Light-emitting unit, light-emitting and light-receiving unit and photoelectric encoder

Abstract

Light-emitting unit, comprising: a light source (10); and a reflector (20; 20a) having a reflective surface of a first partial paraboloid (21) and a reflective surface of a second partial paraboloid (22), wherein the first partial paraboloid (21) and the second partial paraboloid (22) are spaced apart from each other in the direction of an optical axis of the light source (10), wherein the first partial paraboloid (21) and the second partial paraboloid (22) have a focal point (O) at the light source (10), where: the second partial paraboloid (22) between the light source (10) and the first partial paraboloid (21) in the direction of the optical axis; the second partial paraboloid (22) has a coefficient that is different from that of the first partial paraboloid (21); the second partial paraboloid (22) is positioned on a reflection direction side of a light from the light source (10) reflected by the first partial paraboloid (21), with respect to a plane obtained under the assumption that the first partial paraboloid (21) extends to the side of the light source (10), according to the coefficient of the first partial paraboloid (21); the first partial paraboloid (21) and the second partial paraboloid (22) by z + a = (x 2 + y 2 ) / 4a (a > 0) are expressed where the direction of the optical axis is a Y-axis, a reflection direction of the first partial paraboloid (21) and the second partial paraboloid (22) is a Z-axis, an axis perpendicular to the Y-axis and the Z-axis is an X-axis, and a coefficient “a” is; and the coefficient “a” of the second partial paraboloid (22) is smaller than the coefficient “a” of the first partial paraboloid (21).

Description

AREA

[0001] The present invention relates to a light-emitting unit, a light-emitting and light-receiving unit, and a photoelectric encoder or rotary encoder. BACKGROUND

[0002] Japanese patent application JP 2011-059 055 A discloses a photoelectric encoder or rotary encoder comprising a collimating lens and a double-sided telecentric optical system. Japanese patent application JP 2007-151 565 A discloses a photoelectric encoder or rotary encoder comprising an illumination system utilizing a paraboloid mirror.

[0003] Furthermore, German patent application DE 10 2012 202 290 A1 discloses a light module for a motor vehicle headlight, comprising a light source having at least two light-emitting surfaces arranged side by side and directly adjacent to one another in a horizontal row. The light module has a reflector designed and arranged to image the light-emitting surfaces without generating an intermediate image in front of the light module, and which has at least two reflective, strip-shaped facets whose longitudinal direction is oriented parallel rather than perpendicular to the row of light-emitting surfaces and which are each arranged at a distance from the light source such that they image the light-emitting surfaces in front of the light module with the same imaging scale, such that each individual light-emitting surface is imaged as a vertically oriented and continuous strip.

[0004] The German patent application DE 10 2013 206 488 A1 relates to a light module of a motor vehicle lighting system. It comprises several separately controllable light sources grouped into an array for emitting light, several primary optical elements in the form of converging lenses grouped into a primary optical array, each with a light entry surface and a light exit surface, wherein the primary optical elements are designed to focus at least a portion of the light emitted by the light sources and to generate intermediate light distributions on the light exit surfaces, and a secondary optical system for imaging the emitted light onto a road surface in front of the motor vehicle as the resulting overall light distribution of the light module.

[0005] Furthermore, publication WO 2015 / 074757 A1 discloses a mirror arrangement for generating a plurality of beams from the beam of a light source, wherein the plurality of beams comprises at least a first beam with a first principal beam direction, a second beam with a second principal beam direction, and preferably further beams with further principal beam directions, with the following features: a first mirror segment with a first focal point that converts a first sub-region of the beam of the light source into the first beam, and a second mirror segment with a second focal point that converts a second sub-region of the beam of the light source into the second beam, and preferably further mirror segments with further focal points that convert further sub-regions of the beam of the light source into further beams, wherein the back side of the mirror segments has a curvature with radius R s.which lies concentrically to the light source.

