JP7120956B2 - pressure sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure sensor, and more particularly to a pressure sensor comprising a photoelastic polyurethane resin.

Conventionally, it has been proposed to use a photoelastic polyurethane resin such as a polyurethane resin having photoelasticity as a pressure 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 100000×10 ⁻¹² Pa ⁻¹ , and the glass transition temperature is −60° C. to − Light is passed through a resin member made of photoelastic polyurethane resin at 21° C., the light passing through is received by a photodiode, and the attenuation of the light amount is detected, thereby detecting the load applied to the resin member. A pressure sensor has been proposed (see, for example, Patent Document 1 (first embodiment)).

However, with photoelastic polyurethane resin, as the load applied to the photoelastic polyurethane resin increases, the optical signal (voltage) received by the photodiode does not increase at a constant rate, but increases up to a predetermined load. A waveform corresponding to the photoelastic constant is formed such that the load decreases, then increases again until a predetermined load is reached, and then decreases thereafter.

Therefore, there is a problem that a plurality of loads are estimated from the detected optical signal (voltage), and the load cannot be uniquely detected.

Therefore, a method of calculating the load by integrating and analyzing the voltage has been proposed (see Non-Patent Document 1). In this method, by accumulating the voltage, the applied load can be determined uniquely because the load is specified.

International publication WO2016/125905 pamphlet

Masahiko Mitsuka et al., Proceedings of the 28th Japan MRS Annual Meeting (published on December 5, 2018), pp. 154

However, the method of calculating the load by integrating and analyzing the voltage has the problem that the analysis is troublesome and the error is large because the voltage including noise is integrated.

INDUSTRIAL APPLICABILITY The present invention is a pressure sensor that can accurately measure a load with a simple configuration.

The present invention [1] comprises a plurality of photoelastic polyurethane resins having mutually different absolute values of photoelastic constants, an optical sensor for detecting light passing through each of the plurality of photoelastic polyurethane resins, and and a processor to which an optical signal is input, wherein the processor calculates a measured load from the optical signal detected by the optical sensor for each photoelastic polyurethane resin. contains.

In the pressure sensor of the present invention [1], the optical sensor detects light passing through each of a plurality of photoelastic polyurethane resins having different absolute values of photoelastic constants. The detected optical signal differs for each photoelastic polyurethane resin because the absolute values of the photoelastic constants of the plurality of photoelastic polyurethane resins are different from each other. That is, when a specific load is applied, the detected optical signal will be different for each photoelastic polyurethane resin.

Therefore, the processing unit can calculate the measured load from the optical signal that differs for each photoelastic polyurethane resin.

As a result, the load to be measured can be calculated without accumulating optical signals (voltage) detected from one photoelastic polyurethane resin, so that the load can be accurately measured with a simple configuration.

In the present invention [2], the processing unit converts the correlation data between the load applied to the photoelastic polyurethane resin and the intensity of the optical signal passing through the photoelastic polyurethane resin when the load is applied to the A storage area is stored for each photoelastic polyurethane resin, and based on the correlation data from the intensity of the optical signal detected by the optical sensor for each photoelastic polyurethane resin, a plurality of photoelastic polyurethane resins are stored. The sensor according to [1] above, wherein an estimated load is calculated, and an estimated load common to all the photoelastic polyurethane resins is extracted as a measurement load from a plurality of estimated loads calculated for each of the photoelastic polyurethane resins. Contains a pressure sensor.

In the pressure sensor of the present invention [2], the processing unit has a storage area storing correlation data between the load applied to the photoelastic polyurethane resin and the intensity of the optical signal. Then, the processing unit calculates a plurality of estimated loads from the intensity of the detected optical signal for each photoelastic polyurethane resin, and extracts an estimated load common to all photoelastic polyurethane resins as a measured load.

Therefore, the load can be reliably measured by a simple calculation.

The present invention [3] includes the pressure sensor according to [1] or [2] above, wherein the plurality of photoelastic polyurethane resins are arranged to overlap in the direction in which the load is applied. .

In the pressure sensor of the present invention [3], a plurality of photoelastic polyurethane resins are arranged so as to overlap each other in the direction in which the load is applied. Therefore, the applied load uniformly acts on the plurality of photoelastic polyurethane resins. As a result, reliable load measurement can be achieved.

The present invention [4] is the pressure sensor according to [1] or [2] above, wherein the plurality of photoelastic polyurethane resins are arranged side by side in a direction intersecting the direction in which the load is applied. contains.

In the pressure sensor of the present invention [4], a plurality of photoelastic polyurethane resins are arranged side by side in a direction crossing the direction in which the load is applied. Therefore, it is possible to reduce the thickness of the pressure sensor.

In the present invention [5], a portion of the photoelastic polyurethane resin that overlaps with the light path through which the light of the optical sensor passes in the direction in which the load is applied protrudes in the direction opposite to the direction in which the load is applied. The pressure sensor according to any one of [1] to [4] above is included.

In the pressure sensor of the present invention [5], the portion of the photoelastic polyurethane resin that overlaps the optical path protrudes in the direction opposite to the direction in which the load is applied. As such, the measurement object can first come into contact with the protruding portion. Then, a load can be appropriately applied to the portion of the photoelastic polyurethane resin that overlaps the optical path. As a result, more accurate load measurement can be achieved.

The pressure sensor of the present invention can accurately measure a load with a simple configuration.

FIG. 1 is a perspective view showing a first embodiment of the pressure sensor of the present invention. 2A and 2B are perspective views showing selected photoelastic polyurethane resins in the pressure-sensitive sensor shown in FIG. 1, FIG. A photoelastic polyurethane resin is shown, respectively. FIG. 3 is a graph showing an example of correlation data between the load applied to the photoelastic polyurethane resin and the intensity of the light signal that passed through the photoelastic polyurethane resin when the load was applied. An example of correlation data between the load and the voltage value of the photoelastic polyurethane resin A is shown, and FIG. 3B shows an example of correlation data between the load and the voltage value of the photoelastic polyurethane resin B. FIG. FIG. 4 is a schematic diagram showing interference fringes as correlation data between the load applied to the photoelastic polyurethane resin and the intensity of the optical signal that passed through the photoelastic polyurethane resin when the load was applied. FIG. 5 is a perspective view showing a second embodiment of the pressure sensor of the invention. FIG. 6 is a perspective view showing a pressure sensor according to a third embodiment of the present invention. FIG. 7 is a perspective view showing a fourth embodiment of the pressure sensor of the invention.

In the following, among the planar directions in which the photoelastic polyurethane resin extends in sheet form, the longitudinal direction is defined as the first direction (longitudinal direction), and the width direction orthogonal to the first direction is defined as the second direction. 1 to 3 assuming that the thickness direction orthogonal to the third direction (vertical direction).

