JP2020165754A - Bend sensor - Google Patents

Abstract

To provide a bend sensor which can detect a bending direction.SOLUTION: A bend sensor 1 includes: a plurality of optical elastic resins 2 extending in a longer direction; a light sensor 4 detecting light which has passed through the optical elastic resins 2; and a processor 5 for detecting a direction of bending of the optical elastic resins 2 on the basis of a light signal detected by the light sensor 4, the optical elastic resins 2 being arranged in parallel in a direction perpendicular to the longer direction, a Young's modulus of the optical elastic resins 2 being 2-5 MPa when the optical elastic resins are at a temperature of 25°C, the absolute values of the optical photoelastic constant of the optical elastic resins 2 at the temperature of 25°C being 20×10-12 Pa-1 to 1×10-5 Pa-1, and an index of refraction of the optical elastic resins 2 being 1.30 to 1.80.SELECTED DRAWING: Figure 1

Description

The present invention relates to a bending sensor, and more particularly to a bending sensor including a photoelastic resin as a sensor body.

Conventionally, it has been proposed to use a photoelastic resin such as a polyurethane resin having photoelasticity as a bending sensor.

For example, the Young's modulus at 25 ° C. is 2 to 5 MPa, the photoelastic constant at 25 ° C. is 1000 × 10 ^-12 Pa ^{-1 to} 100,000 × 10 ^-12 Pa ^-1 , and the glass transition temperature is -60 ° C to −−. A bending sensor that detects the bending angle of a resin member by passing light through a resin member made of a photoelastic polyurethane resin at 21 ° C., receiving the passing light with a photodiode, and detecting the attenuation of the amount of light. It has been proposed (see, for example, Patent Document 1 (third embodiment)).

International WO2016 / 125905 Pamphlet

On the other hand, depending on the application of the bending sensor, the bending sensor may also be required to detect the bending direction. However, although the above-mentioned bending sensor can detect the presence / absence of bending and the bending angle, it cannot detect the bending direction.

The present invention is a bending sensor capable of detecting a bending direction.

The present invention [1] is based on a plurality of photoelastic resins extending in the longitudinal direction, an optical sensor that detects light passing through each of the plurality of photoelastic resins, and an optical signal detected by the optical sensor. A processing unit that detects the bending direction of the photoelastic resin is provided, and the plurality of the photoelastic resins are arranged in parallel in a direction orthogonal to the longitudinal direction, and the young rate of the photoelastic resin at 25 ° C. is 2. The absolute value of the photoelastic constant at 25 ° C. of the photoelastic resin is 20 × 10 ^-12 Pa ^-1 to 1 × 10 ^-5 Pa ^-1 , and the refractive index of the photoelastic resin is 1. Includes flexion sensors, .30 to 1.80.

The present invention [2] includes the bending sensor according to the above [1], wherein three or more of the photoelastic resins are arranged.

The present invention [3] further includes a cover member that covers a plurality of the photoelastic resins, and the refractive index of the cover member is less than the refractive index of the photoelastic resin. [1] or [2] Includes the flexion sensor described in.

In the bending sensor of the present invention, the Young's modulus of the photoelastic resin, the absolute value of the photoelastic constant, and the refractive index are within a predetermined range. Therefore, when the photoelastic resin is bent, the light passing through the photoelastic resin is attenuated by birefringence and the light passing through the photoelastic resin is attenuated according to the degree of bending (curvature) of the photoelastic resin. Leaks out of the photoelastic resin. Then, in the bending sensor of the present invention, a plurality of photoelastic resins are arranged in parallel, and the light passing through each of the photoelastic resins is detected by the optical sensor. Therefore, the bending direction of the photoelastic resin can be detected by comparing the difference in the degree of light attenuation in each of the photoelastic resins.

FIG. 1 is a perspective view showing a first embodiment of the bending sensor of the present invention. FIG. 2 is a perspective view showing an excerpt of the photoelastic resin in the bending sensor shown in FIG. 1, FIG. 2A is a non-bent photoelastic resin, and FIG. 2B is directed to one side in the parallel direction of the photoelastic resin. 2C shows a photoelastic resin that is bent in parallel direction, and FIG. 2C shows a photoelastic resin that is bent toward the other side in the parallel direction of the photoelastic resin. FIG. 3 is a perspective view showing a second embodiment of the bending sensor of the present invention. FIG. 4 is a perspective view showing a third embodiment of the bending sensor of the present invention. FIG. 5 is a voltage value graph showing the result of bending evaluation of the bending sensor of Example 1.

In the following, the direction in which the photoelastic resin extends is defined as the first direction (longitudinal direction), the direction in which the two photoelastic resins are arranged in parallel is defined as the second direction (parallel direction), and the directions are orthogonal to the first direction and the second direction. The direction will be described in detail with reference to FIG. 1, with the direction as the third direction (vertical direction).

In FIG. 1, the bending sensor 1 includes a plurality of photoelastic resins 2 extending along a first direction (longitudinal direction), a cover member 3 covering the plurality of photoelastic resins 2, and a plurality of photoelastic resins 2, respectively. The bending direction of the photoelastic resin 2 based on the optical sensor 4 that detects the light passing through the photoelastic resin 2, the control unit 6 for controlling the irradiation of the photoelastic resin 2 with the light, and the optical signal detected by the photosensor 4. It is provided with a processing unit 5 for detecting the above. In addition, in FIG. 1, the processing unit 5 and the control unit 6 are integrally formed. That is, one ECU (described later) has both a processing unit 5 and a control unit 6.

The photoelastic resin 2 is a member made of a resin having photoelasticity, and is formed in a rod shape extending in the first direction (longitudinal direction). More specifically, the photoelastic resin 2 is formed into a rod shape according to the molding die, or is externally processed into a bar shape by cutting after demolding, for example.

Examples of the shape of the photoelastic resin 2 include a columnar shape, an elliptical columnar shape, a polygonal columnar shape, and the like, preferably a columnar shape, and more specifically, a rod shape, a fiber shape, and the like. ..

Further, in the bending sensor 1, a plurality of photoelastic resins 2 are provided. The number of the photoelastic resin 2 is two or more, preferably three or more. In addition, it is usually 20 or less, preferably 10 or less, and more preferably 5 or less. The plurality of photoelastic resins 2 are arranged in parallel in a second direction orthogonal to the first direction (longitudinal direction) of the photoelastic resin 2. The plurality of photoelastic resins 2 may be arranged at predetermined intervals from each other, or may be arranged so as to be in close contact with each other.

Note that FIG. 1 shows a form in which two photoelastic resins 2 are provided and the two photoelastic resins 2 are arranged in parallel so as to be in close contact with each other.

Further, in the following, when distinguishing between the two photoelastic resins 2, the photoelastic resin 2 on one side in the second direction is referred to as a photoelastic resin 2A, and the photoelastic resin 2 on the other side in the second direction is referred to. , Called photoelastic resin 2B.