[0006] Publication WO 2016 / 024489 A1 discloses an ADB lamp unit for a vehicle headlight, comprising a light source with a plurality of semiconductor light-emitting elements that can be individually switched on and off, and a reflector with a reflective surface based on a paraboloid of revolution. The reflector consists of several vertically subdivided sub-reflectors, the reflective surfaces of which are designed such that the horizontal scattering of the light reflected by each sub-reflector onto a given projection surface is approximately equal. SUMMARY

[0007] Document JP 2011-059 055 A uses a collimating lens. Therefore, reducing the focal length to shrink the illumination system can lead to a deterioration in illumination homogeneity, a deterioration in the parallelism of light rays, or similar issues. Thus, the technology of Document JP 2007-151 565 A can be used. However, if the technology of Document JP 2007-151 565 A is used for a photoelectric encoder or rotary encoder with multiple tracks, it is necessary to enlarge a paraboloid to cover two tracks. In this case, shrinking the illumination system is difficult.

[0008] The underlying technical problem is solved by the independent claims. Preferred embodiments are the subject of the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A shows a top view of a photoelectric encoder or rotary encoder according to a first embodiment; Fig. Figure 1B shows a side view of the photoelectric encoder; Fig. Figure 1C shows a front view of the photoelectric encoder; Fig. 2 shows a perspective view of a reflector; Fig. Figure 3 shows an optical detector; Fig. 4A to Fig. 4C show a light-receiving region; Fig. Figure 5A shows a side view of a photoelectric encoder or rotary encoder according to a comparative design form; Fig. Figure 5B shows a front view of the photoelectric encoder; Fig. Figure 6A shows a top view of a photoelectric encoder or rotary encoder according to a second embodiment; Fig. Figure 6B shows a side view of the photoelectric encoder; Fig. Figure 6C shows a front view of the photoelectric encoder; Fig. Figure 7 shows a perspective view of a reflector according to the second embodiment; Fig. Figure 8A shows a top view of a photoelectric encoder or rotary encoder according to a third embodiment; Fig. Figure 8B shows a side view of the photoelectric encoder; Fig. Figure 8C shows a front view of the photoelectric encoder; Fig. 9A and Fig. Figure 9B shows an allowed range of positional deviation between a focal point of a paraboloid and a light source; and Fig. Figure 10 shows the permissible range of position deviation between the focal point of the paraboloid and the light source. DESCRIPTION OF EXECUTION FORMS

[0009] The following is a description of embodiments with reference to the attached drawings. [First embodiment]

[0010] Fig. Figure 1A shows a top view of a photoelectric encoder or rotary encoder 100 according to a first embodiment. Fig. Figure 1B shows a side view of the photoelectric encoder 100. Fig. Figure 1C shows a front view of the photoelectric encoder 100. Fig. Figure 2 shows a perspective view of a reflector 20, which will be described later. In the following description, the direction of an arrow on each optical grating formed on a scale 30, which will be described later, is the X-axis. The direction of an optical axis of a light source 10, which will be described later, is the Y-axis. A direction perpendicular to the X-axis and the Y-axis is the Z-axis. The Z-axis corresponds to the direction of an output light from the light source 10 that is reflected by the reflector 20.

[0011] According to the representation in Fig. 1A to Fig. 1C, the photoelectric encoder 100 contains the light source 10, the reflector 20, the scale 30, a first optical detector 40, a second optical detector 50 and a light-receiving element 60.

[0012] The light source 10 is a light-emitting point element, such as a photodiode. As described above, the light source 10 has an optical axis in the Y-axis direction and emits light towards the positive side of the Y-axis. The light source 10 is arranged in a recess formed on a base surface of the reflector 20.

[0013] The reflector 20 is a concave mirror with a plurality of different partial paraboloids for converting emitted light from the light source 10 into collimated light. As shown in Fig. 1B, Fig. 1C and Fig. In embodiment 2, the reflector 20 comprises a first partial paraboloid 21 and a second partial paraboloid 22, which are spaced apart from each other in the Y-axis direction and have different coefficients. The second partial paraboloid 22 is positioned between the light source 10 and the first partial paraboloid 21 in the Y-axis direction. The second partial paraboloid 22 is positioned on the positive side of the Z-axis with respect to a plane obtained by assuming that the first partial paraboloid 21 extends towards the side of the light source 10 (the negative side of the Y-axis), according to the coefficient of the first partial paraboloid 21. The coefficients of the first partial paraboloid 21 and the second partial paraboloid 22 are determined such that a focal point O of the first partial paraboloid 21 and the second partial paraboloid 22 is positioned at a light-emitting point of the light source 10.Thus, an inner surface of the first partial paraboloid 21 and an inner surface of the second partial paraboloid 22 reflect the emitted light from the light source 10 and convert the emitted light into collimated light. Details of the first partial paraboloid 21 and the second partial paraboloid 22 will be described later.

