JP6797592B2 - Lighting device - Google Patents

Description

The present invention relates to a lighting device.

Generally, in surface reflection, the reflectance of S-polarized light is higher than that of P-polarized light. Therefore, if the S-polarized light is cut, the directly reflected light can be reduced and the subject itself can be observed. Conventionally, it has been known that by changing the polarization state of the illumination light, the influence of external light can be minimized and the subject can be observed in detail. Patent Document 1 discloses a defect inspection apparatus having a rotatable polarizing plate and a wave plate arrangably arranged in an optical path in order to acquire an arbitrary polarization component of light applied to an object to be inspected. ing. Patent Document 2 discloses a defect inspection apparatus having a liquid crystal polarizing filter capable of switching the light illuminating the substrate into P-polarized light or S-polarized light.

Japanese Unexamined Patent Publication No. 2003-262595 Japanese Unexamined Patent Publication No. 2006-317314

In the defect inspection apparatus of Patent Document 1, it takes time because a mechanical drive is required to acquire an arbitrary polarization component. Further, in the defect inspection apparatus of Patent Document 2, P-polarized light and S-polarized light can be switched in a short time, but an arbitrary polarized light component cannot be obtained only by switching between P-polarized light and S-polarized light. Further, if the liquid crystal is driven by a voltage intermediate between P-polarized light and S-polarized light, it becomes elliptically polarized light.

In view of such a problem, an object of the present invention is to provide a lighting device capable of illuminating an arbitrary polarization component in a short time with a simple configuration.

The illumination device as one aspect of the present invention is an illumination device that guides light from a light source to an object, and has a π / 2 (rad) between the polarization component in the slow axis direction and the polarization component in the phase advance axis direction. A first retardation plate that gives a fixed relative retardation with, and a second retardation plate that can change the relative retardation given between the polarization component in the slow axis direction and the polarization component in the phase advance axis direction. The first retardation plate, the second retardation plate, and the polarizer are arranged in this order from the side of the object to the side of the light source, provided with a polarizer for extracting a polarizing component leading to the object. The slow axis direction of the second retardation plate is inclined with respect to the slow axis direction and the phase advance axis direction of the first retardation plate, and the relative that the second retardation plate gives. By changing the phase difference, the polarization direction of the light leading to the object can be changed .

According to the present invention, it is possible to provide a lighting device capable of illuminating an arbitrary polarization component in a short time with a simple configuration.

It is a block diagram of the lighting apparatus of Example 1. FIG. It is the schematic of the inspection apparatus using the lighting apparatus of Example 1. FIG. It is a block diagram of the variable retardation plate. It is a figure which shows the polarization direction of the illumination light emitted from the polarization acquisition means corresponding to the phase difference of a variable retardation plate. It is a block diagram of the lighting apparatus of Example 2. It is the schematic of the single-lens reflex camera which attached the strobe device which comprises the lighting device of Example 2. It is a block diagram of the lighting apparatus of Example 3. FIG. It is the schematic of the automobile using the lighting device of Example 3.

Hereinafter, examples of the present invention will be described in detail with reference to the drawings. In each figure, the same member is given the same reference number, and duplicate description is omitted.

FIG. 1 is a block diagram of a lighting device 100 used in the inspection device of this embodiment. The illumination device 100 includes an illumination optical system 1, a light source unit 2, and a polarization acquisition means (optical device) 6. The light source unit 2 includes a lamp 7 and a mirror 13. The light beam emitted from the lamp 7 is directly or partially reflected by the mirror 13 and enters the illumination optical system 1. The light rays shaped and homogenized by the illumination optical system 1 are incident on the polarization acquiring means 6. The light rays incident on the polarization acquiring means 6 are converted into light rays in a desired polarization direction by passing through the polarization acquiring means 6, and are applied to the subject.

FIG. 2 is a schematic view of an inspection device using the lighting device 100. In this embodiment, the lighting device 100 irradiates the product (subject) 103 on the belt conveyor 102 with light rays. The camera 101 receives the light rays reflected from the product 103. The control device (setting means) 104 controls the entire inspection device such as imaging of the camera 101 and lighting of the lighting device 100, for example. Depending on the shape and orientation of the product 103, the product 103 may be difficult to see due to the direct reflection of the illumination light. In that case, the direction that is easy to see may be selected by changing the polarization direction. The easy-to-see direction is a direction that the user thinks easy to see or a direction that the machine can easily determine. Further, by acquiring a plurality of images having different polarization directions, an image that is easy to see may be selected for each region of the product 103, or an image that is less affected by external light may be generated based on the plurality of images. ..