The photoelastic resin 2 is not particularly limited as long as it is a resin exhibiting translucency and photoelasticity, and examples thereof include polyurethane resin, vinyl chloride resin, and acrylic resin. These photoelastic resins can be used alone or in combination of two or more. As the photoelastic resin 2, a polyurethane resin (photoelastic polyurethane resin) is preferably used from the viewpoint of ease of manufacture.

The polyurethane resin (photoelastic polyurethane resin) can be obtained, for example, in accordance with the method described in the internationally published WO2016 / 125905 pamphlet.

More specifically, the polyurethane resin can be obtained as a reaction product by reacting and curing a polyurethane resin composition containing a polyisocyanate component and an active hydrogen group-containing component.

The polyisocyanate component preferably contains an aromatic ring-containing polyisocyanate. In addition, the aromatic ring-containing polyisocyanate preferably has a 1,4-phenylene group (however, some hydrogen atoms in the 1,4-phenylene group may be substituted with a methyl group and / or a methoxy group. ) And / or contains a 1,5-naphthylene group.

Examples of the aromatic ring-containing polyisocyanis containing a 1,4-phenylene group include polymers of 4,4'-diphenylmethane diisocyanate (4,4'-MDI) and 4,4'-diphenylmethane diisocyanate (carbodiimide-modified MDI,). Ureton imine-modified MDI, acylurea-modified MDI, etc.), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 3,3'-dimethylbiphenyl-4,4'-diisocyanate (TODI), 3,3'- Dimethoxybiphenyl-4,4'-diisocyanis, p-phenylenediocyanate, 4,4'-diphenyldiisocyanis, 4,4'-diphenylether diisocyanate, 2,4-tolylene diisocyanate (2,4-TDI), 1,4- Examples thereof include benzene ring-containing polyisocyanates (specifically, benzene ring-containing diisocyanates) such as xylylene diisocyanate (1,4-XDI).

The aromatic ring-containing polyisocyanate containing a 1,5-naphthylene group includes, for example, a naphthalene ring-containing polyisocyanate (specifically, a naphthalene ring-containing) such as 1,5-naphthalene diisocyanate (1,5-NDI). Diisocyanate) and the like.

These 1,4-phenylene group and / or 1,5-naphthylene group-containing aromatic ring-containing polyisocyanate can be used alone or in combination of two or more.

Of the aromatic ring-containing polyisocyanates containing a 1,4-phenylene group and / or a 1,5-naphthylene group, preferably 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 3,3'- Examples thereof include dimethylbiphenyl-4,4'-diisocyanate (TODI) and 1,5-naphthalenediocyanate (1,5-NDI).

Further, the polyisocyanate component may also contain a polyisocyanate other than the above-mentioned aromatic ring-containing polyisocyanate (hereinafter, other polyisocyanates).

Examples of other polyisocyanates include aromatic polyisocyanates (excluding the above-mentioned aromatic ring-containing polyisocyanates), aromatic aliphatic polyisocyanates, (excluding the above-mentioned aromatic ring-containing polyisocyanates), alicyclic polyisocyanates, and fats. Examples include group polyisocyanates.

Examples of the aromatic polyisocyanate include aromatic diisocyanates such as 2,2'-MDI, 2,6-TDI, m-phenylenediisocyanate, and 2,6-NDI.

Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as 1,3-xylene diisocyanate (1,3-XDI) and tetramethylxylene diisocyanate (TMXDI).

Examples of the alicyclic polyisocyanate include 3-isosianatomethyl-3,5,5-trimethylcyclohexylisocyanate (isophorone diisocyanate, IPDI), 4,4'-, 2,4'-or 2,2'-dicyclohexyl. diisocyanate or mixtures thereof _(H 12 MDI), 1,3-bis (isocyanatomethyl) cyclohexane (hydrogenated xylylene _{diisocyanate,} H 6 _XDI), 2,5- or 2,6-bis (isocyanatomethyl) norbornane Or a mixture thereof (NBDI), 1,3-cyclopentane diisocyanate, 1,4- or 1,3-cyclohexanediisocyanate or a mixture thereof, a fat such as methyl-2,4-cyclohexanediisocyanate, methyl-2,6-cyclohexanediisocyanate. Examples include cyclic diisocyanate.

Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate (TMDI), pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), 1,2-, 2,3- or 1,3-butylenediocyanate. , 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate and other aliphatic diisocyanates.

Other polyisocyanates can be used alone or in combination of two or more.

When the polyisocyanate component contains another polyisocyanate and an aromatic ring-containing polyisocyanate containing a 1,4-phenylene group and / or a 1,5-naphthylene group, the 1,4-phenylene group and / or Alternatively, the ratio of the aromatic ring-containing polyisocyanate containing a 1,5-naphthylene group is, for example, 30% by mass or more, more preferably 50% by mass or more, and particularly preferably 90% by mass, based on the total amount of the polyisocyanate component. % Or more.

The polyisocyanate component is preferably composed of an aromatic ring-containing polyisocyanate containing a 1,4-phenylene group and / or a 1,5-naphthylene group without containing other polyisocyanates.

The active hydrogen group-containing component is a compound having an active hydrogen group (for example, a hydroxyl group, an amino group, etc.), and examples thereof include polyols and polyamines, with preference given to polyols.

The polyol preferably contains a high molecular weight polyol.

The high molecular weight polyol is a compound having two or more hydroxyl groups and having an average hydroxyl value (described later) of 500 mgKOH / g or less.

The high molecular weight polyol preferably includes a compound having an average hydroxyl value (described later) of 20 to 500 mgKOH / g. When the average number of functional groups (described later) is 2, a compound having a number average molecular weight of 225 or more can be mentioned, and when the average number of functional groups (described later) is 3, a compound having a number average molecular weight of 337 or more can be mentioned. Can be mentioned.

The average hydroxyl value of the high molecular weight polyol is 20 mgKOH / g or more, preferably 80 mgKOH / g or more, more preferably 100 mgKOH / g or more, 500 mgKOH / g or less, preferably 300 mgKOH / g or less, more preferably. It is 250 mgKOH / g or less, more preferably 220 mgKOH / g or less.

The hydroxyl value (unit: mgKOH / g) of the high molecular weight polyol can be obtained from an acetylation method or a phthalation method based on the A method or the B method of JIS K 1557-1.

The average hydroxyl value (unit: mgKOH / g) of the high molecular weight polyol is the same as the hydroxyl value of the high molecular weight polyol when the high molecular weight polyol is used alone. On the other hand, the average hydroxyl value of the high molecular weight polyol is the average value of the high molecular weight polyols when they are used in combination.

If the average hydroxyl value of the high molecular weight polyol exceeds the above range, the Young's modulus of the polyurethane resin becomes too high, and a desired photoelastic constant (absolute value) may not be obtained. On the other hand, if the average hydroxyl value is less than the above range, the glass transition temperature may become excessively low, and workability and scratch resistance may decrease.

The average number of functional groups of the high molecular weight polyol is, for example, 1.9 or more, preferably 2.0 or more, and for example, 3 or less, preferably 2.5 or less, and more preferably 2.2 or less.