[0014] The scale 30 comprises a transparent body 31 and a plurality of tracks. The number of tracks is the same as the number of partial paraboloids of the reflector 20. Therefore, in this embodiment, the scale 30 has two tracks: a first track 32 and a second track 33. The first track 32 is arranged on a beam path of the collimated light from the first partial paraboloid 21. The second track 33 is arranged on a beam path of the collimated light from the second partial paraboloid 22.

[0015] The first track 32 and the second track 33 feature optical gratings with a predetermined scale period along the X-axis. This means that the optical gratings in the X-axis are array-oriented. The first track 32 and the second track 33 are spaced apart along the Y-axis. The scale period of the first track 32 can be the same as that of the second track 33. The scale period of the first track 32 can also be different from that of the second track 33. For example, one track can be an incremental track with an incremental pattern of brightness and darkness at the same interval. The other track can be an absolute track with an absolute pattern expressing pseudorandom codes. One track can have a coarse pattern, and the other can have a fine pattern.The first track 32 and the second track 33 can have the same pattern grid, but with different phases. For example, each of the first track 32 and the second track 33 can be an incremental pattern with a phase difference of 90°. The output of the light-receiving element 60 can be a two-phase sinusoidal wave signal or a two-phase square wave signal.

[0016] The first optical detector 40 is arranged along a beam path of the collimated light passing through the first track 32. The second optical detector 50 is arranged along a beam path of the collimated light passing through the second track 33. The collimated light passing through the first track 32 exhibits brightness and darkness caused by the optical gratings of the first track 32 and enters the first optical detector 40. The collimated light passing through the second track 33 exhibits brightness and darkness caused by the optical gratings of the second track 33 and enters the second optical detector 50.

[0017] The first optical detector 40 and the second optical detector 50 generate an image of the collimated light at the light-receiving element 60. The first optical detector 40 and the second optical detector 50 can be a double-sided telecentric optical system or a lens-mirror array. Fig. Figure 3 represents the first optical detector 40. In Fig. Figure 3 shows the bilateral telecentric optical system. According to the illustration in Fig. In section 3, the first optical detector 40 has a structure in which a first imaging lens 41, an aperture plate 42, and a second imaging lens 43 are arranged in that order along a beam path. Diffracted light passing through the first track 32 passes through the first imaging lens 41, passes through an aperture or opening of the aperture plate 42, is condensed by the second imaging lens 43, and focused onto the light-receiving element 60. The second optical detector 50 has the same structure as the first optical detector 40.

[0018] The light-receiving element 60 is, for example, a photodiode array. The light-receiving element 60 has a plurality of light-receiving regions. The number of light-receiving regions is the same as the number of partial paraboloids of the reflector 20. In this embodiment, the light-receiving element 60 therefore has two light-receiving regions, a first light-receiving region 61 and a second light-receiving region 62.

[0019] In each of the first light-receiving region 61 and the second light-receiving region 62, a plurality of photodiodes are arranged in the X-axis direction in a predetermined periodic interval.

[0020] The first optical detector 40 generates an image of the collimated light passing through the first track 32 at the first light-receiving region 61 of the light-receiving element 60. The second optical detector 50 generates an image of the collimated light passing through the second track 33 at the second light-receiving region 62 of the light-receiving element 60. The first light-receiving region 61 uses outputs from a plurality of photodiodes and detects brightness and darkness according to the optical gratings of the first track 32. The second light-receiving region 62 uses outputs from a plurality of photodiodes and detects brightness and darkness according to the optical gratings of the second track 33. It is therefore possible to detect a relative position fluctuation between the scale 30 and the light-receiving element 60.More precisely, it is possible to calculate a position fluctuation amount based on the optical intensity detected by the majority of photodiodes.

