Three-dimensional displacement sensing system

Abstract

Provided is a thin three-dimensional displacement sensing system. The present invention comprises a light guide unit including a light guide plate and a first diffraction element disposed in contact with the light guide plate, an imaging element disposed on one surface side of the light guide unit, a transparent deformation layer disposed on the other surface side of the light guide unit, a specular reflector disposed on the opposite side of the transparent deformation layer from the light guide unit, and a light source unit that causes light to be incident on the light guide plate.

Description

Three-dimensional displacement sensing system

[0001] The present invention relates to a three-dimensional displacement sensing system.

[0002] Tactile sensors are used in various fields. For example, in applications of tactile sensing (tactile detection) such as the robotics industry and input interfaces, the requirements for tactile sensors are increasing. Specifically, in robot applications, it is desired to detect pressure, contact area, etc. so that a robot can apply an appropriate force according to the shape, hardness, etc. when grasping something.

[0003] As such a tactile sensor, there is proposed a three-dimensional displacement sensing system having a transparent deformation layer having flexibility such as a gel, and a light reflection layer provided on the transparent deformation layer, and detecting the deformation state of the light reflection layer when an external force is applied to the transparent deformation layer from the light reflection layer side by detecting the reflected light from the light reflection layer with an imaging device, thereby measuring the position, shape, size, etc. of the object that deformed the light reflection layer.

[0004] For example, Patent Document 1 describes an optical element having an interior containing a rigid optically transparent material; a first surface of the optical element, where the first surface includes a region having an optically transparent surface for capturing an image through the optical element; a second surface of the optical element facing the first surface; a central axis of the optical element passing through the first surface and the second surface; an optically transparent elastomeric layer disposed on the second surface and attached to the second surface, a first side surface of a layer adjacent to the second surface of the optical element having a second refractive index matching the first refractive index of the second surface, and a second side surface of a layer facing the second surface of the optical element having an optical coating with a predetermined reflectivity; sidewalls around the interior of the optical element between the first surface and the second surface, where the sidewalls include one or more light shaping features configured to control illumination of the second surface passing through the sidewalls; and a mechanical key outside the optical element for forcing a predetermined position of the optical element within a fixture of an imaging system, where the mechanical key includes at least one radially asymmetric feature around the central axis for forcing a unique rotational orientation of the optical element within the fixture of the imaging system.

[0005] Patent No. 7033608

[0006] According to the inventors' research, conventional three-dimensional displacement sensing systems require a lens to focus the reflected light from the light-reflecting layer onto the imaging surface of the image sensor. Furthermore, in order to use the lens to focus the light reflected by the light-reflecting layer onto the imaging surface of the image sensor, a predetermined distance must be maintained between the light-reflecting layer and the lens, and between the lens and the image sensor. As a result, there is a problem that the thickness of the three-dimensional displacement sensing system becomes excessive.

[0007] The object of this invention is to provide a thin, three-dimensional displacement sensing system.

[0008] As a result of diligent research by the inventors into addressing the above problem, they found that the above problem can be solved by the following configuration.

[0009] [1] A three-dimensional displacement sensing system comprising: a light guide plate and a light guide section including a first diffraction element arranged in contact with the light guide plate; an image sensor arranged on one surface side of the light guide section; a transparent deformation layer arranged on the other surface side of the light guide section; a specular reflector arranged on the opposite side of the transparent deformation layer from the light guide section; and a light source section that incidents light onto the light guide plate. [2] The three-dimensional displacement sensing system according to [1], wherein the first diffraction element has polarization selectivity. [3] The three-dimensional displacement sensing system according to [1] or [2], wherein the first diffraction element is a reflective type diffraction element and is arranged on the surface of the light guide section on the image sensor side. [4] The three-dimensional displacement sensing system according to any one of [1] to [3], wherein the first diffraction element comprises a cholesteric liquid crystal layer having a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. [5] The cholesteric liquid crystal layer is such that when the in-plane retardation is measured from the normal direction to the main surface of the cholesteric liquid crystal layer and from a direction inclined with respect to the normal, the absolute value of the optical axis inclination angle φ, expressed as sinθ2 = n・sinφ (where n is the average refractive index of the cholesteric liquid crystal layer), is 5° or more, when the measurement angle θ2 is the angle that the direction in which the in-plane retardation is minimized is made with the normal in either the slow axis plane or the fast axis plane, is sinθ2 = n・sinφ (where n is the average refractive index of the cholesteric liquid crystal layer), as described in [4]. [6] The 3D displacement sensing system according to any one of [1] to [5], wherein the light guide further has a second diffraction element, and the first diffraction element and the second diffraction element are spaced apart in the in-plane direction. [7] The 3D displacement sensing system according to any one of [1] to [6], wherein the in-plane retardation of the transparent deformation layer at a wavelength of 550 nm is 50 nm or less. [8] A three-dimensional displacement sensing system according to any one of [1] to [7], comprising a phase difference plate disposed between a light guide and a specular reflector, wherein the slow phase axis of the phase difference plate and the slow phase axis of the in-plane phase difference of the transparent deformation layer are arranged to intersect, and the total in-plane phase difference is 50 nm or less.

[0010] According to the present invention, a thin three-dimensional displacement sensing system can be provided.

[0011] Figure 1 is a conceptual diagram showing an example of the three-dimensional displacement sensing system of the present invention. Figure 2 is a diagram for explaining the operation of the three-dimensional displacement sensing system shown in Figure 1. Figure 3 is a conceptual diagram showing another example of the three-dimensional displacement sensing system of the present invention. Figure 4 is a conceptual diagram showing another example of the three-dimensional displacement sensing system of the present invention. Figure 5 is a conceptual diagram showing another example of the three-dimensional displacement sensing system of the present invention. Figure 6 is a conceptual diagram showing another example of the three-dimensional displacement sensing system of the present invention. Figure 7 is a conceptual diagram showing another example of the three-dimensional displacement sensing system of the present invention. Figure 8 is a conceptual diagram showing another example of the three-dimensional displacement sensing system of the present invention. Figure 9 is a conceptual diagram showing another example of the three-dimensional displacement sensing system of the present invention. Figure 10 is a conceptual diagram showing an example of a liquid crystal diffraction element in the three-dimensional displacement sensing system of the present invention. Figure 11 is a plan view of the cholesteric liquid crystal layer in the liquid crystal diffraction element shown in Figure 10. Figure 12 is a conceptual diagram for explaining the method of measuring in-plane retardation. Figure 13 is a graph showing an example of the relationship between the measurement angle and in-plane retardation.

[0012] The present invention will be described in detail below.

[0013] The following description of the constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

[0014] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0015] In this specification, terms such as “same” include a range of error that is generally accepted in the art, for example, a range of ±5%.

[0016] Furthermore, in this specification, parallel, orthogonal, and perpendicular do not mean parallel, orthogonal, and perpendicular in the strict sense, but rather a range of ±5° from parallel, orthogonal, or perpendicular, respectively. The same applies to other angles, which also refer to a range of ±5°.

[0017] Embodiments of the present invention will be described below with reference to the drawings. The following figures are conceptual diagrams for illustrating the three-dimensional displacement sensing system of the present invention. Therefore, the shape, size, thickness, and positional relationships of each component do not necessarily correspond to those of actual components.

[0018] [Three-Dimensional Displacement Sensing System] The three-dimensional displacement sensing system of the present invention is a three-dimensional displacement sensing system that includes a light guide plate and a light guide section including a first diffraction element arranged in contact with the light guide plate, an image sensor arranged on one surface side of the light guide section, a transparent deformation layer arranged on the other surface side of the light guide section, a specular reflector arranged on the opposite side of the transparent deformation layer from the light guide section, and a light source section that incidents light onto the light guide plate.

[0019] Figure 1 is a conceptual diagram illustrating an example of the three-dimensional displacement sensing system of the present invention.

[0020] The three-dimensional displacement sensing system 10a shown in Figure 1 includes a light guide unit 12a, an image sensor 14, a transparent deformation layer 16, a specular reflector 18, and a light source unit 20. In the three-dimensional displacement sensing system 10a shown in Figure 1, the light guide unit 12a and the transparent deformation layer 16 are spaced apart (not in contact), and the light guide unit 12a and the image sensor 14 are also spaced apart (not in contact). This is to prevent light guided within the light guide plate 22 of the light guide unit 12a from deviating from the total internal reflection condition and directly entering the transparent deformation layer 16 or the image sensor 14.

[0021] The distance between the light guide portion 12a and the transparent deformation layer 16, and the distance between the light guide portion 12a and the image sensor 14 are not particularly limited, but from the viewpoint of making the 3D displacement sensing system 10a thinner, it is preferable that they be thin.

[0022] The light guide section 12a includes a substantially plate-shaped light guide plate 22, a first diffraction element 24a positioned in contact with one main surface of the light guide plate 22, and a second diffraction element 26a positioned in contact with the other main surface of the light guide plate 22. The first diffraction element 24a and the second diffraction element 26a are spaced apart in the in-plane direction of the main surface of the light guide plate 22. In the example shown in Figure 1, the first diffraction element 24a and the second diffraction element 26a are reflective diffraction elements. A reflective diffraction element reflects incident light in a direction different from specular reflection. For example, a reflective diffraction element reflects light incident approximately perpendicular to the surface in a predetermined direction inclined at a predetermined angle with respect to the perpendicular to the surface. The main surface is the largest surface of the plate-like object (sheet-like object, film-like object).

