Illumination Optics

Abstract

The illumination optical system of the present invention comprises, in order from the illumination object side, a first lens having positive refractive power, a second lens having negative refractive power, and a third lens having positive refractive power. When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the following formula is satisfied, where the composite focal length is f millimeters, the composite refractive power is Pt=1 / f, the surfaces of the three lenses are the first to sixth surfaces from the illumination object side, the refractive power of the fifth surface is P5, and the central thickness of the second lens is L2. 1.3

Description

[Technical field]

[0001] The present invention relates to an illumination optical system used in vehicle headlamps and the like. [Background technology]

[0002] In recent years, lighting optical systems for adaptive driving beam (ADB) light distribution control in vehicle headlamps have been developed (Patent Document 1). In ADB light distribution control, multiple LEDs (light emitting diodes) arranged as light sources are individually controlled according to the situation of other vehicles ahead of the vehicle to control the illumination target area and illumination intensity. Therefore, in ADB light distribution control, it is required that the illumination area of ​​each LED can be individually controlled. Therefore, in the lighting optical system, it is necessary to reduce flare, which is a phenomenon in which unintended areas are illuminated, as much as possible. In addition, it is desirable for the lighting optical system to be bright.

[0003] Therefore, in the field of vehicle headlamps and the like, there is a need for a bright illumination optical system with little flare. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication 2019-573638 (Patent 002897) Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an illumination optical system that is bright and has little flare. [Means for solving the problem]

[0006] The illumination optical system of the present invention comprises, in order from the illumination object side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power. When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the composite focal length is f millimeters, the composite refractive power is Pt=1 / f, the surfaces of the three lenses are the first to sixth surfaces from the illumination object side, the refractive power of the fifth surface is P5, and the central thickness of the second lens is L2. 1.3 <P5 / Pt 0.1 <L2 / f<0.25 is satisfied.

[0007] According to the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination target side, coma aberration is reduced, and flare of the illumination optical system corresponding to the coma aberration is reduced.

[0008] In the illumination optical system of the first embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the proportion of light rays that reach the image plane among the light beams incident on the illumination object side surface of the first lens at an angle of 25 degrees with respect to the optical axis is in the range of 14% to 20%.

[0009] In the illumination optical system according to the second embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination target side, the F value is F, and F<0.7 is satisfied.

[0010] The illumination optical system of this embodiment provides sufficient luminous intensity.

[0011] In the illumination optical system according to the third embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from an illumination target side, the focal point movement range of the axial chromatic aberration of a light beam having a wavelength of 0.420 micrometers to 0.680 micrometers based on the d-line (588 nanometers) is defined as c millimeters, c / f<0.00292 is satisfied.

[0012] According to the illumination optical system of this embodiment, chromatic dispersion on the illumination surface is reduced.

[0013] In the illumination optical system of the fourth embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the distortion of a light ray incident on the illumination object side surface of the first lens at an angle of 20 degrees with respect to the optical axis is negative, and the absolute value of the distortion is 5 percent or more.

[0014] The illumination optical system of this embodiment can illuminate a wider range compared to a case without distortion.

[0015] In the illumination optical system of the fifth embodiment of the present invention, the materials of the first lens, the second lens and the third lens are acrylic, polycarbonate and acrylic, respectively.

[0016] In the illumination optical system of this embodiment, acrylic and polycarbonate, which have different refractive indices, are used as the materials for the three lenses. This reduces axial chromatic aberration when the illumination optical system is considered as an imaging optical system for a light beam incident from the illumination target side, thereby making it possible to reduce chromatic dispersion on the illumination surface.

