of the highly reflective substrate.

[0050] Figure 9 is an enlarged cross-sectional view taken along line A-A of the dotted line frame b portion in Figure 8. As illustrated in Figures 8 and 9, the encoder reflective optical scale 10B has a high-reflectivity substrate 65 having a glass substrate 1 and a metal layer 66 disposed on the first surface 1a side of the glass substrate 1, and a low-reflectivity layer 64 arranged in a pattern along the circumferential direction of the high-reflectivity substrate 65 on the metal layer 66 side of the high-reflectivity substrate 1. The encoder reflective optical scale 10B has low-reflectivity regions 62 where the low-reflectivity layer 64 is disposed and high-reflectivity regions 61 where the low-reflectivity layer 64 is not disposed alternately in the circumferential direction. The low-reflectivity region 62 has the glass substrate 1, the metal layer 66 and the low-reflectivity layer 64 in the thickness direction of the encoder reflective optical scale 10B. The high-reflectivity region 61 has the glass substrate 1 and the metal layer 66. The reflectance in the high-reflectivity region 61 is higher than the reflectance in the low-reflectivity region 62. Note that the reflectance in the high-reflectance region 61 and the reflectance in the low-reflectance region 62 represent the reflectance at the same wavelength and the same angle of incidence.

[0051] The reflective optical scale for encoders according to this embodiment will be described below for each component.

[0052] (a) High-reflectivity substrate The high-reflectivity substrate in this embodiment has a high reflectivity. The reflectivity of the metal layer side of the high-reflectivity substrate is, for example, 50% or more, may be 55% or more, or may be 60% or more. The above reflectivity is, for example, 100% or less. Specifically, the reflectivity of the metal layer side of the high-reflectivity substrate is 50% or more and 100% or less, may be 55% or more and 100% or less, or may be 60% or more and 100% or less. If the above reflectivity is within the above range, the difference between the reflectivity in the high-reflectivity region and the reflectivity in the low-reflectivity region is large, which prevents false detection by the photodetector and improves the accuracy of signal detection.

[0053] In this specification, reflectance refers to the reflectance to detection light used in an optical encoder. In a highly reflective substrate, when the wavelength of the incident light is within the range of 500 nm to 1000 nm, it is more preferable that the reflectance at an incident angle of 5° to 70° is within the above range.

[0054] For reflectance measurement, a SolidSpec 3700DUV manufactured by Shimadzu Corporation is used. The irradiation beam size is approximately 6 mm x 15 mm. Both P-polarized and S-polarized light are measured, and the average of the sum is taken to calculate the 45° linear polarization and then calculate the reflectance.

[0055] The material for the metal layer is preferably one that satisfies the above-mentioned reflectivity requirements. Examples include chromium, silver, aluminum, rhodium, gold, copper, and alloys mainly composed of these metals. Among these, a metallic chromium film is preferred.

[0056] The thickness of the metal layer is, for example, 0.05 μm or more, and may be 0.1 μm or more. Alternatively, the thickness of the metal layer may be, for example, 0.3 μm or less, and may be 0.2 μm or less. Specifically, the thickness of the metal layer may be, for example, 0.05 μm or more, 0.3 μm or less, 0.1 μm or more, and 0.2 μm or less.

[0057] (b) Low-reflection layer In this embodiment, the low-reflection layer is arranged in a pattern on the metal layer side of the high-reflection substrate.

[0058] The reflectance in the low-reflection region should be lower than the reflectance in the high-reflection region. Specifically, the reflectance in the low-reflection region should be lower than the reflectance of the metal layer side of the high-reflection substrate. In the low-reflection region, the reflectance at any wavelength within the range of 500 nm to 1000 nm is, for example, 10% or less, may be 5% or less, or may be 1% or less. On the other hand, the reflectance in the low-reflection region is, for example, 0% or more. Specifically, the reflectance in the low-reflection region is 0% or more and 10% or less, may be 0% or more and 5% or less, or may be 0% or more and 1% or less. If the above reflectance is within the above range, the difference between the reflectance in the high-reflection region and the reflectance in the low-reflection region can be made large.