In FIG. 1, a pressure sensor 1 includes a plurality of photoelastic polyurethane resins 2 having mutually different absolute values of photoelastic constants, an optical sensor 4 for detecting light passing through each of the plurality of photoelastic polyurethane resins 2, a light A control unit 6 for controlling irradiation of light to the elastic polyurethane resin 2 and a processing unit 5 to which an optical signal detected by the optical sensor 4 is input are provided. In addition, in FIG. 1, the processing unit 5 and the control unit 6 are integrally formed. That is, one ECU (described later) serves both the processing unit 5 and the control unit 6 .

In FIG. 1, the photoelastic polyurethane resin 2 is a member made of resin having photoelasticity, and is formed into a substantially rectangular sheet shape extending in a first direction (longitudinal direction) and a second direction (width direction). there is

Moreover, in the pressure-sensitive sensor 1, a plurality of photoelastic polyurethane resins 2 are provided. The number of photoelastic polyurethane resins 2 is two or more, and usually 20 or less, preferably 10 or less, more preferably 5 or less. In addition, FIG. 1 shows a form in which two photoelastic polyurethane resins 2 are provided.

A plurality (two) of photoelastic polyurethane resins 2 are arranged to overlap each other in a third direction (thickness direction) perpendicular to the first direction (longitudinal direction) and second direction (width direction) of the photoelastic polyurethane resin 2. ing. Thus, a polyurethane laminate 3 having a plurality of photoelastic polyurethane resins 2 is formed. The third direction is the direction in which a load described later is applied, and is, for example, the vertical direction, although it varies depending on the application of the pressure sensor 1 .

Hereinafter, when distinguishing between a plurality of (two) photoelastic polyurethane resins 2, the photoelastic polyurethane resin 2 on one side (upper side) in the third direction is referred to as a photoelastic polyurethane resin 2A. The photoelastic polyurethane resin 2 on the other side (lower side) is referred to as a photoelastic polyurethane resin 2B.

A plurality of photoelastic polyurethane resins 2 can be obtained, for example, according to the method described in International Publication WO2016/125905.

The types and amounts of raw material components are appropriately designed so that the photoelastic constants of the plurality of photoelastic polyurethane resins 2 have mutually different absolute values.

More specifically, each photoelastic polyurethane resin 2 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. Further, the aromatic ring-containing polyisocyanate preferably contains a 1,4-phenylene group (with the proviso that some hydrogen atoms in the 1,4-phenylene group may be substituted with methyl groups and/or methoxy groups. ) and/or contain a 1,5-naphthylene group.

Examples of aromatic ring-containing polyisocyanates containing 1,4-phenylene groups include 4,4'-diphenylmethane diisocyanate (4,4'-MDI), polymers of 4,4'-diphenylmethane diisocyanate (carbodiimide-modified MDI, uretonimine-modified MDI, acyl urea-modified MDI, etc.), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 3,3'-dimethylbiphenyl-4,4'-diisocyanate (TODI), 3,3'- Dimethoxybiphenyl-4,4'-diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 4,4'-diphenyl ether diisocyanate, 2,4-tolylene diisocyanate (2,4-TDI), 1,4- Benzene ring-containing polyisocyanates (specifically, benzene ring-containing diisocyanates) such as xylylene diisocyanate (1,4-XDI) are included.

Examples of the aromatic ring-containing polyisocyanate containing a 1,5-naphthylene group include naphthalene ring-containing polyisocyanates such as 1,5-naphthalene diisocyanate (1,5-NDI) (specifically, naphthalene ring-containing diisocyanate) and the like.

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

Among aromatic ring-containing polyisocyanates containing 1,4-phenylene groups and/or 1,5-naphthylene groups, 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 3,3'- Dimethylbiphenyl-4,4'-diisocyanate (TODI) and 1,5-naphthalenediisocyanate (1,5-NDI) can be mentioned.

The polyisocyanate component can also contain polyisocyanates other than the above-described aromatic ring-containing polyisocyanates (hereinafter referred to as other polyisocyanates).

Examples of other polyisocyanates include aromatic polyisocyanates (excluding the above-described aromatic ring-containing polyisocyanates), araliphatic polyisocyanates (excluding the above-described aromatic ring-containing polyisocyanates), alicyclic polyisocyanates, aliphatic group polyisocyanates.

Aromatic polyisocyanates include, for example, aromatic diisocyanates such as 2,2'-MDI, 2,6-TDI, m-phenylene diisocyanate and 2,6-NDI.

Examples of araliphatic polyisocyanates include araliphatic diisocyanates such as 1,3-xylylene diisocyanate (1,3-XDI) and tetramethylxylylene diisocyanate (TMXDI).

Alicyclic polyisocyanates include, for example, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI), 4,4′-, 2,4′- or 2,2′-dicyclohexyl Methane 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 mixtures thereof (NBDI), 1,3-cyclopentane diisocyanate, 1,4- or 1,3-cyclohexane diisocyanate or mixtures thereof, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate. Cyclic diisocyanates are mentioned.

Aliphatic polyisocyanates include, for example, trimethylene diisocyanate, tetramethylene diisocyanate (TMDI), pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), 1,2-, 2,3- or 1,3-butylene diisocyanate. , 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate.

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

When the polyisocyanate component contains other polyisocyanates and aromatic ring-containing polyisocyanates containing 1,4-phenylene groups and/or 1,5-naphthylene groups, 1,4-phenylene groups 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, relative to the total amount of the polyisocyanate component. % or more.

Also, the polyisocyanate component preferably comprises an aromatic ring-containing polyisocyanate containing 1,4-phenylene groups and/or 1,5-naphthylene groups without containing other polyisocyanates.

The active hydrogen group-containing component is a compound having an active hydrogen group (eg, hydroxyl group, amino group, etc.), and examples thereof include polyols and polyamines, preferably polyols.

The polyol preferably contains a high molecular weight polyol.

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

Preferred high-molecular-weight polyols include compounds having an average hydroxyl value (described later) of 20 to 500 mgKOH/g. Further, when the average number of functional groups (described later) is 2, compounds having a number average molecular weight of 225 or more are included, and when the average number of functional groups (described later) is 3, compounds having a number average molecular weight of 337 or more are included. 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, and 500 mgKOH/g or less, preferably 300 mgKOH/g or less, more preferably 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 determined by an acetylation method or a phthalation method conforming to JIS K 1557-1 method A or B.

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 their average value when the high-molecular-weight polyol is used in combination.

If the average hydroxyl value of the high-molecular-weight polyol exceeds the above range, the Young's modulus of the photoelastic polyurethane resin 2 may become too high and the desired photoelastic constant (absolute value) may not be obtained. On the other hand, when the average hydroxyl value is less than the above range, the glass transition temperature becomes excessively low, and workability and scratch resistance may deteriorate.