[0017] In the illumination optical system according to a third embodiment of the present invention, the first lens is a biconvex lens, the second lens is a biconcave lens, and the third lens is a biconvex lens. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an example of an illumination optical system according to the present invention. [Diagram 2] 2 is a diagram showing the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system shown in FIG. 1, the parallel light beam making an angle of 25 degrees with the optical axis of the illumination optical system. [Diagram 3]This is a diagram showing the area of ​​surface S1 through which light rays pass that reach a surface that includes point O and is perpendicular to the optical axis without being vignetted, out of a parallel light beam that is parallel to the optical axis and enters surface S1 of the optical system. [Figure 4] This figure shows the area of ​​surface S1 through which light rays pass that reach a surface that contains point O and is perpendicular to the optical axis without being vignetted, out of a parallel light beam that is incident on surface S1 of the optical system and forms an angle of 25 degrees with the optical axis. [Diagram 5] 1 is a diagram showing the ratio of light rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted, out of a parallel light beam that is incident on a surface S1 of the optical system. [Figure 6] 2 is a diagram showing the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system shown in FIG. 1, the light beam making an angle of 23 degrees with the optical axis of the illumination optical system. [Figure 7] 2 is a diagram showing the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system shown in FIG. 1, the light beam making an angle of 23 degrees with the optical axis of the illumination optical system. [Figure 8] 13 is a diagram showing the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system of the comparative example, the parallel light beam making an angle of 23 degrees with the optical axis of the illumination optical system. [Figure 9] FIG. 13 is a diagram showing a flare on a plane perpendicular to the z-axis caused by a light source placed at a point on the x-axis away from point O by a distance between points O and E″. [Figure 10] This figure shows the path of light rays when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an optical system in which the central thickness of the second lens is changed to 4.0 millimeters.

[0019] [Figure 11] This figure shows the path of light rays when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an optical system having a diameter of 5.5 millimeters in which the central thickness of the second lens is changed. [Figure 12] This figure shows the path of light rays when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an 8.5 mm optical system in which the central thickness of the second lens is changed. [Figure 13]1 is a diagram showing the field curvature when the embodiment is regarded as an imaging optical system. FIG. [Figure 14] 11A and 11B are diagrams illustrating distortion when the embodiment is regarded as an imaging optical system. [Figure 15] FIG. 11 is a diagram showing axial chromatic aberration when the embodiment is regarded as an imaging optical system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] FIG. 1 is a diagram showing an example of an illumination optical system of the present invention. The illumination optical system includes a first lens L1, a second lens L2, and a third lens L3, and is configured to irradiate an object with light from a light source having a center at a point O. The first lens L1 is closest to the illumination object, and the third lens L3 is closest to the light source. The surfaces of the first lens L1, the second lens L2, and the third lens L3 on the illumination object side are represented by S1, S3, and S5, respectively, and the surfaces of the first lens L1, the second lens L2, and the third lens L3 on the light source side are represented by S2, S4, and S6. The illumination optical system is disposed so that its optical axis passes through the point O. FIG. 1 shows the path of a light ray when a parallel light beam parallel to the optical axis of the illumination optical system is incident on the surface S1 from the illumination object side of the illumination optical system.

[0021] Each lens surface is expressed by the following formula:

number

[0022] Table 1 shows the shapes, materials, and positions of the lenses in the illumination optical system of the embodiment. [Table 1] The radius of curvature is the reciprocal of the curvature c. The "thickness or distance" in the row S1 indicates the thickness (center thickness) of the first lens L1, and the "thickness or distance" in the row S6 indicates the distance along the optical axis from the surface S6 to the point O at the center of the light source.

[0023] Table 2 shows the values ​​of the aspherical coefficients of each lens surface. Any aspherical coefficients not shown in the table have a value of 0. [Table 2]

[0024] In the following, the illumination optical system shown in Fig. 1 will be considered as an imaging optical system. As mentioned above, Fig. 1 shows the path of light rays when a parallel light beam parallel to the optical axis of the illumination optical system is incident on surface S1 from the illumination target side. The parallel light beam is focused at point O.

[0025] Fig. 2 is a diagram showing the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system shown in Fig. 1, forming an angle of 25 degrees with the optical axis of the illumination optical system. The parallel light beam reaches the vicinity of a point E on a plane that includes a point O and is perpendicular to the optical axis. Considering the path of the light ray shown in Fig. 1 and Fig. 2, it is estimated that if a light source such as an LED (light emitting diode) is placed in a range from point O to the distance between point O and point E on a plane that includes point O and is perpendicular to the optical axis, it is possible to illuminate an area that is centered on the light source and forms an angle of 25 degrees or less with the optical axis.

[0026] Table 3 shows the refractive power of each lens surface and the composite refractive power of the imaging optical system in the embodiment. The composite refractive power is the reciprocal of the composite focal length of the imaging optical system. In Table 3, "ratio" means the ratio of the refractive power of each surface to the composite refractive power. The composite focal length of the imaging optical system is 34.697 millimeters. The F-number is 0.65. In general, it is preferable that the F-number is smaller than 0.7. [Table 3]

[0027] In this embodiment, the refractive power of the surface S5 is relatively large, as shown in Table 3. The reason for making the refractive power of the surface S5 relatively large will be explained below.