[0021] Next follows a description of details of the first partial paraboloid 21 and the second partial paraboloid 22 of the reflector 20. The first partial paraboloid 21 and the second partial paraboloid 22 share a focal point. The first partial paraboloid 21 is part of a paraboloid of revolution. The second partial paraboloid 22 is part of a different, or further, paraboloid of revolution. The coefficient of the paraboloid of revolution of the first partial paraboloid 21 differs from that of the second partial paraboloid 22. An i ter The partial paraboloid can be expressed by the following formula (1) with reference to the focus O as the origin. “a i “ is a coefficient. According to the representation in Fig. 1C is “a i“A distance in the negative direction of the Z-axis between each subparaboloid extends to the negative side of the Y-axis direction and the focal point O. As described above, the direction of light emission of the collimated light emitted by each subparaboloid is the positive direction of the Z-axis. A coefficient “a2” of the second subparaboloid is smaller than a coefficient “a1” of the first subparaboloid. “a i “ is a value that a i >0 fulfilled. zi+ai=(xi2+yi2) / 4ai

[0022] The paraboloid expressed by formula (1) has a shape that realizes perfectly parallel light with respect to an ideal spherical wave with focal point O as the origin. However, if a light source device is located at the focal point (for example, an LED package component is connected to a reflector component), optical refraction occurs, for example, at a medium interface with a different refractive index or at an air interface between the light source device and the reflector. Therefore, an aberration from the ideal spherical wave occurs at, or rather at, a wavefront emitted by the light source. Furthermore, the parallelism of reflected light can be degraded. The aberration is determined by a structure from the light source to the paraboloid. It is therefore possible to improve the parallelism by adding or removing a layer of material.Adding a correction term as the following formula (2) improves and eliminates the aberration. zi+ai=(xi2+yi2) / 4ai+ci(x,y) c i (x,y) is an arbitrary correction term added to the subparaboloid according to a coordinate. As a design method for the aberration term, the correction term can be expressed by a high-order multinomial function of x and y, and a coefficient can be optimally designed.

[0023] The reflector 20 consists of a transparent material. For example, the reflector 20 is an optical resin. There are no restrictions on the manufacturing process of the reflector 20. For example, it is possible to form the reflector 20 using resin injection molds. A reflective film with high reflectivity is formed on the outer surfaces of the first partial paraboloid 21 and the second partial paraboloid 22. For example, the reflective film exhibiting high reflectivity can be a metal vapor deposition film (aluminum or the like), a dielectric multilayer film, or the like.

[0024] A portion of the first partial paraboloid 21, which directs the emitted light from the light source 10 into the first light-receiving region 61 of the light-receiving element 60, is hereinafter referred to as a first effective region 23. A portion of the second partial paraboloid 22, which directs the emitted light from the light source 10 into the second light-receiving region 62 of the light-receiving element 60, is hereinafter referred to as a second effective region 24. Each coefficient of the first partial paraboloid 21 and the second partial paraboloid 22 is chosen such that the collimated light from the first effective region 23 and the collimated light from the second effective region 24 do not interfere with or block each other.

[0025] Fig. 4A to 4C show the first light-receiving region 61. According to the representation in Fig. In the first light-receiving region 61, a plurality of light-receiving elements 63 are spaced apart from one another and arranged at a predetermined interval in the X-axis direction. The first effective region 23 is designed to cover all of the light-receiving elements 63 in the first subparaboloid 21, as indicated by a dotted line in Fig. 4A is indicated. In another case, the first effective region 23 covers all of the light-receiving elements 63 in the first subparaboloid 21 in the X-axis direction, as indicated by a dotted line in Fig. 4B is specified. Furthermore, there may also be cases where the first effective region 23 does not cover a portion of each light-receiving element 63 in the Y-axis direction. The second effective region 24 forms the same region with respect to the second light-receiving region 62. In the example of Fig. 1A to Fig. 1C, as it is in Fig. As shown in Figure 4C, the first effective region 23 corresponds to the region determined by the light-receiving region (region obtained by connecting contours or outlines of all light-receiving elements 63) and a magnification of the first optical detector 40 (the same magnification in Figure 4C). Fig. 1A to Fig. 1C). [Comparison form]

[0026] The following is a description of a photoelectric encoder or rotary encoder 200 according to a comparative embodiment, in order to describe an effect of the photoelectric encoder 100 according to the first embodiment. Fig. Figure 5A shows a side view of the photoelectric encoder 200. Fig. Figure 5B shows a front view of the photoelectric encoder 200. The photoelectric encoder 200 differs from the photoelectric encoder 100 in that a reflector 210 is provided instead of the reflector 20.