[0023] In the three-dimensional displacement sensing system 10a shown in Figure 1, the image sensor 14 is positioned on the surface of the light guide section 12a facing the first diffraction element 24a, and the transparent deformation layer 16 is positioned on the other surface. A specular reflector 18 is positioned in contact with the surface of the transparent deformation layer 16 opposite to the light guide section 12a. The image sensor 14, the transparent deformation layer 16, and the specular reflector 18 are positioned in a location that overlaps with the first diffraction element 24a in the in-plane direction of the main surface of the light guide plate 22. The surface of the first diffraction element 24a, the surface of the image sensor 14 (light-receiving surface), and the surface of the specular reflector 18 are positioned approximately parallel to each other.

[0024] Furthermore, in the three-dimensional displacement sensing system 10a shown in Figure 1, the light source unit 20 is positioned on the surface side of the light guide unit 12a opposite to the second diffraction element 26a side. The light source unit 20 is positioned in the in-plane direction of the main surface of the light guide plate 22 at a location that overlaps with the second diffraction element 26a.

[0025] The three-dimensional displacement sensing system 10a having this configuration is a tactile sensor that detects the shape, size, position, etc., of an object in contact with the transparent deformation layer 16 via a specular reflector 18. In the following description, the state in which the object to be measured is in contact with the transparent deformation layer 16 via the specular reflector 18 is also referred to as the object to be measured being in contact with the three-dimensional displacement sensing system 10a.

[0026] Next, the operation of the three-dimensional displacement sensing system 10a will be explained using Figures 1 and 2. Figure 1 shows a state in which the object to be measured is not in contact with the three-dimensional displacement sensing system 10a, and Figure 2 shows a state in which the object to be measured is in contact with the three-dimensional displacement sensing system 10a.

[0027] As shown in Figure 1, light is shone from the light source unit 20 toward the second diffraction element 26a. The light shone from the light source unit 20 is incident on the other main surface of the light guide plate 22 at approximately perpendicular angles and travels toward the second diffraction element 26a, which is located on one main surface of the light guide plate 22, at approximately perpendicular angles. The second diffraction element 26a reflects and diffracts the incident light at an angle that causes total internal reflection within the light guide plate 22. At that time, the second diffraction element 26a reflects and diffracts the incident light toward the direction of the first diffraction element 24a (reflecting and diffracting so that the azimuth direction of the reflected light is toward the direction of the first diffraction element 24a).

[0028] In the illustrated example, light is indicated by arrows, but it may also be a planar light, and in that case, it is preferable that it be parallel light.

[0029] Here, "parallel light" means not only that the relationship between multiple rays emitted from any point on the first diffraction element 24a is parallel, but also that the light propagating within the transparent deformation layer 16 does not mix. Therefore, it is preferable that the angular distribution of each ray emitted from the first diffraction element 24a is within 30 degrees, more preferably within 15 degrees, and even more preferably within 5 degrees, with respect to the direction of maximum brightness. This angle can be measured with a GCMS-3B manufactured by Murakami Color Technology Laboratory Co., Ltd., or an EZcontrast manufactured by ELDIM Corporation.

[0030] Light reflected and diffracted by the second diffraction element 26a undergoes repeated total internal reflection within the light guide plate 22 and is guided toward the first diffraction element 24a in the in-plane direction. When light guided within the light guide plate 22 is incident on the first diffraction element 24a, a portion of it is reflected and diffracted at an angle deviating from the angle of total internal reflection. In the example shown in Figure 1, light guided within the light guide plate 22 is incident on the surface of the first diffraction element 24a (the surface in contact with the light guide plate 22) from an oblique direction. The first diffraction element 24a reflects and diffracts the light incident on its surface from an oblique direction in a direction approximately perpendicular to the surface. The remaining portion of the light is guided within the light guide plate 22 and incident on the first diffraction element 24a again, where a portion of that light is reflected and diffracted at an angle deviating from the angle of total internal reflection (approximately perpendicular direction), and the remaining portion is guided within the light guide plate 22. As the light guided through the light guide plate 22 passes through the position of the first diffraction element 24a, some of the light is repeatedly reflected and diffracted in a nearly perpendicular direction.

[0031] Light reflected and diffracted by the first diffracting element 24a in a direction approximately perpendicular to the surface of the first diffracting element 24a passes through the light guide plate 22 and reaches the other main surface of the light guide plate 22. However, because the angle of incidence to this main surface is outside the conditions for total internal reflection, the light is emitted from the light guide plate 22.

[0032] In the illustrated example, the light diffracted by the first diffraction element 24a (light emitted from the light guide plate 22) is shown by three arrows. However, in reality, each light is planar, and since it is diffracted at numerous positions on the first diffraction element 24a, the light diffracted by the first diffraction element 24a is approximately planar, corresponding to the size of the surface of the first diffraction element 24a. Furthermore, the light diffracted by the first diffraction element 24a is approximately parallel light.

[0033] Light emitted from the light guide plate 22 enters the transparent deformation layer 16, propagates within the transparent deformation layer 16, and enters the specular reflector 18.

[0034] The specular reflector 18 specularly reflects incident light, and the surface of the specular reflector 18 in contact with the transparent deformation layer 16 is approximately parallel to the surface of the first diffraction element 24a. Therefore, light propagating within the transparent deformation layer 16 is incident on the surface of the specular reflector 18 approximately perpendicularly. The specular reflector 18 reflects the light incident approximately perpendicularly in a direction approximately perpendicular to its surface, as shown by the dashed arrow in Figure 1.

[0035] Light reflected by the specular reflector 18 propagates through the transparent deformation layer 16, enters the other main surface of the light guide plate 22 approximately perpendicularly, passes through the light guide plate 22, and enters the first diffraction element 24a located on one main surface of the light guide plate 22. At least a portion of the light that enters the first diffraction element 24a passes through the first diffraction element 24a and enters the light-receiving surface of the image sensor 14 approximately perpendicularly.

[0036] In the example shown in Figure 1, the object to be measured is not in contact with the 3D displacement sensing system 10a, and the specular reflector 18 maintains a flat surface state. Therefore, at any position within the surface of the specular reflector 18, incident light is reflected approximately perpendicularly towards the image sensor 14. As a result, the image sensor 14 receives a light amount that is approximately uniform or has a predetermined distribution at any position on its light-receiving surface. In other words, if the amount of light received in the data (image) captured by the image sensor 14 is approximately uniform or has a predetermined distribution within the surface, it indicates that the object is not in contact with the 3D displacement sensing system 10a.

[0037] Next, we will explain the case where the object P to be measured is in contact with the three-dimensional displacement sensing system 10a, using Figure 2. Note that the actions of each component until light is irradiated onto the specular reflector 18 are the same as those explained in Figure 1, so we will omit that explanation.

[0038] Since the specular reflector 18 and the transparent deformation layer 16 are flexible and deformable, as shown in Figure 2, when the object P to be measured comes into contact with the transparent deformation layer 16 via the specular reflector 18, the specular reflector 18 and the transparent deformation layer 16 deform to conform to the shape of the object P. Furthermore, the amount of deformation changes depending on the pressing force from the object P and the hardness (tensile modulus) of the transparent deformation layer 16.

[0039] In this case, when light is irradiated from the light source unit 20, the light emitted from the light source unit 20 is reflected and diffracted by the second diffraction element 26a, guided through the light guide plate 22, reflected and diffracted by the first diffraction element 24a, propagates through the transparent deformation layer 16, and enters the specular reflector 18 as substantially planar parallel light.

[0040] Of the light incident on the specular reflector 18, the light incident on the region not in contact with object P is specularly reflected by the specular reflector 18, as in the case of Figure 1, and reflected approximately perpendicularly to the surface of the specular reflector 18 in the direction of the image sensor 14, and detected by the image sensor 14.

[0041] On the other hand, the specular reflector 18 in the region in contact with object P is curved and locally inclined (non-parallel) with respect to the surface of the first diffraction element 24a. Therefore, of the light incident on the specular reflector 18, the light incident on the region in contact with object P is locally incident on the surface of the specular reflector 18 from an oblique direction. As a result, of the light incident on the specular reflector 18, the light incident on the region in contact with object P is reflected and diffracted in a direction different from the direction of the image sensor 14, as shown by the dashed line in Figure 2. Consequently, the image sensor 14 either does not detect the reflected light from the region of the specular reflector 18 in contact with object P, or detects it with a reduced light intensity. In other words, if there is a region with a low light intensity in the data (image) captured by the image sensor 14, it can be determined that object P is in contact with the 3D displacement sensing system 10a. Furthermore, the position, size, and shape of object P can be determined from the position, size, and shape of the region with low light intensity.

[0042] As described above, the three-dimensional displacement sensing system 10a of the present invention can detect whether or not an object P is in contact with the three-dimensional displacement sensing system 10a by irradiating light from the light source unit 20 and capturing an image with the image sensor 14, and can also detect the position, size, shape, etc., of the object P that is in contact with it.

[0043] Here, as described above, in a conventional three-dimensional displacement sensing system having a flexible transparent deformation layer, a light reflection layer provided on the transparent deformation layer, and an image pickup device, it was necessary to irradiate light from an oblique direction onto the surface of the light reflection layer on the transparent deformation layer side. In this case, in order to direct at least a part of the light reflected by the light reflection layer toward the image pickup device side, it was necessary to diffuse the light.