The number of functional groups of the high molecular weight polyol is the number of hydroxyl groups of the high molecular weight polyol, specifically, the number of active hydroxyl groups per molecule.

The average number of functional groups of the high molecular weight polyol is the average value of the active hydroxyl groups per molecule of the high molecular weight polyol. That is, when high molecular weight polyols having different functional groups are mixed (combined), the numerical value indicating the ratio of the number of active hydroxyl groups of the mixture to the number of molecules of the high molecular weight polyol mixture is the average of the high molecular weight polyols. The number of functional groups.

The average number of functional groups of the high molecular weight polyol can also be obtained from the following formula (B).

Average number of functional groups = total of (number of functional groups of each high molecular weight polyol x equivalent number) / total number of equivalent numbers of each high molecular weight polyol (B)
The number average molecular weight of the high molecular weight polyol is, for example, 225 or more, preferably 500 or more, and for example, 20,000 or less, preferably 15,000 or less.

The number average molecular weight can be obtained from the following formula (C).

Number average molecular weight = 56100 x average number of functional groups / average hydroxyl value (C)
If the average number of functional groups of the high molecular weight polyol exceeds the above range, it may be difficult to obtain a desired photoelastic constant (absolute value) in the polyurethane resin. On the other hand, if the average number of functional groups is less than the above range, the Young's modulus may become too low and the processability and scratch resistance may decrease.

Examples of such high molecular weight polyols include polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, dimer polyols, polyurethane polyols, polyoxyalkylene polyester block copolymer polyols, acrylic polyols, epoxy polyols, and natural oil polyols. Examples thereof include silicone polyols and fluoropolyesters. These can be used alone or in combination of two or more.

The high molecular weight polyol preferably includes a polyether polyol, a polyester polyol, a polycarbonate polyol, and a polyolefin polyol, and more preferably a polytetramethylene ether polyol and a polycarbonate polyol, and particularly preferably a polytetramethylene ether glycol.

Further, the polyol may contain a low molecular weight polyol in addition to the above-mentioned high molecular weight polyol.

When the polyol contains a low molecular weight polyol, the average hydroxyl value of the polyol is increased, and the isocyanate index (described later) is adjusted to a desired value by that amount, so that the above-mentioned polyisocyanate component (preferably containing an aromatic ring) is contained. Polyisocyanate) can be blended in a large amount in the polyurethane resin composition. Therefore, the absolute value of the photoelastic constant of the polyurethane resin can be increased.

The low molecular weight polyol is a compound having two or more hydroxyl groups and having an average hydroxyl value (described later) exceeding 500 mgKOH / g.

As the low molecular weight polyol, preferably, a compound having an average hydroxyl value (described later) exceeding 500 mgKOH / g and 3000 mgKOH / g or less can be mentioned, and when the number of functional groups (described later) is 2, the molecular weight is 40 or more. When the diol is less than 225 and the number of functional groups (described later) is 3, a triol having a molecular weight of 40 or more and less than 337 can be mentioned.

Examples of such low molecular weight polyols include ethylene glycol, propylene glycol (1,2-propanediol), trimethylene glycol (1,3-propanediol), and 1,4-butylene glycol (1,4-butanediol). ), An aliphatic diol (2 to 13 carbon atoms) such as 1,3-butylene glycol (1,3-butanediol), an alicyclic diol (6 to 13 carbon atoms) such as cyclohexanedimethanol, and further. For example, aromatic diols such as bishydroxyethoxybenzene and xylene glycol (aromatic ring-containing diols containing an aromatic ring and having 6 to 13 carbon atoms), and further, diethylene glycol, trioxyethylene glycol, tetraoxyethylene glycol, and di. Diols (2-9 carbon atoms) (divalent alcohols) such as oxyalkylene alcohols such as propylene glycol and trioxypropylene glycol, such as glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2, Aliphatic triols having 3 to 6 carbon atoms such as 4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol, trimethylolpropane, 2,2-bis (hydroxymethyl) -3-butanol, and Other triols (trivalent alcohols) such as aliphatic triols (7 to 20 carbon atoms), for example, tetraols (tetravalent alcohols) such as tetramethylolmethane (pentaerythritol) and diglycerin (diglycerol) (5 carbon atoms). ~ 27) and the like.

These low molecular weight polyols can be used alone or in combination of two or more.

The low molecular weight polyol preferably includes a dihydric alcohol and a trihydric alcohol, more preferably a trihydric alcohol, and further preferably an aliphatic triol having 3 to 6 carbon atoms, and particularly preferably. , Trimethylolpropane.

The blending ratio of the low molecular weight polyol is, for example, 0.1 part by mass or more, preferably 0.5 part by mass or more, and for example, 30 parts by mass or less, preferably 20 parts by mass with respect to 100 parts by mass of the high molecular weight polyol. It is less than or equal to parts by mass, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less.

If the blending ratio of the low molecular weight polyol exceeds the above range, the polyurethane resin may become opaque and light may not pass through the polyurethane resin, or the Young's modulus of the polyurethane resin may become too high.

Suitable combinations of the components to be blended in the polyurethane resin composition include, for example, a combination of an aromatic ring-containing polyisocyanate containing a 1,4-phenylene group, a polyether polyol, and triol. Is a combination of a benzene ring-containing diisocyanate, a polytetramethylene ether polyol, and an aliphatic triol.

Then, the polyurethane resin can be obtained from the polyurethane resin composition thus obtained by reacting a polyisocyanate component with an active hydrogen group-containing component to cure and mold the polyurethane resin composition.

In order to react the polyisocyanate component with the active hydrogen group-containing component, a known molding method such as a one-shot method or a prepolymer method can be applied.

In the one-shot method, for example, the polyisocyanate component and the active hydrogen group-containing component have an isocyanate index (value obtained by multiplying the ratio of the isocyanate group concentration to the hydroxyl group concentration by 100, NCO concentration / hydroxyl group concentration × 100), for example, 70. Formulated (mixed) to ~ 400, preferably 80 to 150, and injected into a mold, eg, at 0 ° C. to 250 ° C., preferably at room temperature (20 ° C.) to 150 ° C. For example, the curing reaction is carried out for 1 minute to 7 days, preferably 10 minutes to 2 days.

In this curing reaction, for example, a known urethanization catalyst such as an organometallic catalyst or an amine catalyst can be added. Further, the above-mentioned curing reaction can also be carried out in the presence of a known solvent.

Then, a polyurethane resin (photoelastic polyurethane resin) molded into a predetermined shape can be obtained by injecting it into a molding mold, subjecting it to a curing reaction, removing the mold, and processing the outer shape as necessary.

In the prepolymer method, for example, first, a polyisocyanate component and a part of an active hydrogen group-containing component (for example, a high molecular weight polyol) are reacted to synthesize an isocyanate group-terminated prepolymer having an isocyanate group at the molecular terminal. Next, the obtained isocyanate group-terminated prepolymer and the rest of the active hydrogen group-containing component (chain extender: for example, a low molecular weight polyol (and a high molecular weight polyol if necessary)) are reacted (chain extension) to carry out a curing reaction. Let me.

