Strain detection device

Abstract

To provide a strain detection device capable of improving detection accuracy.SOLUTION: A strain detection device in an embodiment includes a flexible base material, first, second, third, and fourth sensor patterns having a plurality of strain gauges each arranged in a line in a first direction and stacked on the base material, and a controller that drives the strain gauges. A first strain gauge of the first sensor pattern, a second strain gauge of the second sensor pattern, a third strain gauge of the third sensor pattern, and a fourth strain gauge of the fourth sensor pattern are disposed opposite to each other in a thickness direction of the base material. The first strain gauge and the fourth strain gauge are disposed symmetrically about a central position in the thickness direction of the base material. The second strain gauge and the third strain gauge are disposed symmetrically about the central position in the thickness direction of the base material.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] An embodiment of the present invention relates to a distortion detection device. [Background technology]

[0002] As an example of a strain detection device, a flexible film- or sheet-shaped strain gauge sensor is known. The strain gauge sensor has strain gauges arranged side by side on the surface of a band-shaped flexible sheet base material, and a plurality of signal lines for passing electricity through these strain gauges. A plurality of strain gauges are also provided on the front and back of the sheet. The strain gauges on the front side are arranged facing the strain gauges on the back side, respectively. The strain gauge sensor is wrapped around a curved object to detect the curved shape of the object by detecting the resistance change of each strain gauge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-185966 A [Patent Document 2] JP 2013-96821 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the embodiments of the present invention is to provide a strain detection device capable of improving detection accuracy. [Means for solving the problem]

[0005] The strain detector according to the embodiment includes a flexible substrate including a plurality of insulating layers, a plurality of first strain gauges arranged in a row at intervals in a first direction, and a plurality of wires respectively connected to the first strain gauges, a first sensor pattern provided on the substrate, a plurality of second strain gauges arranged in a row at intervals in the first direction, and a plurality of wires respectively connected to the second strain gauges, a second sensor pattern laminated on the substrate and facing the first sensor pattern with an insulating layer interposed therebetween, a plurality of third strain gauges arranged in a row at intervals in the first direction, and a plurality of wires respectively connected to the second strain gauges, a third sensor pattern laminated on the base material and facing the second sensor pattern with an insulating layer between them, a fourth sensor pattern including a plurality of fourth strain gauges arranged in a row at intervals in the first direction and a plurality of wirings respectively connected to the fourth strain gauges, laminated on the base material and facing the third sensor pattern with an insulating layer between them, and a controller that applies voltages to the first, second, third and fourth strain gauges via the plurality of wirings and reads detection values ​​of each strain gauge. The first, second, third and fourth strain gauges are disposed opposite each other in a thickness direction of the base material, the first and fourth strain gauges are disposed symmetrically with respect to a center position in the thickness direction of the base material, and the second and third strain gauges are disposed symmetrically with respect to a center position in the thickness direction of the base material. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a perspective view of a strain gauge sensor device according to an embodiment. [Diagram 2] FIG. 2 is a vertical sectional view of the strain gauge sensor device. [Diagram 3] 3 is a cross-sectional view of the strain gauge sensor device taken along line AA in FIG. 2. FIG. [Figure 4] FIG. 4 is a vertical sectional view of a strain gauge sensor device according to a modified example. [Diagram 5]FIG. 5 is a development view showing a schematic diagram of strain gauges and wirings of a second sensor pattern and a third sensor pattern of the strain gauge sensor device according to the embodiment. [Figure 6] FIG. 6 is a perspective view illustrating a laminated structure of a sensor pattern of a first sensor sheet in the strain gauge sensor device. [Figure 7] FIG. 7 is a block diagram of a controller of the strain gauge sensor device. [Figure 8] FIG. 8 is a plan view showing the first to fourth sensor patterns of the strain gauge sensor device, illustrating a scanning operation during detection, and an analog front end of a controller, in an expanded form. [Figure 9] FIG. 9 is a circuit diagram of a differential detection circuit in the analog front end. [Figure 10] FIG. 10 is a side view showing a schematic diagram of the strain gauge sensor device installed on the surface of a test object. [Figure 11] FIG. 11 is a diagram showing a schematic view of a part of the strain gauge sensor device in a state where it is installed on the surface of a test object. [Figure 12] FIG. 12 is a plan view showing the first to fourth sensor patterns of the strain gauge sensor device and an analog front end of a controller, showing a scanning operation during detection. [Figure 13A] 13A is a schematic diagram showing an example of strain detection using strain gauges in second and third layers in a part of the strain gauge sensor device shown in FIG. 11; FIG. [Figure 13B] 13B is a schematic diagram showing an example of strain detection using strain gauges in the first and fourth layers in a part of the strain gauge sensor device shown in FIG. 11; FIG. [Figure 14] FIG. 14 is a diagram showing a curved surface form in which the radius of curvature calculated based on the detection values ​​of strain detected by the strain gauges in the second and third layers is plotted. [Figure 15] FIG. 15 is a diagram showing a curved surface form in which the radius of curvature calculated based on the detection values ​​of strain detected by the strain gauges in the first and fourth layers is plotted. [Figure 16]FIG. 16 is a diagram showing the curved surface form in which the average value of the radius of curvature calculated as the final data is plotted. [Figure 17] FIG. 17 is a diagram showing a schematic diagram of the dynamic range of the inner strain gauge and the outer strain gauge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The disclosure is merely an example, and appropriate modifications that are within the spirit of the invention and that can be easily conceived by a person skilled in the art are naturally included in the scope of the present invention. In addition, in order to make the explanation clearer, the width, thickness, shape, etc. of each part may be shown diagrammatically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each figure, elements similar to those described above with respect to the previous figures may be given the same reference numerals, and detailed explanations may be omitted as appropriate.