[0044] Specifically, in a conventional three-dimensional displacement sensing system, when light incident from an oblique direction onto the surface of the light reflection layer was reflected, in order for at least a part of the light to be directed toward the image pickup device side, it was necessary to use diffused light for the irradiated light or to give the light reflection layer diffusibility. When using diffused light, in order to image the deformed state of the light reflection layer with the image pickup device, it was necessary to use a lens or the like to form an image of the light reflected by the light reflection layer on the imaging surface of the image pickup device. Therefore, it was necessary to separate the distance between the light reflection layer and the lens, and the distance between the lens and the image pickup device by a predetermined distance. Thus, there was a problem that the thickness as a three-dimensional displacement sensing system became thick.

[0045] On the other hand, the three-dimensional displacement sensing system of the present invention has a light guiding unit 12a including a light guide plate 22 and a first diffraction element 24a between the image pickup device 14 and the specular reflector 18, and diffracts the light emitted from the light source unit 20 so that the light travels in a direction substantially perpendicular to the surface of the specular reflector 18 by the light guide plate 22 and the first diffraction element 24a. As a result, the light diffracted by the first diffraction element 24a becomes substantially parallel light that is incident substantially perpendicularly to the surface of the specular reflector 18 and is incident on the specular reflector 18. Since the light is incident substantially perpendicularly to the surface of the specular reflector 18, the light reflected by the specular reflector 18 is incident on a predetermined position (pixel) of the image pickup device 14 for each position within the plane of the specular reflector 18. Therefore, it is not necessary to form an image of the light reflected by the specular reflector 18 on the imaging surface of the image pickup device 14 using a lens or the like, and it is not necessary to secure the distance between the specular reflector 18 and the lens for using the lens, and the distance between the lens and the image pickup device 14. Therefore, the distance between the specular reflector 18 and the image pickup device 14 can be made shorter, and the thickness as a three-dimensional displacement sensing system can be made thinner.

[0046] Here, in the example shown in FIG. 1, the light guide unit 12a has the second diffraction element 26a, and the second diffraction element 26a is a reflective diffraction element, but the present invention is not limited to this configuration.

[0047] FIG. 3 is a diagram conceptually showing another example of the three-dimensional displacement sensing system of the present invention.

[0048] The three-dimensional displacement sensing system 10b shown in FIG. 3 includes a light guide unit 12b, an imaging element 14, a transparent deformation layer 16, a specular reflector 18, and a light source unit 20. Note that the three-dimensional displacement sensing system 10b shown in FIG. 3 has the same configuration as the three-dimensional displacement sensing system 10a shown in FIG. 1 except that it has the light guide unit 12b instead of the light guide unit 12a. Therefore, the following description mainly focuses on the different parts.

[0049] The light guide unit 12b has a substantially plate-shaped light guide plate 22, a first diffraction element 24a disposed in contact with one main surface of the light guide plate 22, and a second diffraction element 26b disposed in contact with the other main surface of the light guide plate 22. The first diffraction element 24a and the second diffraction element 26b are disposed on different main surfaces of the light guide plate 22 and are spaced apart in the in-plane direction of the main surface of the light guide plate 22. In the example shown in FIG. 3, the first diffraction element 24a is a reflective diffraction element. On the other hand, the second diffraction element 26b is a transmissive diffraction element. A transmissive diffraction element transmits incident light in a direction non-parallel to the incident direction. For example, a transmissive diffraction element transmits light incident substantially perpendicular to the surface in a predetermined direction inclined at a predetermined angle with respect to the perpendicular to the surface.

[0050] In the three-dimensional displacement sensing system 10b shown in FIG. 3, the imaging element 14 is disposed on the surface side of the light guide unit 12b on the side of the first diffraction element 24a, and the transparent deformation layer 16 is disposed on the other surface side. Further, a specular reflector 18 is disposed in contact with the surface of the transparent deformation layer 16 on the side opposite to the light guide unit 12b. Further, the imaging element 14, the transparent deformation layer 16, and the specular reflector 18 are disposed at positions overlapping the first diffraction element 24a in the in-plane direction of the main surface of the light guide plate 22. Further, the surface of the first diffraction element 24a, the surface (light receiving surface) of the imaging element 14, and the surface of the specular reflector 18 are disposed substantially parallel to each other.

[0051] Furthermore, in the three-dimensional displacement sensing system 10b shown in Figure 3, the light source unit 20 is positioned on the second diffraction element 26b side of the light guide unit 12b. The light source unit 20 is positioned in the in-plane direction of the main surface of the light guide plate 22 at a location that overlaps with the second diffraction element 26b.

[0052] As shown in Figure 3, in the three-dimensional displacement sensing system 10b, light is irradiated from the light source unit 20 toward the second diffraction element 26b. The light irradiated from the light source unit 20 is incident approximately perpendicularly to the second diffraction element 26b, which is located on the other main surface of the light guide plate 22. The second diffraction element 26b transmits and diffracts the incident light at an angle that causes total internal reflection within the light guide plate 22. At that time, the second diffraction element 26b transmits and diffracts the incident light toward the direction of the first diffraction element 24a (transmission and diffraction occur such that the azimuth direction of the transmitted light is toward the direction of the first diffraction element 24a).

[0053] Light transmitted and diffracted by the second diffraction element 26b undergoes repeated total internal reflection within the light guide plate 22 and is guided toward the first diffraction element 24a in the in-plane direction. The subsequent operation is the same as that of the three-dimensional displacement sensing system 10a shown in Figures 1 and 2. By irradiating light from the light source unit 20 and capturing an image with the image sensor 14, it is possible to detect whether or not an object P is in contact with the three-dimensional displacement sensing system 10b, and to detect the position, size, and shape of the object P if it is in contact.

[0054] Furthermore, in the example shown in Figure 1, the light source unit 20 is positioned on the side of the light guide plate 22 where the transparent deformation layer 16 and specular reflector 18 are located, and the second diffraction element 26a is positioned on the side of the light guide plate 22 where the image sensor 14 is located, but the configuration is not limited to this.

[0055] Figure 4 is a conceptual diagram illustrating another example of the three-dimensional displacement sensing system of the present invention.

[0056] The three-dimensional displacement sensing system 10c shown in Figure 4 includes a light guide unit 12c, an image sensor 14, a transparent deformation layer 16, a specular reflector 18, and a light source unit 20. Note that the three-dimensional displacement sensing system 10c shown in Figure 4 has the same configuration as the three-dimensional displacement sensing system 10a shown in Figure 1, except for the presence of a light guide unit 12c instead of a light guide unit 12a and a different arrangement of the light source unit 20. Therefore, the following explanation will mainly focus on the differences.

[0057] The light guide unit 12c includes a substantially plate-shaped light guide plate 22, a first diffraction element 24a positioned in contact with one main surface of the light guide plate 22, and a second diffraction element 26a positioned in contact with the other main surface of the light guide plate 22. The first diffraction element 24a and the second diffraction element 26a are positioned on different main surfaces of the light guide plate 22 and are spaced apart in the in-plane direction of the main surfaces of the light guide plate 22. That is, the second diffraction element 26a is positioned on the surface of the light guide plate 22 opposite to the surface on which the image sensor 14 is positioned. In the example shown in Figure 4, the first diffraction element 24a and the second diffraction element 26a are reflective diffraction elements.

[0058] In the three-dimensional displacement sensing system 10c shown in Figure 4, the image sensor 14 is positioned on the surface of the light guide section 12c facing the first diffraction element 24a, and the transparent deformation layer 16 is positioned on the other surface. A specular reflector 18 is positioned in contact with the surface of the transparent deformation layer 16 opposite to the light guide section 12c. The image sensor 14, the transparent deformation layer 16, and the specular reflector 18 are positioned in a location that overlaps with the first diffraction element 24a in the in-plane direction of the main surface of the light guide plate 22. The surface of the first diffraction element 24a, the surface of the image sensor 14 (light-receiving surface), and the surface of the specular reflector 18 are positioned approximately parallel to each other.

[0059] Furthermore, in the three-dimensional displacement sensing system 10c shown in Figure 4, the light source unit 20 is positioned on the side of the light guide unit 12c opposite to the side of the second diffraction element 26a. That is, the light source unit 20 is positioned on the side of the light guide plate 22 where the image sensor 14 is located. The light source unit 20 is positioned in the in-plane direction of the main surface of the light guide plate 22 at a location that overlaps with the second diffraction element 26a.

[0060] As shown in Figure 4, in the three-dimensional displacement sensing system 10c, light is irradiated from the light source unit 20 toward the second diffraction element 26a. The light irradiated from the light source unit 20 is incident approximately perpendicularly to the second diffraction element 26a, which is located on the other main surface of the light guide plate 22. The second diffraction element 26a reflects and diffracts the incident light at an angle that causes total internal reflection within the light guide plate 22. At that time, the second diffraction element 26a reflects and diffracts the incident light toward the direction of the first diffraction element 24a (reflecting and diffracting so that the azimuth direction of the reflected light is toward the direction of the first diffraction element 24a).

[0061] The light reflected and diffracted by the second diffraction element 26a undergoes repeated total internal reflection within the light guide plate 22 and is guided toward the first diffraction element 24a in the in-plane direction. The subsequent operation is the same as that of the three-dimensional displacement sensing system 10a shown in Figures 1 and 2. By irradiating light from the light source unit 20 and capturing an image with the image sensor 14, it is possible to detect whether or not an object P is in contact with the three-dimensional displacement sensing system 10c, and to detect the position, size, and shape of the object P if it is in contact.

