JP5192095B2 - Strain sensor - Google Patents

Description

  The present invention makes it easy to reduce the maximum strain or excessive strain that has been recorded in a structure, etc., and the strain generated under actual conditions in various parts that are subject to fatigue damage in structures and rotating shafts that are subject to repeated loads. The present invention relates to an affixing type strain sensing sensor that senses at the same time.

If an excessive load is applied to bridges and other structures, machines, vehicles, aircraft, ships, etc. that are actually put into service, damage to the members will be a problem, so it will affect the repair plan etc. . For earthquake countermeasures, it is necessary to inspect the seismic load resistance of bridge piers.
For this reason, it is necessary to grasp the maximum strain or excessive strain that has been recorded in the structure or vehicle.

As a method conventionally used for estimating a strain state in a material, there is a method in which a strain gauge is attached to a region to be measured and a strain generated in the region is constantly measured.
Since this method requires the use of a precise measuring device such as a transducer, it is difficult to measure a large number of parts at once, so it is difficult to grasp the overall strain history of a large structure or the like.
In addition, it is extremely difficult to detect strain generated during operation on a rotating shaft of a rotating machine.

Patent Document 1 discloses a stress measurement sensor used for grasping the magnitude of stress received by a structure. The method of using strain gauges for large structures makes it very difficult to route the conductors, and in particular, there is a problem that the conductors cannot be repaired with nuclear structures. On the other hand, the disclosed stress measurement sensor has been developed as one that eliminates the need for conducting a conductor and can be easily measured even in a high-temperature environment.
In the disclosed sensor, both ends of a wire made of a material that breaks with less strain than the object to be measured are fixed to the object to be measured, and the stress acting on the object to be measured from the presence or absence of breakage of the wire exceeds a predetermined value. It is a judgment whether it was big or small.

In the stress measurement sensor disclosed in Patent Document 1, a fixing base is fixed to a thin film serving as a base, and both ends of a wire are fixed to the fixing base with an adhesive or the like. For the wire, a material such as nickel, titanium, or carbon steel having a small breaking strain is selected. For the fixing base, a non-conductive polymer material, a ceramic material, a non-ferrous metal material, or the like is selected. Note that a strip-shaped flat plate may be used instead of the wire, and the sensitivity can be improved by providing a locally thinned portion and concentrating the strain.
The presence or absence of breakage or the magnitude of strain may be detected electrically by using a wire or a rectangular flat plate as a conductive one.

  The disclosed stress measurement sensor is formed by fixing a fixed base on a thin film to be attached to an object to be measured and adhering a detection wire or a flat plate to the fixed base. Is difficult to ensure, and it is difficult to perform reproducible measurements.

Patent Document 2 discloses an extremely small and thin crack type fatigue sensor in which a fracture piece having a crack propagation portion at the center is formed on a metal foil substrate. In the illustrated embodiment, there is a fatigue sensor in which a crack progressing portion is formed with a slit with a sharp tip formed from the side end, and a crack is generated corresponding to a repetitive stress generated in a member to be measured. Have been described.
Since the fatigue sensor disclosed in Patent Document 2 is small and highly sensitive, it is affixed in the very vicinity of the target part, and the fatigue damage degree of the fatigue sensor is measured by repeated stress at the applied part to determine the fatigue damage degree of the target part. It is possible to estimate or to estimate the actual life.

  However, various members are used in various forms such as welding, machining, extrusion molding, casting, etc. in structures and transportation machinery. Since conditions vary depending on the member, there is a problem that complicated calculation is required to obtain a sufficiently correct result, and advanced knowledge and skill are required in order to properly use the disclosed fatigue sensor. In addition, the disclosed fatigue sensor establishes a correspondence relationship with a target member with respect to repeated stress and enables representative measurement, and cannot measure the magnitude of strain.

Japanese Patent Laid-Open No. 9-005175 JP 2001-281120 A

  Therefore, the problem to be solved by the present invention is to supply a strain sensing sensor that is attached to a measurement target member and estimates whether or not the strain generated on the target member in operation exceeds a predetermined magnitude. In particular, it is to supply a small and inexpensive strain sensing sensor which can easily know the result visually.

  In order to solve the above-mentioned problems, a strain sensing sensor according to the present invention comprises a thin film substrate, at least a pair of strain transmission pieces and a sensor foil, and the thin film substrate is attached to the measurement object and distorted together with the measurement object. Each piece is formed on a thin film substrate and one end is fixed to the thin film substrate to determine the measurement span. The insulation film is placed between the strain transmission piece and the sensor foil, and the sensor foil and the strain transmission piece are interposed via the insulation film. The sensor foil is made of a good electrical conductor and the cross-sectional area is smaller than the strain transmission piece and is formed so that it is passed between the gaps of the pair of strain transmission pieces. If the sensor foil breaks and the sensor foil breaks, the sensor foil breaks to detect that the strain to be measured exceeds the specified strain. Characterized in that it electrically detected.