[0008] (Embodiment) As an example of a strain detection device, a strain gauge sensor device according to an embodiment will be described in detail. Fig. 1 is a perspective view of the strain gauge sensor device according to the embodiment. As shown in the figure, the strain gauge sensor device 10 constitutes a double-sided strain gauge sensor. The strain gauge sensor device 10 includes a long and thin strip-shaped flexible base substrate 44 functioning as a base material, a first sensor sheet 20A attached to a first main surface (front surface) of the base substrate 44, a second sensor sheet 20B attached to a second main surface (back surface) of the base substrate 44, a pair of flexible wiring boards (FPCs) 14, and an intermediate substrate (drive circuit substrate) 12 connected to the first sensor sheet 20A and the second sensor sheet 20B via the pair of flexible wiring boards 14. In one example, the base substrate 44 is an insulating layer and is formed of a resin such as polyethylene terephthalate (PET) or polyimide to a thickness of about 0.3 to 0.5 mm.

[0009] Each of the first sensor sheet 20A and the second sensor sheet 20B has a long, thin, flexible sheet base material 22 made of an insulating layer and two layers of conductor patterns (sensor patterns) CDA, CDB (CDC, CDD) provided on the sheet base material 22. The sensor pattern in each layer includes a plurality of strain gauges G0 to Gn. The plurality of strain gauges G0 to Gn are aligned in a row in the longitudinal direction X at predetermined intervals from one end to the other end of the longitudinal direction X of the sheet base material 22. In the figure, the longitudinal direction X and the width direction Y of the sensor sheet are two directions that are perpendicular to each other. These directions may intersect at an angle other than 90 degrees.

[0010] FIG. 2 is a vertical cross-sectional view of the strain gauge sensor device 10. As shown in FIG. 2, the base substrate 44 has a front surface and a back surface opposite the front surface. In one example, the first sensor sheet 20A is attached to the front surface of the base substrate 44 by an adhesive layer Ad such as a transparent adhesive sheet (OCA). The second sensor sheet 20B is attached to the back surface of the base substrate 44 by an adhesive layer Ad. The relay board 12 includes a drive circuit 40 and a plurality of wirings provided on one surface side, and a plurality of wirings (not shown) provided on the other surface side. The first sensor pattern CDA and the second sensor pattern CDB of the first sensor sheet 20A are connected to the wirings provided on the upper surface side of the relay board 12 via the FPC 14. Similarly, the third sensor pattern CDC and the fourth sensor pattern CDD of the second sensor sheet 20B are connected to the wirings provided on the lower surface side of the relay board 12 via the FPC 14.

[0011] 3 is a cross-sectional view of the strain gauge sensor device taken along the line AA in FIG. 2. As shown in the figure, the first sensor sheet 20A includes a flexible strip-shaped sheet base material 22, a first sensor pattern CDA (G0-Gn) provided on one surface of the sheet base material 22, a first insulating layer IL1 laminated on the sheet base material 22 over the first sensor pattern CDA, a second sensor pattern CDB (G0-Gn) provided on the first insulating layer IL1, a second insulating layer IL2 laminated on the first insulating layer IL1 over the second sensor pattern CDB, and a protective layer (surface protective film) PTL provided on the second insulating layer IL2. In one example, the sheet base material 22 is made of polyimide, and the first and second insulating layers IL1 and IL2 are made of silicon nitride (SiN). In one example, the first sensor sheet 20A is bonded to the base substrate 44 on the side of the protective layer TPL by an adhesive layer Ad.

[0012] Similarly, the second sensor sheet 20B includes a flexible strip-shaped sheet base material 22, a fourth sensor pattern CDD provided on one surface of the sheet base material 22, a first insulating layer IL1 laminated on the sheet base material 22 over the fourth sensor pattern CDD, a third sensor pattern CDC provided on the first insulating layer IL1, a second insulating layer IL2 laminated on the first insulating layer IL1 over the third sensor pattern, and a protective layer (surface protective film) PTL provided on the second insulating layer IL2. In one example, the sheet base material 22 is formed of polyimide, and the first and second insulating layers IL1 and IL2 are formed of silicon nitride (SiN). In one example, the second sensor sheet 20B is bonded to the base substrate 44 on the side of the protective layer TPL by an adhesive layer Ad.

[0013] The entire base substrate 44, adhesive layer Ad, first sensor sheet 20A, and second sensor sheet 20B are used as the base material, and the strain gauge of the first sensor pattern CDA will be referred to as the first strain gauge GA, the strain gauge of the second sensor pattern CDB as the second strain gauge GB, the strain gauge of the third sensor pattern CDC as the third strain gauge GC, and the strain gauge of the fourth sensor pattern CDD as the fourth strain gauge GD. As shown in FIG. 3, the first strain gauge GA, the second strain gauge GB, the third strain gauge GC, and the fourth strain gauge GD are arranged opposite each other in the thickness direction Z of the base material, sandwiching an insulating layer between them. When the center position of the thickness direction Z of the base material is the center line C, the outer first strain gauge GA and the fourth strain gauge GD are arranged symmetrically with respect to the center line C, and the inner second strain gauge GB and the third strain gauge GC are arranged symmetrically with respect to the center line C. That is, when the distance between the outer first strain gauge GA and the center line C is d1, the distance between the outer fourth strain gauge GD and the center line C is d2, the distance between the inner second strain gauge GB and the center line C is d3, and the distance between the inner third strain gauge GC and the center line C is d4, it is preferable that d1=d2 and d3=d4. d1≠d3 and d2≠d4 may also be satisfied.

[0014] In the base material, the first sensor sheet 20A and the second sensor sheet 20B may each be configured so that the protective layer PTL side is joined to the base substrate 44 by an adhesive layer Ad. Alternatively, as shown in Fig. 4, the base substrate may be omitted and the first sensor sheet 20A and the second sensor sheet 20B may be attached to each other by an adhesive layer Ad such as a transparent adhesive sheet (OCA).