[0059] In the low-reflectance region, when the wavelength of the incident light is within the range of 500 nm to 1000 nm, it is more preferable that the reflectance at any incident angle within the range of 5° to 70° is within the above range.

[0060] The low-reflectance layer is not particularly limited in its composition as long as it satisfies the above-mentioned reflectance. In particular, the low-reflectance layer preferably has a metallic chromium film and, from the side of the high-reflectance substrate, a chromium oxide film and a chromium nitride film arranged in no particular order on the side of the metallic chromium film opposite the high-reflectance substrate. With such a three-layer low-reflectance layer, the reflectance of the low-reflectance region can be reduced to the above-mentioned range. Furthermore, if only metallic chromium is prepared, the chromium oxide film and chromium nitride film can be easily formed by using reactive sputtering or the like. Moreover, with such a low-reflectance layer, high-resolution patterning can be easily performed compared to silicon oxide films.

[0061] In this specification, "chromium oxide film and chromium nitride film arranged in no particular order on the side opposite to the highly reflective substrate of the metallic chromium film" means that they may be arranged in the order of metallic chromium film, chromium oxide film, and chromium nitride film, or in the order of metallic chromium film, chromium nitride film, and chromium oxide film.

[0062] Such a low-reflectivity layer and the method for forming it can be the same as those described in Japanese Patent No. 7574845.

[0063] (c) Other layers The reflective optical scale for encoders of this embodiment may have other layers in addition to the high-reflectivity substrate and low-reflectivity layer described above. For example, the reflective optical scale for encoders of this embodiment may have a protective layer between the high-reflectivity substrate and the low-reflectivity layer.

[0064] The protective layer is preferably transparent and has the function of protecting the high-reflectivity substrate. By providing a protective layer, there is no risk of the surface of the high-reflectivity substrate becoming rough and the surface roughness increasing during etching when forming the low-reflectivity layer in a pattern. Therefore, diffuse reflection of light can be suppressed. The protective layer may be provided over the entire surface of the high-reflectivity substrate or in a part of it when viewed from above. The material of the protective layer is not particularly limited as long as it is transparent and can protect the high-reflectivity substrate, and may be either an organic or inorganic material. As such a protective layer, the protective layer described in Japanese Patent No. 7537649 can be used.

[0065] (ii) Second aspect of a reflective optical scale for an encoder The second aspect of a reflective optical scale for an encoder in this disclosure comprises a glass substrate and a low-reflection substrate having a low-reflection layer disposed on one side of the glass substrate, and a patterned high-reflection layer disposed on the side of the low-reflection substrate that has the low-reflection layer.

[0066] The reflective optical scale for encoders according to this embodiment will be described below for each component.

[0067] (a) Low-reflection substrate The low-reflection substrate in this embodiment has a glass substrate and a low-reflection layer and has a low reflectivity. The reflectivity of the low-reflection substrate is the same as the reflectivity of the low-reflection region in the first embodiment of the reflective optical scale for encoder described above.

[0068] The material for the low-reflection layer is not particularly limited as long as it has low reflectivity, and may be either an organic or inorganic material. Organic materials preferably contain resins. The resin used for the low-reflection layer is not particularly limited as long as it can produce a low-reflection layer, and examples include ionizing radiation-curable resins that harden upon irradiation with ionizing radiation such as ultraviolet light or electron beams, and thermosetting resins that harden upon heating. Specifically, novolac resins, polyolefin resins, polyester resins, urethane resins, polyimide resins, acrylic resins, and epoxy resins are preferred. Among novolac resins, phenol novolac resins are preferred because they have excellent electrical properties and can suppress problems caused by static charge. Among acrylic resins, trifunctional or more acrylates such as pentaerythritol tetraacrylate and dipentaerythritol tetraacrylate are preferred because they can enhance photocurability. Among epoxy resins, epoxy acrylate resins having a fluorene structure are preferred because they improve heat resistance, adhesion, and chemical resistance. Cardo epoxy resins are also preferred among epoxy resins. This is because it can impart heat resistance, surface hardness, and flatness. In addition to the resin, the organic material may also contain polymerization initiators and various additives.

[0069] When the low-reflection layer contains an inorganic material, the low-reflection layer is the same as the low-reflection layer in the first embodiment of the reflective optical scale for the encoder described above.

