Pressure sensor

Abstract

To provide a new pressure sensor with tactile and proximity sense functions.SOLUTION: A pressure sensor includes: an imaging element; a light reflection layer in which a reflection wavelength changes in accordance with pressure facing the imaging element; and a light source that irradiates the light reflection layer with light. In a state where the light reflection layer is not pressurized, the light reflection layer is transparent to light to which the imaging element has sensitivity and light emitted by the light source. In the state where the light reflection layer is not pressurized, the light reflection layer reflects the light emitted by the light source, and the imaging element images the light emitted by the light source and reflected by the light reflection layer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a pressure sensor used in a robot or the like. [Background technology]

[0002] Pressure sensors are used in a variety of fields. For example, there is an increasing demand for pressure sensors in tactile sensing applications such as robotics and input interfaces. As an example, in robotics applications, it is desirable to constantly detect pressure, contact area, and deformation so that when a robot grasps something, it can apply an appropriate force according to the shape, hardness, etc.

[0003] In order to achieve this objective, various contact sensors have been proposed. For example, Patent Document 1 describes a contact sensor for use in robot finger pads and the like, which comprises a block of elastomer illuminated by one or more light sources and having translucency, a reflective coating that covers the elastomer and contains reflective particles that reflect incident light from inside the elastomer, and a light detection mechanism positioned to receive some of the reflected light, in which when an object comes into contact with the reflective coating and pressure is applied, the reflective coating geometrically deforms and its surface normal changes locally, and as a result of this change, the amount of reflected light traveling from the reflective coating toward the light detection mechanism changes locally, and an image-like reflected light that shows one or more characteristics of the object exerting pressure is incident on the light detection mechanism. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2011-525284 Summary of the Invention [Problem to be solved by the invention]

[0005] The contact sensor described in Patent Document 1 can detect small pressure deviations when grasping an object, and is flexible enough to elastically deform in response to pressure applied when grasping an object, for use in applications such as finger pads for robots.

[0006] In recent years, robot arms and the like are required to have a so-called proximity sensing function that detects when an object to be grasped is approaching the tip of the arm. For example, by feeding back the sense of proximity to a robot arm, it is possible to control the amount of force used when grasping an object, adjust the positional relationship between the grasping position of the robot arm and the object being grasped, and control the speed of movement of the robot arm grasping the object, enabling the object to be grasped appropriately.

[0007] Therefore, in applications such as robot arms, there is a demand for pressure sensors that have a proximity sense function in addition to a tactile sense function.

[0008] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to solve the problems of the conventional technology and to provide a novel pressure sensor having both a tactile function and a proximity function. [Means for solving the problem]

[0009] In order to solve this problem, the present invention has the following configuration. [1] An image sensor; a light reflective layer that is disposed facing an imaging surface of the imaging element and spaced apart from the imaging element, and whose reflection wavelength changes in response to pressure; A light source that irradiates light onto the light reflecting layer, When no pressure is applied to the light reflecting layer, the light reflecting layer is transparent to light to which the image sensor is sensitive and to light emitted by the light source; In a state where pressure is applied to the light reflecting layer, the portion of the light reflecting layer to which pressure is applied reflects light emitted from the light source, and the imaging element captures an image of the light emitted from the light source and reflected by the light reflecting layer. [2] The pressure sensor of claim 1, wherein the light-reflecting layer is a liquid crystal layer. [3] The pressure sensor according to [2], wherein the light reflective layer is a cholesteric liquid crystal layer. [4] The pressure sensor according to any one of [1] to [3], wherein the imaging element is a two-dimensional sensor that captures a color image. [5] A pressure sensor according to any one of [1] to [4], wherein the light reflective layer has a selective reflection wavelength range in the infrared wavelength range when no pressure is applied, and has a selective reflection wavelength range in the visible light wavelength range when pressure is applied. [6] The pressure sensor according to any one of [1] to [5], wherein the light reflective layer has a maximum reflectance of 20% or more in a wavelength range in which the reflected wavelength changes according to the pressure when pressure is applied. [7] The pressure sensor according to any one of [1] to [6], which adjusts the output of the light source according to an image captured by the imaging element. [8] The pressure sensor according to any one of [1] to [7], which adjusts the focal position of the imaging element in accordance with an image captured by the imaging element. Effect of the Invention

[0010] According to the present invention, a novel pressure sensor having tactile and proximity sensing capabilities is provided. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram conceptually illustrating an example of a pressure sensor of the present invention. [Diagram 2] FIG. 2 is a diagram conceptually illustrating an example in which the pressure sensor shown in FIG. 1 is used in a robot arm. [Diagram 3] FIG. 2 is a conceptual diagram for explaining the operation of the pressure sensor shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a pressure sensor according to the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.

[0013] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, the term "same" includes a margin of error generally accepted in the technical field.

[0014] In this specification, visible light is electromagnetic light having a wavelength visible to the human eye, and refers to light having a wavelength in the range of 380 to 780 nm. Invisible light refers to light having a wavelength in the range of less than 380 nm or more than 780 nm. In addition, although not limited thereto, in the present specification, blue light refers to light in the wavelength region of 380 to 490 nm among visible light, green light refers to light in the wavelength region of more than 490 nm and not more than 600 nm, and red light refers to light in the wavelength region of more than 600 nm and not more than 750 nm. Furthermore, although not limited thereto, in the present specification, infrared light refers to light in the wavelength region of more than 780 nm and not more than 2000 nm among non-visible light.

[0015] In this specification, the bond direction of a divalent group (e.g., -CO-O-, etc.) is not limited unless otherwise specified. For example, when Y is -CO-O- in a compound represented by the formula "XYZ", the compound may be either "XO-CO-Z" or "X-CO-OZ".

[0016] Note that the drawings shown below are all conceptual diagrams for explaining the present invention, and therefore the shapes, sizes, positional relationships, etc. of the components do not necessarily correspond to the actual ones.

[0017] FIG. 1 conceptually illustrates an example of a pressure sensor of the present invention. The pressure sensor 10 shown in FIG. 1 includes an imaging element 12, a light source 14, and a housing 20. As an example, the pressure sensor 10 of the present invention is provided at one end (grip) of an arm member 48 of a robot arm 46 in a robot application, as conceptually shown in Fig. 2. In this case, the pressure sensor 10 is used as a tactile sensor that measures the pressure and pressure distribution acting on an object when the robot arm 46 grasps, i.e., grabs, the object. The shape of the arm member and the mounting position of the pressure sensor are not limited to the shape in Fig. 2. In other words, when the pressure sensor of the present invention is used in a robot arm, arms of various shapes can be used, and the sensor can be used appropriately in any location on the arm where it is desired to detect touch. Furthermore, the pressure sensor of the present invention is not limited to being mounted on an arm-type robot as shown in Fig. 2, but can also be used in, for example, a hand-type robot imitating a number of fingers. Furthermore, the pressure sensor of the present invention can be mounted not only on the tips of the arms and hands, but also on various parts (surfaces) of the robot that come into contact with objects.

[0018] In the pressure sensor 10 of the present invention, the light reflecting layer 18 changes its reflection wavelength in response to pressure. Furthermore, the light source 14 is disposed so as to irradiate light onto the light reflecting layer 18 . Furthermore, the imaging element 12 is sensitive to the light emitted by the light source 14 and is disposed so as to image the surface of the light reflecting layer 18 .

[0019] In the pressure sensor 10, the light reflecting layer 18 is transparent to the light emitted by the light source 14 and the light to which the imaging element is sensitive when no pressure is applied. That is, in the pressure sensor 10, when no pressure is applied to the light reflecting layer 18, the imaging element 12 can transmit light through the light reflecting layer 18 and capture an image of the outside of the housing 20, i.e., the background of the light reflecting layer 18. Furthermore, when no pressure is applied to the light reflecting layer 18, the light emitted by the light source 14 transmits through the light reflecting layer 18. In contrast, when pressure is applied to the light reflective layer 18, the portion to which pressure is applied reflects the light emitted by the light source 14. That is, in the pressure sensor 10, when pressure is applied to the light reflective layer 18, the light reflective layer 18 reflects the light emitted by the light source 14 at the portion to which pressure is applied, and the imaging element 12 captures an image of this reflected light. The pressure sensor of the present invention, having such a configuration, is capable of providing both a proximity sense function and a tactile sense function, as will be described in detail later.