  In the strain sensing sensor of the present invention, since the sensor foil having a smaller cross-sectional area than the strain transmitting piece is passed between the strain transmitting pieces, the strain generated when the member to be measured is distorted is applied to the sensor foil portion. Concentrate and provide a strain expansion function. The sensor foil has a predetermined breaking elongation, and when the local strain at the shearing portion exceeds the breaking elongation, the minimum cross-sectional portion is broken. When the sensor foil is ruptured, it can be estimated that a strain equal to or greater than a predetermined strain determined from the rupture strength of the sensor foil and the strain concentration is generated in the measurement target member.

The greater the difference between the thickness of the strain transmission piece and the sensor foil and the greater the difference in rigidity between the two, the greater the sensitivity. Therefore, adjust the thickness difference to adjust the measurement range of the maximum strain value of the target member as long as accuracy is ensured. be able to.
Moreover, since the distortion which appears in the sensor foil part with the distortion of the measurement object increases as the distance between the fixed positions of the two strain transmission pieces increases, the detection range can be adjusted by adjusting this distance.

The pair of strain transmitting pieces may be arranged side by side in a direction along the strain detection direction, and the sensor foil may detect a strain in which the strain transmitting pieces are distorted away from each other. In this case, the strain in the extending direction of the member to which the strain sensor is attached can be sensed. In order to improve the sensing sensitivity, a slit may be formed in the sensor foil portion.
Further, the pair of strain transmitting pieces may be arranged side by side in a direction perpendicular to the strain detection direction, and the sensor foil may detect a strain distorted in a direction in which the strain transmitting pieces are displaced from each other. In this case, the expansion and contraction of the member is detected by the shear fracture of the sensor foil. You may make it easy to shear by forming the dent along the expansion-contraction direction in the shape of a sensor foil part.

  The sensor foil can be integrally formed of the same material as the strain transmission piece. When the sensor foil and the strain transmission piece are formed by electroforming, the narrow portion of the sensor foil can be accurately formed by electroforming or etching. The thickness of the sensor foil can be accurately controlled by a two-stage electroforming method.

  The strain transmission piece and the sensor foil may be good electrical conductors, and an electrical insulator thin film may be interposed between the strain transmission piece and the sensor foil. Furthermore, if the sensor foil spreads over the strain transmitting piece to form an electrode, even if it is difficult to make a visual judgment, by electrically detecting resistance change due to breakage and deformation of the sensor foil, The strain status can be easily grasped. Although detection can be performed by applying a tester probe locally, it may be detected at a remote place by connecting an electric wire to the electrode.

The thin film substrate may be formed of stainless steel, and the sensor foil may be formed of electrolytic copper. Further, the thin film substrate may be formed of invar, and the sensor foil may be formed of nickel.
As the sensor foil has a smaller elongation at break, it is possible to configure a sensitive sensor with higher accuracy. Moreover, it is preferable to select a material whose characteristics are well known and easy to manufacture. Therefore, electrolytic copper is easily deposited by electroforming and is sufficiently hard, and nickel is sufficiently hard and information and technology are accumulated in a fatigue sensor or the like. Therefore, it is preferable to use it for a sensor foil.

  The strain sensing sensor of the present invention comprises a thin film substrate and a strain transmitting piece. The thin film substrate is affixed to the measuring object and is distorted together with the measuring object. The strain transmitting piece has a protrusion and a pillar on the thin film substrate. The lever portion is fixed to the thin film substrate via the first hinge portion, the base of the column portion is fixed to the thin film substrate, and the tip is the second hinge at the lever portion via the second hinge portion. It is connected to the vicinity of the part. The hinge portion is formed of the same material as the strain transmission piece, has a narrow plate shape and a thin plate thickness, and includes a strain expansion mechanism.

  When the distance between the fixed portions of the strain transmitting pieces increases or decreases, the lever portion is pushed and pulled by the column portion and rotates at the position of the first hinge portion. Even after the force is pulled out, the tilt of the lever portion remains in the first and second hinge portions due to the hysteresis of the displacement. Since this residual displacement can be evaluated by a scale attached to the bottom of the lever, the amount of strain between the two fixed portions can be estimated from this residual displacement.

Moreover, it is preferable that the strain detection sensor includes a reinforcing frame that surrounds the strain transmission piece to protect the sensor unit.
The reinforcing frame and the strain transmitting piece are preferably formed from the same material. In the case of the electroforming method, an arbitrary deposited shape can be formed, so that the reinforcing frame and the strain transmitting piece can be formed together.

Since the strain sensing sensor of the present invention can be made small, it is possible to accurately sense the strain state by sticking it near the measurement target position of the target member. Further, since it can be manufactured at a low cost, a large number of data can be obtained by attaching a large number to the measurement target member.
Furthermore, since the results can be easily confirmed at the installation site, even unskilled workers can easily collect accurate measurement results and obtain accurate judgments.

  Further, since the sensor does not require a converter and electrical wiring is not necessary, even if the number of measurement points is increased, the strain state can be grasped without significantly increasing the measurement cost. Also, when measuring a rotating member, it can be applied without using a special circuit element such as a slip ring.