[0028] In illumination optical systems, illumination of unintended areas can occur, which is called flare. Flare is a major obstacle to ADB light distribution control, which requires highly accurate determination of the illumination position of each LED. Flare in illumination optical systems corresponds to coma aberration when the illumination optical system is considered as an imaging optical system. In other words, the larger the coma aberration when considered as an imaging optical system, the larger the flare in the illumination optical system. Therefore, in order to reduce flare in illumination optical systems, it is necessary to reduce the coma aberration when considered as an imaging optical system. One method for reducing coma aberration is to use vignetting to reduce the proportion of light rays that reach a plane perpendicular to the optical axis that includes point O among parallel light beams that make a relatively large angle with the optical axis.

[0029] Fig. 3 is a diagram showing the area of ​​surface S1 through which light rays pass that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted, out of a parallel light beam that is incident on surface S1 of the optical system. The diagram on the left side of Fig. 3 shows a plan view of surface S1, and the diagram on the right side of Fig. 3 shows the configuration path of the optical system, similar to Fig. 1. According to Fig. 3, light rays that pass through almost the entire area of ​​surface S1 reach a plane that includes point O and is perpendicular to the optical axis, without being vignetted. The diagram on the right side of Fig. 3 shows the path of the light rays, similar to Fig. 1.

[0030] Fig. 4 is a diagram showing the area of ​​surface S1 through which light rays pass that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted, out of a parallel light beam that is incident on surface S1 of the optical system and forms an angle of 25 degrees with the optical axis. The diagram on the left side of Fig. 4 shows a plan view of surface S1, and the diagram on the right side of Fig. 4 shows the configuration path of the optical system, similar to Fig. 2. According to Fig. 4, the area of ​​surface S1 through which light rays pass that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted is 20 percent or less of the total area.

[0031] Fig. 5 is a diagram showing the proportion of light rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted out of a parallel light beam that is incident on surface S1 of the optical system. The horizontal axis of Fig. 5 indicates the angle that the parallel light beam makes with the optical axis. The vertical axis of Fig. 5 indicates the proportion of light rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted. According to Fig. 5, when the angle that the parallel light beam makes with the optical axis is 25 degrees, the proportion of light rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted is approximately 15 percent.

[0032] As shown in FIG. 4, when the angle that the parallel light beam makes with the optical axis is 25 degrees, by decreasing the radius of curvature of surface S5 and increasing its refractive power, part of the light rays diverging from surface S4 are more likely to be vignetted, and the proportion of light rays that reach the surface that includes point O and is perpendicular to the optical axis without being vignetted decreases.

[0033] In general, it is preferable that the ratio of the refractive power of surface S5 to the composite refractive power is greater than 1.3. Also, when the angle between the parallel light beam and the optical axis is 25 degrees, the percentage of light rays that reach a surface that includes point O and is perpendicular to the optical axis without being vignetted is preferably in the range of 14% to 20%.

[0034] Table 4 shows the values ​​of each aberration of each surface of the imaging optical system. [Table 4] "Total" is the sum of the aberrations of each surface, and indicates the aberration of the entire imaging optical system. According to Table 4, the aberration of surface S5 contributes to reducing the aberration of the entire imaging optical system. Increasing the radius of curvature of surface S5 (reducing the refractive power) tends to increase the aberration of the entire imaging optical system. From this point of view, it is also preferable that the ratio of the refractive power of surface S5 to the composite refractive power be within the above range.

[0035] Fig. 6 is a diagram showing the path of light rays when a parallel light beam is incident on surface S1 from the illumination target side of the illumination optical system shown in Fig. 1, making an angle of 23 degrees with the optical axis of the illumination optical system. The parallel light beam reaches the vicinity of point E' on a plane that includes point O and is perpendicular to the optical axis. In Fig. 6, point O is the origin, and the optical axis of the optical system is the z-axis. The x-axis is perpendicular to the paper surface of Fig. 6.

[0036] Fig. 7 is a diagram showing a flare on a plane perpendicular to the z-axis caused by a light source placed at a point on the x-axis separated from point O by a distance between point O and point E'. One example of the light source is a light-emitting diode. The horizontal axis of Fig. 7 shows the angle between the z-axis and a line projected onto the xz plane of a light ray emitted from the light source. The vertical axis of Fig. 7 shows the angle between the z-axis and a line projected onto the yz plane of a light ray emitted from the light source.

[0037] Another illumination optical system will be considered below as a comparative example.