[0015] FIG. 5 is a plan view showing a schematic expanded view of the second sensor pattern CDB of the first sensor sheet 20A and the third sensor pattern CDC of the second sensor sheet 20B, and FIG. 6 is a perspective view showing a schematic expanded view of the layered structure of the first sensor pattern CDA and the second sensor pattern CDB in the first sensor sheet 20A. As shown in FIG. 5, according to this embodiment, the first sensor sheet 20A and the second sensor sheet 20B are configured to have the same shape, dimensions, and sensor pattern. The pattern configuration will be described by taking the second sensor pattern CDB of the first sensor sheet 20A and the third sensor pattern CDC of the second sensor sheet 20B as representatives. Each of the sensor patterns has a plurality of strain gauges G0 to Gn. The plurality of strain gauges G0 to Gn are arranged in a line in the longitudinal direction X from one end (tip) to the other end (base) of the sheet substrate 22 at an interval L. Each of the strain gauges G0 to Gn extends in the width direction Y in a bellows-like or rectangular wave-like shape, and has one end and the other end in the width direction Y. Each of the strain gauges G0 to Gn has a desired resistance value, and generates a resistance change according to strain.

[0016] Each sensor pattern has a plurality of power supply lines VL0 to VLn, a plurality of ground lines GNL0 to GNLn, a plurality of first signal lines Sa0 to San, and a plurality of second signal lines Sb0 to Sbn extending in the longitudinal direction X along the row of the strain gauges G0 to Gn. The power supply lines VL0 to VLn are located on the side of one end of the strain gauges G0 to Gn. The power supply lines VL0 to VLn have one end connected to one end of the strain gauges G0 to Gn and the other end located on the base end side of the sheet substrate 22, and extend substantially parallel to each other. The first signal lines Sa0-San are located between one end of the strain gauges G0-Gn and the power supply lines VL0-VLn. The first signal lines Sa0-San have one end connected to one end of the strain gauges G0-Gn and the other end located on the base end side of the sheet base material 22, and extend substantially parallel to each other.

[0017] The ground wires GNL0 to GNLn are located on the side of the other ends of the strain gauges G0 to Gn. The ground wires GNL0 to GNLn have one end connected to the other ends of the strain gauges G0 to Gn, respectively, and the other end located on the base end side of the sheet base material 22, and extend approximately parallel to each other. The second signal lines Sb0-Sbn are located between the other ends of the strain gauges G0-Gn and the ground lines GNL0-GNLn. The second signal lines Sb0-Sbn have one end connected to the other end of the strain gauges G0-Gn and the other end located on the base end side of the sheet base material 22, and extend substantially parallel to each other. As described later, in this embodiment, the ground lines GNL0 to GNLn of the second sensor pattern CDB are electrically connected to the power lines VL0 to VLn of the third sensor pattern CDC via through holes SH at the position of the relay substrate 12. As a result, the strain gauges of the second sensor pattern CDB are connected in series to the strain gauges of the third sensor pattern.

[0018] 2 and 3, in the first sensor sheet 20A, the first sensor patterns CDA (G0 to Gn) are formed on a sheet base material 22, and a first insulating layer IL1 is laminated on the sheet base material 22 so as to overlap the first sensor patterns CDA. The second sensor patterns CDB are formed on the first insulating layer IL1, and a second insulating layer IL2 is laminated on the first insulating layer IL1 so as to overlap the second sensor patterns CDB. As shown in FIG. 6, the strain gauges G0 to Gn of the second sensor pattern CDB are positioned opposite the strain gauges G0 to Gn of the first sensor pattern CDA, respectively, in the thickness direction of the first sensor sheet 20A.

[0019] The power supply lines VL0 to VLn, the ground lines GNL0 to GNLn, the first signal lines Sa0 to San, and the second signal lines Sb0 to Sbn of the second sensor pattern CDB are slightly shifted in the width direction Y from the power supply lines VL0 to VLn, the ground lines GNL0 to GNLn, the first signal lines Sa0 to San, and the second signal lines Sb0 to Sbn of the first sensor pattern CDA, respectively. The power lines VL0-VLn, ground lines GNL0-GNLn, first signal lines Sa0-San, and second signal lines Sb0-Sbn of the second sensor pattern CDB each have a tip portion DA connected to the strain gauges G0-Gn, and a base portion PA extending from a midway portion to the base end of the sheet base material 22. Each tip portion DA is provided on the first insulating layer IL1, and the base portion PA is provided on the sheet base material 22. An end of each tip portion DA is electrically connected to an end of the base portion PA via a contact hole CH provided in the first insulating layer IL1. In this way, the base end portions PA of the power lines VL0 to VLn, the ground lines GNL0 to GNLn, the first signal lines Sa0 to San, and the second signal lines Sb0 to Sbn of the second sensor pattern CDB are located on the same plane as the power lines VL0 to VLn, the ground lines GNL0 to GNLn, the first signal lines Sa0 to San, and the second signal lines Sb0 to Sbn of the first sensor pattern CDA, that is, are located on the sheet base material 22, and are connected to the wiring of the common FPC 14.

[0020] The third sensor pattern CDC and the fourth sensor pattern CDD of the second sensor sheet 20B are formed to have the same shape, the same dimensions, and the same structure as the first sensor pattern CDA and the second sensor pattern CDB of the first sensor sheet 20A described above.

[0021] As shown in FIG. 2, the first sensor sheet 20A and the second sensor sheet 20B configured as described above are attached to the front and rear surfaces of the base substrate 44, and face each other with the base substrate 44 in between. That is, the two layers of strain gauges G0-Gn of the first sensor sheet 20A face the two layers of strain gauges G0-Gn of the second sensor sheet 20B with the base substrate 44 in between. Here, it is preferable that the strain gauges G0-Gn of the first sensor sheet 20A and the strain gauges G0-Gn of the second sensor sheet at least partially overlap each other in a plan view seen from a direction perpendicular to the surface of the base substrate 44. Alternatively, it is preferable that the strain gauges G0-Gn of the sensor sheets 20A and 20B overlap each other without being shifted in the width direction Y while allowing at least a shift in the longitudinal direction X. Alternatively, it is more preferable that the strain gauges G0-Gn of the sensor sheets 20A and 20B overlap each other without being shifted in either the longitudinal direction X or the width direction Y.