[0070] (b) High-reflectivity layer In this embodiment, the high-reflectivity layer is arranged in a pattern on the low-reflectivity layer side of the low-reflectivity substrate.

[0071] The reflectance in the high-reflectance region should be higher than the reflectance in the low-reflectance region. Specifically, the reflectance in the high-reflectance region should be higher than the reflectance of the low-reflectance substrate. The reflectance in the high-reflectance region is the same as the reflectance of the metal layer side surface of the high-reflectance substrate in the first embodiment of the reflective optical scale for the encoder.

[0072] The composition of the highly reflective layer is not particularly limited as long as it satisfies the above-mentioned reflectivity, and examples include a metal film. The metal film is preferably composed of a metal having high reflectivity. Examples of metals include chromium, silver, aluminum, rhodium, gold, copper, and alloys mainly composed of these metals. Among these, a metallic chromium film is preferred. The metallic chromium film is a layer made of metallic chromium. The thickness of the metal film is, for example, 0.05 μm or more and 0.3 μm or less, and may be 0.1 μm or more and 0.2 μm or less.

[0073] 3. Method for Manufacturing an Optical Scale for Encoders The method for manufacturing an optical scale for encoders according to this disclosure preferably comprises a multi-panel assembly manufacturing step for manufacturing a multi-panel assembly of optical scales for encoders in which multiple optical scales for encoders are mounted, and a piece-forming step for piece-forming the multi-panel assembly of optical scales for encoders by etching.

[0074] (1) Process for manufacturing a multi-panel optical scale assembly In this process, a multi-panel optical scale assembly for encoders is manufactured, in which multiple optical scales for encoders are mounted. Figure 10 is a schematic plan view showing an example of a multi-panel optical scale assembly for encoders in this disclosure. As shown in Figure 10, the multi-panel optical scale assembly 50 for encoders has multiple optical scales for encoders (transmissive optical scale 10A for encoders or reflective optical scale 10B for encoders) having an optical pattern with two regions having different reflectivity or transmittances.

[0075] In the multi-panel optical scale assembly for encoders described herein, the number of optical scales for encoders is preferably 50 or more, may be 80 or more, or 100 or more. On the other hand, the upper limit of the number of optical scales for encoders in the multi-panel optical scale assembly for encoders is, for example, 300 or less.

[0076] In the case of a multi-panel optical scale assembly for encoders in which multiple reflective optical scales for encoders are mounted, the method for mounting multiple patterned low-reflectivity layers on the first surface of a high-reflectivity substrate is the same as the method for forming the low-reflectivity layer described above. Similarly, in the case of a multi-panel optical scale assembly for encoders in which multiple transmissive optical scales for encoders are mounted, the method for mounting multiple patterned light-shielding layers on the first surface of a transparent substrate is the same as the method for forming the light-shielding layer described above.

[0077] (2) Separation process In this process, the multi-faceted optical scale assembly for encoders is separated into individual pieces by etching. Preferably this process includes, for example, a resist pattern formation process in which a resist pattern is formed on the surface of the multi-faceted optical scale assembly for encoders, and an etching process in which the glass substrate of the multi-faceted optical scale assembly for encoders is etched using the resist pattern as a mask, thereby separating each optical scale for encoders into individual pieces.

[0078] In the resist pattern formation process, a resist material is applied to the surface of a multi-faceted optical scale assembly for an encoder to form a resist layer. Then, exposure and development are performed to form a resist pattern such that areas other than the optical scale for the encoder and the central hole area are exposed. Conventional known resist materials can be used to form the resist pattern.

[0079] The etching process may be a wet etching process in which the multi-panel optical scale for encoders is immersed in an etching solution such as hydrofluoric acid, or a dry etching process in which the multi-panel optical scale for encoders is exposed to an atmosphere containing an etching gas such as fluoride gas. Among these, wet etching using hydrofluoric acid is preferred.

[0080] B. Optical Encoder The present disclosure provides an optical encoder comprising the above-described optical scale for encoders, a light source for irradiating the surface of the optical scale for encoders with measurement light, and a photodetector for detecting reflected or transmitted light from the optical scale for encoders.

[0081] The optical encoder in this disclosure may be a reflective encoder or a transmissive encoder.

