Measurement system

Abstract

To provide a measurement system that can efficiently measure structures and minimize the need to give people unnecessary warnings. [Solution] The measurement system 1 includes a target 2 that is attached to a structure and contains a retroreflective sheet 4, and a laser measuring instrument 3 that emits invisible light laser beam L onto the retroreflective sheet 4 and receives the laser beam L that is retroreflective by the retroreflective sheet 4. The retroreflective sheet 4 retroreflects the laser beam L and suppresses the retroreflection of visible light more than the laser beam L.

Description

Technical Field

[0001] The present invention relates to a measurement system.

Background Art

[0002] In the measurement of structures such as tunnels, bridges, roads, and railway lines, a laser measuring instrument may be used. Patent Document 1 below describes a method for measuring displacement on the displacement meter side of a structure using a laser measuring instrument. In this document, the coordinates of targets attached to the wall surface of a tunnel at predetermined intervals are scanned with a 3D laser scanner to measure the displacement of the tunnel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A laser measuring instrument that irradiates a target with laser light to measure a structure receives the laser light reflected by the target and maps the position of the target based on the received laser light. Therefore, if the reflectivity of the target is high, even when the power of the laser light emitted from the laser measuring instrument is small or the light reception sensitivity of the laser measuring instrument is poor, errors can be reduced and measurement can be performed efficiently. Also, if the reflectivity of the target is high, the laser measuring instrument can be installed at a position far from the target to perform measurement, so measurement can be performed efficiently.

[0005] One example of a target with such high reflectivity is one that uses retroreflective sheets. However, targets may remain attached to structures, and retroreflective sheets efficiently reflect light emitted from vehicles back towards those vehicles, which may cause unnecessary attention to people such as vehicle occupants when not being measured.

[0006] Therefore, the present invention aims to provide a measurement system that can efficiently measure structures and suppress the need to give people unnecessary attention. [Means for solving the problem]

[0007] To achieve the above objective, the measurement system of the present invention comprises a target attached to a structure, which includes a retroreflective sheet, and a laser measuring instrument that emits non-visible laser light onto the retroreflective sheet and receives the laser light retroreflective by the retroreflective sheet, wherein the retroreflective sheet retroreflectively reflects the laser light and suppresses the retroreflection of visible light more than the laser light.

[0008] With this type of measurement system, during measurement, the invisible laser light emitted from the laser measuring instrument is retroreflective by the target's retroreflective sheet, thereby increasing the target's reflectivity to laser light and enabling efficient measurement. Furthermore, since the target's retroreflective sheet suppresses the retroreflection of visible light more than laser light, the retroreflection of light that people are aware of, such as light emitted from a vehicle's headlights, is suppressed. Therefore, it is possible to prevent the light retroreflected by the target from giving people unnecessary attention.

[0009] Furthermore, it is preferable to have a plurality of targets attached to the structure at predetermined intervals.

[0010] In this case, by measuring the distance between multiple targets, it is possible to measure the deformation of the structure, etc.

[0011] Furthermore, it is preferable that the retroreflective sheet has a higher absorption rate of visible light than the laser light.

[0012] Even with this configuration, it is possible to create a setup in which the retroreflective sheet retroreflects laser light and suppresses retroreflection of visible light. In this case, it is preferable that the retroreflective sheet hardly absorbs laser light. By absorbing visible light, the retroreflective sheet can suppress unwanted retroreflection and transmission of visible light.

[0013] Furthermore, it is preferable that the retroreflective sheet has a higher specular reflectance of visible light than that of the laser light.

[0014] Even with this configuration, it is possible to create a setup in which the retroreflective sheet retroreflects laser light and suppresses the retroreflection of visible light. In this case, the retroreflective sheet specularly reflects visible light, thereby suppressing the degradation of the retroreflective element due to the transmission of visible light.

[0015] Furthermore, it is preferable that the retroreflective sheet has a higher transmittance of visible light than the laser light.

[0016] This configuration also allows the retroreflective sheet to retroreflect laser light while suppressing the retroreflection of visible light. In this case, the visibility of the retroreflective sheet can be suppressed, further reducing the need to draw unnecessary attention to people. [Effects of the Invention]

[0017] As described above, the present invention provides a measurement system that can efficiently measure structures and suppress the need to give people unnecessary warnings. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic diagram of the measurement system in the first embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view of the target. [Figure 3] Figure 3 is a cross-sectional view showing a modified version of the target. [Figure 4] Figure 4 is a cross-sectional view of the target in the second embodiment. [Figure 5] Figure 5 is a cross-sectional view of the target in the third embodiment. [Figure 6] Figure 6 is a cross-sectional view of the target in the fourth embodiment.