[0020] The pressure sensor 10 shown in FIG. 1 is configured by incorporating an image sensor 12, a light source 14, and the image sensor 12 in a housing 20. In the illustrated example, the housing 20 is, for example, a rectangular parallelepiped. The components may be held in the housing 20 by a known method using a holding member or the like.

[0021] In the pressure sensor 10, there are no limitations on the shape, size, material of which the housing 20 is made, the thickness of the walls, and the like. Considering the weight and strength of the pressure sensor 10, suitable materials for forming the pressure sensor 10 include plastics and metals such as stainless steel and aluminum.

[0022] As will be described later, when no pressure is applied to the light reflecting layer 18, the pressure sensor 10 shown in Figure 1 realizes a proximity sense function by the imaging element 12 transmitting through the light reflecting layer 18 to capture an image of the outside of the housing 20. Furthermore, the pressure sensor 10 realizes a tactile function by making the light emitted by the light source 14 incident on the light reflecting layer 18 and capturing an image of the light reflected from the light reflecting layer 18 by the imaging element 12.

[0023] Therefore, if external environmental light enters the housing 20 from a place other than the light reflecting layer 18, this light becomes noise and reduces the proximity sense and tactile functions. Therefore, it is preferable that the housing 20 has a light blocking property against light in the wavelength range measured by the image sensor 12. Furthermore, in the case where scattered light inside the housing 20 becomes noise, it is preferable that the inner surface of the housing 20 can absorb the light emitted by the light source 14 and the reflected light from the light reflecting layer 18. There are no limitations on the method for enabling the inner surface of the housing 20 to absorb the measurement light and reflected light, and known methods such as selecting a material for forming the housing 20 or coating the inner surface of the housing 20 with a light absorbing material can be used. As described above, there is no limitation on the thickness of the wall of the housing 20, i.e., the plate material constituting the housing 20. Here, the plate material constituting the housing 20 is preferably thicker in terms of the strength of the pressure sensor 10, while it is preferably thinner in terms of reducing the weight and size of the pressure sensor 10. In consideration of this, the thickness of the plate material constituting the housing 20 is preferably 0.05 to 10 mm, and more preferably 0.1 to 5 mm.

[0024] In the pressure sensor 10, the imaging element 12 is provided on one surface of a wall of a rectangular parallelepiped housing 20. The imaging element 12 captures an image of the light reflecting surface of a light reflecting layer 18 (described later) provided on the opposing surface of the housing 20. In the pressure sensor 10 of the present invention, the imaging element 12 may be any of various known imaging elements. Therefore, the image sensor 12 may be a so-called area sensor in which pixels are arranged two-dimensionally, or a so-called line sensor in which pixels are arranged in only one row according to the color to be imaged. However, it is preferable that the image sensor be an area sensor (two-dimensional sensor) in that it provides suitable contact and proximity sensing functions and enables the pressure exerted by the object grasped by the robot arm 46 to be measured on a surface.

[0025] The imaging element 12 may be a monochrome sensor that captures a black-and-white image (luminance image), a monochrome sensor that captures a single-color image such as a red image, a green image, and a blue image, a color sensor that captures a two-color image such as a red image and a green image, or a color sensor that captures a full-color image of a red image, a green image, and a blue image. Furthermore, the imaging element 12 may capture not only visible light, but also non-visible light such as near-infrared light and far-infrared light. In the pressure sensor of the present invention, a color sensor that captures a full-color image is preferably used as the imaging element. The imaging element 12 of the pressure sensor 10 shown in FIG. 1 is a color area sensor.

[0026] As described above, the imaging element 12 can be any of a variety of known imaging elements. As an example of the imaging element 12, a solid-state imaging element is preferably exemplified, and a CCD image sensor using a photodiode formed of silicon and signal transmission by a charge-coupled device, a CMOS image sensor using a CMOS signal transmission type, etc. can be used. In addition to these, an organic thin-film imaging element using an organic semiconductor, an imaging element using other semiconductors, etc. can also be used as the imaging element 12. Among them, a CCD image sensor, a CMOS image sensor, an organic thin-film imaging element, and the like are preferably used.

[0027] Although there is no limit to the spatial resolution of the imaging element 12, basically, the higher the resolution, the better. The number of pixels of the imaging element 12 is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 1,000,000 or more. There is no particular upper limit to the number of pixels of the imaging element 12, but considering the energy and time required for image processing, it is preferable that the number of pixels be 10 million or less. There is no particular limit to the size of the imaging element 12, but from the viewpoint of miniaturization of the pressure sensor 10, a smaller size is preferable, and from the viewpoint of high sensitivity and high resolution, a larger size is preferable. The size of the image sensor 12 is 1 to 1000 mm. 2 is preferable, and 10 to 500 mm 2 is more preferable, 20~400mm 2 is more preferred.

[0028] In the pressure sensor 10, a light reflecting layer 18 is provided on one surface of the housing 20 which is a rectangular parallelepiped and is opposed to the imaging element 12. As described above, the imaging element 12 is provided so as to capture an image of the light reflecting surface of the light reflecting layer 18. That is, in the pressure sensor 10, the light reflecting layer 18 is provided at a distance from the imaging element 12 so as to face the imaging surface of the imaging element 12. The light reflecting surface of the light reflecting layer 18 is usually the main surface of the light reflecting layer. The main surface is the maximum surface of a sheet-like object (plate-like object, film, layer), and usually both sides in the thickness direction.

[0029] The light reflecting layer 18 is a reflecting layer whose selective reflection wavelength range changes in response to pressure. In the pressure sensor 10 of the present invention, when no pressure is applied, the light reflective layer 18 is transparent to the light emitted by the light source 14 and to the light to which the image sensor 12 is sensitive, and when pressure is applied, the pressured portion reflects the light emitted by the light source 14. In the following description, "transparent to light to which the imaging element 12 is sensitive" may also be simply referred to as "transparent to the imaging element 12".

[0030] In the present invention, "transparent" refers to a state in which the transmittance of the target light is 10% or more. In addition, in the present invention, "transparent" refers to a state in which the transmittance of the target light is preferably 40% or more, and more preferably 70% or more. As an example, when the imaging element 12 has sensitivity to visible light and the light emitted by the light source 14 is visible light, the light reflecting layer 18 has a transmittance of visible light (light in a wavelength range of 380 to 780 nm) of 10% or more, preferably 40% or more, and more preferably 70% or more, when no pressure is applied. Also, as an example, when the imaging element has sensitivity to red light and the light emitted by the light source is red light, the light reflecting layer 18 has a transmittance of red light (light in a wavelength range of more than 600 nm and not more than 750 nm) of 10% or more, preferably 40% or more, and more preferably 70% or more, when no pressure is applied. In the present invention, the state in which pressure is applied to the light reflecting layer 18 refers to a state in which pressure that changes the selective reflection wavelength range of the light reflecting layer 18 compared to the selective reflection wavelength range of the light reflecting layer 18 in a state in which no pressure is applied is applied to at least a part of the light reflecting layer 18. For example, in the case in which the light reflecting layer 18 is a cholesteric liquid crystal layer described later, this refers to a state in which pressure that changes the thickness of the cholesteric liquid crystal layer is applied to at least a part of the light reflecting layer 18.