[0027] According to the representation in Fig. 5A and Fig. 5B is a partial paraboloid 201 formed in the reflector 210. The coefficient of formula (1) is "a" (>0). A first effective region 202 and a second effective region 203 are contained within the partial paraboloid 201. The first effective region 202 is a region of the partial paraboloid 201 and is a region for directing the emitted light from the light source 10 into the first light-receiving region 61. The second effective region 203 is a part of the partial paraboloid 201 and is a region for directing the emitted light from the light source 10 into the second light-receiving region 62. The first effective region 202 is spaced apart from the second effective region 203 in the Y-axis direction. A reason for this Y-axis spacing between the first effective region 202 and the second effective region 203 follows.

[0028] In the photoelectric encoder, which has two distinct tracks, it is possible to detect a highly accurate absolute position by combining highly accurate position information obtained through uniformly spaced grid tracks with track information that stores absolute position data. These tracks are arranged vertically to a measurement direction in one direction (the Y-axis). In the photoelectric encoder, each track has a height in the vertical direction (Y-axis). This is because the track must have a height greater than that of a light-receiving region, thus allowing for a relative deviation in height caused by component mounting or detector movement, in addition to the height of a light-receiving region of a light-receiving element (a photodiode array mounted on an IC).

[0029] Two different tracks are arranged adjacent to each other. When the tracks are close together, the probability of light mixing (scattering) across a nearby track increases. This, in turn, increases the risk of performance degradation, such as noise. For these reasons, it is required that the two tracks be of a suitable height and spaced appropriately apart. For example, a distance of 3 mm between the tracks is preferred. Therefore, it is necessary to space the first effective region 202 from the second effective region 203 along the Y-axis.

[0030] If a partial paraboloid has the first effective region 202 and the second effective region 203, it is necessary to distance the first effective region 202 from the second effective region 203 in the Y-axis direction. Therefore, the first effective region 202 is distanced from the second effective region 203 in the Z-axis direction. Fig. In 5B, it is possible to provide an excessive thickness T of the reflector 210 as a distance. In this case, the reflector becomes thicker in the Z-axis direction. Thus, miniaturizing a lighting system with one light source and one reflector becomes difficult.

[0031] In the photoelectric encoder 100 according to the first embodiment, however, it is possible to eliminate excessive thickness between the first effective region 23 and the second effective region 24, compared to a reflector using a single partial paraboloid. More precisely, it is possible to shift the second partial paraboloid 22 towards the positive side of the Z-axis with respect to a plane obtained by assuming that the first partial paraboloid 21 extends towards the negative side of the Y-axis direction, according to the coefficient of the first partial paraboloid 21. It is therefore possible to eliminate excessive thickness of the reflector 20. Thus, it is possible to reduce the size of the illumination system. Furthermore, it is possible to emit homogeneous parallel light to an area that adequately covers the first effective region 23 and the second effective region 24.And when internal reflection is used, external contamination of the reflective surface is prevented. It is possible to determine the position of the light source 10 with high accuracy and to mount the light source 10, since a reflective surface and a recess for the light source 10 are formed in the same component. [Second embodiment]

[0032] Fig. Figure 6A shows a top view of a photoelectric encoder or rotary encoder 100a according to a second embodiment. Fig. Figure 6B shows a side view of the photoelectric encoder 100a. Fig. Figure 6C shows a front view of the photoelectric encoder 100a. The photoelectric encoder 100a differs from the photoelectric encoder 100 in that a reflector 20a is provided instead of the reflector 20. Fig. Figure 7 shows a perspective view of reflector 20a.

[0033] Reflector 20a differs from reflector 20 in that one shape of reflector 20a is limited. According to the illustration in Fig. 6A to Fig. 6C and Fig. 7. For reflector 20a, the coefficient a1 (>0) of the first subparaboloid 21 and the coefficient a2 (>0) of the second subparaboloid 22 are determined such that a minimum Z-coordinate Z 1MIN the first effective region 23 and a minimum Z-coordinate Z 2MAX the second effective region 24 agree with each other under the assumption that the first effective region 23 and the second effective region 24 are projected onto the XZ plane.