It is a top view with the principal part enlarged view of the distortion | strain detection sensor which concerns on 1st Example of this invention. It is a top view of the distortion | strain transmission piece of 1st Example. It is a top view of sensor foil used for the 1st example. 1 is a conceptual cross-sectional view of a strain sensor of a first embodiment. It is a graph which shows the test result of the distortion | strain detection sensor of 1st Example. It is a top view with the principal part enlarged view of another aspect of 1st Example. It is a top view of another mode of the 1st example. It is a top view with the principal part enlarged view of the distortion | strain detection sensor which concerns on 2nd Example of this invention. It is a conceptual sectional view of a strain sensing sensor of the 2nd example. It is a top view with the principal part enlarged view which shows another embodiment of 2nd Example. It is a top view which shows another embodiment of 2nd Example. It is a top view which shows another embodiment of 2nd Example. It is a top view with the principal part enlarged view which shows another embodiment of 2nd Example. It is a top view of the distortion | strain detection sensor which concerns on 3rd Example of this invention. It is a side view of the distortion | strain detection sensor of 3rd Example. It is a top view which shows another embodiment of 3rd Example. It is a top view which shows another embodiment of 3rd Example. It is a top view which shows another embodiment of 3rd Example. It is a top view of the distortion | strain detection sensor which concerns on 4th Example of this invention.

  Hereinafter, the present invention will be described in detail based on examples with reference to the drawings.

  1 is a plan view with an enlarged view of a main part of a strain sensing sensor according to a first embodiment of the present invention, FIG. 2 is a plan view of a strain transmitting piece, FIG. 3 is a plan view of a sensor foil, and FIG. FIG. 5 is a graph showing a test result, FIG. 6 is a plan view with an enlarged view of a main part of another aspect of the present embodiment, and FIG. 7 is a plan view showing still another embodiment.

  The strain sensing sensor of this embodiment has a three-layer thin film structure in which an insulating film 3 is interposed between a sensor foil 1 and a strain transmission piece 2 as shown in FIGS. The strain sensor is conveniently used by being fixed on the thin film substrate 4. The thin film substrate 4 is attached to the surface of the measurement target member 5 with an adhesive, and faithfully transmits the strain of the measurement target member 5 to the strain detection sensor.

As illustrated in FIG. 2, the strain transmission pieces 2 are each formed of a pair of strip-shaped metal thin films. The pair of strain transmitting pieces 2 face each other with a very narrow gap g, and the other ends are connected to the frame body 6 of the strain sensing sensor.
The frame 6 is integrally formed of the same thickness and the same material as the strain transmitting piece 2 and has a function of maintaining the correct positional relationship by connecting the strain transmitting pieces 2 that can be disassembled separately. The frame 6 can also be used as a fixing allowance when the strain sensor is fixed to the thin film substrate 4 by spot welding or the like.

  As illustrated in FIG. 3, the sensor foil 1 is a metal thin film that is thinner than the strain transmission piece 2, and is formed so that the bridge portion 8 comes to the position of the gap g of the strain transmission piece 2. The portion 9 adjacent to the bridge portion 8 has a function of accurately transmitting the strain of the strain transmission piece 2 to the bridge portion 8 and is formed with the same width W as that of the strain transmission piece 2 and is further passed through a thin wire portion. The electrode part 10 is formed. The sensor foil 1 is fixed to the strain transmission piece 2 through an extremely thin insulating film 3. The conductor portion is provided in order to prevent heat from adversely affecting the bridge portion 8 when an electric wire is soldered to the electrode portion 10.

As shown in the enlarged view of FIG. 1, the bridge portion 8 forms a narrow portion having a narrow width d, stress is concentrated corresponding to the cross-sectional area ratio between the strain transmitting piece 2 and the bridge portion 8, and the member to be measured 5 has an effect of collecting most of the distortion generated in the bridge portion 8.
Furthermore, the narrow portion formed in the bridge portion 8 also has an effect of increasing sensitivity by concentrating the amount of strain generated during the measurement span of the measurement target member on the narrow portion shorter than the gap g.

The strain sensing sensor of this embodiment can be formed by etching or electroforming.
For example, in the strain sensing sensor shown in FIG. 1, a polyimide film having a thickness of 18 to 20 μm is bonded onto a 50 μm thin film of stainless steel SUS304, and a 18 μm copper foil is bonded thereon to form a three-layer structure. To do. Thereafter, the SUS thin film and the polyimide film are etched to form a shape of the strain transmitting piece 2 and the frame 6 having a width of 4 mm having a gap of 100 μm and a total length of 160 mm, and etching the copper foil from the opposite direction. Thus, the shape of the sensor foil 1 including the bridge portion 8 and the electrode 10 for detecting strain is formed.
The shape of the sensor foil 1 can also be formed by die cutting.

  Furthermore, by bonding the surface on the strain transmission piece 2 side to the thin film substrate 4, the handling of the sensor can be facilitated, the sensor can be easily applied to the target member, and the reproducibility of the measurement can be improved. When the thin film substrate 4 is formed of the same metal as the strain transmission piece 2, the strain transmission piece 2 and the thin film substrate 4 can be firmly bonded by spot welding. The thin film substrate 4 may be formed of plastic.