[0031] In the present invention, the light reflecting layer 18 has low elasticity to the extent that its thickness changes depending on the pressure applied by an object held by the robot arm 46, for example. In addition, in the pressure sensor of the present invention, the physical properties of the light reflecting layer 18 can be appropriately selected outside the above-mentioned range depending on the object that is primarily grasped by the robot arm 46 and the force with which the robot arm 46 grasps the object, i.e., the pressure applied to the object, etc.

[0032] As described above, the light reflecting layer 18 has wavelength selectivity in reflecting light, that is, the reflected wavelength changes depending on pressure, and the wavelength of light that is selectively reflected changes depending on deformation (compression and expansion) due to pressure.

[0033] Various types of light reflecting layer 18 can be used as long as the reflected wavelength changes according to pressure. Here, if the light reflecting layer 18 can obtain a sufficient change in reflection characteristics even with a small deformation, pressure can be measured with high sensitivity. Considering this, even when it is desired to detect a very small pressure, a light reflecting layer 18 using a liquid crystal having elasticity (flexibility) that allows sufficient deformation by a small pressure is suitable as the light reflecting layer 18. A preferred example of the light reflecting layer 18 using a liquid crystal having such light reflecting properties is a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase.

[0034] A cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase has a helical structure in which the liquid crystal compounds are spirally rotated and stacked, and the liquid crystal compounds spirally rotate in one turn (360° rotation) and stacked in one helical pitch (helical pitch P), and have a structure in which the helically rotating liquid crystal compounds are stacked in multiple pitches.

[0035] As is well known, a cholesteric liquid crystal phase exhibits selective reflectivity at a particular wavelength. In a typical cholesteric liquid crystal phase, the central wavelength of selective reflection (selective reflection central wavelength λ) depends on the helical pitch (helical pitch P) in the cholesteric liquid crystal phase and follows the relationship λ = n × P with the average refractive index n of the cholesteric liquid crystal phase. Therefore, by adjusting the helical pitch, it is possible to adjust the central wavelength of selective reflection. The central wavelength of selective reflection of the cholesteric liquid crystal phase becomes longer as the helical pitch P becomes longer.

[0036] As described above, the helical pitch P is one pitch (helical period) of the helical structure of the cholesteric liquid crystal phase. In other words, the helical pitch P is one turn of the helix, that is, the length of the helical axis direction in which the director (the long axis direction in the case of rod-shaped liquid crystal) of the liquid crystal compound constituting the cholesteric liquid crystal phase rotates 360°.

[0037] As is well known, cholesteric liquid crystal phases exhibit selective reflection for either left-handed or right-handed circularly polarized light at a specific wavelength. Whether the reflected light is right-handed or left-handed circularly polarized light depends on the twist direction (sense) of the helix of the cholesteric liquid crystal phase. When the helix of the cholesteric liquid crystal phase is twisted to the right, the cholesteric liquid crystal phase reflects right-handed circularly polarized light, and when the helix is ​​twisted to the left, the cholesteric liquid crystal phase reflects left-handed circularly polarized light. For example, in the case of a cholesteric liquid crystal layer that selectively reflects right-handed circularly polarized light, the helical twist direction of the cholesteric liquid crystal phase is right-handed. The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer and / or the type of chiral agent added.

[0038] Furthermore, the half-width Δλ (nm) of the selective reflection wavelength range (circularly polarized light reflection wavelength range) where the cholesteric liquid crystal phase exhibits selective reflection depends on the Δn and helical pitch P of the cholesteric liquid crystal phase, and follows the relationship Δλ = Δn × P. Therefore, the width of the selective reflection wavelength range can be controlled by adjusting Δn. Δn can be adjusted by the type and mixing ratio of the liquid crystal compounds forming the cholesteric liquid crystal layer, as well as the temperature at which the orientation is fixed.

[0039] Therefore, when a cholesteric liquid crystal layer is used as the light-reflecting layer 18, its thickness decreases according to the pressure applied by the object held by the robot arm 46, and the helical pitch P changes accordingly, changing the wavelength range of the light that is selectively reflected. Specifically, when pressure is applied to the light reflecting layer 18, which is a cholesteric liquid crystal layer, the thickness decreases in accordance with the magnitude of the pressure, and the helical pitch P shortens, so that the wavelength that is selectively reflected becomes shorter.

[0040] As an example, a case will be described in which the light reflective layer 18, which is a cholesteric liquid crystal layer, selectively reflects infrared light, which is invisible light, when no pressure is applied. At this time, when the robot arm 46 is not gripping an object, the light reflecting layer 18 selectively reflects infrared light and transmits other light. When the robot arm 46 grasps an object and applies pressure to the light-reflecting layer 18, the light-reflecting layer 18 (cholesteric liquid crystal layer) is compressed, the selective reflection wavelength becomes shorter, and the layer selectively reflects red light and transmits other light. As the robot arm 46 grips the object with increasing force, the light reflective layer 18 is compressed further, shortening the selectively reflective wavelength, so that it selectively reflects green light and transmits all other light.

[0041] As is well known, in a cholesteric liquid crystal layer, the wavelength of selectively reflected light becomes shorter as the angle of incidence of light with respect to a direction perpendicular to the main surface of the cholesteric liquid crystal layer (the normal direction) increases, resulting in a so-called shortwave shift (blue shift).

[0042] As such a cholesteric liquid crystal layer, various known cholesteric liquid crystal layers can be used. One example is a cholesteric liquid crystal elastomer film made of a low molecular weight liquid crystal compound, whose response behavior to force stimuli can be arbitrarily designed and whose color change can be visualized, introduced in "Nanostructure Control Technology of Molecular Materials: Application to Diverse Optical Functional Elements (Ritsumeikan University)" at "https: / / www.jst.go.jp / tt / fair / ij2020 / exhibitor / un20200420.html" by the Japan Science and Technology Agency. In addition, a cholesteric liquid crystal film made from a hydroxypropyl cellulose (HPC) derivative, as described in “New pressure sensing of cellulose derivatives with rubber elasticity (Furuumi Chikaichi, Suzuki Hana, and Fukawa Masashi, Tokyo University of Science)” in the Journal of the Society of Rubber Science and Technology of Japan, Vol. 91, No. 2 (2018), pp. 33-38, can also be used.

[0043] The light reflective layer 18 also preferably contains celluloses. Examples of celluloses include unsubstituted cellulose, cellulose derivatives and hardened products thereof. The term "unsubstituted cellulose" refers to a polymeric compound in which a large number of glucose molecules are polymerized through β-1,4-glycosidic bonds, and in which the hydroxyl groups directly or indirectly bonded to the carbon atoms at positions 2, 3, and 6 in the glucose ring of the cellulose are unsubstituted. Moreover, the term "cellulose derivative" refers to a cellulose in which the hydroxyl groups that are directly or indirectly bonded to the carbon atoms at the 2-, 3- and 6-positions of the glucose ring are substituted with substituents. The cellulose derivative may be a cellulose compound having a polymerizable group (hereinafter, simply referred to as a "specific cellulose compound"). The light reflecting layer 18 may contain a hardened material of the specific cellulose compound. The hardened material of the specific cellulose compound is a hardened material formed by polymerization of the polymerizable group of the specific cellulose compound.

[0044] As the cellulose derivative, a specific cellulose compound is preferable which exhibits thermotropic cholesteric liquid crystallinity or lyotropic cholesteric liquid crystallinity, has elasticity, and can have its orientation fixed at the wavelength of Bragg reflection. The polymerizable group in the specific cellulose compound is not particularly limited, but is preferably a polymerizable group capable of radical polymerization or cationic polymerization. As the radical polymerizable group, a generally known radical polymerizable group can be used, and a suitable one is an acryloyloxy group or a methacryloyloxy group. In this case, it is known that the polymerization rate of the acryloyloxy group is generally fast, and from the viewpoint of improving productivity, the acryloyloxy group is preferred, but the methacryloyloxy group can also be used as the polymerizable group. As the cationic polymerizable group, a generally known cationic polymerizable group can be used, specifically, an alicyclic ether group, a cyclic acetal group, a cyclic lactone group, a cyclic thioether group, a spiro orthoester group, and a vinyloxy group can be mentioned. Among them, an alicyclic ether group or a vinyloxy group is preferable, and an epoxy group, an oxetanyl group, or a vinyloxy group is more preferable.