[0062] Figure 5 is a conceptual diagram illustrating another example of the three-dimensional displacement sensing system of the present invention.

[0063] The three-dimensional displacement sensing system 10d shown in Figure 5 includes a light guide unit 12d, an image sensor 14, a transparent deformation layer 16, a specular reflector 18, and a light source unit 20. Note that the three-dimensional displacement sensing system 10d shown in Figure 5 has the same configuration as the three-dimensional displacement sensing system 10a shown in Figure 1, except for the presence of a light guide unit 12d instead of a light guide unit 12a and a different arrangement of the light source unit 20. Therefore, the following explanation will mainly focus on the differences.

[0064] The light guide unit 12d includes a substantially plate-shaped light guide plate 22, a first diffraction element 24a positioned in contact with one main surface of the light guide plate 22, and a second diffraction element 26b positioned in contact with the other main surface of the light guide plate 22. The first diffraction element 24a and the second diffraction element 26b are positioned on the same main surface of the light guide plate 22 and are spaced apart in the in-plane direction of the main surface of the light guide plate 22. That is, the second diffraction element 26b is positioned on the side of the light guide plate 22 where the image sensor 14 is located. In the example shown in Figure 5, the first diffraction element 24a is a reflective diffraction element, and the second diffraction element 26b is a transmissive diffraction element.

[0065] In the three-dimensional displacement sensing system 10d shown in Figure 5, the image sensor 14 is positioned on the surface of the light guide section 12d facing the first diffraction element 24a, and the transparent deformation layer 16 is positioned on the other surface. A specular reflector 18 is positioned in contact with the surface of the transparent deformation layer 16 opposite to the light guide section 12d. The image sensor 14, the transparent deformation layer 16, and the specular reflector 18 are positioned in a location that overlaps with the first diffraction element 24a in the in-plane direction of the main surface of the light guide plate 22. The surface of the first diffraction element 24a, the surface of the image sensor 14 (light-receiving surface), and the surface of the specular reflector 18 are positioned approximately parallel to each other.

[0066] Furthermore, in the three-dimensional displacement sensing system 10d shown in Figure 5, the light source unit 20 is positioned on the side of the light guide unit 12d where the second diffraction element 26b is located. That is, the light source unit 20 is positioned on the side of the light guide plate 22 where the image sensor 14 is located. The light source unit 20 is positioned in the in-plane direction of the main surface of the light guide plate 22 at a location that overlaps with the second diffraction element 26b.

[0067] As shown in Figure 5, the three-dimensional displacement sensing system 10d irradiates light from the light source unit 20 toward the second diffraction element 26b. The light irradiated from the light source unit 20 is incident approximately perpendicularly to the second diffraction element 26b, which is located on one main surface of the light guide plate 22. The second diffraction element 26b transmits and diffracts the incident light at an angle that causes total internal reflection within the light guide plate 22. At that time, the second diffraction element 26b transmits and diffracts the incident light toward the direction of the first diffraction element 24a (transmission and diffraction are performed so that the azimuth direction of the transmitted light is toward the direction of the first diffraction element 24a).

[0068] The light transmitted and diffracted by the second diffraction element 26b undergoes repeated total internal reflection within the light guide plate 22 and is guided toward the first diffraction element 24a in the in-plane direction. The subsequent operation is the same as that of the three-dimensional displacement sensing system 10a shown in Figures 1 and 2. By irradiating light from the light source unit 20 and capturing an image with the image sensor 14, it is possible to detect whether or not an object P is in contact with the three-dimensional displacement sensing system 10d, and to detect the position, size, and shape of the object P if it is in contact.

[0069] In the examples shown in Figures 1 to 5, the light guide unit is configured to have a second diffraction element for causing light to be incident on the light guide plate 22 in a manner that causes total internal reflection. However, the light guide unit is not limited to this configuration, and may be configured without a second diffraction element. In the case where the light guide unit does not have a second diffraction element, for example, the shape of the light guide plate may be such that one of its sides is inclined relative to the main surface, and light may be incident on the light guide plate at an angle that causes total internal reflection from the inclined side.

[0070] In the examples shown in Figures 1 to 5, the first and second diffraction elements are arranged spaced apart in the in-plane direction of the main surface of the light guide plate 22. However, the design is not limited to this configuration, and the first and second diffraction elements may partially overlap in the in-plane direction of the main surface of the light guide plate 22. Furthermore, if the first and second diffraction elements are arranged on the same main surface of the light guide plate 22, they may be formed integrally.

[0071] Figure 6 is a conceptual diagram illustrating another example of the three-dimensional displacement sensing system of the present invention.

[0072] The three-dimensional displacement sensing system 10e shown in Figure 6 includes a light guide unit 12e, an image sensor 14, a transparent deformation layer 16, a specular reflector 18, and a light source unit 20. Note that the three-dimensional displacement sensing system 10e shown in Figure 6 has the same configuration as the three-dimensional displacement sensing system 10a shown in Figure 1, except that it has a light guide unit 12e instead of a light guide unit 12a; therefore, the following explanation will mainly focus on the different parts.

[0073] The light guide unit 12e includes a substantially plate-shaped light guide plate 22 and a diffraction element 25 positioned in contact with one main surface of the light guide plate 22. In the example shown in Figure 6, the diffraction element 25 is a reflective diffraction element.

[0074] In the three-dimensional displacement sensing system 10e shown in Figure 6, the image sensor 14 is positioned on the surface of the light guide section 12e facing the diffraction element 25, and the transparent deformation layer 16 is positioned on the other surface. A specular reflector 18 is positioned in contact with the surface of the transparent deformation layer 16 opposite to the light guide section 12e. The image sensor 14, the transparent deformation layer 16, and the specular reflector 18 are positioned in a location that overlaps with a portion of the diffraction element 25 in the in-plane direction of the main surface of the light guide plate 22. The region of the diffraction element 25 that overlaps with the image sensor 14, the transparent deformation layer 16, and the specular reflector 18 is a region that functions as a first diffraction element (hereinafter referred to as the first diffraction element section 25a) that diffracts the light guided within the light guide plate 22 toward the specular reflector 18. The surface of the diffraction element 25, the surface of the image sensor 14 (light-receiving surface), and the surface of the specular reflector 18 are positioned approximately parallel to each other.

[0075] Furthermore, in the three-dimensional displacement sensing system 10e shown in Figure 6, the light source unit 20 is located on the side of the light guide unit 12e opposite to the diffraction element 25. The light source unit 20 is located in a position that overlaps with the diffraction element 25 in the in-plane direction of the main surface of the light guide plate 22. The region that overlaps with the light source unit 20 is a region that functions as a second diffraction element (hereinafter referred to as the second diffraction element unit 25b) that diffracts the light emitted from the light source unit 20 and guides it through the light guide plate 22.

[0076] In other words, the diffraction element 25 has a first diffraction element portion 25a and a second diffraction element portion 25b in the in-plane direction. To put it another way, the diffraction element 25 is formed by integrally creating the first diffraction element and the second diffraction element.

[0077] In addition, in the diffraction element 25, the diffraction structure of the first diffraction element portion 25a and the diffraction structure of the second diffraction element portion 25b may be the same or different. Furthermore, in the diffraction element 25, the region between the first diffraction element portion 25a and the second diffraction element portion 25b may have the same diffraction structure as the first diffraction element portion 25a and / or the second diffraction element portion 25b, may have a different diffraction structure, or may be a region without a diffraction structure.

[0078] As shown in Figure 6, in the three-dimensional displacement sensing system 10e, light is irradiated from the light source unit 20 towards the second diffracting element unit 25b of the diffracting element 25. The light irradiated from the light source unit 20 passes through the light guide plate 22 and is incident approximately perpendicularly to the second diffracting element unit 25b of the diffracting element 25, which is located on one main surface of the light guide plate 22. The second diffracting element unit 25b of the diffracting element 25 reflects and diffracts the incident light at an angle that causes total internal reflection within the light guide plate 22. At that time, the second diffracting element unit 25b of the diffracting element 25 reflects and diffracts the incident light toward the direction of the first diffracting element unit 25a (it reflects and diffracts so that the direction of the reflected light is toward the direction of the first diffracting element unit 25a).

[0079] Light reflected and diffracted by the second diffracting element portion 25b of the diffracting element 25 undergoes repeated total internal reflection within the light guide plate 22 and is guided toward the first diffracting element portion 25a in the in-plane direction. When the light guided within the light guide plate 22 enters the first diffracting element portion 25a, a portion of it is reflected and diffracted at an angle deviating from the angle of total internal reflection. The remaining portion of the light is guided within the light guide plate 22 and enters the first diffracting element portion 25a again, where a portion of that light is reflected and diffracted at an angle deviating from the angle of total internal reflection (approximately perpendicular direction), and the remaining portion is guided within the light guide plate 22. As the light guided within the light guide plate 22 passes through the position of the first diffracting element portion 25a, a portion of the light is repeatedly reflected and diffracted in an approximately perpendicular direction.

[0080] Light reflected and diffracted by the first diffraction element 25a in a direction substantially perpendicular to the surface of the first diffraction element 25a passes through the light guide plate 22 and reaches the other main surface of the light guide plate 22. However, because the angle of incidence to this main surface is outside the conditions for total internal reflection, the light is emitted from the light guide plate 22.