The strain sensing sensor shown in FIG. 1 can be formed to include three sensors in the thin film substrate 4 having a width of 17 mm and a length of 166 mm, for example, and is extremely small. Therefore, it is possible to sense the local strain of the member.
The sensor foil 1 may be directly formed on the thin film substrate by electroforming. Since the shape reproducibility of the electroforming method is extremely high, a sensor having a shape formed by the electroforming method can obtain an accurate measurement result.

In addition, the thickness of each thin film, the shape of each thin film layer, the gap amount of the detection unit, and the like are appropriately designed according to the strain to be sensed by the measurement target member.
Actually, for example, the thicknesses of the strain transmission piece 2, the insulating layer 3, and the sensor foil 1 that are 10 μm to several hundred μm are convenient for applying to a large number of measurement points. Further, the gap amount can also be adjusted according to the measurement conditions, and a value of several tens of μm to several mm is used.
Furthermore, the strain transmission piece 2 may be made of Invar and the sensor foil 1 may be made of nickel. Regarding the characteristics and manufacturing method of nickel, it is possible to utilize the technology accumulated by manufacturing and using a fatigue sensor.

Each of the strain transmission pieces 2 is fixed to the measurement target member 5 at one place, and the measurement span L is determined. Since the thin film substrate 4 is firmly adhered to the surface of the measurement target member 5, the strain transmission piece 2 is substantially fixed to the measurement target member by fixing the strain transmission piece 2 to the thin film substrate 4 by, for example, spot welding 7 or the like. 5 can be fixed.
When the measurement target member 5 expands or contracts due to some stress action, the strain ε generated in the portion of the measurement span L is distributed to the strain transmission piece 2 and the sensor foil 1 of the strain sensing sensor. The distribution ratio is influenced by the Young's modulus of the material, but is greatly influenced by the stress concentration related to the cross-sectional area of the part, and most of the strain ε generated in the measurement span L is the bridge portion 8 at the position of the gap g. Concentrate on the sensor foil 1.

Therefore, (strain ε × measurement span L / gap g) is the strain rate of the sensor foil 1, and if this value exceeds the breaking strain εf of the sensor foil 1, the sensor foil 1 is damaged. Therefore, when the sensor foil 1 is broken, by calculating the strain ε0 of the measurement target member 5 corresponding to the breaking strain εf of the sensor foil 1, the strain ε of the measurement target member 5 has exceeded at least the corresponding strain ε0. Can be detected. In addition, when a narrow part is formed in the sensor foil 1, the substantial detection length is further shortened, the strain rate for the same strain ε is increased, and the detection becomes easier.
According to the sensor foil shape of the present embodiment, since the strain concentrates in the narrow portion, the substantial strain rate is increased. Therefore, if the material has a breaking strain εf of 20% or less, it will break relatively easily. Can be configured.

  Since the gap g of the strain transmission piece 2 is extremely small, it may be difficult to visually determine the breaking state of the sensor foil 1. In such a case, the probe of the tester can be brought into contact with the electrode portion 10 provided at the end of the sensor foil 1 to be easily detected electrically. Alternatively, a lead wire may be soldered to the electrode unit 10 and connected to a remote meter so that the rupture status of a large number of sensors can be grasped intensively.

The breaking strain εf changes depending on the material of the sensor foil, the shape of the narrow portion, the size, the stress intensity factor K, the crack generation condition, and the like, so that the breaking strain εf may be adjusted to meet the measurement target. it can.
However, since the strain transmission piece 2 is also distorted by receiving stress, the strain transmitted to the sensor foil 1 is slightly relaxed by the cross-sectional area ratio or the like. Therefore, for accurate measurement, it is necessary to experimentally calculate and correct these relaxation rates.

In the strain sensing sensor of this embodiment, the displacement generated in the measurement span of several mm to several hundred mm is concentrated on the gap portion, the sensor foil is broken, and it is detected visually or by a portable simple instrument such as a tester. It is possible to set and measure a large number of measurement points compared to the above, and to measure and diagnose as a whole.
The sensor is formed in a small size with a length of 200 mm or less, and the measurement cost is enormous even if the number of measurement points is increased, because it is not necessary to connect to the monitor simply by sticking to the structure surface. Absent.

FIG. 5 is a graph showing the results of an experiment conducted to confirm the detection ability of the strain sensing sensor.
In the graph, the experimental result is plotted with the horizontal axis as the theoretical value of stress when the sensor foil of the strain sensing sensor breaks, the vertical axis as the actual measurement value, and the line width d of the narrow portion as a parameter. For three cases with line widths of 50 μm, 100 μm, and 200 μm, the stress when the member to be measured was stressed and fractured was determined. In this experiment, the breaking stress at the same line width was changed by changing the measurement span L to 40 mm, 60 mm, and 80 mm. The test is conducted with a gap of 200 μm when the line width is 50 μm, and with a gap of 100 μm when the line widths are 100 μm and 200 μm.
From the experimental results, it can be seen that the theoretical value and the actually measured value are in good agreement, and can be used as a sensor under certain restrictions.