[0034] In this structure, the back clearance of a tool increases when a metal form of the reflector 20a is machined by a lathe or similar machine. Therefore, a preferential effect of easier machinability is achieved. [Third embodiment]

[0035] In both the first and second embodiments, the number of light sources is one. However, this number is not limited. For example, multiple light sources can be provided. Fig. Figure 8A shows a top view of a photoelectric encoder or rotary encoder 100b according to a third embodiment. Fig. Figure 8B shows a side view of the 100b photoelectric encoder. Fig. Figure 8C shows a front view of the 100b photoelectric encoder.

[0036] In the photoelectric encoder 100b, a reflector 20b is provided instead of the reflector 20. As shown in Fig. 8A to Fig. In 8C, the reflector 20b has the first partial paraboloid 21 and the second partial paraboloid 22, which are provided in the Y-axis direction and spaced apart from each other, as in the first embodiment and the second embodiment. The second partial paraboloid 22 is positioned between a first light source 11 and the first partial paraboloid 21 in the Y-axis direction. The second partial paraboloid 22 is positioned on the plus side of the Z-axis with respect to a plane obtained under the assumption that the first partial paraboloid 21 extends to the side of the first light source 11 (the minus side of the Y-axis), according to the coefficient of the first partial paraboloid 21.

[0037] For example, the first light source 11 and a second light source 12 can be positioned at two different locations along the Z-axis. The first light source 11 and the second light source 12 are each positioned in two recesses formed in the base of the reflector 20b. The coefficient of the first partial paraboloid 21 is determined such that a first focal point O1 of the first partial paraboloid 21 is positioned at an emission or radiation point of the first light source 11. The coefficient of the second partial paraboloid 22 is determined such that a second focal point O2 of the second partial paraboloid 22 is positioned at an emission or radiation point of the second light source 12.

[0038] XYZ axes with reference to the first focus O1 of the first subparaboloid 21 as an origin are X1Y1Z1 axes. XYZ axes with reference to the second focus O2 of the second subparaboloid 22 as an origin are X2Y2Z2 axes. In this case, the X1 axis, the Y1 axis, and the Z1 axis are each parallel to the X2 axis, the Y2 axis, and the Z2 axis, respectively. However, the X1 axis, the Y1 axis, and the Z1 axis can also be offset from or separated from the X2 axis, the Y2 axis, and the Z2 axis, respectively.This means that the majority of light sources can be located at arbitrary positions if the first partial paraboloid 21 and the second partial paraboloid 22, which are distinct from each other, are provided at two different positions in the Y-axis direction and spaced apart from each other, the second partial paraboloid 22 is between the first light source 11 and the first partial paraboloid 21 in the Y-axis direction, the second partial paraboloid 22 is positioned on the plus side of the Z-axis with respect to a plane obtained under the assumption that the first partial paraboloid 21 extends to the side of the first light source 11 (the minus side of the Y-axis), according to the coefficient of the first partial paraboloid 21.

[0039] Next follows a description of an allowed range of positional deviation between the focal point of the partial paraboloid and the light source. Fig. Figure 9A shows a schematic view containing the partial paraboloid, the focal point (focal point O) of the light source, and the position of the track (substance A). According to the representation in Fig. 9A A light beam emitted from focal point O is reflected by the partial paraboloid and reaches substance A. Subsequently, transmitted light is introduced into the optical detector, exhibiting an angle of incidence plus or minus “θ”, and an image is generated.

[0040] Two light rays, specified with an angle plus or minus "α", correspond to diffracted first-order light (α = sin -1(±Φ / p) with a wavelength of λ, obtained through a diffraction grating (track) with a grating spacing or measure "p". This diffracted light and a transmitted zero-order light are light rays that contribute to the image formation of the grating spacing "p". To produce an image with grating spacing "p" with sufficient contrast, it is generally determined that "θ" must be sufficiently larger than "α".