Best Mode for Carrying Out the Invention

[0019] Hereinafter, a preferred embodiment of the measurement system according to the present invention will be described in detail with reference to the drawings. The embodiments illustrated below are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. The present invention can be changed and improved within the scope of the claims. Also, the present invention may appropriately combine the components in the embodiments illustrated below. In the drawings referred to below, for the sake of easy understanding, the dimensions of each member may be shown changed. Also, in the drawings, for the sake of easy viewing, reference numerals may be attached only to a part of the similar components, and a part of the reference numerals may be omitted.

[0020] (First Embodiment) Figure 1 is a schematic diagram of the measurement system in the present embodiment. As shown in Figure 1, the measurement system 1 of the present embodiment mainly includes a target 2 and a laser measuring instrument 3.

[0021] In the present embodiment, the measurement system 1 includes a plurality of targets 2. Each target 2 is attached to the wall surface W of a tunnel, which is an example of a structure, at a predetermined interval. The target 2 of the present embodiment includes a marker M for alignment.

[0022] The laser measuring instrument 3 is installed at a predetermined distance from the target 2. In this example, the laser measuring instrument 3 is installed on the road surface away from the wall W. The laser measuring instrument 3 irradiates the target 2 with laser light L and receives the laser light L that is retroreflected by the target 2. The laser measuring instrument 3 measures the distance between the laser measuring instrument 3 and the target 2 from the timing of the emission of the laser light L and the timing of the reception of the retroreflected laser light L. Furthermore, if the laser measuring instrument 3 is a 3D laser measuring instrument such as LiDAR (Light Detection And Ranging), the laser measuring instrument 3 measures the distance between the laser measuring instrument 3 and the target 2, and the position of the target 2 relative to the laser measuring instrument 3.

[0023] The wavelength of the laser light L is invisible light. In this specification, the wavelength of visible light is 380 nm or more and less than 780 nm. Therefore, the laser light L is, for example, near-infrared light with a wavelength of 780 nm or more and less than 2500 nm. When the laser light L is near-infrared light, it is more preferable that the wavelength is 800 nm or more and less than 1600 nm from the viewpoint of suppressing absorption of the laser light L by water molecules in the air. Alternatively, the laser light L is, for example, ultraviolet light with a wavelength of less than 380 nm. It is preferable that the wavelength is 200 nm or more from the viewpoint of suppressing absorption of the laser light L by oxygen molecules and water molecules in the air. When the laser light L is ultraviolet light, it is more preferable that the wavelength is 280 nm or more and less than 380 nm, and even more preferable that it is 315 nm or more and less than 380 nm, from the viewpoint of safety.

[0024] Figure 2 is a cross-sectional view of target 2. As shown in Figure 2, target 2 in this embodiment includes a retroreflective sheet 4 and an adhesive layer 9.

[0025] The retroreflective sheet 4 retroreflects the laser light L, suppressing the retroreflection of visible light more than the laser light L. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the power of the retroreflected light is greater for the laser light L than for the visible light.

[0026] The retroreflective sheet 4 of this embodiment is a cube-corner type retroreflective sheet and mainly comprises a surface protective layer 30, a printed layer 20, and a retroreflective layer 10.

[0027] The retroreflective layer 10 includes a retroreflective element layer 11 having a plurality of cube-corner type retroreflective elements 111, a holder layer 12, and a reflective layer 13.

[0028] The retaining layer 12 holds the retroreflective element layer 11, and the retroreflective element layer 11 is provided on one side of the retaining layer 12. In this example, the retaining layer 12 and the retroreflective element 111 are made of the same resin and are integrally molded by resin molding. However, the retaining layer 12 and the retroreflective element 111 may be made of different resins. The retroreflective element layer 11 consists of a plurality of retroreflective elements 111 arranged in a planar manner. It is preferable that polyhedral retroreflective elements 111, such as triangular pyramidal or full cube-shaped elements, are provided in the retroreflective element layer 11 in a close-packed manner. By providing the retroreflective elements 111 in this manner, the retroreflective elements 111 can be arranged without gaps, and the reflection efficiency of the retroreflective layer 10 can be increased.