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

The number of functional groups in a high molecular weight polyol is the number of hydroxyl groups in 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 number of active hydroxyl groups per molecule of the high-molecular-weight polyol. In other words, when high-molecular-weight polyols with different numbers of functional groups are mixed (combined), the ratio of the number of active hydroxyl groups in the mixture to the number of molecules in the mixture of high-molecular-weight polyols is the average of the high-molecular-weight polyols. It is 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 = sum of (number of functional groups of each high molecular weight polyol × number of equivalents) / sum of number of equivalents 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.

A number average molecular weight can be calculated|required from following Formula (C).

Number average molecular weight = 56100 × 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 photoelastic polyurethane resin 2 . 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, resulting in deterioration in workability and scratch resistance.

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, natural oil polyols, Examples include silicone polyols and fluorine polyols. These can be used alone or in combination of two or more.

High molecular weight polyols preferably include polyether polyols, polyester polyols, polycarbonate polyols, and polyolefin polyols, more preferably polytetramethylene ether polyols, polycarbonate polyols, and most preferably polytetramethylene ether glycol.

In addition to the high-molecular-weight polyols described above, the polyols can also contain low-molecular-weight polyols.

By containing a low molecular weight polyol in the 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. polyisocyanate) can be blended into the polyurethane resin composition. Therefore, the absolute value of the photoelastic constant of the photoelastic polyurethane resin 2 can be increased.

A 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.

The low-molecular-weight polyol preferably includes a compound having an average hydroxyl value (described later) of more than 500 mgKOH/g and 3000 mgKOH/g or less, and when the number of functional groups (described later) is 2, the molecular weight is 40 or more. Examples include diols having a molecular weight of less than 225, and triols having a molecular weight of 40 or more and less than 337 when the number of functional groups (described later) is 3.

Examples of such low molecular weight polyols include ethylene glycol, propylene glycol (1,2-propanediol), trimethylene glycol (1,3-propanediol), 1,4-butylene glycol (1,4-butanediol ), aliphatic diols (2 to 13 carbon atoms) such as 1,3-butylene glycol (1,3-butanediol), alicyclic diols (6 to 13 carbon atoms) such as cyclohexanedimethanol, and further is, for example, bishydroxyethoxybenzene, xylene glycol and other aromatic diols (aromatic ring-containing diols having 6 to 13 carbon atoms), furthermore, diethylene glycol, trioxyethylene glycol, tetraoxyethylene glycol, di Diols (2-9 carbon atoms) (dihydric alcohols) such as oxyalkylene alcohols such as propylene glycol and trioxypropylene glycol, e.g., glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2, C3-C6 aliphatic triols such as 4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol, trimethylolpropane, 2,2-bis(hydroxymethyl)-3-butanol, and Triols (trihydric alcohols) such as other aliphatic triols (having 7 to 20 carbon atoms), tetraols (tetrahydric alcohols) such as tetramethylolmethane (pentaerythritol) and diglycerin (diglycerol) (having 5 carbon atoms) ~ 27) and the like.

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

Low-molecular-weight polyols preferably include dihydric alcohols and trihydric alcohols, more preferably trihydric alcohols, still more preferably aliphatic triols having 3 to 6 carbon atoms, particularly preferably , and trimethylolpropane.

The blending ratio of the low-molecular-weight polyol is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, 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 not more than 10 parts by mass, more preferably not more than 5 parts by mass.

If the blending ratio of the low-molecular-weight polyol exceeds the above range, the photoelastic polyurethane resin 2 becomes opaque and light does not pass through the photoelastic polyurethane resin 2, or the Young's modulus of the photoelastic polyurethane resin 2 increases. sometimes too much.

The photoelastic polyurethane resin 2 can be obtained by reacting the polyisocyanate component and the active hydrogen group-containing component to cure and mold the polyurethane resin composition.

In order to react the polyisocyanate component and the active hydrogen group-containing component, for example, known molding methods such as the one-shot method and the prepolymer method can be used.

In the one-shot method, for example, the polyisocyanate component and the active hydrogen group-containing component are combined so that the 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) is, for example, 70. 400, preferably 80 to 150, and injected into a mold, for example, 0 ° C. to 250 ° C., preferably room temperature (20 ° C.) to 150 ° C. For example, curing reaction is allowed 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. Moreover, the curing reaction described above can also be carried out in the presence of a known solvent.

The photoelastic polyurethane resin 2 molded into a predetermined shape can be obtained by injecting it into a mold and causing 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 (eg, high molecular weight polyol) are reacted to synthesize an isocyanate group-terminated prepolymer having an isocyanate group at the molecular end. Next, the resulting isocyanate group-terminated prepolymer and the remainder of the active hydrogen group-containing component (chain extender: e.g., low molecular weight polyol (and optionally high molecular weight polyol)) are allowed to react (chain extend) to cause a curing reaction. Let

The photoelastic polyurethane resin 2 molded into a predetermined shape can be obtained by injecting it into a mold and causing a curing reaction, removing the mold, and processing the outer shape as necessary.

The above polyurethane resin composition or photoelastic polyurethane resin 2 may optionally contain, for example, antifoaming agents, plasticizers, leveling agents, delustering agents, flame retardants, thixotropic agents, tackifiers, thickening agents, Known additives such as viscosity agents, lubricants, antistatic agents, surfactants, reaction retardants, dehydrating agents, antioxidants, UV absorbers, hydrolysis inhibitors, and weather stabilizers can be appropriately added.

The photoelastic polyurethane resin 2 is photoelastic, that is, the generation of stress based on a load or the like causes birefringence in light (for example, laser light) passing through the interior of the photoelastic polyurethane resin 2. can be done. Therefore, it can be suitably used in the pressure sensor 1 .

The polyurethane resin composition preferably includes a combination of an aromatic ring-containing polyisocyanate containing a 1,4-phenylene group, a polyether polyol, and a triol. Specifically, a combination of a benzene ring-containing diisocyanate and a poly Combinations of tetramethylene ether polyols and aliphatic triols are included.

Further, in the polyurethane resin composition, the combination of the polyisocyanate component and the active hydrogen group-containing component and the addition ratio of the additive are such that the plurality of photoelastic polyurethane resins 2 have different absolute values of photoelastic constants. are selected as appropriate.

For example, in the photoelastic polyurethane resin 2A, 4,4'-diphenylmethane diisocyanate (4,4'-MDI) and 3,3'-dimethylbiphenyl-4,4'-diisocyanate (4,4'-MDI) are preferably used as benzene ring-containing diisocyanates. TODI) is used in combination. On the other hand, in the photoelastic polyurethane resin 2B, 4,4'-diphenylmethane diisocyanate (4,4'-MDI) is preferably used alone as the benzene ring-containing diisocyanate.