[0081] The subsequent operation is the same as that of the three-dimensional displacement sensing system 10a shown in Figures 1 and 2. The three-dimensional displacement sensing system 10e can detect whether or not an object P is in contact with the three-dimensional displacement sensing system 10e by irradiating light from the light source unit 20 and capturing an image with the image sensor 14, and can also detect the position, size, and shape of the object P that is in contact with it.

[0082] In the examples shown in Figures 1 to 6, the first diffracting element is a reflective type diffracting element and is positioned on the main surface of the light guide plate 22 on the side facing the image sensor 14. However, the configuration is not limited to this, and the first diffracting element may be a transmissive type diffracting element and be positioned on the main surface of the light guide plate 22 on the side opposite to the image sensor 14.

[0083] Figure 7 is a conceptual diagram illustrating another example of the three-dimensional displacement sensing system of the present invention.

[0084] The three-dimensional displacement sensing system 10f shown in Figure 7 includes a light guide unit 12f, an image sensor 14, a transparent deformation layer 16, a specular reflector 18, and a light source unit 20. Note that the three-dimensional displacement sensing system 10f shown in Figure 7 has the same configuration as the three-dimensional displacement sensing system 10a shown in Figure 1, except that it has a light guide unit 12f instead of a light guide unit 12a; therefore, the following explanation will mainly focus on the different parts.

[0085] The light guide unit 12f includes a substantially plate-shaped light guide plate 22, a first diffraction element 24b positioned in contact with the other main surface of the light guide plate 22, and a second diffraction element 26b positioned in contact with the other main surface of the light guide plate 22. The first diffraction element 24b and the second diffraction element 26b are positioned on the same main surface of the light guide plate 22 and are spaced apart in the in-plane direction of the main surface of the light guide plate 22. That is, the first diffraction element 24b is positioned on the side of the light guide plate 22 where the image sensor 14 is positioned. In the example shown in Figure 7, the first diffraction element 24b and the second diffraction element 26b are transmissive diffraction elements.

[0086] In the three-dimensional displacement sensing system 10f shown in Figure 7, the image sensor 14 is positioned on the surface of the light guide section 12f opposite to the first diffraction element 24b, and the transparent deformation layer 16 is positioned on the side of the first diffraction element 24b. A specular reflector 18 is positioned in contact with the surface of the transparent deformation layer 16 opposite to the light guide section 12f. The image sensor 14, the transparent deformation layer 16, and the specular reflector 18 are positioned in a location that overlaps with the first diffraction element 24b in the in-plane direction of the main surface of the light guide plate 22. The surface of the first diffraction element 24b, the surface of the image sensor 14 (light-receiving surface), and the surface of the specular reflector 18 are positioned approximately parallel to each other.

[0087] Furthermore, in the three-dimensional displacement sensing system 10f shown in Figure 7, the light source unit 20 is positioned on the side of the light guide unit 12f where the second diffraction element 26b is located. That is, the light source unit 20 is positioned on the side of the light guide plate 22 where the image sensor 14 is located. The light source unit 20 is positioned in the in-plane direction of the main surface of the light guide plate 22 at a location that overlaps with the second diffraction element 26b.

[0088] As shown in Figure 7, in the three-dimensional displacement sensing system 10f, light is irradiated from the light source unit 20 toward the second diffraction element 26b. The light irradiated from the light source unit 20 is incident approximately perpendicularly to the second diffraction element 26b, which is located on the other main surface of the light guide plate 22. The second diffraction element 26b transmits and diffracts the incident light at an angle that causes total internal reflection within the light guide plate 22. At that time, the second diffraction element 26b transmits and diffracts the incident light toward the direction of the first diffraction element 24b (transmission and diffraction are performed so that the azimuth direction of the transmitted light is toward the direction of the first diffraction element 24b).

[0089] Light transmitted and diffracted by the second diffraction element 26b undergoes repeated total internal reflection within the light guide plate 22 and is guided toward the first diffraction element 24b in the in-plane direction. When light guided within the light guide plate 22 is incident on the first diffraction element 24b, a portion of it is transmitted and diffracted at an angle that deviates from the angle of total internal reflection. In the example shown in Figure 7, light guided within the light guide plate 22 is incident on the surface of the first diffraction element 24b (the surface in contact with the light guide plate 22) from an oblique direction. The first diffraction element 24b reflects and diffracts the light incident on its surface from an oblique direction in a direction approximately perpendicular to the surface. The remaining portion of the light is guided within the light guide plate 22 and incident on the first diffraction element 24b again, where a portion of that light is reflected and diffracted at an angle that deviates from the angle of total internal reflection (approximately perpendicular direction), and the remaining portion is guided within the light guide plate 22. As the light guided through the light guide plate 22 passes through the position of the first diffraction element 24b, some of the light is repeatedly reflected and diffracted in a nearly perpendicular direction.

[0090] Light transmitted and diffracted by the first diffracting element 24b in a direction approximately perpendicular to the surface of the first diffracting element 24b is emitted from the light guide plate 22 because it falls outside the total internal reflection condition.

[0091] Light emitted from the light guide plate 22 enters the transparent deformation layer 16, propagates within the transparent deformation layer 16, and enters the specular reflector 18.

[0092] The specular reflector 18 reflects light incident at approximately perpendicular to its surface in a direction approximately perpendicular to the surface of the specular reflector 18, as shown by the dashed arrow in Figure 7.

[0093] Light reflected by the specular reflector 18 propagates through the transparent deformation layer 16 and is incident on the first diffraction element 24b located on the other main surface of the light guide plate 22. At least a portion of the light incident on the first diffraction element 24b is transmitted in a direction perpendicular to the surface without being diffracted by the first diffraction element 24b. The light that is not diffracted by the first diffraction element 24b is incident on the other surface of the light guide plate 22 approximately perpendicular to it, passes through the light guide plate 22, and is incident on the light-receiving surface of the image sensor 14 approximately perpendicular to it.

[0094] Thus, in the 3D displacement sensing system 10f, by irradiating light from the light source unit 20 and capturing an image with the image sensor 14, it is possible to detect whether or not an object P is in contact with the 3D displacement sensing system 10f, similar to the 3D displacement sensing system 10a shown in Figures 1 and 2, and to detect the position, size, and shape of the object P that is in contact with it.

[0095] Furthermore, even when the first diffraction element is a transmissive diffraction element, as shown in the example in Figure 7, the second diffraction element can be a transmissive diffraction element, a reflective diffraction element, or a configuration without a second diffraction element. Also, even when the first diffraction element is located on the side of the light guide plate 22 facing the specular reflector 18, as shown in the example in Figure 7, the second diffraction element may be located on the side of the light guide plate 22 facing the specular reflector 18, or on the side facing the image sensor 14. In this case, the light source unit 20 may be located on the side of the light guide plate facing the second diffraction element, or on the side opposite to the second diffraction element.

[0096] Furthermore, in the example shown in Figure 7, the first diffraction element and the second diffraction element are arranged spaced apart in the in-plane direction of the main surface of the light guide plate 22, but the configuration is not limited to this, and the first diffraction element and the second diffraction element may partially overlap in the in-plane direction of the main surface of the light guide plate 22. Also, if the first diffraction element and the second diffraction element are arranged on the same main surface of the light guide plate 22, they may be formed integrally.

[0097] In the three-dimensional displacement sensing system of the present invention, it is preferable to have a phase difference plate positioned at any location between the light guide and the specular reflector, wherein the slow phase axis of the phase difference plate and the slow phase axis of the in-plane phase difference of the transparent deformation layer intersect, and the total in-plane phase difference (in-plane retardation) is preferably 50 nm or less, more preferably 20 nm or less, and even more preferably 5 nm or less. Furthermore, while it is sufficient for the slow phase axis of the phase difference plate and the slow phase axis of the in-plane phase difference of the transparent deformation layer to intersect, it is preferable that the angle between the slow phase axis of the phase difference plate and the slow phase axis of the in-plane phase difference of the transparent deformation layer is 80° to 100°, and preferably orthogonal.

[0098] As an example, in the three-dimensional displacement sensing system 10g shown in Figure 8, a phase difference plate 30 is arranged on the light guide portion 12a side of the transparent deformation layer 16. Note that the three-dimensional displacement sensing system 10g in Figure 8 has the same configuration as the three-dimensional displacement sensing system 10a shown in Figure 1, except for the presence of the phase difference plate 30.

[0099] As will be described in detail later, when using a polarization-selective diffraction element as the first diffraction element, which diffracts light according to the polarization state of the incident light, it is desirable to maintain the polarization state of the light incident on the first diffraction element in a desired polarization state. However, if the transparent deformation layer 16 has an in-plane phase difference, the polarization state of the light changes due to the influence of the in-plane phase difference as the light passes through the transparent deformation layer 16.

[0100] In contrast, by having a phase difference plate 30 whose total in-plane phase difference with the transparent deformation layer 16 is 50 nm or less, the polarization state of the light incident on the first diffracting element can be maintained in a desired polarization state.

[0101] The in-plane phase difference of the phase difference plate 30 can be appropriately set according to the in-plane phase difference of the transparent deformation layer 16, such that the total in-plane phase difference with the transparent deformation layer 16 is 50 nm or less. Furthermore, there are no particular restrictions on the phase difference plate 30, and conventionally known phase difference plates can be used. From the viewpoint of ease of manufacturing, etc., the phase difference plate 30 is preferably a layer formed using a liquid crystal compound or a stretched polymer film (stretched film).