  In the embodiment shown in FIG. 1, since three strain sensing sensors are formed together on one thin film substrate 4, three measurement spans can be set independently at a time. it can. For this reason, the same span can be set to improve measurement accuracy, and measurement under three different conditions can be performed.

FIG. 6 is a plan view for explaining another aspect of the strain sensing sensor of the present embodiment.
In the sensor of this aspect, a gap portion along the strain generation direction is provided between a pair of strain transmission pieces 11, and the narrow portion 13 of the sensor foil 12 is disposed with the gap interposed therebetween.
Based on the fact that the local strain of the narrow portion 13 breaks when it exceeds the breaking elongation of the material, it is detected that the strain applied to the member to be measured has exceeded the threshold value. In addition, an electrical insulating layer may be formed between the strain transmission piece 11 and the sensor foil 12 and electrically sensed via the electrode portion 14 formed on the sensor foil 12.
As shown in FIG. 6, when the narrow portion 13 forming the bridge is inclined in the direction in which the member extends, the damage strength differs depending on whether the narrow portion is expanded or contracted due to the expansion and contraction of the member. The sensor has different sensitivities depending on the expansion and contraction.
In the sensor shown in FIG. 6, two sensors are arranged point-symmetrically, and the measurement accuracy is improved by double measurement.

FIG. 7 is a plan view showing still another embodiment.
The strain transmitting pieces 15 are opposed to each other with the gap portion 17 interposed therebetween, and the sensor foil 16 is formed not to cover the edges of the strain transmitting pieces 15 but to be slightly retracted inward. Accordingly, the narrow portion forming the bridge 18 is longer than each of the above embodiments, and the strain rate may be relaxed even when the sensor foil 16 is firmly fixed to the strain transmitting piece 15. The state can be judged well.
Moreover, since the dimensional accuracy in the narrowest part of the bridge part 18 can be ensured easily, the reproducibility of the measurement is improved.

FIG. 8 is a plan view with an enlarged view of a main part of a strain sensing sensor according to a second embodiment of the present invention, FIG. 9 is a cross-sectional view of the main part, and FIG. 10 is an enlarged view of the main part of another aspect of the present embodiment. The accompanying plan views, FIGS. 11, 12, and 13, are plan views showing still another embodiment of the present embodiment.
The strain sensing sensor of the second embodiment is characterized in that it has a single structure in which the strain transmitting piece and the sensor foil are formed of the same material.
Referring to the plan view of FIG. 8 and the cross-sectional view of FIG. 9, a pair of strain transmission pieces 21 are arranged opposite to each other with the gap portion 22 interposed therebetween, and a strain sensing sensor is formed by a metal thin film surrounded by a frame body 25. The

The strain sensor is attached to the thin film substrate 29 so that the strain transmitting piece 21 can freely expand and contract, thereby facilitating the handling of the strain sensor, and when attached to the surface of the measurement target member 30. The position of the parts is not upset.
A bridge portion 24 is formed in the gap portion 22. The bridge portion 24 is thinner than the portion of the strain transmission piece 21, and is formed to have a thickness of 20 μm, for example, while the thickness of the strain transmission piece 21 is 200 μm.

  The bridge portion 24 is formed of, for example, a thin film band 26 having a width of 1 mm with respect to a gap portion having a width of 1 mm, and a pair of slits 27 carved from both sides of the width are formed in the middle portion in the length direction. The slit 27 has, for example, a processing limit width of 0.225 mm and a depth of 0.4 mm. The slit tip is formed at an acute angle. When a load larger than a predetermined load is applied, a crack is easily formed from the slit tip. The remaining portion 28 is easily broken by growth. Note that the distance between the tips of the slits 27 is 0.2 mm, and once the fracture occurs, the remaining portion 28 is broken all at once.

The strain transmitting piece 21, the bridge portion 24, and the frame body 25 are formed by depositing a metal on the entire surface and depositing a thin bridge portion 24, and then applying a mask to the bridge portion 24 to electrocast the thick portion. It is formed accurately by the two-stage electroforming method.
When applied to the measurement target member 30, an appropriate position of the strain transmission piece 21 is fixed to the measurement target member by spot welding 23 so that the measurement span becomes a predetermined value according to the strain measurement range. .

  As the ratio of the cross-sectional area of the portion between the slit tips, which is the narrowest part of the bridge portion 24, and the cross-sectional area of the strain transmitting piece 21 increases, the strain distribution rate is biased toward the bridge portion 24 and the measurement sensitivity improves. Further, since the strain concentrates on the bridge portion 2 as the ratio between the gap width of the gap portion 22 and the measurement span between the welding positions 23 increases, the bridge portion 24 can be broken even if a small stress occurs in the measurement target member. Increases nature.

The strain transmission piece 21, the bridge portion 24, and the frame body 25 are preferably formed from nickel foil. Since nickel is frequently used in fatigue sensors, there is a tremendous accumulation of technology regarding sensor characteristics and manufacturing methods. By utilizing these technologies, it is easy to design and manufacture an accurate sensor that meets the purpose.
Note that it is recommended that the thin film substrate 29 be formed of Invar having a small coefficient of thermal expansion.