Thus, by variously changing the formulation of the polyurethane resin composition in each photoelastic polyurethane resin 2, photoelastic polyurethane resins 2 having different absolute values of photoelastic constants can be obtained.

Examples of changing the prescription according to the absolute value of the photoelastic constant are not limited to the above, and for example, using different polyether polyols as raw material components, or changing the blending ratio of additives. It is also possible to obtain a plurality of types of photoelastic polyurethane resin 2 by, for example,

In all the photoelastic polyurethane resins 2, the absolute value of the photoelastic constant at 25° C. is, for example, 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, for example, 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), particularly preferably 8000×10 ⁻¹² Pa ^-1 or less.

If the absolute value of the photoelastic constant is within the above range, the excellent photoelasticity required in the pressure sensor 1 can be ensured.

The absolute values of the photoelastic constants of the respective photoelastic polyurethane resins 2 differ from each other within the above range.

The difference in the absolute value of the photoelastic constant between the respective photoelastic polyurethane resins 2 is, for example, 100×10 ⁻¹² Pa ⁻¹ or more, preferably 500×10 ⁻¹² Pa ⁻¹ or more, more preferably 1000× 10 ⁻¹² Pa ⁻¹ or more, for example, 10000000×10 ⁻¹² Pa ⁻¹ or less, preferably 100000×10 ⁻¹² Pa ⁻¹ or less, more preferably 10000×10 ⁻¹² Pa ⁻¹ or less .

If the difference in the absolute values of the photoelastic constants is within the above range, the pressure sensor 1 with excellent detection sensitivity can be obtained.

Further, for example, when there are two photoelastic polyurethane resins 2, the absolute value of the photoelastic constant of one of the photoelastic polyurethane resins 2 is, for example, less than 4000×10 ⁻¹² Pa ⁻¹ and the photoelasticity of the other The absolute value of the photoelastic constant of the polyurethane resin 2 is, for example, 4000×10 ⁻¹² Pa ⁻¹ or more.

The photoelastic constant of the photoelastic polyurethane resin 2 is described in “Mitsuo Tsukiji, Hiroyuki Takakazu, Yoshiro Tajimi, “Development of Photoelastic Constant Measurement System for Optical Films”, Precision Society Journal 73, 253-258 (2007)”. It can be measured according to the description of "Photoelastic constant measurement method".

In addition to measuring the photoelastic constant, the strain optical constant and Young's modulus of the photoelastic polyurethane resin 2 are obtained.

The strain optical constant of the photoelastic polyurethane resin 2 indicates the ratio of the intensity of birefringence generated by deformation to the amount of deformation of the photoelastic polyurethane resin 2 .

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

Photoelastic constant = Strain optical constant / Young's modulus (1)
Therefore, in order to set the photoelastic constant of the photoelastic polyurethane resin 2 within the above 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.

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

If the Young's modulus of the photoelastic polyurethane resin 2 is less than the above range, the photoelastic polyurethane resin 2 is too soft and easily damaged, resulting in poor workability. If the Young's modulus of the photoelastic polyurethane resin 2 exceeds the above range, the photoelastic polyurethane resin 2 is too hard, resulting in reduced photoelasticity.

Therefore, the Young's moduli of the plurality of photoelastic polyurethane resins 2 are preferably similar to each other.

On the other hand, from the viewpoint of obtaining different photoelastic constants as described above, the strain optical constants of the photoelastic polyurethane resin 2 at 25° C. are preferably different from each other.

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

When the distortion optical constants of the respective photoelastic polyurethane resins 2 are different from each other within the above range, the difference in the distortion optical constants of the respective photoelastic polyurethane resins 2 is, for example, 100×10 ⁻⁶ or more, preferably 500×10 ⁻⁶ or more, more preferably 1000×10 ⁻⁶ or more, for example, 20000×10 ⁻⁶ or less, preferably 10000×10 ⁻⁶ or less, more preferably 8000×10 ⁻⁶ or less be.

If the difference in strain optical constant is within the above range, the pressure sensor 1 with excellent detection sensitivity can be obtained.

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

If the glass transition temperature of the photoelastic polyurethane resin 2 is lower than the lower limit described above, the workability and scratch resistance of the photoelastic polyurethane resin 2 may deteriorate. Further, when the glass transition temperature of the photoelastic polyurethane resin 2 is equal to or higher than the above upper limit, it may be difficult to obtain the above desired photoelastic constant.

Therefore, the glass transition temperatures of the plurality of photoelastic polyurethane resins 2 are preferably similar to each other.

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

In the measurement of the glass transition temperature described above, the storage elongation modulus E′, the loss elongation modulus E″ and the loss tangent tan δ are obtained at the same time.

The storage elongation modulus E′ of the photoelastic polyurethane 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 ˜1×10 ⁸ Pa, and the loss tangent tan δ at 25° C. is, for example, 0.01 to 0.2.

As shown in FIG. 1, the plurality of photoelastic polyurethane resins 2 are formed in sheets of substantially the same size and substantially rectangular in plan view, and are arranged in the third direction (thickness direction) as described above. A polyurethane laminate 3 is formed by being laminated.

The size of each photoelastic polyurethane resin 2 is not particularly limited. be. Also, the width (length in the second direction) is, for example, 1 mm or more, preferably 5 mm or more, and is, for example, 150 mm or less, preferably 50 mm or less. Further, the thickness (third direction length) is, for example, 0.5 mm or more, preferably 1 mm or more, and for example, 10 mm or less, preferably 3 mm or less.

Further, the total thickness of the polyurethane laminate 3 is, for example, 1 mm or more, preferably 2 mm or more, and for example, 30 mm or less, preferably 10 mm or less.

Such photoelastic polyurethane resin 2 and polyurethane laminate 3 are placed, for example, on a flat support member (stage) (not shown).

Moreover, the photoelastic polyurethane resin 2 and the polyurethane laminate 3 can be housed in a case, if necessary. In this case, in order to cause the photoelastic polyurethane resin 2 to deform based on a load, which will be described later, it is preferable to use a case with relatively low rigidity, or to create a gap between the inner wall of the case and the photoelastic polyurethane resin 2 . set up.

As shown in FIG. 1, the optical sensor 4 includes a light emitting part 7 arranged on one side of the polyurethane laminate 3 in the first direction (longitudinal direction of the photoelastic polyurethane resin 2), 2) and a light receiving portion 8 disposed on the other side.

In the pressure-sensitive sensor 1, the one side end of the polyurethane laminate 3 and the light emitting section 7 are usually in close contact, and the other side end of the polyurethane laminate 3 and the light receiving section 8 are in close contact. In FIG. 1, the polyurethane laminate 3, the light emitting section 7 and the light receiving section 8 are shown separated from each other for explanation.