Then, a polyurethane resin (photoelastic polyurethane resin) molded into a predetermined shape can be obtained by injecting it into a molding mold, subjecting it to a curing reaction, removing the mold, and processing the outer shape as necessary.

The above-mentioned polyurethane resin composition or polyurethane resin (photoelastic resin 2) is provided with, for example, a defoaming agent, a plasticizer, a leveling agent, a matting agent, a flame retardant, a rocking agent, and an adhesive, if necessary. Known additives such as agents, thickeners, lubricants, antistatic agents, surfactants, reaction retarders, dehydrating agents, antioxidants, ultraviolet absorbers, antioxidants, and weather stabilizers should be added as appropriate. Can be done.

Then, the polyurethane resin can cause birefringence in the light (for example, laser light) passing through the inside of the photoelastic resin 2 due to the generation of photoelasticity, that is, stress based on bending or the like.

Therefore, it can be suitably used as the photoelastic resin 2 of the bending sensor 1.

The absolute value of the photoelastic constant of the photoelastic resin 2 at 25 ° C. is 20 × 10 ^-12 Pa ^-1 or more, preferably 500 × 10 ^-12 Pa ^-1 or more, more preferably 1000 × 10 ^-12 Pa ^{−. 1} or more, more preferably 2000 × 10 ^-12 Pa ^-1 or more, particularly preferably 3000 × 10 ^-12 Pa ^-1 or more, and 1 × 10 ^-5 Pa ^-1 or less (= 10000000 × 10 ^-12 Pa). ^-1 or less), preferably 1 × 10 ^-6 Pa ^-1 or less (= 1000000 × 10 ^-12 Pa ^-1 or less), more preferably 1 × 10 ^-7 Pa ^-1 or less (= 100000 × 10 ^-12) Pa ^-1 or less), more preferably 1 × 10 ^-8 Pa ^-1 or less (= 10000 × 10 ^-12 Pa ^-1 or less), and particularly preferably 8000 × 10 ^-12 Pa ^-1 or less.

When the absolute value of the photoelastic constant is in the above range, the excellent photoelasticity required for the bending sensor 1 can be secured.

The photoelastic constants of the photoelastic resin 2 are described in "Development of Photoelastic Constant Measurement System for Optical Films" by Mitsuo Tsukiji, Hiroyuki Takakazu, and Yoshiro Tadashi, Journal of the Japan Society of Precision Science 73, 253-258 (2007). It can be measured according to the description of "Photoelastic constant measuring method".

Further, along with the measurement of the photoelastic constant, the strain optical constant and Young's modulus of the photoelastic resin 2 are obtained.

The strain optical constant of the photoelastic resin 2 indicates the ratio of the strength of birefringence generated by such deformation to the amount of deformation (bending) of the photoelastic resin 2.

The photoelastic constant, the distorted optical constant, and Young's modulus satisfy the following equation (1).

Photoelastic constant = Distorted optical constant ÷ Young's modulus (1)
Therefore, in order to set the photoelastic constant of the photoelastic resin 2 in the above-mentioned desired range, the strain optical constant and Young's modulus are adjusted.

Specifically, the higher the strain optical constant and the lower the Young's modulus, the higher the photoelastic constant, but if the Young's modulus is excessively low, the moldability and flexibility may decrease.

Therefore, the Young's modulus of the photoelastic resin 2 at 25 ° C. is 2.0 MPa or more, preferably 3.0 MPa or more, more preferably 4.0 MPa or more, 5.0 MPa or less, preferably 4.9 MPa or less. , More preferably, it is 4.8 MPa or less.

When the Young's modulus of the photoelastic resin 2 is less than the above range, the photoelastic resin 2 is too soft and easily damaged, and the workability is lowered. When the Young's modulus of the photoelastic resin 2 exceeds the above range, the photoelastic resin 2 is too hard and the photoelasticity is lowered.

Preferably, in order to obtain the above-mentioned desired photoelastic constant, when the Young's modulus of the photoelastic resin 2 at 25 ° C. is 2 MPa or more and 3 MPa or less, the strain optical constant at 25 ° C. is, for example, 6000 × ^10-6. or (usually, 10000 × ^{10 -6} or less), and when 25 ° C. Young's modulus of photoelasticity resin 2 exceeds the 3MPa following 5MPa, the strain-optical constants of 25 ° C., for example, 10000 × 10 ^{- 6} or more (usually 30000 × ^10-6 or less).

The glass transition temperature of the photoelastic resin 2 is, for example, −60 ° C. or higher, preferably −50 ° C. or higher, more preferably −40 ° C. or higher, and for example, less than 25 ° C., preferably less than 0 ° C. Preferably, it is less than -25 ° C.

If the glass transition temperature of the photoelastic resin 2 is less than the above-mentioned lower limit, the processability and scratch resistance of the photoelastic resin 2 may decrease. Further, when the glass transition temperature of the photoelastic resin 2 is equal to or higher than the above-mentioned upper limit, it may be difficult to obtain the above-mentioned desired photoelastic constant.

The glass transition temperature of the photoelastic resin 2 can be obtained by measuring the temperature dispersion mode (heating rate 5 ° C./min) at a frequency of 10 Hz using a dynamic viscoelasticity measuring device.

Further, in the above-mentioned measurement of the glass transition temperature, a storage elongation elastic modulus E ″, a loss elongation elastic modulus E ″ and a loss tangent tan δ can be obtained at the same time.

The storage elongation elastic modulus E'of the photoelastic resin 2 at 25 ° C. is, for example, 1 × 10 ⁶ to 1 × 10 ⁸ Pa, and the loss elongation elastic modulus E ″ at 25 ° C. is, for example, 1 × 10 ⁴ to 1. It is 1 × 10 ⁸ Pa, and the loss tangent tan δ at 25 ° C. is, for example, 0.01 to 0.2.

The refractive index of the photoelastic resin 2 is 1.30 or more, preferably 1.35 or more, more preferably 1.40 or more, still more preferably 1.45 or more, and particularly preferably 1.50 or more. It is 1.80 or less, preferably 1.70 or less, more preferably 1.65 or less, still more preferably 1.60 or less, and particularly preferably 1.55 or less.

When the refractive index is in the above range, birefringence can be generated according to the degree of bending of the photoelastic resin 2 and the amount of light can be attenuated.

When the photoelastic resin 2 is bent, the light passing through the inside thereof depends on the degree of bending with respect to the side wall of the photoelastic resin 2 (the interface between the inside and the outside of the photoelastic resin 2) at the bent portion. It is incident at an angle. In this case, if the degree of bending is less than the critical angle, the light leaks to the outside without being totally reflected inside the photoelastic resin 2.

Therefore, in the following, the phenomenon that the light is attenuated by the birefringence corresponding to the bending of the photoelastic resin 2 and the leakage to the outside is included as the attenuation of the light caused by the bending of the photoelastic resin 2.

Then, as shown in FIG. 1, a plurality of photoelastic resin 2s (two in FIG. 1) are provided in the bending sensor 1. Each photoelastic resin 2 may be formed of the same photoelastic resin (polyurethane resin or the like), or may be formed of different photoelastic resins (polyurethane resin or the like). Preferably, each photoelastic resin 2 is formed of the same photoelastic resin.