[0022] The wiring of the first sensor pattern CDA and the second sensor pattern CDB of the first sensor sheet 20A extends onto the upper surface of the relay board 12 via the FPC 14. The wiring of the third sensor pattern CDC and the fourth sensor pattern CDD of the second sensor sheet 20B extends onto the rear surface of the relay board 12 via the FPC 14. In this embodiment, the ground lines GNL0 to GNLn of the first sensor pattern CDA are electrically connected to the power lines VL0 to VLn of the fourth sensor pattern CDD by plated through holes SH as connection lines formed in the relay board 12. Furthermore, the ground lines GNL0 to GNLn of the second sensor pattern CDB are electrically connected to the power lines VL0 to VLn of the third sensor pattern CDC by plated through holes SH as connection lines formed in the relay board 12.

[0023] The connection lines are not limited to plated through holes SH, and may be wiring patterns on the relay board 12. It is also possible to adopt a configuration in which the ground lines GNL0-GNLn of the first sensor sheet 20A are connected to the power lines VL0-VLn of the second sensor sheet 20B via wiring on the relay board 12, instead of plated through holes, by connecting the FPC 14 on the second sensor sheet 20B side to the upper surface side of the relay board 12. It is also possible to adopt a configuration in which the FPC 14 on the first sensor sheet 20A side and the FPC 14 on the second sensor sheet 20B side are connected to a drive circuit 40 provided on the upper surface side of the relay board 12, and the ground lines GNL0-GNLn of the first sensor sheet 20A are connected to the power lines VL0-VLn of the second sensor sheet 20B within the drive circuit 40.

[0024] Next, a drive circuit (controller) for driving the first sensor sheet 20A and the second sensor sheet 20B configured as above will be described. Fig. 7 is a block diagram showing a schematic diagram of the drive circuit of the strain gauge sensor device 10, and Fig. 8 is a block diagram showing the first to fourth sensor patterns, the selector of the controller, and the analog front end. In Fig. 8, in order to simplify the drawing, the power supply lines VL0 to VLn of each sensor pattern are collectively represented as one power supply line, and the ground lines GNL0 to GNLn are collectively represented as one power supply line. As shown in FIG. 7, a drive circuit 40 provided on a relay board (control circuit board) 12 includes a selector SEL, an analog front end (AFE: signal conditioning circuit) 30, a timing controller 34, a communication interface 36, and the like.

[0025] The communication interface 36 is connected to an external host controller 38 wirelessly or via a wire, receives a driving signal (setting) from the host controller 38, and transmits detection data (Data) to the host controller 38. The timing controller 34 outputs a drive signal to the selector SEL and the analog front end 30 in response to a drive signal (setting). The selector SEL is composed of a plurality of shift registers, multiplexers, etc. In response to a drive signal from the timing controller 34, the selector SEL sequentially connects the power supply lines VL0-VLn of the first and second sensor patterns CDA, CDB in the first sensor sheet 20A to a power supply, and sequentially applies voltages PW0-PWn to the strain gauges G0-Gn. In synchronization with this, the selector SEL sequentially reads the detection signals (voltage values) RXa0-RXan, RXb0-RXbn on one end side and the other end side of each of the strain gauges G0-Gn via the first signal lines Sa0-San and the second signal lines Sb0-Sbn.

[0026] The voltages PW0-PWn supplied to the power lines VL0-VLn of the first and second sensor patterns CDA, CDB are sequentially applied to the power lines VL0-VLn of the third and fourth sensor patterns CDC, CDD via the ground lines GNL0-GNLn and the connection lines SH. In synchronization with the above reading, the selector SEL sequentially reads the detection signals (voltage values) RXc0-RXcn, RXd0-RXdn of one end side and the other end side of each of the strain gauges G0-Gn via the first signal lines Sa0-San and the second signal lines Sb0-Sbn of the third and fourth sensor patterns CDC, CDD in the second sensor sheet 20B.

[0027] As shown in Fig. 8, the analog front end 30 includes a read circuit 31, difference detection circuits 30a and 30b, an AD converter 32, a digital filter 33, a memory 37, and the like. Fig. 9 is a circuit diagram of a difference detection circuit in the analog front end. As shown in the figure, according to this embodiment, the analog front end 30 includes a difference detection circuit (subtraction circuit) 30a that processes a detection signal of the first sensor sheet 20A, and a difference detection circuit (subtraction circuit) 30b that processes a detection signal of the second sensor sheet 20B. The analog front end 30 performs signal conditioning (amplification, AD conversion, filtering) on ​​the detection signals RXa, RXb and detection signals RXc, RXd of the strain gauges G0 to Gn sent from the selector SEL in response to a drive signal, and outputs the result to the communication interface 36. At this time, since the voltage drop value of each strain gauge G is required to calculate the radius of curvature, the differential detection circuits 30a, 30b calculate the difference between the detection values ​​Rxa, Rxb of each strain gauge G0 to Gn, and the difference between the detection values ​​Rxc, Rxd of each strain gauge G0 to Gn, and output a signal.

[0028] 7, the host controller 38 includes a reading circuit 38a, a memory 38b, an arithmetic processing unit 38c, etc. The reading circuit 38a reads the output signal (differential data) sent from the communication interface 36 and stores it in the memory 38b. The arithmetic processing unit 38c, for example, a CPU, performs arithmetic processing such as data shaping and curved surface calculation based on the differential data, and calculates the distortion (curvature radius), curved surface form (curved surface coordinates), etc. of the subject detected by the first and second sensor sheets 20A and 20B. The memory 38b stores the differential data, the calculated curvature radius, curved surface form, a detection operation program, etc.