The light-emitting portion 7 includes a known light-emitting member. For example, one or a plurality of light emitting members are provided on one side of the polyurethane laminate 3 in the first direction so that light can be uniformly introduced into each photoelastic polyurethane resin 2 . In other words, the light-emitting member is arranged to face one end surface of the photoelastic polyurethane resin 2 in the first direction (longitudinal direction of the photoelastic polyurethane resin 2). Thus, the light-emitting member allows light to enter each photoelastic polyurethane resin 2 from one end surface in the first direction (longitudinal direction of the photoelastic polyurethane resin 2). The number of light emitting members provided in one light emitting portion 7 is not particularly limited. For example, one light emitting member may be provided for one photoelastic polyurethane resin 2, or a plurality (preferably , one light emitting member may be provided for all the photoelastic polyurethane resins 2 . Examples of the light-emitting member include, but are not limited to, semiconductor lasers (wavelength: 405 nm to 1064 nm), light-emitting diodes, fluorescent lamps, halogen lamps, hangsten lamps, and the like.

In addition, the light emitting section 7 may include an optical waveguide such as an optical fiber, if necessary, so that light can enter the photoelastic polyurethane resin 2 from the light emitting member via the optical waveguide.

Also, the light emitting unit 7 is electrically connected to the control unit 6 as indicated by the phantom lines 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 the light emission of the light emitting member is controlled according to the electric signal emitted from the control section 6 as described above.

The light receiving section 8 includes a known light receiving member. For example, a plurality of light-receiving members are provided according to the number of light-emitting members, and are arranged to face the other end surface of the photoelastic polyurethane resin 2 in the first direction (longitudinal direction of the photoelastic resin 2). Thereby, each light-receiving member can receive the light that has passed through each photoelastic polyurethane resin 2 from one side in the longitudinal direction to the other side. Examples of the light-receiving member include an element capable of converting the intensity of received light into an electric signal (optical signal), such as a photodiode.

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

In addition, as indicated by a phantom line in FIG. 1 , the processing section 5 is electrically connected to the light receiving section 8 .

The processing unit 5 is provided to calculate the measured load from the optical signal detected by the optical sensor 4 for each photoelastic polyurethane resin 2 .

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

Correlation data between the load applied to the photoelastic polyurethane resin 2 and the intensity of the optical signal that passed through the photoelastic polyurethane resin 2 when the load was applied is stored in the memory unit of the processing unit 5 . Stored for each resin 2 .

Furthermore, the optical sensor 4 includes one or more (preferably two) polarizing plates 10 . The polarizing plate 10 is arranged, for example, between the light emitting section 7 and the polyurethane laminate 3, between the light receiving section 8 and the polyurethane laminate 4, and the like. These polarizing plates 10 allow different vibration waves to pass therethrough.

More specifically, for example, a polarizing plate 10A is arranged between the light-emitting portion 7 and the polyurethane laminate 3 to allow the lateral oscillation wave (transverse wave) of light to pass therethrough.

On the other hand, between the light receiving portion 8 and the polyurethane laminate 3, a polarizing plate 10B is arranged to pass vertical vibration waves (longitudinal waves) of light.

With such a polarizing plate 10, the correlation between the light received by the light receiving section 8 and the load applied to the polyurethane laminate 3 can be obtained.

That is, the light generated in the light emitting section 7 is irradiated onto the polyurethane laminate 3 after passing through the polarizing plate 10A.

At this time, as shown in FIG. 2A, if no load is applied to the polyurethane laminate 3, each photoelastic polyurethane resin 2 is not deformed, and birefringence does not occur.

Therefore, the light passing through the polarizing plate 10A and the photoelastic polyurethane resin 2 is blocked by the polarizing plate 10B. As a result, the intensity of the optical signal received by the light receiving section 8 is reduced.

On the other hand, as shown in FIG. 2B, when a load is applied to the polyurethane laminate 3 from one side (upper side) to the other side (lower side) in the third direction, each photoelastic polyurethane resin 2 produces deformation according to load and produces birefringence.

Therefore, the light that has passed through the polarizing plate 10A and the photoelastic polyurethane resin 2 and has been birefringent passes through the polarizing plate 10B and is received by the light receiving section 8 . As a result, the intensity of the optical signal received by the light receiving section 8 increases. Note that the relationship between the degree of birefringence and the magnitude of the load is not proportional, but is shown as a graph of a predetermined waveform corresponding to the absolute value of the photoelastic constant.

In FIG. 2B, since the photoelastic constants of the photoelastic polyurethane resins 2 differ from each other, the intensity of the light emitted from the light emitting unit 7 (emission intensity) is the same. Even if the load applied to the resin 2 is the same, the degree of birefringence in each photoelastic polyurethane resin 2 is different. different.

Therefore, in the pressure sensor 1, correlation data between the magnitude of the load applied to each photoelastic polyurethane resin 2 and the intensity of light after attenuation due to birefringence (light receiving intensity) is acquired in advance, and the processing unit 5.

For example, when a photodiode is used as a light receiving member, the intensity (light receiving intensity) of light that has passed through each photoelastic polyurethane resin 2 (light after being attenuated by birefringence) is converted into a voltage value by each photodiode. Correlation data between each voltage value and the magnitude of the applied load is acquired. Such correlation data are shown as graphs of different waveforms for each photoelastic polyurethane resin 2, for example.

As an example of correlation data, a photoelastic polyurethane resin 2A having a specific photoelastic constant (absolute value) provides correlation data of a specific waveform, as shown in FIG. 3A.

On the other hand, the photoelastic polyurethane resin 2B has a photoelastic constant (absolute value) different from the photoelastic constant (absolute value) of the photoelastic polyurethane resin 2A. Correlation data with a different waveform is obtained.

These correlation data are stored in the memory section of the processing section 5 .

Further, the memory section of the processing section 5 stores a load detection program for calculating the load from the light signal from the above correlation data by a method described later.

As a result, the processing unit 5 calculates the estimated load applied to the photoelastic polyurethane resin 2 based on the optical signal (for example, voltage value) based on the light detected by the light receiving unit 8 by the following load detection method. It is possible.

Next, referring to FIGS. 1 to 3, a method (load detection method) for calculating an estimated load when a load is applied to the photoelastic polyurethane resin 2 using the pressure sensor 1 by means of a load detection program. to explain.

In this load detection method, light is first made incident on each photoelastic polyurethane resin 2 (photoelastic polyurethane resin 2A and photoelastic polyurethane resin 2B) from a light emitting member (such as a diode) of the light emitting part 7 under the control of the control part 6. .

Light passing through each photoelastic polyurethane resin 2 (photoelastic polyurethane resin 2A and photoelastic polyurethane resin 2B) is received by a light receiving member (such as a photodiode) of the light receiving unit 8, and the intensity of the received light is measured. , is input to the processing unit 5 as an optical signal. For example, when a photodiode is used as a light receiving member, the intensity of light passing through each photoelastic polyurethane resin 2 is converted into a voltage value by each photodiode, and each voltage value is sent to the processing unit 5 as an optical signal (electrical signal). input.