Further, as shown in FIG. 1, each photoelastic resin 2 is formed into a rod shape extending along the first direction. In molding the photoelastic resin 2, as described above, a molding mold having a desired shape may be used, or the photoelastic resin 2 may be cut after being removed from the mold. Further, for example, by using a molding die (tube) made of a resin material (silicone resin or the like) described later as the molding die, a photoelastic resin 2 coated with the resin material can be obtained, and further, the resin material can be used. The coated photoelastic resin 2 can be used as it is for the bending sensor 1.

The size of the photoelastic resin 2 is not particularly limited, but the length (length in the first direction) is, for example, 10 mm or more, preferably 30 mm or more, and for example, 2000 mm or less, preferably 300 mm or less. The thickness (length in the second direction) is, for example, 0.1 mm or more, preferably 0.5 mm or more, and for example, 10 mm or less, preferably 10 mm or less.

In FIG. 1, the cover member 3 is provided to protect the photoelastic resin 2 without hindering the bending of the photoelastic resin 2 and to fix the relative positions of the plurality of photoelastic resins 2.

The cover member 3 is made of, for example, a known resin material, and the plurality of photoelastic resins 2 are bound by the resin material.

The resin material constituting the cover member 3 is not particularly limited, and examples thereof include silicone resin, isoprene resin, butadiene resin, chloroprene resin, acrylic resin, and polyurethane resin. These can be used alone or in combination of two or more.

As the resin material, a silicone resin is preferable.

If the cover member 3 is a silicone resin, the photoelastic resin 2 can be satisfactorily protected without hindering the bending of the photoelastic resin 2, and the relative positions of the plurality of photoelastic resins 2 can be satisfactorily positioned. Can be fixed.

The refractive index of the cover member 3 is less than or equal to the refractive index of the photoelastic resin 2 and preferably less than the refractive index of the photoelastic resin 2. More specifically, the refractive index of the cover member 3 is, for example, 1.5 or less, preferably 1.45 or less, more preferably 1.43 or less, and usually 1.2 or more. ..

If the refractive index of the cover member 3 exceeds the above upper limit, light is reflected at the interface between the photoelastic resin 2 and the cover member 3, so that the detection sensitivity may decrease.

As shown in FIG. 1, the optical sensor 4 has a light emitting portion 7 arranged on one side in the first direction (longitudinal direction of the photoelastic resin 2) and the other side in the first direction (longitudinal direction of the photoelastic resin 2). It is provided with a light receiving unit 8 arranged in.

The light emitting unit 7 includes a cap member and a light emitting member arranged inside the cap member. The cap member is a resin member formed in a substantially elliptical cylinder with a bottom, and the photoelastic resin 2 and the cover member 3 are sealed at one end in the first direction (longitudinal direction of the photoelastic resin 2). ..

A plurality of light emitting members are provided, for example, according to the number of photoelastic resins 2, and at the bottom of the cap member, with one end surface of each photoelastic resin 2 in the first direction (longitudinal direction of the photoelastic resin 2). They are arranged facing each other. As a result, each light emitting member allows light to be incident on each photoelastic resin 2 from one side end surface in the first direction (longitudinal direction of the photoelastic resin 2). The light emitting member is not particularly limited, and examples thereof include a semiconductor laser (wavelength 405 nm to 1064 nm), a light emitting diode, a fluorescent lamp, a halogen lamp, and a Hungsten lamp.

Further, the light emitting unit 7 may be provided with an optical waveguide such as an optical fiber, if necessary, so that light can be incident on the photoelastic resin 2 from the light emitting member via the optical waveguide.

Further, the light emitting unit 7 is electrically connected to the control unit 6 as shown by a virtual line in FIG.

The control unit 6 is an ECU (Electronic Control Unit) that electrically controls the light emitting unit 7, and includes a calculation unit as a calculation area and a memory unit as a storage area. ON / OFF of light emission of the light emitting member is controlled according to the electric signal emitted from such a control unit 6.

The light receiving unit 8 includes a cap member and a light receiving member arranged inside the cap member. The cap member is a resin member formed in a substantially elliptical cylinder with a bottom, and the photoelastic resin 2 and the cover member 3 are sealed at the other end in the longitudinal direction of the photoelastic resin 2 and the cover member 3. ..

A plurality of light receiving members are provided, for example, according to the number of photoelastic resins 2, and at the bottom of the cap member, with the other end surface of each photoelastic resin 2 in the first direction (longitudinal direction of the photoelastic resin 2). They are arranged facing each other. As a result, each light receiving member can receive light that has passed through each photoelastic resin 2 from one side in the longitudinal direction to the other side. Examples of the light receiving member include elements capable of converting the intensity of received light into an electric signal (optical signal), and examples thereof include a photodiode.

Further, the light receiving unit 8 may be provided with a reflecting member such as a reflecting plate, if necessary, so that light can be introduced from the photoelastic resin 2 to the light receiving member via the reflecting member.

Further, as shown by a virtual line in FIG. 1, a processing unit 5 is electrically connected to the light receiving unit 8.

The processing unit 5 is provided to detect the bending direction of the photoelastic resin 2 based on the optical signal detected by the light receiving unit 8.

The processing unit 5 is an analysis processing unit for analyzing the intensity of light received by the light receiving unit 8, and includes a calculation unit as a calculation area and a memory unit as a storage area.

The memory unit of the processing unit 5 stores a bending detection program for detecting the bending direction by a method described later. As a result, the processing unit 5 can detect the bending direction of the photoelastic resin 2 based on an optical signal (for example, a voltage value) based on the light detected by the light receiving unit 8 by the following detection method.

Next, a detection method for detecting the bending direction of the photoelastic resin 2 using the bending sensor 1 will be described with reference to FIGS. 1 and 2. Note that FIG. 2 shows an excerpt of the photoelastic resin 2 in FIG.

In this detection method, first, light is incident on each photoelastic resin 2 (photoelastic resin 2A and photoelastic resin 2B) from a light emitting member (diode or the like) of the light emitting unit 7 under the control of the control unit 6.

Then, the light that has passed through each photoelastic resin 2 (photoelastic resin 2A and photoelastic resin 2B) is received by a light receiving member (photodiode or the like) of the light receiving unit 8, and the intensity of the received light is an optical signal. Is input to the processing unit 5. For example, when a photodiode is used as a light receiving member, the intensity of light that has passed through each photoelastic resin 2 is converted into a voltage value by the photodiode, and each voltage value is input to the processing unit 5 as an optical signal (electric signal). To do.

At this time, as shown in FIG. 2A, if the photoelastic resin 2 is not bent, the light incident on each photoelastic resin 2 from the light emitting portion 7 is attenuated due to the bending of the photoelastic resin 2. It passes through each photoelastic resin 2 and is received by the light receiving unit 8 without causing the above.