[0029] When using a retroreflective element layer 11 that includes polyhedral retroreflective elements 111, it is preferable that the length of one side of the retroreflective element 111 is 0.1 mm or more. By having a side length of 0.1 mm or more of the retroreflective element 111, the diffusion of the laser light L retroreflective from the retroreflective sheet 4 is suppressed, and the laser measuring instrument 3 can receive the laser light L more reliably.

[0030] The retaining layer 12 and the retroreflective element 111 are preferably made of a material that has excellent light transmittance to the wavelength of the laser light L. Examples of such materials include polycarbonate resins, vinyl chloride resins, vinylidene fluoride resins, acrylic resins, epoxy resins, styrene resins, polyester resins, fluororesins, polyethylene resins, olefin resins, cellulose resins, and urethane resins.

[0031] The reflective layer 13 is a layer provided on the surface of the retroreflective element 111 opposite to the holder layer 12, and is a layer for reflecting laser light L. This reflective layer 13 is made of a metal with excellent reflective properties, such as aluminum, silver, copper, or nickel. Alternatively, the reflective layer 13 is made of a dielectric multilayer film that efficiently reflects laser light L. These metals and dielectric multilayer films are provided by means such as vacuum deposition or sputtering. The maximum thickness of the reflective layer 13 is, for example, 0.1 μm.

[0032] The printed layer 20 is printed on the side of the retainer layer 12 opposite to the retroreflective element layer 11, and is a layer in which the transmission of visible light is suppressed. Therefore, the pattern formed by the printed layer 20 is visible. In addition, the transmission of laser light L may be suppressed, or it may be transmitted. The pattern is not particularly limited, but in this embodiment, the printed layer 20 forms the marker M shown in Figure 1. The printed layer 20 in this embodiment is formed by printing. The printing method is not particularly limited, but examples include gravure printing, screen printing, flexographic printing, and inkjet printing. The maximum thickness of the printed layer 20 is, for example, 10 μm.

[0033] Examples of materials for the printed layer 20 include resin components and colorants. In addition to resin components and colorants, various additives such as plasticizers, defoamers, leveling agents, light stabilizers, heat stabilizers, and crosslinking agents may be added as needed.

[0034] The resin component of the printing layer 20 is not particularly limited as long as it suppresses the transmission of visible light, but examples include melamine resin, epoxy resin, urethane resin, vinyl resin, polyester resin, alkyd resin, and acrylic resin, which have excellent dispersibility and stability of colorants, solubility in solvents, weather resistance, printability, and adhesion to the film. These may be materials polymerized individually or materials copolymerized by combining two or more of these.

[0035] The coloring agent for the printing layer 20 is not particularly limited, but examples include pigments and dyes of colors produced by mixing pigments and dyes such as black, red, green, and blue. Furthermore, the printing layer 20 may use a coloring agent with a higher visible light absorption rate than the laser light L. Examples of such coloring agents include those containing anthraquinone-based dyes and phthalocyanine-based dyes.

[0036] The surface protection layer 30 is a layer that transmits at least laser light L and protects the printed layer 20 and the retroreflective layer 10. The surface protection layer 30 is provided on the side of the retroreflective layer 10 opposite to the retroreflective element layer 11, and the printed layer 20 is sandwiched between the retroreflective layer 10 and the surface protection layer 30. The material of the surface protection layer 30 can be, for example, the same material as that of the retroreflective layer 10. The surface protection layer 30 is the layer on the side of the retroreflective sheet 4 where light is incident from the outside.

[0037] An adhesive layer 9 is provided on the side of the retroreflective sheet 4 opposite to the surface protective layer 30. In this embodiment, the adhesive layer 9 is laminated on the surface of the reflective layer 13 opposite to the retroreflective element layer 11. Examples of materials for the adhesive layer 9 include acrylic resin, epoxy resin, phenolic resin, vinyl acetate resin, nitrile rubber resin, and silicone rubber resin. The maximum thickness of the adhesive layer 9 is, for example, 70 μm.

[0038] If target 2 is not attached, a release sheet (not shown) is laminated on the side of the adhesive layer 9 opposite to the retroreflective sheet 4 side, preventing dust and other debris from adhering to the adhesive layer 9.

[0039] As shown in Figure 2, when laser light L is incident on the retroreflective sheet 4 from the surface protective layer 30 side, the laser light L passes through the surface protective layer 30 and the retaining layer 12, and is retroreflected by being reflected multiple times at the interface between the retroreflective element 111 and the reflective layer 13. The retroreflected laser light L passes through the retaining layer 12 and the surface protective layer 30 and is emitted from the retroreflective sheet 4.