[0102] Furthermore, in the example shown in Figure 8, the phase difference plate 30 is arranged on the light guide portion 12a side of the transparent deformation layer 16, but the configuration is not limited to this, and a configuration in which the phase difference plate 30 is arranged between the transparent deformation layer 16 and the specular reflector 18 is also possible, as in the three-dimensional displacement sensing system 10h shown in Figure 9.

[0103] The components of the three-dimensional displacement sensing system of the present invention will be described below.

[0104] <Light Guide Section> The light guide section comprises a light guide plate and a first diffraction element positioned in contact with the light guide plate. In a preferred embodiment, the light guide section further comprises a second diffraction element.

[0105] [Light Guide Plate] The light guide plate guides incident light by totally reflecting it within the plate. There are no particular limitations on the light guide plate, and conventionally known light guide plates can be used as appropriate. Specifically, examples of materials for the light guide plate include glass, acrylic, polycarbonate, polystyrene, urethane, polyolefin, polyvinyl chloride, polyethylene terephthalate (PET), and triacetylcellulose (TAC).

[0106] There are no restrictions on the thickness of the light guide plate; it should be set appropriately considering factors such as the thickness required to support the first diffraction element, the lightness and thickness of the light guide plate, and the uniformity of the brightness (light intensity) of the light emitted from the light guide plate. The thickness of the light guide plate is preferably 0.04 mm to 30 mm, more preferably 0.1 mm to 20 mm, and even more preferably 0.5 mm to 1 mm.

[0107] [Diffraction Elements] The first diffraction element is used to diffract the light guided through the light guide plate and cause it to exit the light guide plate. The second diffraction element is used to diffract the light emitted from the light source and cause the light to enter (guide) into the light guide plate.

[0108] There are no particular limitations on the first diffraction element and the second diffraction element (hereinafter collectively referred to as the diffraction element), and conventionally known diffraction elements can be used as appropriate. As mentioned above, the diffraction element may be a transmission type diffraction element that transmits and diffracts incident light, or a reflection type diffraction element that reflects and diffracts incident light.

[0109] The diffraction element is preferably a surface relief type diffraction element, a volume hologram type diffraction element, or a polarization diffraction element. The diffraction element is preferably a polarization diffraction element with polarization selectivity. Polarization selectivity means that the diffraction, diffraction direction, etc., differ depending on the polarization state of the light incident on the diffraction element.

[0110] A polarization-selective polarization diffraction element may diffract polarization according to the polarization state of mutually orthogonal linearly polarized light, or it may diffract right-circularly polarized light and left-circularly polarized light according to their polarization states.

[0111] The polarizing diffracting element is preferably a liquid crystal diffracting element having a liquid crystal alignment pattern, formed using a composition containing a liquid crystal compound. Furthermore, the reflective liquid crystal diffracting element is preferably a cholesteric liquid crystal layer having a liquid crystal alignment pattern, formed by fixing a cholesteric liquid crystal phase.

[0112] In this case, if the first diffraction element does not have polarization selectivity, as in the examples in Figures 1 to 8, when the light diffracted by the first diffraction element and reflected by the specular reflector 18 (indicated by the dashed arrows in the figures) is incident on the first diffraction element, some of the light will pass through the first diffraction element and be incident on the image sensor 14, depending on the diffraction efficiency of the first diffraction element, but some of the other light will be diffracted by the first diffraction element. As a result, the efficiency of light utilization will decrease.

[0113] In contrast, if the first diffraction element has polarization selectivity, for example, if the first diffraction element reflects and diffracts right-circularly polarized light and transmits left-circularly polarized light, the first diffraction element reflects and diffracts the right-circularly polarized light (solid arrow in the figure) guided through the light guide plate toward the specular reflector 18. At that time, the right-circularly polarized light is reflected and diffracted as right-circularly polarized light. When this right-circularly polarized light is incident on the specular reflector 18, it is reflected by the specular reflector 18. During reflection by the specular reflector 18, the right-circularly polarized light is converted to left-circularly polarized light (dashed arrow in the figure). The light reflected by the specular reflector 18 is incident on the first diffraction element in a left-circularly polarized state. Since the first diffraction element transmits left-circularly polarized light, the incident light is hardly reflected and passes through the first diffraction element before being incident on the image sensor 14. Therefore, the efficiency of light utilization can be increased.

[0114] In the above explanation, the first diffracting element was described as reflecting and diffracting right-circularly polarized light and transmitting left-circularly polarized light. However, the explanation is not limited to this, and the first diffracting element may also reflect and diffract left-circularly polarized light and transmit right-circularly polarized light.

[0115] Furthermore, the diffraction efficiency of the first diffraction element may be uniform in the plane or may vary depending on its position in the plane. For example, the diffraction efficiency of the first diffraction element may increase gradually or in steps in the direction from the second diffraction element toward the first diffraction element (from right to left in Figure 1). This makes it possible to make the light diffracted by the first diffraction element and irradiated onto the specular reflector 18 uniform in the plane.

[0116] <<Surface Relief Diffraction Element>> Known surface relief diffraction elements can be used as surface relief diffraction elements. A surface relief diffraction element is constructed in which linear fine irregularities are arranged alternately in parallel on the surface at a predetermined period. The period of the diffraction structure, material, and height of the protrusions can be appropriately set depending on the diffraction angle, diffraction efficiency, and wavelength range of the diffracted light.

[0117] Furthermore, a surface relief type diffraction element may have a diffraction structure (uneven structure) formed on the surface of a film-like material made of resin or the like, or it may have a diffraction structure (uneven structure) directly formed on the surface of a light guide plate.

[0118] Furthermore, by adjusting the period, material, height, and shape of the diffracting structure, a surface relief type diffracting element can be made into a polarization diffracting element that reflects and diffracts one type of linearly polarized light while transmitting the other type of linearly polarized light without diffraction.

[0119] <<Volume Holographic Diffraction Element>> Known volume holographic diffraction elements can be used as volume holographic diffraction elements. A volume holographic diffraction element is composed of linear regions with a high refractive index and linear regions with a low refractive index arranged alternately in parallel at a predetermined period. The period of the diffraction structure, the material, and the refractive index of each region can be appropriately set depending on the diffraction angle, diffraction efficiency, and wavelength range of the diffracted light.

[0120] Furthermore, by adjusting the periodicity of the diffraction structure and the material, a volume hologram type diffraction element can be made into a polarization diffraction element that reflects and diffracts one type of linearly polarized light, while transmitting the other type of linearly polarized light without diffraction.

[0121] <<Polarization Diffractive Element>> Known polarization diffractive elements can be used as polarization diffractive elements. A polarization diffractive element is a diffractive element that controls the diffraction direction, polarization state, and diffractive light intensity of the emitted light according to the polarization state of the incident light by controlling the polarization state in a micro-region. Examples of polarization diffractive elements include a polarization diffractive element that forms a diffractive structure using the structural birefringence described in "Erez Hasman et al., Polarization dependent focusing lens by use of quantized Pancharatnm-Berry phase diffractive optics, Applied Physics Letters, Volume 82, Number 3 pp.328-330", and a polarization diffractive element that forms a diffractive structure using the birefringent material described in Japanese Patent No. 5276847.

[0122] As the polarizing diffraction element, a conventionally known liquid crystal diffraction element can be used, which has a liquid crystal layer formed using a composition containing a liquid crystal compound, and which has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0123] The diffraction angle, diffraction efficiency, and diffraction wavelength of a liquid crystal diffraction element can be adjusted as needed to suit the application. The diffraction angle depends on the in-plane pitch (one period of the liquid crystal alignment pattern), and the diffraction efficiency depends on the film thickness. The diffraction wavelength depends on the film thickness in the case of a transmission type, and on the chiral pitch length (helical pitch) in the case of a reflection type, so these should be adjusted as needed according to the application.

[0124] (Transmissive Liquid Crystal Diffractometer) A transmissive liquid crystal diffractometer is a liquid crystal diffractometer having a liquid crystal orientation pattern that rotates continuously along at least one direction in the plane, and having a liquid crystal layer (optical anisotropy layer) in the thickness direction in which the liquid crystal compound does not form a cholesteric liquid crystal phase. In addition, the liquid crystal layer of the liquid crystal diffractometer may have a configuration in which the liquid crystal compound is twisted and rotated in the thickness direction to such an extent that it does not form a cholesteric liquid crystal phase. A transmissive liquid crystal diffractometer may have a support and an alignment film in addition to the liquid crystal layer having a liquid crystal orientation pattern. Such transmissive liquid crystal diffractometers are described in International Publication No. 2020 / 226078, International Publication No. 2020 / 122128, etc.

[0125] (Reflective Liquid Crystal Diffractive Elements) Examples of reflective liquid crystal diffractive elements include optical elements comprising a cholesteric liquid crystal layer having a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, with a fixed cholesteric liquid crystal phase. Such reflective liquid crystal diffractive elements are described in International Publication Nos. 2019 / 131950, 2019 / 131966, 2019 / 189852, 2020 / 071169, 2020 / 226078, and 2020 / 122128, among others.

[0126] A reflective liquid crystal diffraction element may have a support and an alignment film, in addition to a cholesteric liquid crystal layer having a liquid crystal alignment pattern.