[0041] If the focal point O is offset from the optical axis by “ε” in the vertical direction, an inclination error (ε / f) of a light ray, obtained by dividing the error “ε” between the focal point and the center of the light source by the focal point f from the light source to the partial paraboloid, can occur at an angle of incidence to or onto the substance A. In this case, the two diffracted lights of plus or minus “α”, which are in Fig. Figure 9B shows the two diffracted lights being uniformly inclined. However, if the two diffracted lights are within the angle of incidence plus or minus “θ”, these two diffracted lights contribute to image formation, assuming any optical aberration caused by the inclination of the light beam is ignored.

[0042] In the description above, a virtual light source point of no size coincides perfectly with the focus of the partial paraboloid. However, an actual light source has a finite size "w". Therefore, a light ray spreads out around an ideal parallel light source. The broadening angle is defined as the number of apertures or f-stops of the light source (NAs = sin (w / 2f) ("f" is a focal length of the partial paraboloid). Consequently, light emitted from a light source of finite size spreads out around the focal point by a broadening angle of w / 2f. Therefore, the permissible range of error in the center position of the light source increases with this angle.

[0043] Provided that diffracted light contributing to image formation is introduced into an image formation system, a limit is checked that is allowed for the error “ε” of the center position of a light source. Fig. Figure 10 shows a limited relationship of light rays around substance A, under the condition that one angle is exaggerated. From the left side of Fig. 10. The light rays are emitted with an inclination of ε / f and a broadening angle w / 2f. The smallest inclination angle is ε / f - w / 2f.

[0044] On the right side of substance A, diffracted light (surrounded by ± α), which contributes to image formation, is indicated within the light incidence angle "θ". An angle of the light beam corresponding to the transmitted zero-order light is "θ - α". As an approximation of which angle is sufficiently small, it is therefore possible to obtain a relationship ε / f - w / 2f = θ - α, that is, ε = f (θ - α) + w / 2 (0 = θ - α). This means that an allowable range of error "ε" of the central position of the light source is approximately w / 2, that is, half the width of the light source in the strictest state. It can be assumed that the allowable range increases based on a tolerance (θ - α) of the incidence angle of the imaging system and the focal length "f" of the partial paraboloid.

[0045] It is not necessary to ensure that the center of the emission or radiation point of the light source coincides with the focal point in the optical component of the embodiments. It is preferred that the positional error of the light source center satisfies the condition obtained from the approximation formulas mentioned above.

[0046] Regarding the structure of the illumination system, a bright-field illumination is required, which introduces the transmitted zero-order light directly into the image generation system. However, a dark-field illumination structure that detects scattered light from or into a substance, or a structure that uses scattered illumination light through a diffusion plate, can also be used for the component of the embodiments.

[0047] The present invention is not limited to the specifically disclosed embodiments and variations may include other embodiments and variations without departing from the scope of the present invention.