[0045] The specific cellulose compound preferably has a repeating unit represented by the following formula (I).

[0046] Formula (I) [ka]

[0047] In the above formula (I), D 1 , D 2 and D.3 each independently represents a single bond, -CO-, -O-, -S-, -C(=S)-, or -CR 1 R 2 -, -CR 3 =CR 4 -, -NR 5 -, or a divalent linking group consisting of two or more of these, R 1 ~R 5 each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 12 carbon atoms. In addition, in the above formula (I), SP 1 , S.P. 2 and S.P. 3 each independently represents a single bond, a linear or branched alkylene group having 1 to 12 carbon atoms, or a -CH 2 represents a divalent linking group in which one or more - is substituted with -O-, -S-, -NH-, -N(Q)-, or -CO-, and Q represents a substituent. In addition, in the above formula (I), L 1 , L 2 and L 3 each independently represents a hydrogen atom, a hydroxyl group, or a monovalent organic group; L 1 , L 2 and L 3 At least one of represents a polymerizable group.

[0048] In the above formula (I), D 1 , D 2 and D. 3 Examples of the divalent linking group in one embodiment include -O-CO-, -O-, -C(=S)O-, -CR 1 R 2 -, -CR 1 R 2 -CR 1 R 2 -, -O-CR 1 R 2 -, -O-CR 1 R 2 -CR 1 R 2 -O-CR 1 R 2 -CR1 R 2 -,-CO-O-CR 1 R 2 -, -O-CO-CR 1 R 2 -, -O-CO-NR 5 -, -O-CO-NR 5 -CR 1 R 2 -CR 1 R 2 -, -CO-NR 5 -CR 1 R 2 -CR 1 R 2 -, -NR 5 -CR 1 R 2 - and -CO-NR 5 - is one of them. 1 , R 2 and R 5 each independently represents a hydrogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms. Of these, -O-CO-, -O-, -C(=S)O-, -O-CR 1 R 2 -, -O-CR 1 R 2 -CR 1 R 2 -O-CR 1 R 2 -CR 1 R 2 -,-CO-O-CR 1 R 2 -, -O-CO-CR 1 R 2 -, -O-CO-NR 5 -, -O-CO-NR 5 -CR 1 R 2 -CR 1 R 2 -, -CO-NR 5 -CR 1 R 2 -CR 1 R 2 - and -CO-NR 5 - is preferably any one of -O-CO-, -O-, and -O-CO-NR 5- and -O-CO-NR 5 -CR 1 R 2 -CR 1 R 2 It is more preferable that either

[0049] In the above formula (I), SP 1 , S.P. 2 and S.P. 3 Examples of the linear or branched alkylene group having 1 to 12 carbon atoms in one embodiment include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a methylhexylene group, and a heptylene group. In addition, SP 1 and S.P. 2 As described above, is a -CH 2 may be a divalent linking group in which one or more of - is substituted with -O-, -S-, -NH-, -N(Q)-, -CO-, or -O-CO-NH-, and -CH 2 It is also preferred that one or more of - is a divalent linking group substituted with -O- or -O-CO-NH-.

[0050] Examples of the substituent represented by Q include an alkyl group, an alkoxy group, an alkylcarbonyl group, an alkoxycarbonyl group, an alkylcarbonyloxy group, an alkylamino group, and an alkylamide group. Among these, an alkyl group is preferable.

[0051] In the above formula (I), L 1 , L 2 and L 3 Examples of the monovalent organic group represented by the formula (I) include an alkyl group, an aryl group, and a heteroaryl group. The alkyl group may be linear, branched or cyclic, but is preferably linear. The alkyl group preferably has 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, and even more preferably 1 to 10 carbon atoms. The aryl group may be either monocyclic or polycyclic, but is preferably monocyclic. The aryl group preferably has 6 to 25 carbon atoms, and more preferably has 6 to 10 carbon atoms. The heteroaryl group may be a monocyclic or polycyclic ring. The number of heteroatoms constituting the heteroaryl group is preferably 1 to 3. The heteroatoms constituting the heteroaryl group are preferably nitrogen atoms, sulfur atoms, or oxygen atoms. The number of carbon atoms in the heteroaryl group is preferably 6 to 18, and more preferably 6 to 12. The alkyl group, aryl group and heteroaryl group may be unsubstituted or may have a substituent.

[0052] In the above formula (I), L 1 , L 2 and L 3 The polymerizable group represented by at least one of the above is not particularly limited, and is preferably a polymerizable group capable of radical polymerization or cationic polymerization. As the radical polymerizable group, a generally known radical polymerizable group can be used, and a suitable one is an acryloyloxy group or a methacryloyloxy group.In this case, it is known that the polymerization rate of the acryloyloxy group is generally fast, and from the viewpoint of improving productivity, the acryloyloxy group is preferred, but the methacryloyloxy group can also be used as the polymerizable group. As the cationic polymerizable group, a generally known cationic polymerizable group can be used, specifically, an alicyclic ether group, a cyclic acetal group, a cyclic lactone group, a cyclic thioether group, a spiro orthoester group, and a vinyloxy group can be mentioned. Among them, an alicyclic ether group or a vinyloxy group is preferable, and an epoxy group, an oxetanyl group, or a vinyloxy group is more preferable. Particularly preferred examples of the polymerizable group include the polymerizable groups represented by any of the following formulas (P-1) to (P-20).

[0053] [ka]

[0054] It is also preferable that the specific cellulose compound has a repeating unit represented by the following formula (II).

[0055] Formula (II) [ka]

[0056] In the above formula (II), R 1 , R 2 and R 3 each independently represents a hydroxyl group, -OR 4 , -(O-CH 2 -CH(CH 3 )) m -R 5 or a polymerizable group. 4 is a hydrogen atom, -CO-R 6 or -CO-NH-R 7 Represents R 5 is a hydroxyl group, -OCO-R 8 , -OCO-NH-R 9 or a polymerizable group. 6 , R 7 , R 8 , and R 9 each independently represents an alkyl group which may have a polymerizable group as a substituent, or an aryl group; R 1 , R 2 and R 3 At least one of them has a polymerizable group. In addition, m represents an integer of 1 to 10.

[0057] A specific example of the specific cellulose compound is preferably a compound represented by the following formula (III). Specifically, D 1 , D 2 and D. 3 , S.P. 1 , S.P. 2 and S.P. 3 , L 1 , L 2 and L 3Examples of the compounds having the side chain structures shown in Table 1 below are given as examples.

[0058] Formula (III) [ka]

[0059] [Table 1]

[0060] The cellulose preferably contains a hardened product of a cellulose compound having a polymerizable group and an unsubstituted cellulose compound in terms of controlling flexibility, liquid crystallinity, stability, and the like.

[0061] The molecular weight of the cellulose is not particularly limited, but the number average molecular weight (Mn) is preferably in the range of 5,000 to 1,000,000, more preferably in the range of 10,000 to 500,000, further preferably in the range of 20,000 to 200,000, and particularly preferably in the range of 30,000 to 100,000. The mass average molecular weight (Mw) is preferably in the range of 7,000 to 5,000,000, more preferably in the range of 15,000 to 2,500,000, further preferably in the range of 20,000 to 1,500,000, and particularly preferably in the range of 30,000 to 500,000. The molecular weight distribution (MWD) is preferably in the range of 1.1 to 5.0, more preferably in the range of 1.2 to 3.5, and even more preferably in the range of 1.3 to 3.0. By setting the average molecular weight within this range, it is possible to further improve the moldability of the molded product, etc. Also, by setting the molecular weight distribution within this range, it is possible to further improve the moldability, etc. In the present invention, the number average molecular weight (Mn), weight average molecular weight (Mw) and molecular weight distribution (MWD) can be measured by gel permeation chromatography (GPC). Specifically, they can be determined by using tetrahydrofuran as a solvent, polystyrene gel and a converted molecular weight calibration curve previously obtained from the constituent curve of standard monodisperse polystyrene.