At this time, as described above, the correlation between the intensity of light received by the light receiving portion 8 and the load applied to the photoelastic polyurethane resin 2 differs among the photoelastic polyurethane resins 2 .

That is, as shown in FIG. 2A, if no load is applied to the photoelastic polyurethane resin 2, each photoelastic polyurethane resin 2 is in an undeformed state. In this case, light incident on each photoelastic polyurethane resin 2 passes through each photoelastic polyurethane resin 2 without causing birefringence and is blocked by the polarizing plate 10B. That is, when the photoelastic polyurethane resin 2 is in an undeformed state, the intensity of light received by the light receiving section 8 is reduced.

On the other hand, for example, as shown in FIG. 2B, when a load is applied from one side (upper side) in the third direction of the photoelastic polyurethane resin 2 to the other side (lower side) in the third direction, each photoelastic polyurethane resin 2 produces deformation according to the load. The light incident on each photoelastic polyurethane resin 2 is birefringent at the deformed portion, and the birefringent light passes through the polarizing plate 10B and is received by the light receiving section 8. FIG. That is, when the photoelastic polyurethane resin 2 is in a deformed state, the intensity of light received by the light receiving section 8 increases.

At this time, since the photoelastic polyurethane resins 2 have different absolute values of photoelastic constants, the intensity of light (light receiving intensity L _R ) that has passed through each photoelastic polyurethane resin 2 in the deformed state is The degree of attenuation changes according to the magnitude of the load, but the correlation between the light intensity and the load differs between the photoelastic polyurethane resins 2 .

Therefore, in this detection method, first, a plurality of estimated loads are calculated for each photoelastic polyurethane resin 2 based on the above correlation data from the intensity of the optical signal detected by the optical sensor 4 for each photoelastic polyurethane resin 2. do.

That is, as shown in FIGS. 3A and 3B, the correlation data between the intensity of the optical signal and the load has a specific waveform. value) is detected, a plurality of load candidates having that strength are selected.

More specifically, as shown in FIG. 3A, when the light receiving section 8 detects the light passing through the photoelastic polyurethane resin 2A as a specific optical signal intensity (for example, voltage value 0.6 V), , a plurality of estimated weight candidates are selected as the intensity of the optical signal (for example, 5.2N, 7.4N, 9.5N, 12.0N, 15.1N, 16.0N, 18.3N, 19 .4N).

Further, as shown in FIG. 3B, when the light receiving unit 8 detects the light passing through the photoelastic polyurethane resin 2B as the intensity of a specific optical signal (for example, voltage value of 0.8 V), the optical signal A plurality of candidates for the estimated load having the intensity of are also selected (eg, 6.9N, 10.0N, 13.7N, 16.0N, 19.9N, 26.4N, 27.8N).

Therefore, in this load detection method, from a plurality of estimated loads calculated for each photoelastic polyurethane resin 2, an estimated load common to all photoelastic polyurethane resins 2 is extracted as a measurement load.

For example, estimated load candidates (eg, 5.2N, 7.4N, 9.5N, 12.0N, 15.1N, 16.0N, 18.0N, 18.0N, 18.0N, 18.0N, 5.2N, 7.4N, 9.5N, 12.0N, 15.1N, 16.0N) selected from the intensity of light that has passed through the photoelastic polyurethane resin 2A. 3N, 19.4N) and estimated load candidates (for example, 6.9N, 10.0N, 13.7N, 16.0N, 19.9N, 26.4N, 27.8N), and a common estimated load (for example, 16.0N) is extracted as the measured load.

That is, in this load detection method, among the estimated loads selected for each photoelastic polyurethane resin 2, the value common to all the photoelastic polyurethane resins 2 is used as the measurement load.

Thus, in the pressure-sensitive sensor 1 described above, the optical sensor 4 detects light passing through each of the plurality of photoelastic polyurethane resins 2 having different absolute values of photoelastic constants. The detected optical signal differs for each photoelastic polyurethane resin 2 because the absolute values of the photoelastic constants of the plurality of photoelastic polyurethane resins 2 are different from each other. That is, when a specific load is applied, the detected optical signal differs for each photoelastic polyurethane resin 2 .

Therefore, the processing unit 5 can calculate the measured load from optical signals that differ for each photoelastic polyurethane resin 2 .

As a result, the load to be measured can be calculated without accumulating optical signals (voltage) detected from one photoelastic polyurethane resin 2, so that the load can be measured with high accuracy with a simple configuration.

In particular, in the pressure-sensitive sensor 1 described above, the processing section 5 includes a memory section in which correlation data between the load applied to the photoelastic polyurethane resin 2 and the intensity of the optical signal is stored.

Then, the processing unit 5 calculates a plurality of estimated loads from the intensity of the detected optical signal for each photoelastic polyurethane resin 2, and extracts the estimated load common to all the photoelastic polyurethane resins 2 as the measured load. .

Therefore, the load can be reliably measured by a simple calculation.

Further, in the above-described pressure sensor 1, a plurality of photoelastic polyurethane resins 2 are arranged so as to overlap each other in the direction in which the load is applied. Therefore, the applied load uniformly acts on the plurality of photoelastic polyurethane resins 2 . As a result, reliable load measurement can be achieved.

In the above description, the third direction in which the load is applied is the vertical direction, but the direction in which the load is applied is not particularly limited. It can be a direction.

In the above description, the load applied to the photoelastic polyurethane resin 2 is calculated from the correlation data between the load measured in advance and the intensity of the optical signal. Not limited to the above.

For example, as shown in FIG. 4, the photoelastic polyurethane resin 2 produces birefringence depending on the load. Therefore, when birefringent light is observed through a polarizing plate, interference fringes S appear depending on the load. . Therefore, correlation data between the load applied to the photoelastic polyurethane resin 2 and the interference fringes of birefringent light generated by the load can be obtained for each of the plurality of photoelastic polyurethane resins 2 . The processing unit 5 (see FIG. 1) can also observe the interference fringes S generated when the load is applied, and calculate the load from the interference fringes S based on the above correlation data.

In the above description, the pressure-sensitive sensor 1 includes two photoelastic polyurethane resins 2, but the number of photoelastic polyurethane resins 2 may be two or more, and the number is not particularly limited. The pressure sensor 1 may comprise three or more photoelastic polyurethane resins 2 .

FIG. 5 shows a pressure sensor 1 comprising three photoelastic polyurethane resins 2 as a second embodiment. The three photoelastic polyurethane resins 2 are hereinafter referred to as a photoelastic polyurethane resin 2A, a photoelastic polyurethane resin 2B, and a photoelastic polyurethane resin 2C, respectively, for distinction.