[0029] Next, the detection operation mode of the strain gauge sensor device 10 will be described. FIG. 10 is a diagram showing a state where the strain gauge sensor device 10 is installed on the surface of the test object 50. As shown in the figure, in one example, the test object 50 has a surface 50a curved in a wave-like or sinusoidal shape. The strain gauge sensor device 10 is installed in close contact with the surface 50a of the test object 50 to detect the curved surface shape of the test object 50. In this case, the strain gauge sensor device 10 is installed in a state where the second sensor sheet 20B is in contact with the surface 50a of the test object 50. In one example, each of the sensor patterns of the first sensor sheet 20A and the second sensor sheet 20B includes about 4 to 8 strain gauges G0 to Gn. The interval L between adjacent strain gauges is, for example, about 5 to 20 mm, more preferably about 10 to 15 mm.

[0030] 11 is a schematic enlarged view of a part of the strain gauge sensor device 10 installed on the surface 50a of the specimen 50. As shown in the figure, when installed on the surface 50a, the neutral plane of the base substrate 44 is curved with a radius of curvature r. Here, the neutral plane is a plane where no expansion (tension) or contraction (compression) occurs before or after bending the strain gauge sensor device (i.e., the strain is zero even after bending). In this embodiment, the neutral plane is located at the center (thickness×½) of the base substrate 44 in the thickness direction. The strain gauge (sometimes called the first strain gauge) GA of the first sensor pattern CDA in the first sensor sheet 20A located on the outer periphery side and the strain gauge (sometimes called the second strain gauge) GB of the second sensor pattern face each other in the radial direction (thickness direction) with an insulating layer sandwiched therebetween. The strain gauge (sometimes called the third strain gauge) GC of the third sensor pattern CDC in the second sensor sheet 20B located on the inner periphery side and the strain gauge (sometimes called the fourth strain gauge) GD of the fourth sensor pattern CDD face each other in the radial direction (thickness direction) with an insulating layer sandwiched therebetween. That is, the four strain gauges GA, GB, GC, and GD stacked in four layers face each other with a radial gap between them. The strain gauge GA is located at the outermost periphery, the strain gauge GD is located at the innermost periphery, and the two layers of strain gauges GB and GC are located between them. If the gap d between the two opposing layers of strain gauges is constant, the thickness of the strain gauge sensor device is 3d.

[0031] If the distance between the outermost strain gauge GA and the neutral plane is d1, the distance between the innermost strain gauge GD and the neutral plane is d2, the distance between the middle strain gauge GB and the neutral plane is d3, and the distance between the middle strain gauge GC and the neutral plane is d4, it is desirable that d1 = d2 and d3 = d4. It is also acceptable that d1 ≠ d3 and d2 ≠ d4.

[0032] In the detection operation mode, the power supply lines and signal lines are scan-driven to sequentially drive the strain gauges G0-Gn and sequentially read the detection values ​​of the strain gauges G0-Gn. In detail, during detection, the timing controller 34 inputs a start signal and a clock signal synchronized therewith to the selector SEL in response to an instruction from the host controller 38, and sequentially drives (sets) the strain gauges G0-Gn of the first and second sensor sheets 20A and 20B in one frame period.

[0033] As shown in Fig. 8, the selector SEL first applies a voltage to the two outer strain gauges GA and GD to detect strain. The selector SEL drives the power line VL0 of the first sensor pattern CDA, i.e., applies a power supply voltage to the power line VL0 and applies a desired voltage PW0 to the strain gauge G0. This causes a current I to flow through the strain gauge G0 for a certain period of time. At the same time, the selector SEL acquires a detection signal (voltage value) RXa0 from one end of the strain gauge G0 and a detection signal (voltage value) RXb0 from the other end of the strain gauge G0 via the first signal line Sa0 and the second signal line Sb0. The ground line GNL0 of the first sensor pattern CDA is connected to the power line VL0 of the fourth sensor pattern CDD of the second sensor sheet 20B. More specifically, the strain gauge G0 (GA) of the first sensor pattern CDA and the strain gauge G0 (GD) of the fourth sensor pattern CDD are connected in series via the ground line GNL0 of the first sensor pattern CDA, the connection line (plated through hole) SH, and the power line VL0 of the fourth sensor pattern CDD. Therefore, when the strain gauge G0 of the first sensor pattern CDA is driven, the strain gauge G0 of the fourth sensor pattern CDD is driven in synchronization, and the current I is also passed through the strain gauge G0. At the same time, the selector SEL acquires the detection signal (voltage value) RXc0 of one end of the strain gauge G0 and the detection signal (voltage value) RXd0 of the other end of the strain gauge G0 via the first signal line Sa0 and the second signal line Sb0 of the fourth sensor pattern CDD. The acquired detection signals RXa0, RXb0, RXc0, ​​and RXd0 are sent to the analog front-end 30, and the difference between the detection values ​​Rxa, Rxb and the detection values ​​Rxc, Rxd are detected and adjusted by the difference detection circuits 30a, 30b, and then stored in the memory 37.

[0034] Next, the selector SEL drives the power supply line VL1 of the first sensor pattern CDA to apply a desired voltage PW1 to the strain gauge G1 of the first sensor pattern CDA and the strain gauge G1 of the fourth sensor pattern CDD. This causes a current I to flow through the two opposing strain gauges G1 for a certain period of time. At the same time, the selector SEL acquires a detection signal RXa1 from one end of the strain gauge G1 and a detection signal RXb1 from the other end of the strain gauge G1 via the first signal line Sa1 and the second signal line Sb1 of the first sensor pattern CDA. At the same time, the selector SEL acquires a detection signal RXc1 from one end of the strain gauge G1 and a detection signal RXd1 from the other end of the strain gauge G1 via the first signal line Sa1 and the second signal line Sb1 of the fourth sensor pattern CDD. The acquired detection signals RXa1, RXb1, RXc1, and RXd1 are sent to the analog front-end 30, where the differences are detected and adjusted by the difference detection circuits 30a and 30b, and then stored in the memory 37.