Next, the configuration of the polarized light acquisition means 6 will be described. The polarization acquiring means 6 includes a λ / 4 plate (first retardation plate) 3, a variable retardation plate (second retardation plate) 4, and a polarizing plate (polarizer, polarizing component extraction element) 5. The λ / 4 plate 3, the variable retardation plate 4, and the polarizing plate 5 are arranged so that their respective axes are in a plane perpendicular to the optical axis of the illumination optical system 1. Further, the λ / 4 plate 3, the variable retardation plate 4, and the polarizing plate 5 are arranged adjacent to each other. In this embodiment, the illumination optical system 1 and the polarizing plate 5 are arranged apart from each other as shown in FIG. 1 (a), but are arranged together as shown in FIG. 1 (b). You may.

The λ / 4 plate 3 is composed of a stretched film and gives a relative phase difference of π / 2 (rad) between the orthogonal polarization components of the incident light. The relative phase difference of π / 2 given by the λ / 4 plate 3 is invariant (fixed). In this embodiment, a λ / 4 plate is used, but a 3λ / 4 plate or a variable retardation plate may be used as long as a relative phase difference of π / 2 can be given.

Similar to the λ / 4 plate 3, the variable retardation plate 4 can change the relative phase difference (hereinafter referred to as the phase difference of the variable retardation plate 4) between the orthogonal polarization components of the incident light. In this embodiment, the variable retardation plate 4 is an element using a liquid crystal, and the phase difference of the variable retardation plate 4 is changed according to the voltage applied based on the signal (instruction) from the control device 104. .. In this embodiment, the control device 104 changes the phase difference of the variable retardation plate 4, but the lighting device 100 may include means having a function of changing the phase difference of the variable retardation plate 4.

FIG. 3 is a configuration diagram of the variable retardation plate 4, and the circular portion in the figure is an enlarged view of the liquid crystal layer. The variable retardation plate 4 is configured such that the liquid crystal layer 11 is sandwiched between the substrate 8, the electrode layer 9, and the alignment film 10. The liquid crystal layer 11 is a VA type liquid crystal layer (VA liquid crystal layer), and the liquid crystal molecules 12 are oriented so as to imitate the alignment film 10. In this embodiment, when the applied voltage is changed to 0 [V], A [V], B (> A) [V], the orientation angle (tilt angle) of the liquid crystal molecules 12 is an intermediate value from the minimum value θ _min. It changes to the maximum value θ _max via θ. The configuration of the variable retardation plate 4 in FIG. 3 is an example, and the present invention is not limited thereto. For example, liquid crystal elements having different drive methods that change the orientation direction instead of the tilt angle may be used. Further, a configuration that utilizes a change in the refractive index due to the electro-optical effect, a configuration that precisely controls the lattice height and spacing of the birefringence due to the fine structure, or a configuration that combines them may be used. Further, the variable retardation plate 4 may not have a configuration in which the phase difference is uniformly changed in the plate surface, but may have a configuration in which different phase differences are generated in different regions in the plate surface.

The polarizing plate 5 transmits (extracts) a component in the transmission axis direction (transmission polarization direction) among the polarization components of the incident light. Since the polarization acquiring means 6 is used in the illumination device 100, it is preferable to use a polarizing plate of a type that reflects unnecessary light, such as a wire grid polarizer, as the polarizing plate 5. By using a type of polarizing plate that reflects unwanted light, part of the unwanted light returns to the optical system of the light source and may be recursively used as illumination light. On the other hand, when a polarizing plate of a type that absorbs unnecessary light is used, the absorbed light is converted into heat and becomes a heat source of the device itself, and there is a concern that it may adversely affect other elements. In addition, the polarizing plate itself may deteriorate faster.

The lighting device 100 fixes the transmission axis direction of the polarizing plate 5 and changes the phase difference of the variable retardation plate 4 by electrical control, so that the linearly polarized light of the illumination light is changed to polarized light in an arbitrary direction. It can be illuminated with the illumination light in the polarization direction of. Hereinafter, the lighting method of the lighting device 100 will be described with reference to FIG. FIG. 4 is a diagram showing the polarization direction φo of the illumination light emitted from the polarization acquisition means 6 corresponding to the phase difference of the variable retardation plate 4. The broken line arrows on the λ / 4 plate 3 and the variable retardation plate 4 indicate the slow axis direction, and the broken line arrows on the polarizing plate 5 indicate the transmission axis direction.