[0040] Next, we will describe a configuration in which the retroreflective sheet 4 of this embodiment retroreflects laser light L and suppresses the retroreflection of visible light more than the laser light L.

[0041] (Example 1) This example shows a case where the retroreflective sheet 4 has a higher visible light absorption rate than the laser light L. In other words, when the same power laser light L and visible light are incident on the retroreflective sheet 4, the retroreflective sheet 4 absorbs more visible light than the laser light L. In this example, a visible light absorbing layer with a higher visible light absorption rate than the laser light L is provided on the retroreflective sheet. In the example in Figure 2, at least one of the retaining layer 12, the retroreflective element layer 11, and the surface protective layer 30 also serves as the visible light absorbing layer.

[0042] The visible light absorbing layer is made of a resin containing a material that has a higher visible light absorption rate than the laser light L. Examples of such materials include anthraquinone dyes, perinone dyes, perylene dyes, methine dyes, phthalocyanine dyes, and coumarin dyes when the laser light L is infrared light. Examples of such materials when the laser light L is ultraviolet light include anthraquinone dyes, nitroso dyes, cyanine dyes, phthalocyanine dyes, coumarin dyes, azo dyes, and benzophenone dyes. From the viewpoint of easily adjusting the visible light absorption rate, it is preferable to include at least one anthraquinone dye or a phthalocyanine dye.

[0043] When the visible light absorbing layer is at least one of the retaining layer 12, the retroreflective element layer 11, and the surface protection layer 30, the lamination of a layer solely for absorbing visible light is unnecessary, and the retroreflective sheet 4 can be simplified. Also, since the lamination of a layer solely for absorbing visible light can be omitted, the total thickness of the retroreflective sheet 4 can be reduced, the flexibility of the sheet can be improved, and adhesion to curved substrates can be improved. When the visible light absorbing layer is at least one of the retaining layer 12 and the retroreflective element layer 11, the visible light absorbing layer is provided inside the retroreflective sheet 4, so even if the surface protection layer 30 is scratched, the decrease in visible light absorption performance can be suppressed. Furthermore, when the visible light absorbing layer is the retroreflective element layer 11, light is reflected multiple times within the retroreflective element 111 as it propagates, so the optical path can be made longer and more visible light can be absorbed compared to when another layer of the same thickness is the visible light absorbing layer.

[0044] Figure 3 is a cross-sectional view showing a modified example of target 2. In this example, the holder layer 12, the retroreflective element layer 11, and the surface protection layer 30 do not also serve as visible light absorption layers, and a visible light absorption layer 40 is laminated. The visible light absorption layer 40 is laminated so as to be located on the optical path of light incident on the retroreflective sheet 4. This position is not particularly limited as long as it is on the optical path. In the example of Figure 3, the visible light absorption layer 40 is provided between the retroreflective layer 10 and the surface protection layer 30. The visible light absorption layer 40 may also be provided on the side of the surface protection layer 30 opposite to the retroreflective layer 10. Alternatively, if the holder layer 12 and the retroreflective element layer 11 are separate components, the visible light absorption layer 40 may be provided between the holder layer 12 and the retroreflective element layer 11. Furthermore, since the surface protection layer 30 is intended to protect the retroreflective sheet 4, it is preferable that the surface protection layer 30 be exposed. Therefore, it is preferable that the visible light absorbing layer be provided on the retroreflective element layer 11 side of the surface protection layer 30.

[0045] When the retaining layer 12, the retroreflective element layer 11, and the surface protective layer 30 do not also serve as visible light absorbing layers, and a visible light absorbing layer 40 is laminated and provided as in this modified example, it may be possible to fully demonstrate the performance of each layer.

[0046] In the retroreflective sheet 4 of this example shown in Figures 2 and 3, light propagates as follows: Laser light L incident on the retroreflective sheet 4 from the surface protective layer 30 is retroreflective by the retroreflective element 111 and the reflective layer 13 in the same manner as described above, and is emitted from the retroreflective sheet 4. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is absorbed in the visible light absorption layer with a higher absorption rate than the laser light L before being retroreflective by the retroreflective element 111. Furthermore, even if only a portion of the visible light is retroreflective by the retroreflective element 111, the retroreflective visible light is absorbed in the visible light absorption layer with a higher absorption rate than the laser light L before being emitted from the surface protective layer 30. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the retroreflective visible light is less than the energy of the retroreflective laser light L.