[0035] Thereafter, the selector SEL sequentially drives the strain gauges G2-Gn of the first sensor pattern CDA and the strain gauges G2-Gn of the fourth sensor pattern CDD, and sequentially acquires the detection signals RXa2-RXan, RXb2-RXbn, RXc2-RXcn, and RXd2-RXdn of the strain gauges G2-Gn. The acquired detection signals are sequentially sent to the analog front end 30, adjusted and subjected to difference detection, and then stored in the memory 37.

[0036] As shown in Fig. 12, the selector SEL then applies a voltage to two strain gauges GB, GC located in the middle layer (inner side) to detect strain. In Fig. 12, in order to simplify the drawing, the power supply lines VL0 to VLn of each sensor pattern are collectively represented as one power supply line, and the ground lines GNL0 to GNLn are collectively represented as one power supply line. In detail, the selector SEL drives the power line VL0 of the second sensor pattern CDB of the first sensor sheet 20A to apply a desired voltage PW0 to the strain gauge G0. This causes a current I to flow through the strain gauge G0 for a certain period of time. At the same time, the selector SEL acquires a detection signal (voltage value) RXa0 from one end of the strain gauge G0 and a detection signal (voltage value) RXb0 from the other end of the strain gauge G0 via the first signal line Sa0 and the second signal line Sb0.

[0037] The ground line GNL0 of the second sensor pattern CDB is connected to the power line VL0 of the third sensor pattern CDC of the second sensor sheet 20B. More specifically, the strain gauge G0 (GB) of the second sensor pattern CDB and the strain gauge G0 (GC) of the third sensor pattern CDC are connected in series via the ground line GNL0 of the second sensor pattern CDB, the connection line (plated through hole) SH, and the power line VL0 of the third sensor pattern CDC. Therefore, when the strain gauge G0 of the second sensor pattern CDB is driven, the strain gauge G0 of the third sensor pattern CDC is driven in synchronization, and the current I is also passed through the strain gauge G0. At the same time, the selector SEL acquires the detection signal (voltage value) RXc0 of one end of the strain gauge G0 and the detection signal (voltage value) RXd0 of the other end of the strain gauge G0 via the first signal line Sa0 and the second signal line Sb0 of the third sensor pattern CDC. The acquired detection signals RXa0, RXb0, RXc0, ​​and RXd0 are sent to the analog front-end 30, and the difference between the detection values ​​Rxa, Rxb and the detection values ​​Rxc, Rxd are detected and adjusted by the difference detection circuits 30a, 30b, and then stored in the memory 37.

[0038] Next, the selector SEL drives the power supply line VL1 of the second sensor pattern CDB to apply a desired voltage PW1 to the strain gauge G1 of the second sensor pattern CDB and the strain gauge G1 of the third sensor pattern CDC. This causes a current I to flow through the two opposing strain gauges G1 for a certain period of time. At the same time, the selector SEL acquires a detection signal RXa1 from one end of the strain gauge G1 and a detection signal RXb1 from the other end of the strain gauge G1 via the first signal line Sa1 and the second signal line Sb1 of the second sensor pattern CDB. At the same time, the selector SEL acquires a detection signal RXc1 from one end of the strain gauge G1 and a detection signal RXd1 from the other end of the strain gauge G1 via the first signal line Sa1 and the second signal line Sb1 of the third sensor pattern CDC. The acquired detection signals RXa1, RXb1, RXc1, and RXd1 are sent to the analog front-end 30, where the differences are detected and adjusted by the difference detection circuits 30a and 30b, and then stored in the memory 37.

[0039] Thereafter, the selector SEL sequentially drives the strain gauges G2-Gn of the second sensor pattern CDB and the strain gauges G2-Gn of the third sensor pattern CDD, and sequentially acquires the detection signals RXa2-RXan, RXb2-RXbn, RXc2-RXcn, and RXd2-RXdn of the strain gauges G2-Gn. The acquired detection signals are sequentially sent to the analog front end 30, adjusted and subjected to difference detection, and then stored in the memory 37.

[0040] As described above, the analog front end 30 sequentially reads out the transmitted detection signals RXa1-RXan, RXb1-RXbn, and detection signals RXc1-RXcn, RXd1-RXdn by the readout circuit 31, converts them into voltage signals, and further converts them into digital data by the AD converter 32 and the digital filter 33. Furthermore, the analog front end 30 detects the differences between the detection signals RXa0-RXan and RXb0-RXbn, and the differences between the detection signals RXc0-RXcn and RXd0-RXdn by the difference detection circuits 30a and 30b. The detected difference data is sequentially stored in the memory 37. When the scan for one frame period is completed, the analog front end 30 reads out the difference data for one frame from the memory 37 and outputs it to the host controller 38. The host controller 38 calculates the curved surface form of the surface 50a of the subject 50 based on the transmitted data.

[0041] A method for calculating the shape of a curved surface, for example, the radius of curvature, will now be described. Fig. 13A is a cross-sectional view of a strain gauge sensor showing a schematic diagram of a case where the radius of curvature is calculated using the detection values ​​of the middle (inner) two layers of strain gauges GB, GC among the four layers of strain gauges shown in Fig. 11, and Fig. 13B is a cross-sectional view of a strain gauge sensor showing a schematic diagram of a case where the radius of curvature is calculated using the detection values ​​of the strain gauges GA, GD of the outermost inner layer (outer side) among the four layers of strain gauges shown in Fig. 11. The strain gauges GA, GB located on the outside and the strain gauges GC, GD located on the inside face each other in the radial direction (thickness direction of the base material) and are curved with different radii of curvature. 13A and 13B and in the formula below, 3d: substrate thickness, θ: strain gauge opening angle, r: radius of curvature of the neutral plane, k: gauge factor, R0: initial resistance of the strain gauge, ΔR0, ΔR0': changes in strain gauge resistance.