The λ / 4 plate 3 and the polarizing plate 5 are arranged so that the slow axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5 are parallel to each other. However, it does not have to be strictly parallel, and even if it deviates by several degrees, it is considered to be substantially parallel (substantially parallel). Further, the variable retardation plate 4 is arranged so that the slow phase axial direction is tilted counterclockwise by 45 degrees with respect to the slow phase axial direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5. However, it does not have to be exactly 45 degrees, and even if it deviates by several degrees, it is considered to be substantially 45 degrees (approximately 45 degrees).

In this embodiment, the azimuth (degree) of the λ / 4 plate 3 in the slow axis direction and the polarizing plate 5 in the transmission axis direction with respect to the x-axis direction is 90 degrees. However, it does not have to be exactly 90 degrees, and even if it deviates by several degrees, it is considered to be substantially 90 degrees (approximately 90 degrees). Further, the azimuth angle of the variable retardation plate 4 with respect to the x-axis direction in the slow phase axial direction is 45 degrees. However, it does not have to be exactly 45 degrees, and even if it deviates by several degrees, it is considered to be substantially 45 degrees (approximately 45 degrees).

The λ / 4 plate 3 and the polarizing plate 5 may be arranged so that the phase-advancing axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5 are parallel to the y-axis direction. In this case, the variable retardation plate 4 is arranged so that the phase advance axis direction is tilted clockwise by 45 degrees with respect to the phase advance axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5.

In FIG. 4A, the phase difference of the variable retardation plate 4 is set to 0, and the polarization direction φo of the illumination light is 90 degrees. In FIG. 4B, the phase difference of the variable retardation plate 4 is set to λ / 4, and the polarization direction φo of the illumination light is 45 degrees. In FIG. 4C, the phase difference of the variable retardation plate 4 is set to λ / 2, and the polarization direction φo of the illumination light is 0 degrees. In FIG. 4D, the phase difference of the variable retardation plate 4 is set to 3λ / 4, and the polarization direction φo of the illumination light is 135 degrees. In this way, the illumination device 100 can perform polarized illumination substantially equivalent to that when the polarizing plate is rotated in the transmission axis direction by performing illumination while changing the phase difference of the variable retardation plate 4.

The image acquired based on the illumination light of the illumination device 100 may be output as an image as it is without undergoing arithmetic processing such as image processing. Further, by performing arithmetic processing between images having different polarization information, it is possible to acquire an image in which the characteristics of the subject are more emphasized on a pixel-by-pixel basis. For example, an image in which the scattered light component of the subject is emphasized or a subject is generated by generating an image only with the value having the lowest light intensity among the acquired data or generating an image only with the value having the highest light intensity. It is possible to generate an image in which the specular reflection component is emphasized.

By optically acquiring the object information of the subject by the change of the polarization information of the illumination light in this way, it is possible to generate an image in which the feature amount is emphasized or suppressed. In addition, the combination of these makes it possible to generate an image that matches the intention of the observer. Further, an image in which the enhancement effect is given by different polarized illumination for each region of the image may be generated. In addition, it is possible to acquire an image suitable for the purpose by performing various illuminations utilizing the intensity dependence of the polarization of the subject.

FIG. 5 is a configuration diagram of a lighting device 200 used in the strobe device of the camera of this embodiment. The lighting device 200 includes an illumination optical system 21, a light source unit 22, and a polarization acquiring means 26. The light source unit 22 has a lamp 27 and a mirror 13. The lamp 27 is a xenon tube, and the light beam emitted from the lamp 27 is directly or partially reflected by the mirror 13 and incident on the polarization acquiring means 26. The polarization acquiring means 26 includes a λ / 4 plate (first retardation plate) 3, a variable retardation plate (second retardation plate) 4, and a polarization conversion element (polarizer, polarization component extraction element) 25. .. The illumination optical system 21 is arranged inside the polarization acquiring means 26, specifically, between the variable retardation plate 4 and the polarization conversion element 25. Since the configurations of the λ / 4 plate 3 and the variable retardation plate 4 are the same as the configurations of the λ / 4 plate 3 and the variable retardation plate 4 of the first embodiment, detailed description thereof will be omitted. Further, in this embodiment, the λ / 4 plate 3 and the variable retardation plate 4 are arranged by being bonded together, but they may be arranged separately.