[0038] Table 5 shows the shapes, materials, and positions of the lenses in the illumination optical system of the comparative example. [Table 5] The "thickness or spatial length" in the S1 row indicates the thickness (center thickness) of the first lens L1, and the "thickness or spatial length" in the S6 row indicates the distance along the optical axis from the surface S6 to the point O at the center of the light source.

[0039] Table 6 shows the aspheric coefficients of each lens surface. [Table 6]

[0040] Table 7 shows the refractive power of each lens surface and the composite refractive power of the imaging optical system of the comparative example. The composite refractive power is the reciprocal of the composite focal length of the imaging optical system. The composite focal length of the imaging optical system is 34.799 millimeters. The F-number is 0.66. [Table 7]

[0041] Fig. 8 is a diagram showing the path of a light ray when a parallel light beam is incident on surface S1 from the illumination target side of the illumination optical system of the comparative example, making an angle of 23 degrees with the optical axis of the illumination optical system. The above-mentioned parallel light beam reaches the vicinity of point E" on a plane that includes point O and is perpendicular to the optical axis. In Fig. 8, point O is the origin, and the optical axis of the optical system is the z-axis. The x-axis is a direction perpendicular to the paper surface of Fig. 8.

[0042] FIG. 9 is a diagram showing a flare on a plane perpendicular to the z-axis caused by a light source placed at a point on the x-axis away from point O by a distance between point O and point E″. One example of the light source is a light-emitting diode. The horizontal axis of FIG. 9 represents the angle between the z-axis and a line obtained by projecting a light ray emitted from the light source onto the xz plane. The vertical axis of FIG. 9 represents the angle between the z-axis and a line obtained by projecting a light ray emitted from the light source onto the yz plane.

[0043] Comparing Fig. 7 showing the flare of the illumination optical system of the embodiment with Fig. 9 showing the flare of the illumination optical system of the comparative example, a large inward flare is observed in Fig. 9. The inward flare of the illumination optical system corresponds to the outward coma aberration in the imaging optical system. Therefore, it is considered that the coma aberration is not sufficiently reduced when the comparative example is used as the illumination optical system.

[0044] Comparing Tables 3 and 7, the refractive power of surface S5 is almost the same. On the other hand, according to Table 2, the center thickness of the second lens of the embodiment is 6.992 millimeters, and according to Table 5, the center thickness of the second lens of the comparative example is 2.500 millimeters.

[0045] According to Fig. 6, when a parallel light beam is incident at an angle of 23 degrees with the optical axis, the light beam is incident on the surface S5 of the embodiment in an area above the optical axis. On the other hand, according to Fig. 8, when a parallel light beam is incident at an angle of 23 degrees with the optical axis, the light beam is incident on both the area above and the area below the optical axis on the surface S5 of the comparative example. In the comparative example, it is considered that the light beam incident on both the area above and the area below the optical axis on the surface S5 increases the coma aberration. Considering the shapes of the lenses of the embodiment and the comparative example, it is considered that by adjusting the center thickness of the second lens, it is possible to adjust the area on the surface S5 where the light beam is incident when a parallel light beam is incident at an angle of 23 degrees with the optical axis.

[0046] Therefore, the path of the light beam was obtained when a parallel light beam making an angle of 23 degrees with the optical axis was incident on the optical system in which the center thickness of the second lens was changed in the optical system of the embodiment. Note that the data other than the center thickness of the second lens of the optical system in which the center thickness of the second lens was changed is the same as that of the embodiment 1.

[0047] FIG. 10 is a diagram showing the path of a light ray when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an optical system in which the central thickness of the second lens is changed to 4.0 millimeters.

[0048] FIG. 11 is a diagram showing the path of a light ray when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an optical system having a center thickness of 5.5 mm in which the second lens is changed.

[0049] FIG. 12 is a diagram showing the path of a light ray when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an optical system in which the central thickness of the second lens is changed and the optical system is 8.5 mm.

[0050] According to Fig. 10 to Fig. 12, when a parallel light beam is incident at an angle of 23 degrees with the optical axis, the light beam is incident on the surface S5 of each imaging optical system in an area above the optical axis. Therefore, it is considered that the coma aberration can be reduced. The values ​​of the center thicknesses of the second lens, 4.0 mm, 5.5 mm, and 8.5 mm, normalized by the composite focal length of the imaging optical system of the embodiment (34.697 mm), are 0.115, 0.159, and 0.245. On the other hand, if the center thickness of the lens is too large, the molding time during manufacturing will increase and the material cost will also increase, which is not preferable. Therefore, the value of the center thickness of the second lens normalized by the composite focal length of the imaging optical system is preferably in the range of 0.1 to 0.25.