  FIG. 10 is a diagram showing another aspect of the present embodiment. Like FIG. 6, a gap portion 32 is provided between the pair of strain transmission pieces 31 along the strain generation direction, and the bridge is sandwiched by sandwiching the gap. A portion 33 is provided. The gap width was about 1 mm. The strain sensor can be precisely formed of, for example, nickel metal using a two-stage electroforming method, and is used in a form fixed to a thin film substrate 35 made of Invar, for example.

The bridge portion 33 is made of the same material as that of the strain transmission piece 31 and has a thickness of 20 μm, which is about 1/10 of the strain transmission piece 31, and a width such as 0.166 mm that is close to the processing limit in consideration of processing accuracy. A narrow portion 34 having In addition, when it has such a narrow part 34, it thinks that the distortion which generate | occur | produced in the to-be-measured member is concentrated on the narrowest part of the narrow part 34 substantially, for example, the part of about 200 micrometers in length, etc., The distortion rate of the bridge portion 33 may be greatly estimated.
The total length of the two strain transmitting pieces 31 is about 100 mm, and the measurement span can be selected to an appropriate value of 100 mm or less, for example, about 60 mm, 80 mm, or 100 mm.
These dimensions can be changed according to the amount of strain to be detected.

Since the two strain transmission pieces 31 move in the opposite directions by the same amount as the strain generated in the measurement span determined by the spot welding position of the strain transmission piece 31, the shear force acts on the bridge portion 33, and the local strain of the narrow portion 34. Exceeds the breaking elongation of the material, the narrow portion 34 is broken.
Based on the breakage of the narrow portion 34, it is sensed that the strain applied to the member to be measured has exceeded a threshold value. Breakage can be confirmed visually.

11 and 12 are plan views showing still another aspect of the present embodiment.
The embodiment of FIG. 11 senses the strain of the member to be measured when the narrow portion formed integrally with the strain transmitting piece extends and breaks. In the drawing, the strain in two directions of extension and compression can be measured. Thus, a combined sensor is represented.

  The sensor on the upper side of the drawing senses strain in the extension direction, and a narrow portion 37 is formed at substantially the center of the strain transmitting piece 36, and is measured by spot welding or the like at a fixed position 41 sandwiching the narrow portion 37. Fix to the target member and measure. The strain generated between the measurement spans is concentrated on the narrow portion 37, the deformation ratio of the narrow portion 37 is enlarged, and the fracture occurs when the local strain exceeds the breaking elongation of the narrow portion. It can be seen that the corresponding strain has occurred. On the other hand, since the resistance force to the compression of the narrow portion 37 is large, the narrow portion 37 is not easily damaged even if the measurement target member is distorted in the compressing direction. The narrow portion 37 can be further improved in sensitivity by reducing the thickness and increasing the stress intensity factor.

The sensor on the lower side of the drawing senses strain in the compression direction. The other strain transmission piece 39 is provided at the other end of one strain transmission piece 38 so as to be folded back through the narrow portion 40. When each of the strain transmitting pieces 38 and 39 is fixed to the measurement target member by spot welding or the like, the narrow portion 40 expands when strain in the compressing direction occurs in the measurement span between the fixed positions 42, and the limit is reached. When it exceeds, it will break. In this case, when the measurement span is distorted in the extending direction, the narrow portion 40 is subjected to compressive stress, so that it is not easily damaged and the strain cannot be sensed.
In this way, since the two sensors share the strain in the compression direction and the extension direction, they are juxtaposed on one thin film substrate 43 to combine the functions, thereby forming a strain detection sensor in both directions.

The sensor of the embodiment of FIG. 12 is provided with a gap portion 46 along a strain generation direction between a pair of strain transmission pieces 44 and 45, and a bridge portion 47 disposed with the gap interposed therebetween. The bridge portion 47 is formed integrally with the transmission pieces 44 and 45 by a two-stage electroforming method.
As shown in FIG. 12, when the bridge portion 47 is formed so as to be inclined in the extending direction of the member to be measured, the sensing ability is high when the narrow portion is extended by the extension of the member, but it is broken when the member is compressed by the compression of the member. Since it is difficult to perform and the sensing ability is inferior, a pair of bridge portions 47 having opposite inclinations are formed so that it can sense that the strain exceeds the threshold value in both directions.

FIG. 13 is a plan view illustrating still another aspect of the present embodiment.
The aspect of this figure is characterized in that the gap portion 50 formed between the strain transmission pieces 48 and 49 has an inclination with respect to the strain detection direction. Since the bridge portion 51 is formed perpendicular to the gap portion 50, the bridge portion 51 has an angle with respect to the direction of strain, and the narrow portion of the bridge portion 51 is easily broken because it is sheared, thereby improving the sensing sensitivity.