[0042] A case where the radius of curvature is calculated based on the detection values ​​of the strain gauges GB and GC will be described. As shown in Fig. 13A, if the length of the strain gauge in the longitudinal direction X on the neutral surface of the base substrate 44 is defined as the initial length of the strain gauge, the middle outer strain gauge GB is deformed to a state in which its length is extended by bending, and the middle inner strain gauge GC is deformed to a state in which its length is shortened by bending. If the initial resistance of strain gauges GB and GC before deformation is R0, the measured voltage of strain gauge GB after deformation (the difference between the voltage value at one end of the strain gauge and the voltage value at the other end) is VB, the measured voltage of strain gauge GC after deformation is VC, the change in resistance of the strain gauge is ΔR0, and the current flowing through each strain gauge GB and GC is I, then the measured voltage VB of strain gauge GB and the measured voltage VC of strain gauge GC are,

number

number

number

[0043] From the above equation, the calculation formula for the radius of curvature r of the neutral plane is as follows.

number

[0044] A case where the radius of curvature is calculated based on the detection values ​​of the strain gauges GA and GD will be described. As shown in FIG. 13B, if the length of the strain gauge in the longitudinal direction X at the neutral plane of the base substrate 44 is defined as the initial length of the strain gauge, the strain gauge GA in the outermost layer is deformed to a state in which its length is extended by bending, and the strain gauge GD in the innermost layer is deformed to a state in which its length is shortened by bending. If the initial resistance of strain gauges GA and GD before deformation is R0, the measured voltage of strain gauge GA after deformation (the difference between the voltage value at one end of the gauge and the voltage value at the other end) is VA, the measured voltage of strain gauge GD after deformation is VD, the change in resistance of the strain gauge is ΔR0', and the current flowing through each strain gauge GA and GD is I', then the resistance value VA of strain gauge GA and the resistance value VD of strain gauge GD are,

number

number

number

[0045] From the above equation, the calculation formula for the radius of curvature r' of the neutral plane is as follows:

number

[0046] The host controller 38 calculates the curved surface form of the surface 50a of the specimen 50 based on the transmitted data. It calculates the average value ((P0+P0') / 2, (P1+P1') / 2, (P2+P2') / 2, ...) of the radii of curvature (curved surface coordinates) P0 to Pn calculated based on the detection values ​​of the strain gauges GB and GC and the radii of curvature (curved surface coordinates) P'0 to P'n calculated based on the detection values ​​of the strain gauges GA and GD, and obtains the radii of curvature (curved surface coordinates) of each part as final data. FIG. 16 shows the curved surface form obtained by plotting the radii of curvature P0 to Pn calculated as the final data. As described above, the strain gauge sensor device 10 can detect the curved shape of the entire surface 50a by sequentially calculating the radii of curvature at a plurality of points on the surface 50a.

[0047] Next, a material for forming the sensor pattern including the strain gauge will be described. If the strain gauges GB and GC of the strain gauge sensor device and the strain gauges GA and GD are made of the same material and have the same resistance, the dynamic range of the output value of the inner strain gauge closer to the neutral plane described above becomes smaller. Therefore, by making the resistance value of the inner strain gauge closer to the neutral plane larger than the resistance value of the outer strain gauge, the dynamic range of the output value of the inner strain gauge is increased. In one example, the strain gauge GB of the second sensor pattern CDB and the strain gauge GC of the third sensor pattern CDC, which are located on the inner side of the four layers of strain gauges, that is, on the side of the center (neutral plane) in the thickness direction of the strain gauge sensor device, are made of the same material and are made of a material with a large resistance value, for example, titanium. The strain gauge GA of the first sensor pattern CDA and the strain gauge GD of the fourth sensor pattern CDD, which are located on the outer side of the four layers of strain gauges, that is, away from the center (neutral plane) in the thickness direction of the strain gauge sensor device, are made of the same material and are made of a material with a small resistance value, for example, aluminum. In this way, the inner strain gauges GB and GC are made of different materials from the outer strain gauges GA and GD, and the inner strain gauges GB and GC are made to have a higher resistance than the outer strain gauges GA and GD. In this configuration, by optimizing the resistance values ​​of the inner strain gauges GB, GC and the outer strain gauges GA, GD, it is possible to increase the dynamic range of the inner strain gauges and set it to a range equivalent to the dynamic range of the outer strain gauges, as shown in Figure 17. Therefore, the dynamic range of the inner strain gauges GB, GC can be increased, and the quantization error during strain detection can be reduced. In the case of bellows-shaped or rectangular wave-shaped strain gauges, the resistance value increases with the number of teeth. Therefore, by forming the strain gauges GA, GB, GC, and GD from the same material and making the number of teeth on the inner strain gauges GB and GC greater than the number of teeth on the outer strain gauges GA and GD, it is also possible to increase the resistance of the inner strain gauges GB and GC.