That is, if the photoelastic resin 2A is not bent, the intensity of the light received by the light receiving portion 8 (light receiving intensity _{LR (A)} ) is the intensity of the light incident on the photoelastic resin 2A (emission intensity LE (emission intensity LE _{). A)} ) is about the same as ( _{LR (A)} ≒ LE _(A) ).

The same degree includes the intensity when a part of the light generated in the light emitting unit 7 is slightly attenuated, for example, by being absorbed by the photoelastic resin 2.

Similarly, if the photoelastic resin 2B is not bent, the intensity of the light received by the light receiving portion 8 (light receiving intensity _{LR (B)} ) is also the intensity of the light incident on the photoelastic resin 2B (emission intensity). It is about the same as _{LE (B)} ) ( _{LR (B)} ≈ LE _(B) ).

In other words, in each of the photoelastic resin 2, and the intensity of light incident on each optical elastic resin 2 (the light reception intensity L _R), the intensity of light passing through the respective photoelastic resin 2 (emission intensity L _E) When is about the same, the processing unit 5 can determine that the damping caused by the bending of the photoelastic resin 2 has not occurred, and thereby it can be determined that the photoelastic resin 2 is not bent.

On the other hand, for example, as shown in FIG. 2B, the photoelastic resin 2A and the photoelastic resin 2 so that the other side end portion (light receiving side end portion) in the first direction of the photoelastic resin 2 faces one side in the second direction. When the resin 2B is bent, the light incident on each photoelastic resin 2 causes attenuation due to the bending of the photoelastic resin 2. That is, the light generated in the light emitting unit 7 passes through each photoelastic resin 2 while being attenuated by birefringence and leakage, and is received by the light receiving unit 8.

That is, when the photoelastic resin 2A is bent as shown in FIG. 2B, the intensity of the light received on the photoelastic resin 2A side (light receiving intensity _{LR (A)} ) is incident on the photoelastic resin 2A. It is smaller than the light intensity (emission intensity LE _(A) ) ( _{LR (A)} <LE _(A) ). As a result, the optical signal (voltage value, etc.) generated from the light receiving member (photodiode) on the photoelastic resin 2A side is lower than that in the case where it is not bent.

Similarly, when the photoelastic resin 2B is bent as shown in FIG. 2B, the intensity of the light received on the photoelastic resin 2B side (light receiving intensity _{LR (B)} ) is also the photoelastic resin 2B. It is smaller than the intensity of the light incident on the light (emission intensity LE _(B) ) ( _{LR (B)} <LE _(B) ). As a result, the optical signal (voltage value, etc.) generated from the light receiving member (photodiode) on the photoelastic resin 2B side is also reduced as compared with the case where it is not bent.

Thus, each photoelastic resin 2 Oite, than the intensity of light incident on each optical elastic resin 2 (emission intensity L _E), the intensity of the light passing through the respective photoelastic resin 2 (the light reception intensity L _R) is If it is small, the processing unit 5 can determine that the damping caused by the bending has occurred, and can determine that the bending sensor 1 is bent. Further, since the larger the bending angle is, the larger the attenuation caused by the bending is, the bending angle can be estimated based on the degree of light attenuation.

Further, in the above-mentioned bending sensor 1, the degree of bending of the photoelastic resin 2B arranged inside in the bending direction is larger than the degree of bending of the photoelastic resin 2A arranged outside in the bending direction. Become.

Therefore, the degree of light attenuation generated by the photoelastic resin 2B arranged inside the bending direction is larger than the degree of light attenuation generated by the photoelastic resin 2A arranged outside the bending direction.

As a result, when the photoelastic resin 2 is bent as shown in FIG. 2B, the intensity of the light (light receiving intensity _{LR (B)} ) that passes through the photoelastic resin 2B and is received by the light receiving unit 8 is changed to the photoelastic resin. It is smaller than the intensity of light that passes through 2A and is received by the light receiving unit 8 (light receiving intensity _{LR (A)} ) ( _{LR (B)} < _{LR (A)} ).

In other words, when the intensity of light passing through the photoelastic resin 2B (light receiving intensity _{LR (B)} ) is smaller than the intensity of light passing through the photoelastic resin 2A (light receiving intensity _{LR (A)} ) ( In _{LR (B)} < _{LR (A)} ), the processing unit 5 can determine that the bending sensor 1 is bent so that the photoelastic resin 2B is inside the photoelastic resin 2A.

On the other hand, for example, as shown in FIG. 2C, the photoelastic resin 2A so that the other side end portion (light receiving side end portion) of the photoelastic resin 2 in the first direction faces the other side in the second direction. And even when the photoelastic resin 2B is bent, the light incident on each photoelastic resin 2 causes attenuation due to the bending of the photoelastic resin 2. That is, the light generated in the light emitting unit 7 passes through each photoelastic resin 2 while being attenuated by birefringence and leakage, and is received by the light receiving unit 8.

That is, when the photoelastic resin 2A is bent as shown in FIG. 2C, the intensity of the light received on the photoelastic resin 2A side (light receiving intensity _{LR (A)} ) is incident on the photoelastic resin 2A. It is smaller than the light intensity (emission intensity LE _(A) ) ( _{LR (A)} <LE _(A) ). As a result, the optical signal (voltage value, etc.) generated from the light receiving member (photodiode) on the photoelastic resin 2A side is lower than that in the case where it is not bent.

Similarly, when the photoelastic resin 2B is bent as shown in FIG. 2C, the intensity of the light received on the photoelastic resin 2B side (light receiving intensity _{LR (B)} ) is also the photoelastic resin 2B. It is smaller than the intensity of the light incident on the light (emission intensity LE _(B) ) ( _{LR (B)} <LE _(B) ). As a result, the optical signal (voltage value, etc.) generated from the light receiving member (photodiode) on the photoelastic resin 2B side is also reduced as compared with the case where it is not bent.

As described above, in each photoelastic resin 2, when the intensity of light passing through each photoelastic resin 2 (light receiving intensity LR) is smaller than the intensity of light incident on each photoelastic resin 2 (emission intensity LE). , The processing unit 5 can determine that the damping caused by the bending has occurred, and can determine that the bending sensor 1 is bent. Further, since the larger the bending angle is, the larger the attenuation caused by the bending is, the bending angle can be estimated based on the degree of light attenuation.

Further, in the above bending sensor 1, the degree of bending of the photoelastic resin 2A arranged inside in the bending direction is larger than the degree of bending of the photoelastic resin 2B arranged outside in the bending direction. Become.

Therefore, the degree of light attenuation generated by the photoelastic resin 2A arranged inside the bending direction is larger than the degree of light attenuation generated by the photoelastic resin 2B arranged outside the bending direction.

As a result, when the photoelastic resin 2 is bent as shown in FIG. 2C, the intensity of the light (light receiving intensity _{LR (A)} ) that passes through the photoelastic resin 2A and is received by the light receiving unit 8 is changed to the photoelastic resin. It is smaller than the intensity of the light that passes through 2B and is received by the light receiving unit 8 (light receiving intensity _{LR (B)} ) ( _{LR (B)} > _{LR (A)} ).