Claims

[1] Light-emitting unit comprising: a light source (10); and a reflector (20; 20a) having a reflective surface of a first partial paraboloid (21) and a reflective surface of a second partial paraboloid (22), wherein the first partial paraboloid (21) and the second partial paraboloid (22) are spaced apart from each other in the direction of an optical axis of the light source (10), wherein the first partial paraboloid (21) and the second partial paraboloid (22) have a focal point (O) at the light source (10), where: the second partial paraboloid (22) between the light source (10) and the first partial paraboloid (21) in the direction of the optical axis; the second partial paraboloid (22) has a coefficient that is different from that of the first partial paraboloid (21); the second partial paraboloid (22) is positioned on a reflection direction side of a light from the light source (10) reflected by the first partial paraboloid (21), with respect to a plane obtained under the assumption that the first partial paraboloid (21) extends to the side of the light source (10), according to the coefficient of the first partial paraboloid (21); the first partial paraboloid (21) and the second partial paraboloid (22) by z + a = (x 2 + y 2 ) / 4a (a > 0) are expressed where the direction of the optical axis is a Y-axis, a reflection direction of the first partial paraboloid (21) and the second partial paraboloid (22) is a Z-axis, an axis perpendicular to the Y-axis and the Z-axis is an X-axis, and a coefficient “a” is; and the coefficient “a” of the second partial paraboloid (22) is smaller than the coefficient “a” of the first partial paraboloid (21). [2] Light-emitting unit comprising: a light source (10); and a reflector (20; 20a) having a reflective surface of a first partial paraboloid (21) and a reflective surface of a second partial paraboloid (22), wherein the first partial paraboloid (21) and the second partial paraboloid (22) are spaced apart from each other in the direction of an optical axis of the light source (10), wherein the first partial paraboloid (21) and the second partial paraboloid (22) have a focal point (O) at the light source (10), where: the second partial paraboloid (22) between the light source (10) and the first partial paraboloid (21) in the direction of the optical axis; the second partial paraboloid (22) has a coefficient that is different from that of the first partial paraboloid (21); the second partial paraboloid (22) is positioned on a reflection direction side of a light from the light source (10) reflected by the first partial paraboloid (21), with respect to a plane obtained under the assumption that the first partial paraboloid (21) extends to the side of the light source (10), according to the coefficient of the first partial paraboloid (21); the first partial paraboloid (21) and the second partial paraboloid (22) by z + a = (x 2 + y 2 ) / 4a + c i (x,y) (a > 0) are expressed where the direction of the optical axis is a Y-axis, a reflection direction of the first partial paraboloid (21) and the second partial paraboloid (22) is a Z-axis, an axis perpendicular to the Y-axis and the Z-axis is an X-axis, a coefficient “a” and “c i (x,y) is an arbitrary correction term; and the coefficient “a” of the second partial paraboloid (22) is smaller than the coefficient “a” of the first partial paraboloid (21). [3] Light-emitting unit according to claim 1 or 2, wherein the second partial paraboloid (22) is positioned on one side in a direction in which light from the light source (10), reflected from the first partial paraboloid (21), propagates, compared with the plane obtained assuming that the first partial paraboloid (21) extends to the side of the light source (10), according to the coefficient of the first partial paraboloid (21). [4] Light-emitting and light-receiving unit comprising: a light-emitting unit according to any one of claims 1 to 3; a first light-receiving element (60, 61) that receives light from the first partial paraboloid (21); and a second light-receiving element (60, 62) that receives light from the second partial paraboloid (22). [5] Photoelectric encoder (100; 100a; 100b), comprising: a light-emitting and light-receiving unit according to claim 4; a first track (32) which has optical gratings along a measuring axis, moves relative to the light-emitting and light-receiving unit and transmits light from the first partial paraboloid (21); and a second track (33) which has optical gratings along the measuring axis, moves relative to the light-emitting and light-receiving unit and transmits light from the second partial paraboloid (22), where: the first light-receiving element (60, 61) is arranged to receive light passing through the first track (32); and the second light-receiving element (60, 62) is arranged to receive light passing through the second track (33). [6] Light-emitting unit comprising: a first light source (11) and a second light source (12); and a reflector (20b) having a reflective surface of a first partial paraboloid (21) and a reflective surface of a second partial paraboloid (22), wherein the reflective surface of the first partial paraboloid (21) has a focal point (O1) at the first light source (11), and the reflective surface of the second partial paraboloid (22) has a focal point (O2) at the second light source (12); where: the first partial paraboloid (21) and the second partial paraboloid (22) are spaced apart from each other in the direction of an optical axis of the first light source (11); the second partial paraboloid (22) between the first light source (11) and the first partial paraboloid (21) in the direction of the optical axis of the first light source (11); the second partial paraboloid (22) has a coefficient that is different from that of the first partial paraboloid (21); the second partial paraboloid (22) is positioned on or at a reflection direction of a light from the first light source (11) that is reflected by the first partial paraboloid (21), with respect to a plane obtained under the assumption that the first partial paraboloid (21) extends to the side of the first light source (11), according to the coefficient of the first partial paraboloid (21); the first partial paraboloid (21) and the second partial paraboloid (22) by z + a = (x 2 + y 2 ) / 4a (a > 0) are expressed where the direction of the optical axis is a Y-axis, a reflection direction of the first partial paraboloid (21) and the second partial paraboloid (22) is a Z-axis, an axis perpendicular to the Y-axis and the Z-axis is an X-axis, and a coefficient “a” is; and the coefficient “a” of the second partial paraboloid (22) is smaller than the coefficient “a” of the first partial paraboloid (21).

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