In the second embodiment shown in FIG. 5, photoelastic polyurethane resin 2C, photoelastic polyurethane resin 2B, and photoelastic polyurethane resin 2A are arranged from the other side (lower side) in the third direction toward the one side (upper side) in the third direction. , are sequentially stacked.

In the second embodiment as described above, the correlation data between the load and the intensity of the optical signal is acquired for each of the photoelastic polyurethane resin 2A, the photoelastic polyurethane resin 2B, and the photoelastic polyurethane resin 2C, and stored in the memory of the processing unit 5. stored in the department.

When a load is applied to the polyurethane laminate 3, load candidates based on the intensity of the optical signal are selected for each of the photoelastic polyurethane resin 2A, the photoelastic polyurethane resin 2B, and the photoelastic polyurethane resin 2C. .

Then, among the estimated loads selected for each photoelastic polyurethane resin 2, the value common to all the photoelastic polyurethane resins 2 is used as the estimated load.

It should be noted that the more the photoelastic polyurethane resin 2 provided, the more accurately the pressure-sensitive sensor 1 can detect the bending direction. Therefore, the number of photoelastic polyurethane resins 2 in pressure sensor 1 is preferably three or more. On the other hand, the more the photoelastic polyurethane resin 2 is provided, the lower the production efficiency and cost performance. Preferably no more than 4, especially preferably 3.

In the above description, each photoelastic polyurethane resin 2 is formed in a sheet shape that is substantially rectangular in plan view, but the shape of the photoelastic polyurethane resin 2 is not particularly limited, and can vary depending on the object to be measured. can be changed.

For example, when the load on the photoelastic polyurethane resin 2 becomes non-uniform and there is a possibility that the load cannot be appropriately applied to the optical path through which the light of the optical sensor 4 passes, FIG. 6 shows a third embodiment. , the photoelastic polyurethane resin 2 can be projected toward one side in the third direction.

In this third embodiment, the portion of the photoelastic polyurethane resin 2A of the uppermost layer in the direction (third direction) in which the load is applied, which overlaps with the optical path through which the light of the optical sensor 4 passes, is aligned in the direction in which the load is applied (the third direction). It protrudes in the opposite direction (from the bottom to the top in the third direction).

The projecting portion may be all or part of the portion of the photoelastic polyurethane resin 2 that overlaps the optical path through which the light from the optical sensor 4 passes. For example, in FIG. 6, the central portion in the width direction (second direction) of the photoelastic polyurethane resin 2A protrudes most toward one side in the third direction, and both ends in the width direction (second direction) and the vicinity thereof do not protrude. formed.

In such a pressure sensor 1, the portion of the photoelastic polyurethane resin 2 that overlaps the optical path protrudes in the direction opposite to the direction in which the load is applied. As such, the measurement object can first come into contact with the protruding portion. Then, a load can be appropriately applied to the portion of the photoelastic polyurethane resin 2 that overlaps the optical path. As a result, more accurate load measurement can be achieved.

Also in the second embodiment shown in FIG. 5, similarly to the above, the photoelastic polyurethane resin 2 can be projected toward one side in the third direction (see the phantom line in FIG. 5).

In the above description, the plurality of photoelastic polyurethane resins 2 are stacked along the third direction in which the load is applied, but the arrangement of the plurality of photoelastic polyurethane resins 2 is not limited to the above.

More specifically, for example, as shown in FIG. 7 as a fourth embodiment, a plurality of photoelastic polyurethane resins 2 may be arranged so as to line up along a direction intersecting the third direction in which a load is applied. can also

FIG. 7 shows, as a fourth embodiment, a pressure sensor 1 in which three photoelastic polyurethane resins 2 are arranged in parallel along a second direction perpendicular to the third direction in which a load is applied. The three photoelastic polyurethane resins 2 are hereinafter referred to as a photoelastic polyurethane resin 2D, a photoelastic polyurethane resin 2E, and a photoelastic polyurethane resin 2F, respectively, for distinction.

In the fourth embodiment shown in FIG. 7, a photoelastic polyurethane resin 2D, a photoelastic polyurethane resin 2E, and a photoelastic polyurethane resin 2F are arranged in order from one side in the second direction to the other side in the second direction.

In such a fourth embodiment, the correlation data between the load and the intensity of the optical signal is acquired for each of the photoelastic polyurethane resin 2D, the photoelastic polyurethane resin 2E, and the photoelastic polyurethane resin 2F, and stored in the memory of the processing unit 5. stored in the department.

When a uniform load is applied to each of the photoelastic polyurethane resin 2D, the photoelastic polyurethane resin 2E and the photoelastic polyurethane resin 2F, the photoelastic polyurethane resin 2D, the photoelastic polyurethane resin 2E and the photoelastic polyurethane resin 2F For each of the resins 2F, candidate weights are selected based on the intensity of the optical signal.

Then, among the estimated loads selected for each photoelastic polyurethane resin 2, the value common to all the photoelastic polyurethane resins 2 is used as the estimated load.

In such a pressure-sensitive sensor 1, it is necessary to uniformly apply a load to all the photoelastic polyurethane resins 2, but the plurality of photoelastic polyurethane resins 2 are arranged in a direction intersecting the direction in which the load is applied. Since they are arranged side by side, the thickness of the pressure sensor 1 can be reduced.

Also in the fourth embodiment shown in FIG. 7, similarly to the above, the photoelastic polyurethane resin 2 can be projected toward one side in the third direction (see the phantom line in FIG. 7).

In the above-described pressure-sensitive sensor 1, the light generated by the birefringence of the photoelastic polyurethane resin 2 is extracted by the polarizing plate 10 of the optical sensor 4, and the load is calculated from the correlation data between the light signal and the load. However, for example, without using the polarizing plate 10, the load may be calculated from the correlation data between the light intensity attenuation due to birefringence and the load.

The pressure sensor 1 is a transmissive sensor in which light is emitted from one side of the photoelastic polyurethane resin 2 in the first direction and light is emitted from the other side in the first direction. A reflective sensor in which light is emitted from one side of the resin 2 in the first direction, light is reflected by the retroreflective material on the other side in the first direction, and light is emitted from the one side of the photoelastic polyurethane resin 2 in the first direction. may be

And such a pressure sensor 1 can accurately measure a load with a simple configuration. Therefore, in various industrial fields, it can be suitably used as a pressure-sensitive member for robots, equipment, and the like.

Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited by the following examples. "Parts" and "%" are based on mass unless otherwise specified.

Production Example 1 <Photoelastic polyurethane resin A>
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 heated to 80°C. and returned to normal pressure with nitrogen. Then, while stirring, 1.0 part by mass of TMP (trimethylolpropane) was added, and the temperature was adjusted to 70°C. Then, 20.2 parts by mass of MDI-PH (4,4'-diphenylmethane diisocyanate, manufactured by Mitsui Chemicals, Inc.) dissolved at 70° C. (isocyanate index 105) was added and mixed with stirring.