The polarization conversion element 25 has a columnar prism 14 having an isosceles right triangle cross section and a columnar prism 15 having a parallelogram cross section. A polarizing beam splitter (PBS) is arranged on the contact surface 16 of the columnar prisms 14 and 15. The polarization beam splitter transmits P-polarized light among the illumination light incident from the surface 17 of the columnar prism 15 and reflects S-polarized light. The transmitted P-polarized light is emitted from the exit surface 18B of the columnar prism 15B. The reflected S-polarized light is reflected on the slope of the columnar prism 15B and is incident on the exit surface 19B of the columnar prism 15B. A 1 / 2λ plate is arranged on the exit surface 19B at an orientation of 45 degrees with respect to S-polarized light, and S-polarized light is converted to P-polarized light when transmitted. The exit surface 18B and the exit surface 19B are adjacent to each other, and P-polarized light is emitted from both sides. The light rays emitted from the exit surface 18B and the exit surface 19B are incident on the illumination optical system 21.

A plurality of Fresnel lenses are formed on the surface of the illumination optical system 21 on the light emitting surface side. The illumination optical system 21 is arranged so that the centers of the Fresnel lenses corresponding to the respective optical axes of the exit surface 18 and the exit surface 19 are aligned. The illumination optical system 21 is arranged and arranged closest to the light source unit 22 and has a light distribution angle on the widest angle side (state in FIG. 5A) and is arranged farthest from the light source unit 22. It is configured to be movable along the optical axis between the state where the light angle is the most telescopic angle (the state shown in FIG. 5B). The illumination light controlled by the illumination optical system 1 to a desired light distribution angle is incident on the variable retardation plate 4 and the λ / 4 plate 3. The λ / 4 plate 3 and the variable retardation plate 4 may be moved according to the movement of the illumination optical system 21, but in this embodiment, in order to increase the strength and waterproofness of the strobe device, the exterior parts It is fixed to a fixing member (not shown). Further, since the Fresnel lens is formed on the surface of the illumination optical system 21, it is desirable to use a plastic having a relatively weak strength or a low melting point glass. Further, for the λ / 4 plate 3, it is preferable to use a hardness material for the substrate.

FIG. 6 is a schematic view of a single-lens reflex camera 201 to which a strobe device including a lighting device 200 is attached. The strobe device is attached to the upper part of the single-lens reflex camera 201 via the strobe shoe. The lighting device 200 causes the light source unit 22 to emit light in response to the release signal of the single-lens reflex camera 201. The illuminating device 200 changes the phase difference of the variable retardation plate 4 for each release, and illuminates in different polarized states. For example, if the phase difference of the variable retardation plate 4 is changed to 0λ, 1 / 4λ, and 1 / 2λ, polarized illumination with polarization directions of 90 degrees, 45 degrees, and 0 degrees can be performed, respectively. By taking an image of the single-lens reflex camera 201 for each polarized illumination, images in different polarized states can be acquired, and various processes can be performed on the acquired images.

FIG. 7 is a configuration diagram of a lighting device 300 used for the automobile headlight of this embodiment. The lighting device 300 includes an illumination optical system 31, a light source unit 32, and a polarization acquiring means 36. The light source unit 32 has a lamp 37 and a mirror 13. The lamp 37 is a xenon arc lamp, and the light beam emitted from the lamp 37 is directly or partially reflected by the mirror 13 and incident on the polarization acquiring means 36. The polarization acquiring means 36 includes a λ / 4 plate 3, a variable retardation plate 4, and a polarizing plate 35 (polarizer, polarization component extracting element). The illumination optical system 31 is arranged on the subject side of the polarization acquiring means 36. Since the configurations of the λ / 4 plate 3 and the variable retardation plate 4 are the same as the configurations of the λ / 4 plate 3 and the variable retardation plate 4 of Examples 1 and 2, respectively, detailed description thereof will be omitted. The polarizing plate 35 is a wire grid polarizer which is a type of polarizing plate that reflects unnecessary light.