[0047] The visible light absorbing layer has a minimum absorption value in one of the visible light wavelength ranges (380 nm to less than 780 nm) from the viewpoint of improving visibility to observers in dark places such as at night or inside tunnels, and it is preferable that this minimum absorption value is 85% or less, more preferably 75% or less, and even more preferably 65% ​​or less. Furthermore, from the viewpoint of further suppressing unnecessary attention to people, it is preferable that this minimum absorption value is 40% or more, more preferably 45% or more, and even more preferably 50% or more.

[0048] From the viewpoint of more efficiently measuring structures, the visible light absorbing layer preferably has an absorption rate of 20% or less in the near-infrared wavelength range (780 nm to 2500 nm) or the ultraviolet wavelength range (less than 380 nm), more preferably 10% or less, and even more preferably 5% or less.

[0049] The absorption of the visible light absorption layer in the visible light and laser light L wavelength ranges can be measured using a general method with a spectrophotometer.

[0050] (Second example) This example shows a case where the reflective layer 13 suppresses the reflection of visible light more than the reflection of laser light L. In this example, the configuration of the retroreflective sheet 4 is similar to the example shown in Figure 2. In this example, the reflective layer 13 is a dichroic mirror and is composed of, for example, a dielectric multilayer film. Specifically, a dielectric with a low refractive index and a dielectric with a high refractive index are stacked with a thickness that is a multiple of 1 / 4 of the wavelength of the laser light L. Examples of low refractive index dielectrics include silicon dioxide, and examples of high refractive index materials include titanium oxide, zirconium oxide, tantalum pentoxide, titanium monoxide, and cerium oxide. In this case, the reflective layer 13 can transmit visible light and reflect laser light L. Therefore, a retroreflective sheet 4 with such a configuration has a higher transmittance of visible light than laser light L.

[0051] In this example, light propagates through the retroreflective sheet 4 as follows: Laser light L incident on the retroreflective sheet 4 from the surface protective layer 30 is retroreflective in the same manner as described above. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is transmitted through the reflective layer 13. In other words, visible light is transmitted through the reflective layer 13 with a higher transmittance than laser light L. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the retroreflective visible light is less than the energy of the retroreflective laser light L.

[0052] In this example, it is preferable that the adhesive layer 9 transmits visible light. In this case, the visible light that has passed through the retroreflective sheet 4 also passes through the adhesive layer 9, which can make the target 2 less conspicuous.

[0053] (Second Embodiment) Next, a second embodiment of the present invention will be described. Note that, unless otherwise specified and denoted by the same reference numerals, redundant descriptions of components identical or equivalent to those in the first embodiment will be omitted. The measurement system 1 of this embodiment differs from the configuration of the target 2 in the first embodiment in that the target 2 is configured differently.

[0054] Figure 4 is a cross-sectional view of target 2 in the embodiment. As shown in Figure 4, target 2 in this embodiment differs from target 2 in the first embodiment in that the retroreflective sheet 4 is a micro-spherical retroreflective sheet.

[0055] The retroreflective sheet 4 in this embodiment differs from the retroreflective sheet 4 of the first embodiment in that the retroreflective layer 10 has a retaining layer 12, a plurality of microspheres 15, a focal-forming layer 16, and a reflective layer 13.

[0056] The microspheres 15 are made of a light-transmitting material, such as glass. The particle size of the microspheres is, for example, about 50 μm. Each microsphere 15 is arranged in a generally planar manner. Approximately half of each microsphere 15 is held in the retaining layer 12. Therefore, a portion of each microsphere 15 is embedded in and held in the retaining layer 12.

[0057] The focal-forming layer 16 covers the surface of each microsphere 15 that is not held by the retaining layer 12. The focal-forming layer 16 is made of a light-transmitting resin layer with a refractive index lower than that of the microspheres 15, and has a thickness such that light transmitted through the microspheres 15 is focused onto the surface of the focal-forming layer 16 opposite to the microsphere 15 side. Examples of materials constituting the focal-forming layer 16 include acrylic resin, alkyd resin, fluororesin, polyvinyl chloride resin, polyester resin, urethane resin, polycarbonate resin, and butyral resin, either alone or in combination. However, from the viewpoint of weather resistance, coating suitability, and thermal stability, the material constituting the focal-forming layer 16 is preferably acrylic resin.

[0058] A reflective layer 13 is provided on the surface of the focal-forming layer 16 opposite to the microsphere 15 side. Therefore, the reflective layer 13 is located at a position where light transmitted through the microsphere 15 and the focal-forming layer 16 is focused. The reflective layer 13 is a layer that reflects the light transmitted through the microsphere 15.