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

Next, the obtained polyurethane composition was poured into a 2 mm thick sheet mold and cured at 70° C. for 18 hours to obtain a sheet-like photoelastic polyurethane resin.

Production Example 2 <Photoelastic polyurethane resin B>
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 heated to 80°C. and returned to normal pressure with nitrogen. Then, 9.2 parts by mass of TODI (3,3'-dimethylbiphenyl-4,4'-diisocyanate, manufactured by Nippon Soda Co., Ltd.) (isocyanate index 35) was added while stirring. Then, while stirring, 1.0 part by mass of TMP (trimethylolpropane) was added, and the temperature was adjusted to 70°C. Then, 20.2 parts by mass of MDI-PH (4,4'-diphenylmethane diisocyanate, manufactured by Mitsui Chemicals, Inc.) dissolved at 70° C. (isocyanate index 105) was added and mixed with stirring.

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

Next, the obtained polyurethane composition was poured into a 2 mm thick sheet mold and cured at 70° C. for 18 hours to obtain a sheet-like photoelastic polyurethane resin.

<Evaluation of physical properties of photoelastic polyurethane resin>
(1) Photoelastic constant and Young's modulus "Mitsuo Tsukiji, Hiroyuki Takakazu, Yoshiro Tajimi, ``Development of a photoelastic constant measurement system for optical films'', Journal of Precision Society 73, 253-258 (2007)" Elastic constant measurement method", the strain optical constant and Young's modulus of the photoelastic polyurethane resin at 25°C were obtained, and the photoelastic constant at 25°C was calculated therefrom. A laser beam with a wavelength of 630 nm was used for the above measurements. Table 1 shows the photoelastic constant and Young's modulus.

(2) Dynamic viscoelasticity A photoelastic polyurethane resin was measured using a dynamic viscoelasticity measuring device (VES-F-III, VISCO-ELASTIC SPECTROMETER, manufactured by Iwamoto Seisakusho Co., Ltd.) at a temperature increase rate of 5 ° C./min and a frequency of 10 Hz. , measured in a temperature dispersion mode with an amplitude of ± 0.01 mm to obtain the storage elongation modulus (E'), the loss elongation modulus (E'') and the loss tangent (tan δ), and the loss tangent of the obtained data The temperature of the peak value of (tan δ) was defined as the glass transition temperature (Tg). Table 1 shows the storage elongation modulus (E′), loss elongation modulus (E″), loss tangent (tan δ) and glass transition temperature (Tg).

Example 1 <Pressure sensor>
Using the photoelastic polyurethane resins obtained in Production Examples 1 and 2, a pressure sensor was produced as shown in FIG.

That is, photoelastic polyurethane resin A and photoelastic polyurethane resin B were laminated.

Both ends of each photoelastic polyurethane resin were cut and smoothed, and a light source and an optical fiber U-49 (trade name, manufactured by Keyence) were fixed to one end of each with an adhesive. This made it possible for light to enter each photoelastic polyurethane resin. At the other end of each photoelastic polyurethane resin, an amplifier FS-N11MN (trade name, manufactured by Keyence) equipped with a photodiode is provided to detect light passing through the photoelastic polyurethane resin, and a reflector is provided. connected through Then, the voltage value output from the amplifier was recorded with a data logger NR-600 (trade name, manufactured by Keyence).

<<Load-Voltage Graph>>
A light source and photodiode were connected to each single photoelastic polyurethane resin in the same manner as the pressure sensors described above.

A load was gradually applied to each photoelastic polyurethane resin using a force gauge, and voltage values corresponding to the load were observed and graphed. The load-voltage graph of Photoelastic Polyurethane Resin A is shown in FIG. 3A. A load-voltage graph of the photoelastic polyurethane resin B is shown in FIG. 3B.

Then, when a load of unknown mass was applied to the pressure sensor in which the photoelastic polyurethane resin A and the photoelastic polyurethane resin B were laminated, the light passing through the photoelastic polyurethane resin A showed an output value of 0.6V. , the light passing through the photoelastic polyurethane resin B showed an output value of 0.8V.

Next, each output value was compared with the above load-voltage graph.

Referring to the load-voltage graph of the photoelastic polyurethane resin A shown in FIG. 3A, when the light passing through the photoelastic polyurethane resin A exhibits a voltage value of 0.6V, the load candidates are 5.2N and 7.4N. , 9.5N, 12.0N, 15.1N, 16.0N, 18.3N, 19.4N.

On the other hand, referring to the load-voltage graph of photoelastic polyurethane resin B shown in FIG. .0N, 13.7N, 16.0N, 19.9N, 26.4N, 27.8N.

Among these load candidates, the common estimated load was 16.0N.

Therefore, the load applied to the pressure sensor was estimated to be 16.0N.

In addition, when the load actually applied to the pressure sensor was measured with a commercially available measuring instrument, it was 16.0N.

REFERENCE SIGNS LIST 1 pressure sensor 2 photoelastic polyurethane resin 3 cover member 4 optical sensor 5 processing unit 6 control unit 7 light emitting unit 8 light receiving unit

Claims (5)

A process in which a plurality of photoelastic polyurethane resins having different absolute values of photoelastic constants, an optical sensor for detecting light passing through each of the plurality of photoelastic polyurethane resins, and an optical signal detected by the optical sensor are input. A pressure sensor comprising:
The pressure-sensitive sensor, wherein the processing unit calculates the measured load from the optical signal detected by the optical sensor for each of the photoelastic polyurethane resins. The processing unit is
A storage area in which correlation data between the load applied to the photoelastic polyurethane resin and the intensity of the light signal passing through the photoelastic polyurethane resin when the load is applied is stored for each photoelastic polyurethane resin. with
calculating a plurality of estimated loads for each of the photoelastic polyurethane resins based on the correlation data from the intensity of the optical signal detected by the optical sensor for each of the photoelastic polyurethane resins;
2. The pressure sensor according to claim 1, wherein an estimated load common to all said photoelastic polyurethane resins is extracted as a measured load from a plurality of estimated loads calculated for each of said photoelastic polyurethane resins. . 3. The pressure sensor according to claim 1, wherein a plurality of said photoelastic polyurethane resins are stacked in a direction in which a load is applied. 3. The pressure sensor according to claim 1, wherein the plurality of photoelastic polyurethane resins are arranged side by side in a direction intersecting the direction in which the load is applied. The photoelastic polyurethane resin is characterized in that a portion of the photoelastic polyurethane resin that overlaps with the optical path through which the light of the optical sensor passes in the direction in which the load is applied protrudes in the direction opposite to the direction in which the load is applied. 5. The pressure sensor according to any one of 1 to 4.

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