[0062] Even when the light reflecting layer 18 contains the above-mentioned celluloses, it is preferable that a cholesteric liquid crystal layer is formed. From the viewpoint of controlling the wavelength region of reflection, it is preferable that the cellulose exhibits thermotropic liquid crystallinity. When the cellulose exhibits thermotropic liquid crystallinity, it is easy to control the temperature during curing.

[0063] The cholesteric liquid crystal layer can be formed by a known method. As an example, a coating composition containing a liquid crystal compound and a chiral agent is prepared, and the coating composition is applied to an alignment film, and then heated to align the liquid crystal compound in a cholesteric liquid crystal phase. The coating composition is then dried to form a cholesteric liquid crystal layer. The alignment of the liquid crystal compound and the drying of the coating composition may be performed simultaneously. After the coating composition is dried, the liquid crystal compound may be polymerized by, for example, irradiation with ultraviolet light, if necessary.

[0064] When forming a cholesteric liquid crystal layer, an alignment film for aligning a liquid crystal compound is usually formed on the surface of a support such as a resin film, and the cholesteric liquid crystal layer is then formed on the surface of this alignment film. Therefore, when the light reflecting layer 18 is a cholesteric liquid crystal layer, it may be peeled off from the alignment film before use. Alternatively, when the light reflecting layer 18 is a cholesteric liquid crystal layer, the pressure sensor 10 may have a cholesteric liquid crystal layer peeled off from the support and an alignment film. Alternatively, when the light reflecting layer 18 is a cholesteric liquid crystal layer, the pressure sensor 10 may have a cholesteric liquid crystal layer, an alignment film, and a support. When the pressure sensor 10 has an alignment film or further a support in addition to the cholesteric liquid crystal layer as the light-reflecting layer 18, a laminate including the cholesteric liquid crystal layer may be arranged so that the cholesteric liquid crystal layer faces the imaging element 12, or the alignment film and the support may be on the imaging element 12 side. In addition, when the pressure sensor 10 has an alignment film and a support, the optical properties of both must be appropriately selected and / or adjusted so that they are transparent to the light emitted by the image sensor 12 and the light source 14, just like the light reflective layer 18 in an unpressurized state.

[0065] Furthermore, when a cholesteric liquid crystal layer is used as the light reflecting layer 18, the light reflecting layer 18 may have two cholesteric liquid crystal layers having the same selective reflection center wavelength and opposite rotation directions of the circularly polarized light that is selectively reflected.

[0066] The light-reflecting layer 18, which selectively reflects different wavelengths of light depending on deformation (compression and expansion) due to pressure, is not limited to an organic cholesteric liquid crystal layer, and various known layers having the low elasticity described above can be used. One example is the inorganic nanosheet structural color gel (Fukuoka Institute of Technology) which is made of inorganic nanosheet liquid crystals obtained by exfoliating and dispersing inorganic layered compounds including smectite clay minerals, layered potassium hexaniobate, layered perovskite, and graphite, and which is introduced in https: / / prtimes.jp / main / html / rd / p / 000000012.000047155.html.

[0067] There is no restriction on the thickness of the light reflecting layer 18, and the thickness can be appropriately set to obtain the required light reflecting characteristics and the required low elasticity, i.e., the required amount of film thickness variation in response to pressure from the object being held, depending on the material from which the light reflecting layer 18 is formed, etc. Here, in terms of increasing the reflectance of the measurement light, it is preferable that the light reflecting layer 18 is thicker. On the other hand, the thicker the light reflecting layer is, the more disadvantageous it is in terms of deformation under pressure and the thickness of the pressure sensor 10. In consideration of this point, the thickness of the light reflecting layer 18 is preferably 0.1 to 1000 μm, and more preferably 1 to 600 μm.

[0068] The light reflective layer 18 may be composed of a wet gel. The wet gel means a solid component having flowability, and preferably contains a liquid component. In other words, the light reflecting layer 18 may contain a liquid component. When the light reflecting layer 18 is made of a wet gel, it is possible to achieve a good balance between liquid crystallinity and flexibility that responds to slight pressure. The liquid component is not particularly limited, and may be a liquid component in which the material contained therein (particularly, the liquid crystal material) is well dissolved or dispersed. As the liquid component, it is preferable that the component contained in the light reflecting layer 18 is a liquid component that easily exhibits liquid crystallinity. For example, when the light reflecting layer 18 contains cellulose, water or an organic solvent is preferably selected as the liquid component.

[0069] In addition, when the light reflecting layer contains a liquid component, it is preferable that the light reflecting layer has a mechanism for preventing the liquid component from volatilizing in order to ensure stability. In other words, the light reflecting layer is preferably sealed with a sealant. For example, it is preferable that a sealant or a base material that inhibits the liquid component from volatilizing is provided on the top, bottom, and side surfaces of the light reflecting layer. It is desirable to select a material with low moisture permeability depending on the liquid component. For example, inorganic thin films such as silicon compounds such as aluminum oxide and silicon oxide, organic thin films such as parylene and acrylic resin, and laminated films thereof can be used as the gas barrier film. In addition, as materials constituting the sealing material or the base material, polyolefin (PO) resins such as homopolymers or copolymers of ethylene, polypropylene, and butene, etc.; amorphous polyolefin resins (APO) such as cyclic polyolefins, etc.; polyester-based resins such as polyethylene terephthalate (PET) and polyethylene 2,6-naphthalate (PEN); polyamide-based (PA) resins such as nylon 6, nylon 12, and copolymer nylons; polyvinyl alcohol-based resins such as polyvinyl alcohol (PVA) resins and ethylene-vinyl alcohol copolymers (EVOH); polyimide (PI) resins; polyetherimide (PEI) resins; polysulfone (PS) resins; polyethersulfone (PES) resins; polyetheretherketone (PEEK) resins; polycarbonate (PC) resins; polyvinyl butyrate (PVB) resin; polyarylate (PAR) resin; fluorine-based resins such as ethylene-tetrafluoroethylene copolymer (ETFE), trifluorochloroethylene (PFA), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (FEP), vinylidene fluoride (PVDF), vinyl fluoride (PVF) and perfluoroethylene-perfluoropropylene-perfluorovinyl ether copolymer (EPA); resin compositions made of acrylate compounds having radical reactive unsaturated compounds; resin compositions made of the above acrylate compounds and mercapto compounds having thiol groups; photocurable resins such as resin compositions in which oligomers such as epoxy acrylate, urethane acrylate, polyester acrylate and polyether acrylate are dissolved in polyfunctional acrylate monomers. Furthermore, it is also possible to use as the resin substrate a substrate in which one or more of these materials are laminated by means of lamination, coating, etc. Furthermore, a substrate made of the above-mentioned material and coated with the above-mentioned inorganic thin film and organic thin film can also be used.

[0070] In the illustrated example, as a preferred embodiment, the light reflective layer 18 has a reflection wavelength range in the infrared wavelength range (infrared range) when no pressure is applied, and has a reflection wavelength range in the visible light wavelength range (visible light range) when pressure is applied. Furthermore, in the illustrated pressure sensor 10, as a preferred embodiment, the light reflecting layer 18 is a cholesteric liquid crystal layer having such selective reflection wavelength characteristics. Therefore, in the illustrated pressure sensor 10, the light reflective layer 18 transmits visible light when no pressure is applied, selectively reflects red light and transmits everything else when pressure is applied, selectively reflects green light and transmits everything else when further pressure is applied, and selectively reflects blue light and transmits everything else when stronger pressure is applied.