[0082] Figure 11 is a schematic perspective view showing an example of an optical encoder in this disclosure, and is an example of a transmissive encoder. The optical encoder 100A comprises a transmissive optical scale 10A for encoders, a light source 81 disposed on one side of the transmissive optical scale 10A for encoders, and a photodetector 82 disposed on the other side of the transmissive optical scale 10A for encoders. In Figure 11, a lens 83 is disposed between the light source 81 and the transmissive optical scale 10A for encoders.

[0083] Figure 12 is a schematic perspective view showing an example of an optical encoder in this disclosure, and is an example of a reflective encoder. The optical encoder 100B comprises a reflective optical scale 10B for the encoder, and a light source 91 and a photodetector 92 arranged on the same plane as the reflective optical scale 10B for the encoder. In Figure 12, a fixed slit 93 is positioned between the photodetector 92 and the reflective optical scale 10B for the encoder.

[0084] According to this disclosure, since it is equipped with the above-described optical scale for encoders, it achieves the same effects as the above-described optical scale for encoders.

[0085] The optical encoder described in this disclosure will be explained below for each component.

[0086] 1. Optical Scale for Encoders: The optical scale for encoders is described in "A. Optical Scale for Encoders" above, so its explanation is omitted here.

[0087] 2. Light Source Examples of light sources include LEDs (light-emitting diodes) and lasers. The wavelength λ of the light emitted from the light source is, for example, in the blue to infrared region, i.e., approximately 400 nm to 1000 nm. In the case of a reflective encoder, the angle of incidence of light on the optical reflective scale is, for example, 5° to 70°.

[0088] 3. Photodetector A photodetector detects light that has been reflected or transmitted on an optical scale. A photodetector includes, for example, a photoreceiving element such as a photodiode or an image sensor. Examples of photoreceiving elements include photoelectric conversion elements.

[0089] 4. In the case of a reflective type optical encoder in this disclosure, a fixed slit may be provided between the photodetector and the optical reflective scale for the encoder. By providing a fixed slit, the change in the amount of light received by the photodetector becomes larger, and the detection sensitivity can be improved. The fixed slit may be provided between the light source and the optical scale for the encoder.

[0090] In the case of a transmissive encoder in this disclosure, an optical encoder may be provided with a lens between the light source and the optical transmissive scale for the encoder. By providing a lens, the light from the light source can be changed from diffuse light to parallel light.

[0091] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure.

[0092] The present disclosure will be further explained below with reference to examples and comparative examples.

[0093] (Example) An encoder optical scale was obtained from a multi-faceted assembly of encoder optical scales by etching with hydrofluoric acid solution, resulting in a perforated disc-shaped glass substrate with a thickness of 1.06 mm, an outer diameter of 25 mm, and an inner diameter of 8.8 mm. Cross-sectional measurement samples were obtained from five of the obtained encoder optical scales using the method described above. Each cross-sectional measurement sample was observed with a scanning electron microscope, and the distance L1 between ends A and B of the glass substrate was measured. In all cases, the distance L1 was 0 mm. In addition, at the outer peripheral edge on the first surface side of the glass substrate, a region with a width of 0.5 mm from the outer peripheral side surface was observed with a scanning electron microscope at a magnification of 20x, and the number of microcracks was counted. The number of microcracks per 1 mm of outer peripheral length was calculated. Furthermore, the maximum height Sz of the outer peripheral side surface of the glass substrate was measured using a laser microscope (Keyence Corporation "VK-X1000"). The objective lens was set to 50x, and the measurement area was 100 μm × 100 μm. Furthermore, Sz was defined as the average value of measurements taken at five arbitrary locations. The results are shown in Table 1.