[0059] As shown in Figure 4, when laser light L is incident on the retroreflective sheet 4 from the surface protective layer 30 side, the laser light L passes through the surface protective layer 30, the retaining layer 12, the microsphere 15, and the focus-forming layer 16, focuses onto the reflection layer 13, and is reflected by the reflection layer 13. Subsequently, the laser light L passes through the focus-forming layer 16, the microsphere 15, the retaining layer 12, and the surface protective layer 30 and is emitted from the retroreflective sheet 4. In this way, the laser light L incident on the retroreflective sheet 4 is retroreflective.

[0060] Next, we will explain the configuration in which the retroreflective sheet 4 of this embodiment retroreflectives laser light L and suppresses retroreflective visible light.

[0061] (Example 1) This example is similar to the first example of the first embodiment in which the retroreflective sheet 4 has a higher absorption rate of visible light than the laser light L. In other words, in this example as well, a visible light absorbing layer is provided on the optical path of the light incident on the retroreflective sheet 4, and when laser light L and visible light of the same power are incident on the retroreflective sheet 4, it absorbs more visible light than laser light L. In this example, the visible light absorbing layer is provided in the same manner as the first example of the first embodiment, except that the focal-forming layer 16 may be the visible light absorbing layer instead of the retroreflective element layer 11. Therefore, at least one of the holder layer 12, the focal-forming layer 16, and the surface protection layer 30 may be a visible light absorbing layer, and in addition to the configuration shown in Figure 4, a visible light absorbing layer 40 may be provided on the optical path.

[0062] When the visible light absorbing layer is the focal-forming layer 16, the visible light absorbing layer is formed inside the retroreflective sheet 4, so even if the sheet surface is damaged, the decrease in visible light absorption performance can be suppressed.

[0063] In this example, light propagates in the retroreflective sheet 4 as follows: Laser light L incident on the retroreflective sheet 4 from the surface protective layer 30 is retroreflective by the microspheres 15, the focal-forming layer 16, and the reflective layer 13, in the same manner as described above in this embodiment, and exits from the retroreflective sheet 4. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is absorbed in the visible light absorption layer with a higher absorption rate than the laser light L before being retroreflective by the microspheres 15, the focal-forming layer 16, and the reflective layer 13. Furthermore, even if only a portion of the visible light is retroreflective, the retroreflective visible light is absorbed in the visible light absorption layer with a higher absorption rate than the laser light L before exiting from the surface protective layer 30. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the retroreflective visible light is less than the energy of the retroreflective laser light L.

[0064] (Second example) This example is similar to the second example of the first embodiment in which the reflective layer 13 suppresses the reflection of visible light. In this example, the reflective layer 13 is configured in the same way as the second example of the first embodiment. Therefore, the reflective layer 13 transmits visible light and reflects the laser light L.

[0065] In this example, light propagates through the retroreflective sheet 4 as follows: Laser light L incident on the retroreflective sheet 4 from the surface protective layer 30 is retroreflective in the same manner as described above. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is transmitted through the reflective layer 13. In other words, visible light is transmitted through the reflective layer 13 with a higher transmittance than laser light L. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the retroreflective visible light is less than the energy of the retroreflective laser light L.

[0066] In this example, as with the second example of the first embodiment, it is preferable that the adhesive layer 9 transmits visible light. In this case, the visible light that has passed through the retroreflective sheet 4 also passes through the adhesive layer 9, making the target 2 less conspicuous.

[0067] (Third embodiment) Next, a third embodiment of the present invention will be described. Note that, unless otherwise specified and denoted by the same reference numerals, redundant descriptions of components identical or equivalent to those in the first embodiment will be omitted. The measurement system 1 of this embodiment differs from the configuration of the target 2 in the first embodiment in that the target 2 is configured differently.

[0068] Figure 5 is a cross-sectional view of target 2 in this embodiment. As shown in Figure 5, target 2 in this embodiment differs from target 2 in the first embodiment in that the retroreflective sheet 4 is a capsule-shaped retroreflective sheet.

[0069] The retroreflective sheet 4 in this embodiment differs from the retroreflective sheet 4 of the first embodiment in that the retroreflective layer 10 does not include a reflective layer 13, but rather includes a binder layer 70.

[0070] The binder layer 70 has a main body portion 71 which is a layered portion, and a plurality of columnar support portions 72 which are columnar portions. The support portions 72 extend in the planar direction of the main body portion 71, with one end connected to the main body portion 71 and the other end connected to some of the retroreflective elements 111 of the retroreflective element layer 11. As a result, a space AR is formed between the main body portion 71 and the other portion of the retroreflective elements 111, and the other portion of the retroreflective elements 111 are in contact with the space AR. The thickness of the space AR in the stacking direction is, for example, 20 to 100 μm.