14 is a plan view of a strain sensor according to a third embodiment of the present invention, FIG. 15 is a side view thereof, and FIGS. 16-18 are plan views showing other embodiments.
The strain sensing sensor of the present embodiment is characterized in that a sensor foil having a narrow portion is formed directly on the surface of the strain transmission piece with a metal different from the strain transmission piece.
14 and 15, the strain sensing sensor of the present embodiment has a sensor foil 53 passed through a gap formed between a pair of strain transmitting pieces 52, and a slit is provided at the center from both edges. What is provided with the strain sensing part 54 so as to leave a narrow remaining part is fixed to the thin film substrate 55. A measurement span is determined by fixing the strain transmission piece 52 to a measurement target member by a method such as spot welding at an appropriate position 56.

When the strain of the member between the measurement spans concentrates on the strain sensing unit 54 and exceeds the breaking strain of the sensor foil 53, the strain sensing unit 54 breaks. By visually confirming the breakage of the sensor foil 53, it can be estimated whether or not the measurement target member has exceeded a preset strain threshold.
Note that the greater the layer thickness ratio of the sensor foil 53 to the strain transmitting piece 52, the higher the stress concentration rate, and the greater the strain is distributed to the sensor foil, the easier it is to break at the narrow portion.
When stress is applied to the strain sensing portion 54, two small cracks are generated at one or both ends of the slit to form a deformation band, and the deformation bands on both sides gradually develop and eventually merge to reach a fracture.

  In the embodiment of FIG. 16, the sensor foil 59 is disposed across the gap portion 58 formed in the strain direction between the pair of strain transmission pieces 57, and the narrow portion 60 is disposed at the position of the gap portion 58 of the sensor foil 59. Formed. Since the narrow portion 60 is broken by a shearing force generated according to the amount of strain of the measurement target member, it can be determined whether or not a strain exceeding a predetermined threshold has occurred in the measurement target member.

In the embodiment of FIG. 17, the gap portion formed between the strain transmission pieces 61 is bent by the hand of the key, and the bridge portion 63 of the sensor foil 62 formed at the bent position is the fixed portion of the strain transmission piece 61. 65 is configured to have sensitivity when moving in the direction of contraction. The strain detection part in the bridge part 63 is selected so that the cross-sectional area matches the conditions so that the fracture occurs when stress is applied in the tensile direction. A cutout may be provided in the center to induce breakage.
The strain sensor is used while being fixed on the thin film substrate 64.

In the embodiment of FIG. 18, a pair of strain transmitting pieces 66 forms a gap 68 along the center line of the width, and a sensor foil 67 having a narrow portion straddling the gap 68 is provided and fixed to the thin film substrate 69. It has been done. The narrow portion of the sensor foil 67 is easily broken when pulled in the extension direction, and is not easily buckled when pressed in the compression direction.
This strain sensing sensor is used with the end portion 70 of the strain transmitting piece 66 fixed to the rotating shaft 71 with the gap 68 in the axial direction on the surface of the rotating shaft 71, for example. When the rotating device is operated, it can be detected whether the torsional strain generated in the extending direction of the narrow portion has exceeded a predetermined threshold.
It should be noted that the sensitivity to the torsional strain in the opposite direction is low and difficult to detect.

FIG. 19 is a plan view of a strain sensing sensor according to a fourth embodiment of the present invention.
The strain sensing sensor of this embodiment estimates the strain history by enlarging and showing the residual strain remaining in the sensor component due to hysteresis after the strain of the measurement target member disappears. Although the sensor component does not break, it is possible to sense the strain of the measurement target member by deformation.
The strain sensing sensor of the present embodiment is a single layer type sensor that is shaped by etching a metal thin film forming the strain transmitting piece 81 or depositing it by an electroforming method or the like. Although not shown in FIG. 18, it is preferable that the strain detection sensor is fixed to the thin film substrate in the same manner as the sensors of the above-described embodiments so that the positional relationship between the components is easily maintained correctly.

As shown in FIG. 19, the strain transmission piece 81 includes a column portion 82 that transmits strain, and a lever portion 83 and a frame body 84 that have a function of enlarging the strain. A narrowed hinge portion 86 is formed between the base end portion of the lever portion 83 and the frame body 84, and a narrow portion 85 connected to the tip end of the column portion 82 is formed in the vicinity of the root side end portion of the lever portion 83. . It is preferable that the narrowed portion 85 of the hinge portion 86 is narrowed to give flexibility, and the narrowed portion 85 is further reduced in thickness to increase the stress concentration rate.
The base of the column portion 82 is fixed to the surface of the measurement target member, and the frame portion near the hinge portion 86 of the lever portion 83 is fixed to the surface of the measurement target member.

  When the measurement span L between the fixed position 87 of the pillar portion 82 and the fixed position 88 of the lever portion 83 is extended while the measurement target device having the strain sensor is fixed, the lever portion 83 moves the narrow portion 85. Since it is pulled by the column part 82 via the hinge part 86, it rotates with the hinge part 86 as a fulcrum, and the front-end | tip part inclines below. When the operation of the device to be measured is finished, the measurement span L returns to the original state, but the narrow portion 85 has hysteresis, so that residual deformation corresponding to the deformation amount remains. Therefore, the tip of the lever portion 83 does not return to the original position, and shows a deflection angle corresponding to the maximum strain amount. Therefore, by measuring the residual deflection angle, it is possible to estimate the strain generated in the measurement span L during operation.