Of the light rays emitted from the light source unit 32, the light rays in the polarization direction orthogonal to the transmission axis direction are reflected by the polarizing plate 35 and return to the light source unit 32. Some of the light rays that have returned to the light source unit 32 are incident on the polarizing plate 35 again. The polarized light transmitted through the polarizing plate 35 is incident on the variable retardation plate 4. The polarized light whose phase is changed by the variable retardation plate 4 passes through the λ / 4 plate 3 and is converted into linearly polarized light in a desired direction. For example, when the phase difference of the variable retardation plate 4 is changed to 0λ, 1 / 4λ, 1 / 2λ, and 3/4λ, the polarization directions of the illumination light are 90 degrees, 45 degrees, and 0 as shown in FIG. It becomes 135 degrees. The illumination light converted in the predetermined polarization direction by the polarization acquisition means 36 is incident on the illumination optical system 31.

The illumination device 300 is a so-called projection lamp, and the illumination optical system 31 includes a lens having a rotating quadric surface. The rotational quadric surface is a general term for a shape that is rotationally symmetric to the optical axis and that can approximate a spherical surface near the center of the optical axis. This includes rotating paraboloids, spheroids, and rotating hyperboloids. Naturally, this includes so-called aspherical surfaces, in which the shape deviates from the spherical surface as the distance from the optical axis increases.

FIG. 8 is an external view of an automobile using the lighting device 300 as an automobile headlight. The in-vehicle camera 301 can acquire various polarized images by performing polarized illumination in different states of the illuminating device 300. By performing image processing between the respective polarized images, the polarized components can be extracted, and it is possible to acquire an image excluding the influence of the illumination light.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and modifications can be made within the scope of the gist thereof.

1, 21, 31 Illumination optical system 2, 22, 32 Light source unit 3 λ / 4 plate (first retardation plate)
4 Variable retardation plate (second retardation plate)
5,35 Polarizing plate (polarizer)
25 Polarization conversion element (polarizer)
6, 26, 36 Polarization acquisition means (optical device)
100, 200, 300 lighting equipment

Claims (15)

A lighting device that guides light from a light source to an object.
A first retardation plate that provides a fixed relative phase difference of π / 2 (rad) between the polarization component in the slow axis direction and the polarization component in the advance axis direction.
A second retardation plate capable of changing the relative phase difference given between the polarization component in the slow axis direction and the polarization component in the advance axis direction,
It is equipped with a polarizer that extracts the polarizing component that leads to the object.
The first retardation plate, the second retardation plate, and the polarizer are arranged in order from the side of the object to the side of the light source.
The slow-phase axial direction of the second retardation plate is inclined with respect to the slow-phase axial direction and the phase-advancing axial direction of the first retardation plate .
An illuminating device characterized in that the polarization direction of light guided to the object can be changed by changing the relative phase difference given by the second retardation plate . The illuminating device according to claim 1, wherein the slow-phase axial direction or the phase-advancing axial direction of the second retardation plate is inclined by 45 degrees with respect to the transmission axis direction of the polarizer. The lighting device according to claim 1 or 2, wherein the slow axis direction or the phase advance axis direction of the first retardation plate is parallel to the transmission axis direction of the polarizer. The slow axis direction of the first retardation plate is parallel to the transmission axis direction, and the slow axis direction of the second retardation plate is the transmission axis when viewed from the light source side. The lighting device according to claim 3, wherein the lighting device is tilted counterclockwise by 45 degrees with respect to a direction. The phase-advancing axis direction of the first retardation plate is parallel to the transmission axis direction, and the slow-phase axis direction of the second retardation plate is the transmission when viewed from the light source side. The lighting device according to claim 3, wherein the lighting device is tilted clockwise by 45 degrees with respect to the axial direction. The second phase difference plate, the lighting device according to any one of 5 the liquid crystal from claim 1, wherein the early days free. The lighting apparatus according to claim 6, further comprising a setting means for setting a relative retardation given by the second retardation plate by applying a voltage to the liquid crystal. The lighting device according to any one of claims 1 to 7, further comprising an optical system for shaping light from the light source. The lighting device according to claim 8, wherein the optical system includes a Fresnel lens. The lighting device according to claim 8 or 9, wherein the optical system includes a lens surface that is rotationally symmetric with respect to an optical axis. The lighting device according to any one of claims 8 to 10, wherein the optical system is arranged between the light source and the polarizer. The lighting device according to any one of claims 8 to 10, wherein the optical system is arranged between the polarizing element and the second retardation plate. The lighting device according to any one of claims 8 to 10, wherein the optical system is arranged on the side of the object with respect to the first retardation plate. The lighting device according to any one of claims 1 to 13, wherein the polarizer is a wire grid polarizer. The lighting device according to any one of claims 1 to 13, wherein the polarizing element is a polarization converting element.