[0071] Preferably, the main body 71 and the support column 72 are made of the same material and formed integrally. However, the main body 71 and the support column 72 may be made of different materials. The binder layer 70 is made of the same material as the retroreflective element 111, for example. For example, the binder layer 70 may be made of amorphous polyester. Preferably, the support column 72 is made of a material with a lower refractive index than the retroreflective element 111. In this case, light can be retroreflected at the interface between the retroreflective element 111 and the support column 72.

[0072] As shown in Figure 5, when laser light L is incident on the retroreflective sheet 4 from the surface protective layer 30 side, the laser light L passes through the surface protective layer 30 and the retaining layer 12, and is retroreflected by being reflected multiple times at the interface between the retroreflective element 111 and the space AR. The retroreflected laser light L passes through the retaining layer 12 and the surface protective layer 30 and is emitted from the retroreflective sheet 4. It is preferable that, with respect to the wavelength of light of the laser light L, the refractive index of the support portion 72 is lower than that of the retroreflective element 111, as described above, because the laser light L can be retroreflected multiple times at the interface between the retroreflective element 111 and the support portion 72.

[0073] Next, we will explain the configuration in which the retroreflective sheet 4 of this embodiment retroreflectives laser light L and suppresses retroreflective visible light.

[0074] In this embodiment, similar to the first example of the first embodiment, the retroreflective sheet 4 absorbs visible light with a higher absorption rate than the laser light L. In other words, in this embodiment as well, similar to the first embodiment, a visible light absorption layer is provided on the optical path of the light incident on the retroreflective sheet 4, and when laser light L and visible light of the same power are incident on the retroreflective sheet 4, it absorbs more visible light than the laser light L.

[0075] In this embodiment, light propagates in the retroreflective sheet 4 as follows: Laser light L incident on the retroreflective sheet 4 from the surface protective layer 30 is retroreflective in the same manner as described above and exits from the retroreflective sheet 4. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is absorbed in the visible light absorption layer with a higher absorption rate than the laser light L before being retroreflective by the retroreflective element 111. Furthermore, even if only a portion of the visible light is retroreflective by the retroreflective element 111, the retroreflective visible light is absorbed in the visible light absorption layer with a higher absorption rate than the laser light L before exiting from the surface protective layer 30. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the retroreflective visible light is less than the energy of the retroreflective laser light L.

[0076] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. Note that, unless otherwise specified and denoted by the same reference numerals, redundant descriptions of components identical or equivalent to those in the first embodiment will be omitted. The measurement system 1 of this embodiment differs from the configuration of the target 2 in the first embodiment in that the target 2 is configured differently.

[0077] Target 2 in this embodiment differs from Target 2 in the first embodiment in that the retroreflective sheet 4 has a higher specular reflectance of visible light than the laser light L. Figure 6 is a cross-sectional view of Target 2 in this embodiment. As shown in Figure 6, Target 2 in this embodiment differs from Target 2 in the first embodiment in that the retroreflective sheet 4 includes a filter layer 50.

[0078] The filter layer 50 is a layer that transmits laser light L and specularly reflects visible light. The filter layer 50 is made of, for example, a dielectric multilayer film. As the material of the dielectric multilayer film, the same material as the dielectric multilayer film in the second example of the first embodiment can be used. However, in this embodiment, the thickness of each film in the dielectric multilayer film is adjusted to reflect visible light and transmit light of the wavelength of the laser light L.

[0079] In the example shown in Figure 6, the filter layer 50 is provided between the retroreflective layer 10 and the surface protection layer 30. However, the position of the filter layer 50 is not particularly limited as long as it is provided on the optical path of the retroreflective sheet 4 on the side of the incident light surface of the retroreflective sheet 4, relative to the retroreflective elements 111 in the retroreflective sheet 4. Therefore, the filter layer 50 may be provided, for example, on the surface of the surface protection layer 30 opposite to the retroreflective layer 10 side.