[0071] In the pressure sensor 10 of the present invention, there is no limitation on the light reflectance of the light reflective layer 18, but basically, the higher the reflectance, the more preferable it is. Specifically, it is preferable that the maximum reflectance in the wavelength range in which the reflected wavelength changes according to the pressure is 20% or more when pressure is applied. In the following description, this "maximum reflectance" is also simply referred to as "reflectance." As described above, in the pressure sensor 10 of the present invention, the proximity function is realized by capturing an image of the outside of the housing 20 with the imaging element 12. That is, in the pressure sensor 10, external ambient light is incident on the housing through the light reflecting layer 18. Therefore, if the reflectance of the light reflecting layer 18 is insufficient, it may be difficult to distinguish the change in the reflection wavelength range of the light reflecting layer 18 according to the applied pressure, that is, the color of the light reflecting layer 18. In contrast, by setting the reflectance of the light reflecting layer 18 to 20% or more, it becomes possible to appropriately distinguish the color of the light reflecting layer 18 according to the pressure, and it becomes possible to appropriately detect pressure in the tactile function.

[0072] It is more preferable that the reflectance of the light reflecting layer 18 is 30% or more.

[0073] In the pressure sensor 10 of the present invention, a lens may be provided between the imaging element 12 and the light reflecting layer 18, which are arranged apart from each other, as necessary.

[0074] As described above, the pressure sensor 10 shown in FIG. 1 is suitable for use as a tactile sensor or the like in the gripping portion (tip) of a robot arm 46. In such applications, in order to effectively realize the proximity function and to measure pressure with high resolution and precision as a tactile sensor, it is necessary to align the focus of the image captured by the imaging element 12 with the surface of the light reflecting layer 18. To achieve this, it is necessary to take measures such as bringing the imaging element 12 into contact with the light reflecting layer 18 or as close as possible to the light reflecting layer 18, or matching the measurement area of ​​the light reflecting layer 18 with the imaging area of ​​the imaging element. Here, it is preferable that the pressure sensor 10 used in a tactile sensor of a robot arm or the like is capable of measuring pressure over a certain area, for example, 2 x 2 cm, 3 x 3 cm, etc. Therefore, in order to perform proper imaging, the imaging surface of the imaging element 12 must also be the same size. However, the imaging surface of an image sensor is usually about 1×1 cm, and the larger the imaging surface, the more expensive it becomes and the more power it consumes.

[0075] In contrast to this, in the pressure sensor 10 of the present invention, a lens may be provided between the imaging element 12 and the light reflecting layer 18, if necessary. With such a configuration, the focus of the image captured by the imaging element 12 can be adjusted to the light reflecting layer 18 . This enables high-quality imaging by the imaging element 12, i.e., enables highly accurate pressure measurement. Furthermore, even if the light reflective layer 18 of the pressure sensor 10 is large, such as 3 x 3 cm, a normal or small imaging element 12 of about 1 x 1 cm can be used. In other words, by using a lens, it becomes possible to easily configure the device using a general-purpose imaging element 12. Furthermore, by selecting the lens, it is possible to prevent the distance between the image sensor 12 and the light reflecting layer 18 from becoming wider than necessary, that is, to prevent the pressure sensor 10 from becoming larger. There is no limit to the interval (distance) between the imaging element 12 and the light reflecting layer 18, but considering that it will be mounted on a robot or the like, it is preferable that it is short in order to make the pressure sensor 10 smaller (thinner). On the other hand, considering that a lens will be disposed and that the imaging element 12 will be small, it is preferable that there is an optically significant distance. Considering this point, the distance between the imaging element 12 and the light reflecting layer 18 is preferably 0.1 to 50 mm, more preferably 1 to 30 mm, and even more preferably 3 to 20 mm.

[0076] Furthermore, when the size of the pressure sensor 10, the cost and driving power of the image sensor 12, etc. are taken into consideration, it is preferable that the area of ​​the imaging surface of the image sensor 12 in the pressure sensor 10 be smaller than the area of ​​the light reflecting layer .

[0077] In the pressure sensor 10 of the present invention, the light source 14 emits measurement light for realizing the tactile function of the pressure sensor 10 . Therefore, the light source 14 is provided so as to irradiate the light reflecting surface of the light reflecting layer 18 inside the housing 20 as shown in FIG.

[0078] There is no limitation on the light source 14, and various light sources (light-emitting elements) can be used as long as they can emit the desired measurement light. Examples of the light source 14 include a light emitting diode (LED), a laser diode (LD), and a fluorescent lamp.

[0079] The light source 14 may be a white light source, or may be a light source that emits monochromatic light such as red light, blue light, and green light, for example, light in a wavelength range that is selectively reflected by the light reflecting layer 18 when pressure is applied, or may be a light source that emits light of multiple colors such as red light and green light. The light source 14 may also be a light source that emits invisible light such as infrared light. In the present invention, the light reflecting layer 18 transmits the light emitted by the light source 14 when no pressure is applied, and reflects the light emitted by the light source 14 when pressure is applied. In other words, the measurement light emitted by the light source 14 is light that transmits through the light reflecting layer 18 when no pressure is applied and is reflected by the light reflecting layer 18 when pressure is applied. In the illustrated pressure sensor 10, the light source 14 is preferably a white light source.

[0080] When a cholesteric liquid crystal layer is used as the light reflecting layer 18, the light source 14 may have a circular polarizer so that circularly polarized light that is selectively reflected by the cholesteric liquid crystal layer is incident on the light reflecting layer 18. An example of the circular polarizer is a circular polarizer made of a linear polarizer and a quarter-wave plate (λ / 4 plate).

[0081] Hereinafter, the pressure sensor of the present invention will be described in detail by explaining the operation of the pressure sensor 10 with reference to FIG.

[0082] As described above, in the illustrated pressure sensor 10, the image sensor 12 is a color area sensor (two-dimensional color sensor). In addition, the light reflective layer 18 is a cholesteric liquid crystal layer that has a selective reflection wavelength range in the infrared wavelength range when no pressure is applied, and has a selective reflection wavelength range in the visible light wavelength range when pressure is applied. Furthermore, the light source 14 is a white light source.

[0083] As described above, the pressure sensor 10 is used, for example, for tactile sensing in robot applications, and as one example, is attached to the tip (grip) of an arm member 48 of a robot arm 46 and used as a tactile sensor for the robot arm 46. The pressure sensor 10 is connected to a control device (not shown) of a robot arm such as a computer having an image processing function, for example, and the image captured by the image sensor 12 is sent to this control device. Note that this control device may control the operation of the pressure sensor 10. In FIG. 3, the upper part conceptually illustrates the positional relationship between the pressure sensor 10 and the object O grasped by the robot arm 46, and the lower part conceptually illustrates an image captured by the imaging element 12 in the state illustrated at the corresponding upper end.

[0084] When tactile sensing of the robot arm 46 is performed by the pressure sensor 10, first, the light source 14 is turned on to cause measurement light to be incident on the light reflecting layer 18, and imaging by the imaging element 12 is started. The lighting of the light source 14 and the start of image capture by the image sensor 12 may be performed in response to an instruction from a control device to which the pressure sensor 10 is connected, or may be performed by providing a switch on the housing 20 of the pressure sensor 10 .

[0085] In this example, as described above, the light-reflective layer 18 is a cholesteric liquid crystal layer that has a selective reflection wavelength range in the infrared wavelength range when no pressure is applied, the image sensor 12 is a color image sensor, and the light source 14 is a white light source. Therefore, in a state where the robot arm 46 is not positioned to grasp the object O, as shown in the left side of the upper part of Fig. 3, the imaging element 12 captures an image of the outside of the housing 20 through the light reflecting layer 18, as shown in the captured image P on the left side of the lower part of Fig. 3. Note that the image captured by the imaging element 12 may be displayed on a display connected to the control device, if necessary. Furthermore, the measurement light emitted by the light source 14 passes through the light reflecting layer 18 and illuminates the outside of the housing 20 .