[0127] In this case, if the reflective liquid crystal diffraction element has a configuration that includes a wavelength-selective cholesteric liquid crystal layer, the diffraction element may have one wavelength-selective cholesteric liquid crystal layer or two or more layers.

[0128] When the diffracting element has two or more cholesteric liquid crystal layers, it is preferable that the two or more cholesteric liquid crystal layers have different helical pitches. That is, it is preferable that the two or more cholesteric liquid crystal layers have different wavelength selectivity.

[0129] For example, the diffracting element may have two cholesteric liquid crystal layers, one cholesteric liquid crystal layer that selectively reflects red light and one cholesteric liquid crystal layer that selectively reflects green light, or it may have three liquid crystal layers, one cholesteric liquid crystal layer that selectively reflects red light, one cholesteric liquid crystal layer that selectively reflects green light, and one cholesteric liquid crystal layer that selectively reflects blue light.

[0130] In the case where the diffracting element has a configuration having multiple cholesteric liquid crystal layers, for example, by configuring each cholesteric liquid crystal layer to reflect red, green, and blue light respectively, white light can be reflected and diffracted.

[0131] Furthermore, for example, the diffracting element may have three cholesteric liquid crystal layers with different selective reflection center wavelengths, and may be configured to reflect one or two colors selected from visible light such as red, green, and blue light, as well as infrared and / or ultraviolet light, or it may be configured to reflect only light other than visible light.

[0132] Alternatively, the diffracting element may have two or more cholesteric liquid crystal layers with different selective reflection center wavelengths. Furthermore, the diffracting element may be configured to reflect not only visible light such as red, green, and blue light, but also non-visible light such as infrared and / or ultraviolet light, or each cholesteric liquid crystal layer may be configured to reflect non-visible light such as infrared and / or ultraviolet light.

[0133] Here, if the first diffraction element includes a cholesteric liquid crystal layer having a liquid crystal alignment pattern, it is preferable that the absolute value of the optical axis inclination angle φ, expressed as sinθ2 = n・sinφ (where n is the average refractive index of the cholesteric liquid crystal layer), is 5° or more, when the in-plane retardation is measured from the normal direction to the main surface of the cholesteric liquid crystal layer and from a direction inclined with respect to the normal, in either the slow axis plane or the fast axis plane, and the measurement angle θ2 is the angle that the direction in which the in-plane retardation is minimized makes with the normal.

[0134] This point will be explained using Figures 10 to 13.

[0135] Figure 10 is a conceptual diagram showing an example of a liquid crystal diffraction element including a cholesteric liquid crystal layer having a liquid crystal alignment pattern. Figure 11 is a plan view of the cholesteric liquid crystal layer shown in Figure 10. In Figure 11, in order to clearly show the structure of the cholesteric liquid crystal layer, only the liquid crystal compound 40 on the surface of the alignment film is shown.

[0136] The liquid crystal diffraction element 50 shown in Figure 10 comprises a support 54, an alignment film 56, and a cholesteric liquid crystal layer 52. The cholesteric liquid crystal layer 52 is made up of a fixed cholesteric liquid crystal phase and has a liquid crystal alignment pattern in which the orientation of the optical axis 40A originating from the liquid crystal compound 40 changes while continuously rotating along at least one direction in the plane (see Figure 10).

[0137] As shown in Figure 11, the liquid crystal compound 40 constituting the cholesteric liquid crystal layer 52 is arranged two-dimensionally in a predetermined direction indicated by arrow X, and in a direction perpendicular to this direction (arrow X direction) (Y direction), according to the orientation pattern formed on the underlying alignment film 56. In other words, in Figure 10, the Y direction is perpendicular to the plane of the paper.

[0138] Furthermore, as shown in Figure 11, the liquid crystal compound 40 forming the cholesteric liquid crystal layer 52 has a liquid crystal orientation pattern in which the orientation of the optical axis 40A changes continuously while rotating along the direction of arrow X within the plane of the cholesteric liquid crystal layer 52. In the illustrated example, the liquid crystal orientation pattern of the liquid crystal compound 40 has a liquid crystal orientation pattern in which the optical axis 40A changes continuously while rotating counterclockwise along the direction of arrow X.

[0139] The statement that the orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in the direction of arrow X (a predetermined one direction) means that, specifically, the angle between the optical axis 40A of the liquid crystal compounds 40 arranged along the direction of arrow X and the direction of arrow X differs depending on the position in the direction of arrow X, and that the angle between the optical axis 40A and the direction of arrow X changes sequentially from θ to θ+180° or θ-180° along the direction of arrow X. The difference in angle between the optical axes 40A of liquid crystal compounds 40 adjacent to each other in the direction of arrow X is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0140] On the other hand, in the liquid crystal compound 40 that forms the cholesteric liquid crystal layer 52, the orientation of the optical axis 40A is the same in the Y direction, which is perpendicular to the direction of arrow X. In other words, in the liquid crystal compound 40 that forms the cholesteric liquid crystal layer 52, the angle between the optical axis 40A of the liquid crystal compound 40 and the direction of arrow X is the same in the Y direction.

[0141] In such a cholesteric liquid crystal layer, the symbol P shown in Figure 10 represents the helical pitch of the cholesteric liquid crystal layer. Also, the symbol Λ shown in Figures 10 and 11 represents one period of the liquid crystal alignment pattern.

[0142] The cholesteric liquid crystal layer 52, which has a liquid crystal alignment pattern, reflects the incident right-circularly polarized R in a direction different from specular reflection, while retaining its right-circular polarization.

[0143] In the cholesteric liquid crystal layer 52 shown in Figures 10 and 11, when the in-plane retardation Re is measured from the normal direction and a direction inclined with respect to the normal, the absolute value of the optical axis inclination angle φ, calculated using the measurement angle θ2 that the direction in which the in-plane retardation Re is minimized makes with the normal in either the slow-phase axis plane or the fast-phase axis plane, is 5° or more.

[0144] Specifically, as conceptually shown in Figure 12, the in-plane retardation Re of the cholesteric liquid crystal layer 52 is measured by incident light from the normal Z direction. Furthermore, as indicated by the arrow S, the in-plane retardation Re of the cholesteric liquid crystal layer 52 is measured by sequentially changing the incident direction of the measurement light in the leading-phase axis plane. A similar measurement is performed in the slow-phase axis plane. The incident direction of the measurement light is the angle of incidence with respect to the normal of the cholesteric liquid crystal layer 52.

[0145] In measuring the in-plane retardation Re in such a cholesteric liquid crystal layer 52, it is preferable that the absolute value of the optical axis inclination angle φ, calculated using the following formula, is 5° or more, using the absolute value of the measurement angle θ2, which is the angle formed between the direction in which the in-plane retardation Re is minimized and the normal, in either the slow axis plane or the fast axis plane. That is, the cholesteric liquid crystal layer 52 has an optical axis inclination angle φ of 5° or more, calculated using the following formula, which is the measurement angle θ2 formed between the incident direction of the measurement light in which the in-plane retardation Re is minimized and the normal Z. sinθ2 = n・sinφ (where n is the average refractive index of the cholesteric liquid crystal layer)

[0146] The measurement angle θ2 is the angle between the incident direction of the measurement light and the normal Z, which minimizes the in-plane retardation Re before the measurement light passes through the air-side interface A of the cholesteric liquid crystal layer 52, as shown in Figure 12.

[0147] The slow-phase axis and fast-phase axis of the cholesteric liquid crystal layer 52 can be detected, for example, by an AxoScan polarization phase difference analyzer manufactured by Axometrics. Furthermore, it is preferable to measure this in-plane retardation with light of a wavelength outside the selective reflection wavelength range of the cholesteric liquid crystal layer 52, for example, by infrared light, which is invisible light.

[0148] In the cholesteric liquid crystal layer 52, the leading phase axis plane usually coincides with the direction in which the optical axis 40A rotates continuously in the in-plane direction (arrow X direction), and the slowing phase axis direction coincides with the direction perpendicular to the direction in which the optical axis 40A rotates continuously, i.e., the arrow Y direction.

[0149] Figure 13 shows an example of the measurement results of the in-plane retardation Re in the cholesteric liquid crystal layer described above.

[0150] As shown in Figure 13, in this cholesteric liquid crystal layer, within the phase-advancing axis plane, the in-plane retardation Re decreases as the incident angle with respect to the normal increases, and is minimized at an incident angle of -60°.

[0151] On the other hand, within the slow axis plane, the in-plane retardation Re increases as the absolute value of the incident angle increases, with the measurement from the normal direction, i.e., at an incident angle of 0°, being the minimum. Furthermore, within the slow axis plane, the change in the in-plane retardation Re is symmetrical around an incident angle of 0°.

[0152] In other words, in this case, the measurement angle θ2 at which the in-plane retardation Re is minimized lies within the phase-advancing axis plane, and the absolute value of the measurement angle θ2 formed by the direction in which the in-plane retardation Re is minimized (incident direction of the measurement light) and the normal Z is 60°, and the optical axis tilt angle φ is 35°, assuming the average refractive index of the cholesteric liquid crystal layer 52 is 1.5.

[0153] The fact that the cholesteric liquid crystal layer 52 has such characteristics is thought to be because, as shown in Figure 10, the liquid crystal compound 40 (director of the liquid crystal compound) in the cholesteric liquid crystal layer 52 is inclined with respect to the main surface, and the direction of inclination substantially coincides with the bright and dark lines observed in the cross-sectional SEM (scanning electron microscope) image of the cholesteric liquid crystal layer.