In other words, when the intensity of light passing through the photoelastic resin 2A (light receiving intensity _{LR (A)} ) is smaller than the intensity of light passing through the photoelastic resin 2B (light receiving intensity _{LR (B)} ) ( _{LR (B)} > _{LR (A)} ), the processing unit 5 can determine that the bending sensor 1 is bent so that the photoelastic resin 2A is inside the photoelastic resin 2B.

In this way, the bending sensor 1 observes the degree of light attenuation in the photoelastic resin 2A and the degree of light attenuation in the photoelastic resin 2B, and compares the differences between them to obtain the photoelastic resin. The bending direction of 2 can be detected.

In the bending sensor 1, the Young's modulus of the photoelastic resin 2, the absolute value of the photoelastic constant, and the refractive index are within a predetermined range. Therefore, when the photoelastic resin 2 is bent, the light passing through the photoelastic resin 2 is attenuated by birefringence according to the degree of bending (curvature) of the photoelastic resin 2, and the photoelastic resin 2 is bent. The light passing through the photoelastic resin leaks to the outside of the photoelastic resin. Then, in the bending sensor 1, a plurality of photoelastic resins 2 are arranged in parallel, and the light passing through each of the photoelastic resins 2 is detected by the optical sensor 4. Therefore, the bending direction of the photoelastic resin 2 can be detected by comparing the difference in the degree of light attenuation in each of the photoelastic resins 2.

On the other hand, the bending sensor 1 can detect the bending direction when the bending sensor 1 bends along the second direction, but when the bending sensor 1 bends along the third direction, it can detect the bending direction. Since the degree of light attenuation of the photoelastic resin 2A and the photoelastic resin 2B is about the same ( _{LR (B)} < _{LR (A)} ), the bending direction cannot be detected.

Therefore, when detecting the bending direction in the third direction in addition to the bending direction in the second direction, three or more photoelastic resins 2 are arranged in the direction orthogonal to the longitudinal direction as shown below. ..

More specifically, for example, as shown in FIG. 3 as the second embodiment, the bending sensor 1 can include three photoelastic resins 2 extending along the first direction.

Hereinafter, the three photoelastic resins 2 will be referred to as photoelastic resin 2A, photoelastic resin 2B and photoelastic resin 2C, respectively.

In the second embodiment, the photoelastic resin 2A and the photoelastic resin 2B are arranged in parallel along the second direction orthogonal to the first direction, as in the first embodiment described above.

Further, in the second embodiment, the photoelastic resin 2C is parallel to the photoelastic resin 2A and the photoelastic resin 2B along a direction orthogonal to the first direction and intersecting the second direction. It is arranged to do.

That is, each photoelastic resin 2 is arranged so as to be parallel to each other along a plane direction (a plane direction including the second direction and the third direction) orthogonal to the first direction. Preferably, the three photoelastic resins 2 are substantially equilateral triangles in a radial cross-sectional view of the bending sensor 1 (a cross-sectional view along a plane orthogonal to the first direction (a plane including the second and third directions)). It is arranged so that it becomes the apex.

In such a bending sensor 1, as in the first embodiment described above, the degree of bending of the photoelastic resin 2 arranged on the innermost side in the bending direction is the photoelastic resin arranged on the outside in the bending direction. It becomes larger than the degree of bending of 2.

Therefore, the degree of light attenuation generated by the photoelastic resin 2 arranged on the innermost side in the bending direction is larger than the degree of light attenuation generated by the photoelastic resin 2 arranged on the outer side in the bending direction. ..

As a result, even when the photoelastic resin 2 is bent along either the second direction or the third direction, it passes through the photoelastic resin 2 arranged on the innermost side in the bending direction, and the light receiving portion 8 The intensity of the light received in (light receiving intensity _LR ) is smaller than the intensity of the light received by the light receiving unit 8 after passing through the other photoelastic resin 2 (light receiving intensity _LR ).

That is, the processing unit 5 detects the intensity of the light received by the light receiving unit 8 (light receiving intensity _LR ) in each of the photoelastic resins 2, and the light having the lowest light intensity (light receiving intensity _LR ). By specifying the elastic resin 2, the photoelastic resin 2 arranged on the innermost side in the bending direction can be specified. Therefore, in the above bending sensor 1, the light receiving intensity of the photoelastic resin 2A, the light receiving intensity of the photoelastic resin 2B, and the light receiving intensity of the photoelastic resin 2C are compared with each other in the second and third directions. It is possible to detect in which direction of 360 ° in the plane direction including.

In the second embodiment described above, the bending sensor 1 includes three photoelastic resins 2. For example, as shown in FIG. 4 as the third embodiment, the bending sensor 1 is a photoelastic resin 2. It is also possible to have four or more.

More specifically, for example, as shown in FIG. 4 as a third embodiment, the bending sensor 1 can include four photoelastic resins 2 extending along the first direction.

Hereinafter, the four photoelastic resins 2 are referred to as photoelastic resin 2A, photoelastic resin 2B, photoelastic resin 2C, and photoelastic resin 2D, respectively, to distinguish them.

In the third embodiment, the photoelastic resin 2A and the photoelastic resin 2B are arranged in parallel along the second direction orthogonal to the first direction, as in the first embodiment described above.

Further, in the third embodiment, the photoelastic resin 2C is parallel to the photoelastic resin 2A along a third direction (a direction orthogonal to the first direction and orthogonal to the second direction). It is arranged to do.

In addition, in the third embodiment, the photoelastic resin 2D is oriented with respect to the photoelastic resin 2B along a third direction (a direction orthogonal to the first direction and orthogonal to the second direction). They are arranged in parallel.

That is, each photoelastic resin 2 is arranged so as to be parallel to each other along a plane direction (a plane direction including the second direction and the third direction) orthogonal to the first direction. Preferably, the four photoelastic resins 2 have substantially square vertices in a radial cross-sectional view of the bending sensor 1 (a cross-sectional view along a plane orthogonal to the first direction (a plane including the second and third directions)). It is arranged so as to be.

In such a bending sensor 1, as in the first embodiment described above, the degree of bending of the photoelastic resin 2 arranged on the innermost side in the bending direction is the photoelastic resin arranged on the outside in the bending direction. It becomes larger than the degree of bending of 2. Therefore, in the above bending sensor 1, the light receiving intensity of the photoelastic resin 2A, the light receiving intensity of the photoelastic resin 2B, the light receiving intensity of the photoelastic resin 2C, and the light receiving intensity of the photoelastic resin 2D are compared with each other. Therefore, it is possible to more accurately detect which direction of the plane direction 360 ° including the second direction and the third direction is bent.

The more the photoelastic resin 2 is provided in the bending sensor 1, the more accurately the bending direction can be detected. Therefore, the number of photoelastic resins 2 in the bending sensor 1 is preferably 3 or more. On the other hand, the more the photoelastic resin 2 is provided, the lower the production efficiency and the costability. Therefore, the number of the photoelastic resin 2 in the bending sensor 1 is usually 10 or less, preferably 5 or less, more preferably 5. Four or less, particularly preferably three.