[0080] In this embodiment, light propagates in the retroreflective sheet 4 as follows. That is, as shown in Figure 6, when laser light L is incident on the retroreflective sheet 4 from the surface protective layer 30 side, the laser light L passes through the surface protective layer 30, the filter layer 50, and the retaining layer 12, and is retroreflected by being reflected multiple times at the interface between the retroreflective element 111 and the reflective layer 13. The retroreflected laser light L passes through the retaining layer 12 and the surface protective layer 30 and is emitted from the retroreflective sheet 4. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is specularly reflected by the filter layer 50 and is emitted from the retroreflective sheet 4. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the retroreflected visible light is smaller than the energy of the retroreflected laser light L.

[0081] Based on the embodiments described above, the following aspects of the measurement system 1 of the present invention have been shown. That is, the measurement system 1 of the present invention includes a target 2 that is attached to a structure and includes a retroreflective sheet 4, and a laser measuring instrument 3 that emits non-visible laser light L onto the retroreflective sheet 4 and receives the laser light L retroreflective by the retroreflective sheet 4, wherein the retroreflective sheet 4 retroreflectively reflects the laser light L and suppresses the retroreflection of visible light more than the laser light L.

[0082] According to this measurement system 1, during measurement, the invisible laser light L emitted from the laser measuring instrument 3 is retroreflective by the retroreflective sheet 4 of target 2, thereby increasing the reflectivity of target 2 for the laser light L and enabling efficient measurement. Furthermore, since the retroreflective sheet 4 of target 2 suppresses the retroreflection of visible light more than the laser light L, the retroreflection of light that people are aware of, such as light emitted from the headlights of a vehicle, is suppressed. Therefore, it is possible to prevent the light retroreflected by target 2 from giving people unnecessary attention.

[0083] Furthermore, the measurement system 1 includes a plurality of targets 2 attached to a structure at predetermined intervals. In this case, by measuring the interval between the plurality of targets 2, the deformation of the structure can be measured, and it is particularly suitable for measuring the displacement of tunnels. However, in the present invention, the target 2 may be a single unit.

[0084] Furthermore, the retroreflective sheet 4 may have a higher absorption rate of visible light than the laser light L. Even with this configuration, the retroreflective sheet 4 can retroreflect the laser light L and suppress the retroreflection of visible light. In this case, it is preferable that the retroreflective sheet 4 hardly absorbs the laser light L. By absorbing visible light, the retroreflective sheet 4 can suppress unwanted retroreflection and transmission of visible light.

[0085] Furthermore, the retroreflective sheet 4 may have a higher specular reflectance of visible light than the laser light L. By specularly reflecting visible light, the retroreflective sheet can suppress the degradation of the retroreflective element due to the transmission of visible light.

[0086] Furthermore, the retroreflective sheet 4 may have a higher transmittance of visible light than the laser light L. In this case, the visibility of the retroreflective sheet 4 can be suppressed, further reducing the need to draw unnecessary attention to people.

[0087] Although the present invention has been described above with reference to embodiments, the present invention is not limited to these embodiments.

[0088] For example, in the above embodiment, the retroreflective sheet 4 has a printed layer 20, and a marker M is formed by the printed layer 20, but the marker M is not essential. Therefore, the printed layer 20 is not essential.

[0089] Furthermore, the surface protection layer 30 is not mandatory. However, from the viewpoint of achieving high weather resistance, it is preferable that the retroreflective sheet 4 be provided with the surface protection layer 30. [Industrial applicability]

[0090] According to the present invention, a measurement system can be provided that can efficiently measure structures and suppress the giving of unnecessary attention to people, and can be used in fields such as surveying. [Explanation of Symbols]

[0091] 1. Measurement System 2. Target 3. Laser measuring instrument 4. Retroreflective sheet 10. Retroreflective layer 11. Retroreflective element layer 111... Retroreflective element 12...Holder layer 13...Reflection layer 15...microsphere 16...focal formation layer 20...printing layer 30...Surface protective layer 40. Visible light absorption layer 50 filter layers

Claims

1. A target that includes a retroreflective sheet and is attached to a structure, A laser measuring instrument that emits invisible laser light onto the retroreflective sheet and receives the laser light retroreflective by the retroreflective sheet, Equipped with, The retroreflective sheet retroreflects the laser light and suppresses the retroreflection of visible light more than the laser light. A measurement system characterized by the following features.

2. The structure comprises a plurality of targets attached at predetermined intervals. The measurement system according to feature 1.

3. The retroreflective sheet has a higher absorption rate of visible light than the laser light. The measurement system according to feature 1.

4. The retroreflective sheet has a higher specular reflectance of visible light than the laser light. The measurement system according to feature 1.

5. The retroreflective sheet has a higher transmittance of visible light than the laser light. The measurement system according to feature 1.

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