[0086] Next, the robot arm 46 moves to a position for gripping the object O, as shown in the second from the left in the upper part of Fig. 3. In the illustrated example, the object O is a sphere, for example. In this state, as shown in the second captured image P from the left in the lower part of FIG. 3, the object O is transmitted through the light reflecting layer 18 and captured by the imaging element 12 (image Oi). When the robot arm 46 starts to grasp the object O and the distance between the tips of the arm members 48 narrows, the object O gradually approaches the pressure sensor 10, as shown in the second and third captured images P from the left in the upper part of Fig. 3. In response to this, the image Oi of the object O captured by the imaging element 12 also gradually becomes larger, as shown in the second and third captured images P from the left in the lower part of Fig. 3. In the above state, the white measurement light emitted by the light source 14 passes through the light reflecting layer 18 and illuminates the object O and the background.

[0087] As described above, the image captured by the imaging device 12 is sent to the control device of the robot arm 46. Therefore, as is clear from the above explanation, the control device processes the image captured by the imaging element 12, thereby detecting a situation in which the object O is approaching the tip of the arm member 48, and the robot arm 46 (control device) can have a sense of proximity. That is, in this state, the pressure sensor 10 acts as a proximity sensor for the robot arm 46 .

[0088] 3. Furthermore, when the tip of the arm member 48 approaches and abuts against the object O to grip it, the light reflective layer 18 of the pressure sensor 10 is pressed by the object O, as shown on the right side of the upper part of FIG. As described above, the light-reflecting layer 18 is a cholesteric liquid crystal layer that has a selective reflection wavelength range in the infrared wavelength range when no pressure is applied, and a selective reflection wavelength range in the visible light wavelength range when pressure is applied. The portion (halftone dot) of the light reflecting layer 18 that the object O comes into contact with is pressed to reduce the film thickness, shortening the helical pitch of the cholesteric liquid crystal phase and shortening the wavelength of the selective reflection range. That is, the color of the light reflecting layer 18, which is a cholesteric liquid crystal layer, changes to red. Therefore, the portion of the light reflecting layer 18 that the object O comes into contact with selectively reflects red light.

[0089] As described above, the light source 14 emits white light as the measurement light. Therefore, of the measurement light incident on the light reflecting layer 18, the red light component of the white light incident on the area where the object O contacts is reflected by the light reflecting layer 18 and imaged by the imaging element 12. As a result, as shown in the captured image P on the right side of the lower part of Fig. 3, in the image Oi of the object O captured by the imaging element 12, the portion (halftone dot) that contacts the light reflecting layer 18 becomes a reddish image. In the following description, the portion of the object O that first comes into contact with the light reflecting layer 18 will also be referred to as the "top" for convenience.

[0090] As described above, the object O is a sphere. Therefore, when the gripping force of the object O by the robot arm 46 becomes stronger, the pressure of the object O on the light reflecting layer 18 becomes stronger. As a result, the helical pitch of the portion of the light reflecting layer 18 where the top of the object O abuts becomes shorter, and this portion selectively reflects green light. Moreover, the pressure that the light reflecting layer 18 receives from the object O decreases from the top of the object O toward the periphery, so the helical pitch of the cholesteric liquid crystal phase increases from the position corresponding to the top toward the periphery. Therefore, in this state, the image Oi of the object O captured by the imaging element 12 gradually becomes redder from green toward the periphery from the position corresponding to the top of the object O toward the periphery, and the periphery of the position where the object O is in contact becomes a red image.

[0091] As described above, the image captured by the imaging device 12 is sent to the control device of the robot arm 46. In other words, according to the pressure sensor 10 of the present invention, the control device analyzes the image captured by the imaging element 12, and the robot arm 46 can detect which part of the object O is under pressure and which part of the object O is under strong pressure when the object O is being grasped.

[0092] Also, in FIG. 3, the object O is a sphere, but the robot arm 46 can grasp materials other than spheres. Therefore, by processing the image captured by the imaging element 12, various tactile sensations can be known, such as whether the robot arm 46 is gripping the object with a surface or with one or more points. For example, when the image captured by the imaging element 12 captures reflected light from the light reflecting layer 18 corresponding to two separate points on the object, it can be known that the object has two convex parts at the position where the robot arm 46 is gripping it. Furthermore, when the reflected light from both points is the same color, it can be known that the same pressure is being applied to the two points on the object. On the other hand, when one reflected light is red and the other reflected light is green, it can be known that a stronger pressure is being applied to the part reflecting green light than to the part reflecting red light. Furthermore, by detecting in advance the relationship between the pressure applied to the light reflecting layer 18 and the wavelength of the reflected light selectively reflected by the light reflecting layer 18, and storing the relationship between the two, for example, in a table format in the control device, it is also possible to know the pressure applied to the object when it is grasped by the robot arm 46.

[0093] As described above, the pressure sensor 10 functions as a tactile sensor for the robot arm 46, enabling the robot arm 46 (controller) to have a sense of touch. That is, the pressure sensor of the present invention is a pressure sensor that has a proximity sense function in addition to a tactile function, and by using it in, for example, a robot arm, the robot arm can have both a proximity sense and a tactile sense.

[0094] In the above example, in a preferred embodiment, the image sensor 12 is a color area sensor, the light reflecting layer 18 is a cholesteric liquid crystal layer whose selective reflection wavelength range changes from infrared to visible light in response to pressure, and the light source 14 is a white light source. However, the pressure sensor of the present invention is not limited thereto, and the imaging element 12, the light reflecting layer 18 and the light source 14 can be appropriately adjusted and selected depending on the wavelength of light to be used.

[0095] For example, the imaging element 12 may be an area sensor that captures green light, the light reflecting layer 18 may be a cholesteric liquid crystal layer that selectively reflects red light when no pressure is applied and selectively reflects green light when pressure is applied, and the light source 14 may be a light source that emits green light. Even in this case, a proximity sensor can be realized by the green image captured by the imaging element 12 through the light reflective layer 18 when the robot arm 46 is not grasping an object, and a tactile sensor can be realized by the change in the reflection wavelength of the light reflective layer 18 from red to green in response to the change in pressure received by the light reflective layer 18 when the robot arm 46 grasps an object. Alternatively, the imaging element 12 may be an area sensor that captures near-infrared light (wavelength 700 to 900 nm), the light reflective layer 18 may be a cholesteric liquid crystal layer that selectively reflects mid-infrared light (wavelength 1000 to 2000 nm) when no pressure is applied and selectively reflects near-infrared light when pressure is applied, and the light source 14 may be a light source that emits near-infrared light. In this case, too, a proximity sensor can be realized by the near-infrared image captured by the imaging element 12 through the light reflective layer 18 when the robot arm 46 is not grasping an object, and a tactile sensor can be realized by the change in the reflection wavelength of the light reflective layer 18 from far-infrared to near-infrared in response to the change in pressure received by the light reflective layer 18 when the robot arm 46 grasps an object.

[0096] However, taking into consideration the fact that the object O close to the pressure sensor 10 can be imaged with good image quality, that a general imaging element 12 can be used, and that the change in the selective reflection wavelength (color) of the light reflective layer 18 when the object O is grasped can be easily seen, it is preferable to use a color area sensor as the imaging element 12, a white light source as the light source 14, and a cholesteric liquid crystal layer as the light reflective layer 18, as shown in the illustrated example, which selectively reflects infrared light when no pressure is applied and reflects visible light when pressure is applied.

[0097] In the pressure sensor of the present invention, when monochromatic light is used for measurement in this manner, an optical filter that passes only a portion of the light and a filter such as a semi-transmissive filter (ND filter) that adjusts the amount of light may be provided as necessary at least in one location between the light source 14 and the light reflecting layer 18 and between the light reflecting layer 18 and the image sensor 12. Such a filter may have wavelength selectivity and transmittance adjusted by a light absorbing material, and may be an interference filter made of a liquid crystal film, a laminated film, or the like, or a polarizing filter. If necessary, the semi-transmissive filter can also be used in a configuration that uses the above-mentioned color area sensor, a cholesteric liquid crystal layer whose reflection wavelength changes from infrared light to visible light, and a white light source.