Further, the bending sensor 1 is a transmissive sensor in which light is emitted from one side of the photoelastic resin 2 in the first direction and light is emitted from the other side in the first direction. For example, the photoelastic resin 2 Even in a reflective sensor in which light is emitted from one side in the first direction, light is reflected by a retroreflective material on the other side in the first direction, and light is emitted from one side in the first direction of the photoelastic resin 2. Good.

Since such a bending sensor 1 can detect the bending direction, it can be suitably used as a detection member for robots, devices, and the like in various industrial fields.

Next, the present invention will be described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. In addition, "part" and "%" are based on mass unless otherwise specified.

Production Example 1 <Photoelastic resin>
A glass flask was charged with 100 parts by mass of PTG-1000 (polytetramethylene ether glycol, hydroxyl value 111.5 mgKOH / g, manufactured by Hodogaya Chemical Co., Ltd.), dried under reduced pressure at 120 ° C. for 2 hours, and the temperature was 80 ° C. And returned to normal pressure with nitrogen. Next, 9.2 parts by mass (isocyanate index 35) of TODI (3,3'-dimethylbiphenyl-4,4'-diisocyanate, manufactured by Nippon Soda Corporation) was added while stirring. Then, while stirring, 1.0 part by mass of TMP (trimethylolpropane) was added to adjust the temperature to 70 ° C. Next, 20.2 parts by mass (isocyanate index 105) of MDI-PH (4,4'-diphenylmethane diisocyanate, manufactured by Mitsui Chemicals, Inc.) dissolved at 70 ° C. was added, and the mixture was stirred and mixed.

Then, it was defoamed under reduced pressure for 30 seconds, returned to normal pressure with nitrogen, and then taken out from the flask to obtain a polyurethane composition.

Next, the obtained polyurethane composition was poured into a silicone resin tube (molded mold, inner diameter 2.5 mm × length 15 cm, refractive index 1.43, manufactured by Shin-Etsu Polymer Co., Ltd.) and cured at 70 ° C. for 18 hours to form a rod. A photoelastic resin (photoelastic polyurethane resin) having a shape was obtained.

<Evaluation of physical properties of photoelastic polyurethane resin>
(1) Photoelastic constant and Young's modulus "Mitsuo Tsukiji, Hiroyuki Takakazu, Yoshiro Tadashi," Development of Photoelastic Constant Measurement System for Optical Films, "Journal of the Japan Society of Precision Science 73, 253-258 (2007)" The measurement was performed in accordance with the description of "Method for measuring elastic constant", and the strain optical constant and Young's modulus of the photoelastic resin at 25 ° C. were obtained, and the photoelastic constant at 25 ° C. was calculated from them. A laser beam having a wavelength of 630 nm was used for the above measurement. Table 1 shows the photoelastic constant and Young's modulus.

(2) Dynamic viscoelasticity Using a dynamic viscoelasticity measuring device (VES-F-III, VISCO-ELASTICS PECTROMETER, manufactured by Iwamoto Seisakusho Co., Ltd.), a temperature rise rate of 5 ° C./min, frequency of 10 Hz, Measured in a temperature dispersion mode with an amplitude of ± 0.01 mm, the storage elongation elastic modulus (E'), the loss elongation elastic modulus (E'') and the loss positive tangent (tan δ) are obtained, and the loss positive tangent (tan δ) of the obtained data is obtained. The temperature of the peak value of tan δ) was defined as the glass transition temperature (Tg). Table 1 shows the storage elongation elastic modulus (E'), the loss elongation elastic modulus (E ″), the loss tangent (tan δ), and the glass transition temperature (Tg).

(3) Refractive index In a tabletop refractometer (manufactured by Atago Co., Ltd.), a sodium lamp (Fiber-Lite, MODEL3100, manufactured by Dolan-Jenner Industries) was used as a light source, and the refractive index of the photoelastic resin was measured at a measurement temperature of 20 ° C. It was measured.

The results are shown in Table 1.

Example 1 <Bending sensor>
As shown in FIG. 1, a bending sensor was produced using two photoelastic resins obtained in Production Example 1.

That is, the photoelastic resin A and the photoelastic resin B were arranged in parallel, sealed with a silicone resin (refractive index 1.43), and bound to each other.

Further, both ends of each photoelastic resin were cut and smoothed, and a light source and an optical fiber U-48 (trade name, manufactured by KEYENCE) were fixed to one end of each with an adhesive. As a result, light can be incident on each photoelastic resin. Further, at the other end of each photoelastic resin, an amplifier FS-N11MN (trade name, manufactured by KEYENCE) equipped with a photodiode is installed via a reflector in order to detect light that has passed through the photoelastic resin. Connected. Then, the voltage value output from the amplifier was recorded by a data logger NR-600 (trade name, manufactured by KEYENCE).

<< Bending evaluation >>
In the bending sensor, first, two photoelastic resins (photoelastic resin A and photoelastic resin B) were fixed so as to be horizontal in the longitudinal direction, and the light source and the photodiode were calibrated. The output value at this time was taken as the voltage value at bending 0 ° (no bending, FIG. 2A).

Then, when the bending sensor is bent along the vertical direction (bending state 1) and when the photoelastic resin A is bent so as to be on the outside along the parallel direction of the two photoelastic resins (bending). In each of the state 2) and the case where the photoelastic resin A is bent so as to be inside (bending state 3), the voltage at which light is incident on each photoelastic resin from the light source and output via the photodiode. The value was measured. The obtained voltage value graph is shown in FIG.

As shown in FIG. 5, when the photoelastic resin A is bent so as to be on the outside, the voltage value of the light passing through the photoelastic resin A is larger than the voltage value of the light passing through the photoelastic resin B. , I got bigger. On the other hand, when the photoelastic resin A was bent so as to be inside, the voltage value of the light passing through the photoelastic resin A became smaller than the voltage value of the light passing through the photoelastic resin B.

1 Bending sensor 2 Photoelastic resin 3 Cover member 4 Optical sensor 5 Processing unit 6 Control unit 7 Light emitting unit 8 Light receiving unit

Claims (3)

Multiple photoelastic resins extending in the longitudinal direction,
An optical sensor that detects light that has passed through each of multiple photoelastic resins,
A processing unit that detects the bending direction of the photoelastic resin based on the optical signal detected by the optical sensor is provided.
The plurality of the photoelastic resins are arranged in parallel in a direction orthogonal to the longitudinal direction.
The Young's modulus of the photoelastic resin at 25 ° C. is 2 to 5 MPa.
The absolute value of the photoelastic constant of the photoelastic resin at 25 ° C. is 20 × 10 ^-12 Pa ^-1 to 1 × 10 ^-5 Pa ^-1 .
A bending sensor characterized in that the refractive index of the photoelastic resin is 1.30 to 1.80. The bending sensor according to claim 1, wherein three or more of the photoelastic resins are arranged. Further, a cover member for coating the plurality of the photoelastic resins is provided.
The bending sensor according to claim 1 or 2, wherein the refractive index of the cover member is less than the refractive index of the photoelastic resin.