[0154] The cholesteric liquid crystal layer 52, having these characteristics, can diffract circularly polarized light with higher diffraction efficiency.

[0155] More detailed information regarding the structure and manufacturing method of cholesteric liquid crystal layers with these characteristics is described in International Publication No. 2020 / 122127.

[0156] <Transparent Deformation Layer> The transparent deformation layer 16 is positioned on the light-guiding side of the specular reflector 18. When the object P to be measured comes into contact with the specular reflector 18, the transparent deformation layer 16 deforms along with the specular reflector 18 to conform to the shape of the object P. When the object P is separated, the transparent deformation layer 16 is an elastic member that returns the specular reflector 18 to its original state (approximately planar shape).

[0157] The transparent deformation layer 16 is a layer made of a flexible and elastic material that is optically transparent and can deform in response to external pressure when an object P comes into contact with it and external pressure is applied. In the present invention, the transparent deformation layer 16 is preferably a layer with a Shore OO hardness value of about 5 to 60, more preferably 10 to 50, and even more preferably 15 to 40.

[0158] The transparent deformation layer 16 may be formed from a gel or other relatively flexible material. Silicone is preferred as the material for the transparent deformation layer 16, and polyacrylic acid esters, polymethacrylic acid esters, polyurethanes, agarose, gelatin, polyacrylamide, polyvinyl alcohol, etc., can be used.

[0159] The transparent deformation layer 16 preferably has a tensile modulus of 0.1 MPa to 1000 MPa, more preferably 0.5 MPa to 100 MPa, and even more preferably 1 MPa to 10 MPa.

[0160] Furthermore, the transparent deformation layer 16 is preferably 0.1 mm to 10 mm thick, more preferably 0.3 mm to 5 mm thick, and even more preferably 0.5 mm to 1 mm thick.

[0161] The Shore OO hardness of the transparent deformation layer can be measured using a Shore OO durometer according to the procedure described in ASTM D2240.

[0162] Furthermore, the tensile modulus of the transparent deformation layer 16 can be measured using A&D's Tensilon RTF series and RTG series.

[0163] Here, the transparent deformation layer 16 preferably has an in-plane retardation of 50 nm or less at a wavelength of 550 nm, more preferably 20 nm or less, and even more preferably 5 nm or less.

[0164] Furthermore, the transparent deformation layer 16 preferably has a thickness directional retardation of 50 nm or less at a wavelength of 550 nm, more preferably 20 nm or less, and even more preferably 5 nm or less.

[0165] When a polarization-selective polarization diffraction element is used as the first diffraction element, if the in-plane retardation and / or thickness-direction retardation of the transparent deformation layer 16 is large, the polarization state of the light (polarized light) changes due to the retardation as it passes through the transparent deformation layer 16. As a result, some of the light that should pass through the first diffraction element is reflected and diffracted by the first diffraction element, which may reduce the efficiency of light utilization. That is, for example, if the first diffraction element reflects and diffracts right-circularly polarized light and transmits left-circularly polarized light, the right-circularly polarized light guided through the light guide plate 22 is reflected and diffracted by the first diffraction element, passes through the transparent deformation layer 16, is reflected by the specular reflector 18 and converted to left-circularly polarized light, and then passes through the transparent deformation layer 16 again and is incident on the first diffraction element. If the in-plane retardation and / or thickness-direction retardation of the transparent deformation layer 16 is large, the polarization state of the left-circularly polarized light will be disturbed and it will be incident on the first diffraction element containing a right-circularly polarized component. Therefore, some of the incident light (reflected light) may be reflected and diffracted by the first diffracting element, which may reduce the amount of light incident on the image sensor 14 and potentially decrease the efficiency of light utilization.

[0166] In contrast, by setting the in-plane retardation and / or thickness-direction retardation of the transparent deformation layer 16 to the above range, it is possible to suppress changes in the polarization state when polarized light passes through the transparent deformation layer 16, and to suppress the reflection and diffraction of a portion of the light that should pass through the first diffraction element by the first diffraction element, thereby increasing the efficiency of light utilization.

[0167] <Specular Reflector> The specular reflector 18 is laminated on the side of the transparent deformation layer 16 opposite to the light guide. The specular reflector 18 specularly reflects incident light. Furthermore, the specular reflector 18 is a layer that can deform in response to external pressure when an object P comes into contact with it and external pressure is applied.

[0168] As the specular reflector 18, for example, a layer made of a metal such as silver, aluminum, chromium, nickel, or platinum, or a layer made of a dielectric multilayer film of a metal or organic material, or a cholesteric liquid crystal layer can be used. The light-reflecting layer made of a metal such as silver or aluminum can be formed on the surface of the transparent deformation layer 16 by, for example, vapor deposition.

[0169] Furthermore, the specular reflector 18 is preferably thin in order to be deformable, with a thickness of 1 nm to 100 μm being preferred, more preferably 1 nm to 15 μm, and even more preferably 1 nm to 100 nm.

[0170] <Image Sensor> The image sensor 14 detects light that has been reflected by the specular reflector 18 and passed through the first diffracting element. The image sensor 14 is located on the side of the light guide that is opposite to the transparent deformation layer 16 and the specular reflector 18.

[0171] There are no particular limitations on the image sensor 14. For example, a solid-state image sensor is preferably used, and known image sensors such as CCD (Charge-Coupled Device) image sensors, CMOS (Complementary Metal-Oxide-Semiconductor) image sensors, organic thin-film image sensors, and other semiconductor-based image sensors can be used.

[0172] <Light source unit> The light source unit 20 irradiates light onto the light guide plate 22 of the light guide unit.

[0173] The light source unit 20 has a light source that emits light, and may further have optical elements such as a collimating lens, a linear polarizer, a phase difference plate, a louver film, etc., for making the light parallel. For example, if the first diffraction element and / or the second diffraction element are polarization diffraction elements that diffract right circularly polarized light, the light source may have a linear polarizer and a phase difference plate (λ / 4 plate) for converting unpolarized light emitted from the light source into right circularly polarized light.

[0174] There are no particular limitations on the light source of the light source unit 20; various light sources (light-emitting elements) can be used as long as they can emit a predetermined amount of light. Examples of light sources include LEDs (Light Emitting Diodes), LDs (Laser Diodes), and fluorescent lamps. The light source may be a white light source, a light source that emits monochromatic light such as red light, blue light, and green light, or a light source that emits light of multiple colors such as red light and green light. The light source may also be a light source that emits invisible light such as infrared light.

[0175] The three-dimensional displacement sensing system of the present invention may further have other functional layers in the optical path from the light source unit 20 to the image sensor 14. For example, it may have an adhesive layer, a linear polarizing plate, a phase difference layer, a louver film, a bandpass filter, a color filter, etc.

[0176] 10a-10h Three-dimensional displacement sensing system 12a-12f Light guide section 14 Image sensor 16 Transparent deformation layer 18 Specular reflector 20 Light source section 22 Light guide plate 24a-24b First diffraction element 25 Diffraction element 25a First diffraction element section 25b Second diffraction element section 26a-26b Second diffraction element 30 Phase difference plate 40 Liquid crystal compound 40A Optical axis 50 Liquid crystal diffraction element 52 Cholesteric liquid crystal layer 54 Support 56 Alignment film

Claims

1. A three-dimensional displacement sensing system comprising: a light guide plate and a light guide section including a first diffraction element arranged in contact with the light guide plate; an image sensor arranged on one surface side of the light guide section; a transparent deformation layer arranged on the other surface side of the light guide section; a specular reflector arranged on the opposite side of the transparent deformation layer from the light guide section; and a light source section that incidents light onto the light guide plate.

2. The three-dimensional displacement sensing system according to claim 1, wherein the first diffraction element has polarization selectivity.

3. The three-dimensional displacement sensing system according to claim 1 or 2, wherein the first diffraction element is a reflective diffraction element and is arranged on the surface of the light guide portion facing the image sensor.

4. The three-dimensional displacement sensing system according to claim 1 or 2, wherein the first diffraction element includes a cholesteric liquid crystal layer having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

5. The three-dimensional displacement sensing system according to claim 4, wherein the cholesteric liquid crystal layer has an absolute value of 5° or more of the optical axis inclination angle φ, expressed as sinθ2 = n・sinφ (where n is the average refractive index of the cholesteric liquid crystal layer), when the in-plane retardation is measured from the normal direction to the main surface of the cholesteric liquid crystal layer and from a direction inclined with respect to the normal, in either the slow-phase axis plane or the fast-phase axis plane, the measurement angle θ2 is the angle that the direction in which the in-plane retardation is minimized makes with the normal.

6. The three-dimensional displacement sensing system according to claim 1 or 2, wherein the light guide further comprises a second diffraction element, and the first diffraction element and the second diffraction element are spaced apart in the in-plane direction.

7. The three-dimensional displacement sensing system according to claim 1 or 2, wherein the in-plane retardation of the transparent deformation layer at a wavelength of 550 nm is 50 nm or less.

8. A three-dimensional displacement sensing system according to claim 1 or 2, comprising a phase difference plate disposed between the light guide portion and the specular reflector, wherein the slow phase axis of the phase difference plate and the slow phase axis of the in-plane phase difference of the transparent deformation layer intersect, and the total in-plane phase difference is 50 nm or less.

Images