[0048] According to the strain gauge sensor device 10 according to the present embodiment configured as described above, the two layers of strain gauges G0-Gn of the first sensor sheet 20A and the two layers of strain gauges G0-Gn of the second sensor sheet 20B are arranged facing each other in the thickness direction of the base material, and further, by connecting the power supply line of the first sensor sheet and the ground line of the second sensor sheet, the strain gauges of the first sensor sheet and the strain gauges of the second sensor sheet are connected in series. Therefore, the strain gauges G0-Gn of the second sensor sheet can be sequentially driven (scanned) in synchronization with the sequential driving (scanning) of the strain gauges G0-Gn of the first sensor sheet, and the same part can be simultaneously detected by the two strain gauges facing each other on the front and back. Furthermore, during detection, a constant current I can be applied to the two opposing strain gauges, and by taking the difference in detection signals of both strain gauges, it becomes possible to detect the curved surface shape with high accuracy. Furthermore, according to this embodiment, the strain gauge sensor device includes multiple layers (here, four layers) of strain gauges GA, GB, GC, and GD arranged in layers in the thickness direction, and obtains the average value of a pair of detection values, for example, a detection value detected by the strain gauges GA and GD and a detection value detected by the strain gauges GB and GC, as the final detection data. In this way, by using the average of detection values ​​detected at multiple different positions in the thickness direction, the strain gauge sensor device can detect the curved surface shape of the subject with even higher accuracy. As described above, according to this embodiment, it is possible to obtain a strain detection device capable of improving detection accuracy.

[0049] Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. The new embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. The embodiment and its modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. All configurations that can be implemented by a person skilled in the art through appropriate design modifications based on the respective configurations described above as the embodiments of the present invention belong to the scope of the present invention as long as they include the gist of the present invention.

[0050] For example, the number of layers of the sensor pattern in the strain gauge sensor device, i.e., the number of layers of the strain gauges, is not limited to four layers, but may be six, eight, ten or more layers. The number of strain gauges arranged in the sensor pattern of the sensor sheet is not limited to the above-mentioned embodiment, but may be selected arbitrarily. The constituent materials, dimensions, and shape of the sensor sheet are not limited to the above-mentioned embodiment, but may be changed as appropriate. The connection lines connecting the power supply lines and the ground lines are not limited to plated through holes, but may be formed by wiring within the selector SEL. Braiding [Explanation of symbols]

[0051] 10... strain gauge sensor device, 12... relay board, 20A... first sensor sheet, 20B: second sensor sheet; 22: sheet base material; 30a, 30b: difference detection circuit; 44...Base board, G0~Gn, GA, GB, GC, GD...Strain gauge, VL...Power line, GNL: Ground line, Sa: First signal line, Sb: Second signal line, SEL: Selector, CDA: First sensor pattern; CDB: Second sensor pattern; CDC: 3rd sensor pattern, CDD: 4th sensor pattern

Claims

1. a flexible substrate including a plurality of insulating layers; a first sensor pattern provided on the substrate, the first sensor pattern including a plurality of first strain gauges arranged in a row at intervals in a first direction and a plurality of wires respectively connected to the first strain gauges; a second sensor pattern including a plurality of second strain gauges arranged in a row at intervals in the first direction and a plurality of wires respectively connected to the second strain gauges, the second sensor pattern being laminated on the base material and facing the first sensor pattern with an insulating layer interposed therebetween; a third sensor pattern including a plurality of third strain gauges arranged in a row at intervals in the first direction and a plurality of wires respectively connected to the third strain gauges, the third sensor pattern being laminated on the base material and facing the second sensor pattern with an insulating layer interposed therebetween; a fourth sensor pattern including a plurality of fourth strain gauges arranged in a row at intervals in the first direction and a plurality of wires respectively connected to the fourth strain gauges, the fourth sensor pattern being laminated on the base material and facing the third sensor pattern with an insulating layer interposed therebetween; a controller that applies voltages to the first strain gauge, the second strain gauge, the third strain gauge, and the fourth strain gauge via the plurality of wirings and reads detection values ​​of each strain gauge; the first strain gauge, the second strain gauge, the third strain gauge, and the fourth strain gauge are disposed opposite to each other in a thickness direction of the base material; A strain detection device, wherein the first strain gauge and the fourth strain gauge are arranged symmetrically with respect to a center position in the thickness direction of the substrate, and the second strain gauge and the third strain gauge are arranged symmetrically with respect to a center position in the thickness direction of the substrate.

2. the plurality of wirings of the first sensor pattern include a plurality of power supply lines and a plurality of first signal lines each connected to one end of the first strain gauge, and a plurality of ground lines and a plurality of second signal lines each connected to the other end of the first strain gauge; the plurality of wirings of the fourth sensor pattern include a plurality of power supply lines and a plurality of first signal lines each connected to one end of the fourth strain gauge, and a plurality of ground lines and a plurality of second signal lines each connected to the other end of the fourth strain gauge; 2 . The strain detection device according to claim 1 , wherein each of the first strain gauges is connected in series to the fourth strain gauge via a ground line of the first sensor pattern and a power supply line of the fourth sensor pattern.

3. the plurality of wirings of the second sensor pattern include a plurality of power supply lines and a plurality of first signal lines each connected to one end of the second strain gauge, and a plurality of ground lines and a plurality of second signal lines each connected to the other end of the second strain gauge, the plurality of wirings of the third sensor pattern include a plurality of power supply lines and a plurality of first signal lines each connected to one end of the third strain gauge, and a plurality of ground lines and a plurality of second signal lines each connected to the other end of the third strain gauge; 3. The strain detection device according to claim 2, wherein each of the second strain gauges is connected in series to the third strain gauge via a ground line of the second sensor pattern and a power supply line of the third sensor pattern.

4. The strain detection device of claim 3, wherein the controller calculates a first measurement value based on a difference between detection values ​​of the first strain gauge and the fourth strain gauge, calculates a second measurement value based on a difference between detection values ​​of the second strain gauge and the third strain gauge, and calculates an average value of the first measurement value and the second measurement value.

5. the second strain gauge and the third strain gauge are disposed closer to the center in a thickness direction of the base material than the first strain gauge and the fourth strain gauge; The strain detector according to claim 2 , wherein the second strain gauge and the third strain gauge have a higher resistance than the first strain gauge and the fourth strain gauge.

6. 6. The strain detector according to claim 5, wherein a resistance of the second strain gauge is the same as a resistance of the third strain gauge, and a resistance of the first strain gauge is the same as a resistance of the fourth strain gauge.

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