[0051] FIG. 13 is a diagram showing the curvature of field when the embodiment is regarded as an imaging optical system. The horizontal axis of FIG. 13 indicates the coordinate of the image point position in the z-axis direction. The origin of the coordinate is point O, and the sign of the coordinate is negative on the illumination target side. The unit is millimeters. The vertical axis of FIG. 13 indicates the angle between the parallel light beam incident on the surface S1 and the optical axis. The unit is degrees. 0.42T indicates the position of the image point on the tangential plane of the light beam with a wavelength of 0.42 micrometers, and 0.42S indicates the position of the image point on the sagittal plane of the light beam with a wavelength of 0.42 micrometers. 0.68T indicates the position of the image point on the tangential plane of the light beam with a wavelength of 0.68 micrometers, and 0.68S indicates the position of the image point on the sagittal plane of the light beam with a wavelength of 0.68 micrometers.

[0052] FIG. 14 is a diagram showing distortion when the embodiment is considered as an imaging optical system. Distortion is the ratio of the lateral magnification of the imaging optical system to the lateral magnification of an ideal lens. The horizontal axis of FIG. 14 shows distortion, in percent. The vertical axis of FIG. 14 shows the angle between the parallel light beam incident on surface S1 and the optical axis, in degrees. Distortion at an angle of 20 degrees is approximately -5 percent. Because distortion is negative at relatively large angles, the illumination range of the illumination optical system is larger than that of an ideal optical system with zero distortion.

[0053] In general, when the angle between the parallel light beam incident on the surface S1 and the optical axis is 20 degrees, the distortion is negative, and the absolute value of the distortion is preferably 5 percent or more.

[0054] FIG. 15 is a diagram showing axial chromatic aberration when the embodiment is regarded as an imaging optical system. The horizontal axis of FIG. 15 indicates the coordinate in the z-axis direction of the position of the image point. The origin of the coordinate is point O, and the sign of the coordinate is negative on the illumination target side. The unit is micrometers. The vertical axis of FIG. 15 indicates the wavelength of the light ray. The unit is micrometers. The imaging optical system is an achromatic lens with the d-line (588 nanometers) as the dominant wavelength, in which the horizontal coordinate of the d-line is the same as the horizontal coordinate of the light ray with a wavelength of 488 nanometers, and chromatic dispersion on the illumination surface of the illumination optical system is reduced. In general, in order to reduce chromatic dispersion on the illumination surface of the illumination optical system, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination target side, the focal movement range of the axial chromatic aberration of light rays with wavelengths of 0.420 micrometers to 0.680 micrometers based on the d-line (588 nanometers) is c millimeters, c / f<0.00292 It is preferable that the following conditions are satisfied:

Claims

1. An illumination optical system comprising, in order from the illumination object side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the composite focal length is f millimeters, the F-number is F, the composite refractive power is Pt=1 / f, the surfaces of the three lenses are referred to as the first to sixth surfaces from the illumination object side, the refractive power of the fifth surface is P5, and the central thickness of the second lens is L2, 1.3 <P5 / Pt 0.1 <L2 / f<0.25 F<0.7 Meet the lighting optical system.

2. 2. The illumination optical system according to claim 1, wherein, when the illumination optical system is regarded as an imaging optical system for a light beam incident from an illumination object side, a ratio of light rays reaching an image plane among light rays of a light beam incident on a surface of the first lens on the illumination object side at an angle of 25 degrees with respect to the optical axis is in a range of 14% to 20%.

3. When the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination target side, the focal movement range of the axial chromatic aberration of light beams with wavelengths of 0.420 micrometers to 0.680 micrometers based on the d-line (588 nanometers) is defined as c millimeters, c / f<0.00292 The illumination optical system according to claim 1 , which satisfies the following:

4. 2. The illumination optical system according to claim 1, wherein, when the illumination optical system is regarded as an imaging optical system for a light beam incident from an illumination object side, distortion of a light ray incident on a surface of the first lens on the illumination object side at an angle of 20 degrees with respect to an optical axis is negative and the absolute value of the distortion is 5 percent or more.

5. 2. The illumination optical system according to claim 1, wherein the materials of the first lens, the second lens and the third lens are acrylic, polycarbonate and acrylic, respectively.

6. 2. The illumination optical system according to claim 1, wherein the first lens is a biconvex lens, the second lens is a biconcave lens, and the third lens is a biconvex lens.