[0098] In the above example, the light reflecting layer 18 selectively reflects infrared rays when no pressure is applied. Therefore, in this case, it is preferable that the imaging element 12 has an infrared cut filter in front of (upstream of) the imaging surface.

[0099] In the pressure sensor 10 of the present invention, the output of the light source 14, i.e., the intensity (brightness) of the measurement light, may be uniform. However, it is preferable that the pressure sensor 10 of the present invention adjusts the output of the light source 14 according to the image captured by the image capture element 12.

[0100] As described above, when the robot arm 46 (arm member 48) is not gripping the object O, the pressure sensor 10 of the present invention functions as a proximity sensor by having the imaging element 12 capture an image of the outside (background) of the housing 20 through the light reflective layer 18. When the robot arm 46 is gripping the object O, the pressure sensor 10 functions as a tactile sensor by having the imaging element 12 capture an image of light emitted by the light source 14 and reflected by the reflective layer 18. Here, when the pressure sensor 10 is functioning as a proximity sensor, the image sensor 12 captures an image using external light outside the housing 20. In this state, a high-quality and high-resolution background image can be captured without the measurement light (white light) emitted by the light source 14. Considering this point, when the pressure sensor 10 is functioning as a proximity sensor, it is preferable that the measurement light emitted by the light source 14 has a low intensity.

[0101] Accordingly, in the pressure sensor 10 of the present invention, it is preferable to weaken the output of the light source 14, i.e., the measurement light, when it is functioning as a proximity sensor, and to strengthen the output of the light source 14, i.e., the measurement light, when it is functioning as a tactile sensor. The state in which the output of the light source 14 is weakened also includes the state in which the light source 14 is turned off. This switching may be performed according to the image captured by the imaging element 12. As an example, the output of the light source 14 may be initially weakened, and then increased when the imaging element 12 captures the light reflected by the light reflecting layer 18, i.e., when a change in the reflection wavelength (color) of the light reflecting layer 18 is detected. Alternatively, the output of the light source 14 may be initially weakened, and then increased when the size of the image Oi of the object O being captured exceeds a threshold. Alternatively, the output of the light source 14 may be initially weakened, and then increased when a predetermined time has elapsed since the imaging element 12 captured the image Oi of the object O and the robot arm 46 started the gripping operation. This determination may be made by known image processing of the captured image. This also applies to the adjustment of the focal position of the image sensor, which will be described later.

[0102] In the pressure sensor 10 of the present invention, the focus of the imaging element 12 may be constant. However, in the pressure sensor 10 of the present invention, it is preferable that the focus of the image pickup element 12 is variable, and the focal position of the image pickup element 12 is adjusted according to the image captured by the image pickup element 12 .

[0103] As described above, the pressure sensor 10 of the present invention basically functions as a tactile sensor by measuring pressure by the imaging element 12 capturing an image of the light reflecting layer 18. Therefore, for accurate pressure measurement, it is preferable to focus the imaging element 12 on the light reflecting layer 18. However, the pressure sensor 10 also functions as a proximity sensor by utilizing an image of the background captured by the image capture element 12 through the light reflecting layer 18. In consideration of this point, it is preferable that the focal point of the image capture element 12 is outside the housing 20 when the pressure sensor 10 is functioning as a proximity sensor.

[0104] Accordingly, in the pressure sensor 10 of the present invention, when functioning as a proximity sensor, it is preferable that the focal position of the image sensor 12 is outside the housing 20, and when functioning as a tactile sensor, the focal position of the image sensor 12 is inside the housing 20, particularly on the surface (near the surface) of the light reflecting layer 18. This switching may be performed according to the image captured by the imaging element 12. As an example, the focal position of the imaging element 12 may be initially set to the outside of the housing 20, and when the imaging element 12 captures the light reflected by the light reflecting layer 18, i.e., when a change in the reflection wavelength (color) of the light reflecting layer 18 is detected, the focal position of the imaging element 12 may be initially set to the outside of the housing 20, and when the size of the image Oi of the object O to be captured exceeds a threshold, the focal position of the imaging element 12 may be initially set to the inside of the housing 20, and particularly the surface (near the surface) of the light reflecting layer 18. Alternatively, the focal position of the imaging element 12 may be initially set to the outside of the housing 20, and when a predetermined time has elapsed since the robot arm 46 started the gripping operation after the imaging element 12 captures the image Oi of the object O, the focal position of the imaging element 12 may be initially set to the inside of the housing 20, and particularly the surface (near the surface) of the light reflecting layer 18.

[0105] Such adjustment of the focal position of the image sensor 12 may be performed by utilizing a known autofocus function. Furthermore, in the case where the pressure sensor 10 has the above-mentioned lens between the light reflecting layer 18 and the image sensor 12, the focus adjustment may be performed by this lens.

[0106] It is preferable that such adjustment of the output of the light source 14 and the adjustment of the focal position of the image sensor 12 are performed automatically by a control device such as a computer that controls the pressure sensor 10, by performing image analysis of the image captured by the image sensor 12, based on the results of the image analysis. As described above, the control device for the robot arm 46 may also function as the control device for the pressure sensor 10.

[0107] Although the above description is an example in which the pressure sensor of the present invention is used in a robot arm that grips an object, the pressure sensor of the present invention can be used for various other purposes. One example is detection of proximity and contact of an object in mobility such as an unmanned guided vehicle. The pressure sensor of the present invention is not necessarily limited to being used as both a tactile sensor and a proximity sensor, but can also be suitably used as only a tactile sensor and as a proximity sensor.

[0108] Although the pressure sensor of the present invention has been described in detail above, the present invention is not limited to the above-described examples, and various improvements and modifications may of course be made without departing from the gist of the present invention. [Industrial Applicability]

[0109] The present invention can be suitably used for tactile sensing and proximity sensing in robotics applications, etc. [Explanation of symbols]

[0110] 10 Pressure Sensor 12 Image sensor 14 Light source 18 Light reflective layer 20. Cabinet 46 Robot Arm 48 Arm parts

Claims

1. An imaging element; a light reflecting layer that is disposed facing an imaging surface of the imaging element and spaced apart from the imaging element, and whose reflection wavelength changes in response to pressure; A light source that irradiates the light reflecting layer with light, When no pressure is applied to the light reflecting layer, the light reflecting layer is transparent to light to which the image sensor is sensitive and to light emitted by the light source; A pressure sensor in which, when pressure is applied to the light reflecting layer, the portion of the light reflecting layer to which pressure is applied reflects light emitted by the light source, and the imaging element captures an image of the light emitted by the light source and reflected by the light reflecting layer.

2. The pressure sensor of claim 1 , wherein the light reflective layer is a liquid crystal layer.

3. The pressure sensor of claim 2 , wherein the light reflective layer is a cholesteric liquid crystal layer.

4. The pressure sensor according to claim 1 , wherein the imaging element is a two-dimensional sensor that captures a color image.

5. 2. The pressure sensor according to claim 1, wherein the light reflective layer has a selective reflection wavelength range in the infrared wavelength range when no pressure is applied, and has a selective reflection wavelength range in the visible light wavelength range when pressure is applied.

6. 6. The pressure sensor according to claim 4, wherein the light reflective layer has a maximum reflectance of 20% or more in a wavelength range in which the reflected wavelength changes according to the pressure when pressure is applied.

7. The pressure sensor according to claim 4 , wherein an output of the light source is adjusted in accordance with the image captured by the imaging element.

8. The pressure sensor according to claim 4 , further comprising: a focal position of said imaging element being adjusted in accordance with an image captured by said imaging element.

Images