As described above in detail, it is possible to estimate the magnitude of strain generated in the target member during operation by fixing the strain sensing sensor of the present invention to the surface of the measurement target member and then operating the target device. it can.
The strain sensor of the present invention can be supplied in the form of a thin and small sensor sheet, and can be easily applied to narrow surfaces. Also, the sensing result can be easily known visually or by a tester. Therefore, the cost of application and measurement is greatly reduced as compared with the prior art, and even if a large number of measurement points sufficient for analysis are set for the apparatus, no excessive cost is required.

DESCRIPTION OF SYMBOLS 1 Sensor foil 2 Strain transmission piece 3 Insulating film 4 Thin film substrate 5 Measuring object 6 Frame 7 Spot welding part 8 Bridge part 9 The part adjacent to a bridge part 10 Electrode part 11 Strain transmission piece 12 Sensor foil 13 Bridge part 14 Electrode part DESCRIPTION OF SYMBOLS 15 Strain transmission piece 16 Sensor foil 17 Gap part 18 Bridge part 21 Strain transmission piece 22 Gap part 23 Spot weld part 24 Bridge part 25 Frame body 26 Bridge part thin film band 27 Slit 28 Remaining part 29 Thin film substrate 30 Measuring object 31 Strain transmission Piece 32 Gap portion 33 Bridge portion 34 Narrow portion 35 Thin film substrate 36 Strain transmitting piece 37 Narrow portion 38, 39 Strain transmitting piece 40 Narrow portion 41, 42 Spot welding fixing position 43 Thin film substrate 44, 45 Strain transmitting piece 46 Gap portion 47 Bridge 48, 49 Strain transmission Piece 50 Gap portion 51 Bridge portion 52 Strain transmission piece 53 Sensor foil 54 Strain sensing portion 55 Thin film substrate 56 Fixed position 57 Strain transmission piece 58 Gap portion 59 Sensor foil 60 Bridge portion 61 Strain transmission piece 62 Sensor foil 63 Bridge portion 64 Thin film substrate 65 Fixed portion 66 Strain transmitting piece 68 Gap 67 Sensor foil 69 Thin film substrate 70 Fixed end portion 71 Rotating shaft 81 Strain transmitting piece 82 Column portion 83 Lever portion 84 Frame body 85 Narrow portion 86 Hinge portion 87, 88 Fixed position

Claims (11)

The thin film substrate includes at least one pair of strain transmission pieces, an insulating film, and a sensor foil. The thin film substrate is attached to the measurement target and is distorted together with the measurement target. The strain transmission pieces are formed on the thin film substrate. One end is fixed to the thin film substrate to determine the measurement span, the insulating film is disposed between the strain transmitting piece and the sensor foil, and the sensor foil and the strain transmitting piece are attached via the insulating film. The sensor foil is formed of a good electric conductor and has a cross-sectional area smaller than the strain transmitting piece so as to be passed between the gaps of the pair of strain transmitting pieces, and the strain between the measurement spans is reduced. When the sensor foil concentrates on the sensor foil and exceeds the breaking strain of the sensor foil, the sensor foil breaks to detect that the strain to be measured exceeds a predetermined strain, Strain detecting sensor, characterized in that the breaking of the capacitors foil can be electrically detected. The strain sensing sensor according to claim 1, wherein the bridge portion has a portion having a width narrower than a width of the strain transmitting piece. 3. The strain sensor according to claim 1, wherein the insulating film extends in a range covering substantially the entire surface of the sensor foil excluding the bridge portion. The pair of strain transmission pieces are arranged side by side in a direction along a strain detection direction, and the sensor foil detects a strain in which the strain transmission pieces are distorted in a direction away from each other. 4. The strain sensing sensor according to any one of 3 above. The pair of strain transmission pieces are arranged side by side in a direction perpendicular to a strain detection direction, and the sensor foil detects a strain distorted in a direction in which the strain transmission pieces are displaced from each other. 4. The strain sensing sensor according to any one of 3 above. 6. The strain sensing sensor according to claim 1, wherein the sensor foil has a shape that concentrates the stress of the strain transmitting piece and expands the stress. 7. The strain sensing sensor according to any one of claims 1 to 6, wherein the sensor foil extends over the strain transmitting piece to form an electrode. The strain sensor according to any one of claims 1 to 7, wherein the sensor foil is made of a material having a breaking strain of 20% or less. The strain sensing sensor according to any one of claims 1 to 8, wherein the thin film substrate is formed of invar and the sensor foil is formed of nickel. The strain transmitting piece includes a reinforcing frame that surrounds the strain transmitting piece and to which a part of the strain transmitting piece is connected, and the strain transmitting piece and the reinforcing frame are formed of the same thin film material. The strain sensing sensor according to any one of claims 1 to 9. 11. The strain sensing sensor according to claim 1, wherein the strain transmitting piece is formed by any one of an electroforming method, an etching method, and a die cutting method.

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