[0094] (Comparative Example) An encoder optical scale was obtained by machining a multi-faceted optical scale assembly using a drill to chamfer the corners of the outer and inner edges of the glass substrate, thereby obtaining an encoder optical scale having a perforated disc-shaped glass substrate with a thickness of 1.06 mm, an outer diameter of 25 mm, and an inner diameter of 8.8 mm. Cross-sectional measurement samples were obtained from five of the obtained encoder optical scales using the method described above. Each cross-sectional measurement sample was observed with a scanning electron microscope, and the distance L11 between ends A and B of the glass substrate was measured. In addition, on the outer edge of the first surface of the glass substrate, a region with a width of 0.5 mm from the outer edge was observed with a scanning electron microscope at a magnification of 20x, and the number of microcracks was counted. The number of microcracks per 1 mm of outer length was calculated. Furthermore, the maximum height Sz of the outer edge of the glass substrate was measured using a laser microscope (Keyence "VK-X1000"). The objective lens was set to 50x, and the measurement area was 100 μm × 100 μm. Furthermore, Sz was defined as the average value of measurements taken at five arbitrary locations. The results are shown in Table 2.

[0095]

[0096]

[0097] [Evaluation] Three-point bending tests were performed on the optical scales for encoders obtained in the three-point bending test examples and comparative examples using the method described above, and the load at failure and the displacement at failure were measured. The arithmetic mean values ​​of the load at failure and the displacement at failure for the five samples are shown in Tables 3 and 4.

[0098]

[0099]

[0100] The bending stress σ and bending strain ε were calculated from the arithmetic mean of the load at failure and the arithmetic mean of the displacement at failure using equations (1) and (2) described above. The width b of the sample placed on the support was measured with a ruler and was 19.3 mm. In the example, the bending stress σ was 334 MPa and the bending strain ε was 0.68%. In the comparative example, the bending stress σ was 111 MPa and the bending strain ε was 0.25%.

[0101] It was confirmed that the glass substrate in the example was less prone to cracking than the glass substrate in the comparative example.

[0102] In other words, the present disclosure provides the following inventions: [1] An optical scale for an encoder having a disc-shaped glass substrate with a central hole formed therein, and an optical pattern having two regions with different reflectance or transmittance, wherein the glass substrate comprises a first surface, a second surface facing the first surface, and an outer peripheral surface located between the first surface and the second surface, and in a cross-sectional view in the thickness direction, when the point where the glass substrate separates from the extended surface of the first surface is defined as end A, and the point on the first surface side where the glass substrate separates from the extended surface of the outer peripheral surface is defined as end B, the distance between end A and end B is 0.20 mm or less, and the number of microcracks observed in a region with an outer peripheral length of 1 mm and a width of 0.5 mm on the outer peripheral edge on the first surface side is 30 or less. [2] The optical scale for an encoder according to [1], wherein the glass substrate does not have a chamfered portion on the outer peripheral edge on the first surface side. [3] An optical scale for an encoder according to [1] or [2], having a patterned light-shielding layer disposed on the first surface side of the glass substrate. [4] An optical encoder comprising an optical scale for an encoder according to any one of [1] to [3], a light source for irradiating the surface of the optical scale for an encoder with measuring light, and a photodetector for detecting reflected or transmitted light from the optical scale for an encoder.

[0103] 1… Glass substrate 10, 10A, 10B… Optical scale for encoder 50… Multi-faceted optical scale for encoder 100A, 100B… Optical encoder

Claims

1. An optical scale for an encoder having a disc-shaped glass substrate with a central hole formed therein, and an optical pattern having two regions with different reflectivity or transmittance, wherein the glass substrate comprises a first surface, a second surface facing the first surface, and an outer peripheral surface located between the first surface and the second surface, and in a cross-sectional view in the thickness direction, when the point where the glass substrate separates from the extended surface of the first surface is defined as end A, and the point on the first surface side where the glass substrate separates from the extended surface of the outer peripheral surface is defined as end B, the distance between end A and end B is 0.20 mm or less, and the number of microcracks observed in a region with an outer peripheral length of 1 mm and a width of 0.5 mm on the outer peripheral edge on the first surface side is 30 or less.

2. The optical scale for an encoder according to claim 1, wherein the glass substrate does not have a chamfered portion on the outer peripheral edge of the first surface.

3. The optical scale for an encoder according to claim 1, comprising a patterned light-shielding layer disposed on the first surface side of the glass substrate.

4. An optical encoder comprising: an optical scale for an encoder according to any one of claims 1 to 3; a light source for irradiating the surface of the optical scale for an encoder with measuring light; and a photodetector for detecting reflected or transmitted light from the optical scale for an encoder.

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