Strain detection device

Abstract

A strain detection device according to an embodiment of the present invention comprises: a plurality of strain gauges G1-Gn arranged in a line at intervals; a power line VL, a ground line GNL, a first signal line SG1, and a second signal line SG2 each extending along the row of the strain gauges; a plurality of first open / close switches SW1 connected between one end of the respective strain gauges and the power line; a plurality of second open / close switches SW2 connected between the other end of the respective strain gauges and the ground line; a plurality of third open / close switches SW3 connected between the one end of the respective strain gauges and the first signal line; and a plurality of fourth open / close switches SW4 connected between the other end of the respective strain gauges and the second signal line.

Description

[Technical Field]

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

[0002] One example of a strain detection device is a flexible film- or sheet-shaped strain gauge sensor. The strain gauge sensor has multiple strain gauges arranged side by side on a strip-shaped flexible sheet substrate and multiple signal lines for energizing the strain gauges. The strain gauge sensor is wrapped around a curved object and the resistance value of each strain gauge is detected to detect the curved shape of the object. Typically, strain gauge sensors detect strain while all of the strain gauges are energized. This means that strain gauge sensors tend to consume a lot of power during detection. Furthermore, in these strain gauge sensors, individual signal lines are connected to each strain gauge. This means that the wiring occupies a large area, hindering efforts to miniaturize the sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 60-67804 [Patent Document 2] Japanese Patent Application Publication No. 2-80902 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 detector that can reduce power consumption and size. [Means for solving the problem]

[0005] The strain detection device according to the embodiment comprises a plurality of strain gauges, each having one end and the other end, arranged in a row at intervals; a power supply line, a ground line, a first signal line, and a second signal line, each extending along the row of the strain gauges; a plurality of first open / close switches, each connected between the one end of the strain gauges and the power supply line; a plurality of second open / close switches, each connected between the other end of the strain gauges and the ground line; a plurality of third open / close switches, each connected between the one end of the strain gauges and the first signal line; and a plurality of fourth open / close switches, each connected between the other end of the strain gauges and the second signal line. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a perspective view of a strain gauge sensor device according to a first embodiment. [Figure 2] FIG. 2 is a plan view schematically showing a gauge pattern and a wiring pattern of the strain gauge sensor device. [Figure 3] FIG. 3 is a plan view showing a sensor sheet of the strain gauge sensor device. [Figure 4] 4 is a cross-sectional view of the sensor sheet taken along line AA in FIG. 3. FIG. [Figure 5] 5 is a cross-sectional view of the sensor sheet taken along line BB in FIG. 3. FIG. [Figure 6] FIG. 6 is a block diagram of a controller of the strain gauge sensor device. [Figure 7] FIG. 7 is a circuit diagram of a differential detection circuit in the analog front end of the controller. [Figure 8] FIG. 8 is a timing chart of various signals when the strain gauge sensor device is in sleep mode. [Figure 9] FIG. 9 is a timing chart of various signals in the strain gauge sensor device in active mode. [Figure 10] FIG. 10 is a diagram schematically showing a part of the strain gauge sensor device in a state where it is installed on the peripheral surface of a test object. [Figure 11]FIG. 11 is a diagram schematically showing an equivalent circuit of the sensor sheet. [Figure 12] FIG. 12 is a plan view showing a sensor sheet of the strain gauge sensor device according to the second embodiment. [Figure 13] 13 is a cross-sectional view of the sensor sheet taken along line CC in FIG. 12. [Figure 14] 14 is a cross-sectional view of the sensor sheet taken along line DD in FIG. 12. [Figure 15] FIG. 15 is a perspective view of a strain gauge sensor device according to a third embodiment. [Figure 16] FIG. 16 is a perspective view schematically showing a base end portion of a sensor sheet and an intermediate substrate in the strain gauge sensor device according to the third embodiment. [Figure 17] FIG. 17 is a plan view schematically showing gauge patterns and wiring patterns of the first sensor sheet and the second sensor sheet in the strain gauge sensor device according to the third embodiment. [Figure 18] FIG. 18 is a block diagram of a controller of the strain gauge sensor device according to the third embodiment. [Figure 19] FIG. 19 is a circuit diagram of a difference detection circuit included in the analog front end of the controller. [Figure 20] FIG. 20 is a timing chart of various signals in the sleep mode of the strain gauge sensor device according to the third embodiment. [Figure 21] FIG. 21 is a timing chart of various signals in the strain gauge sensor device according to the third embodiment in active mode. [Figure 22] FIG. 22 is a diagram schematically showing a part of the strain gauge sensor device in a state where it is installed on the peripheral surface of a test object. [Figure 23] FIG. 23 is a diagram schematically showing equivalent circuits of the first sensor sheet and the second sensor sheet. [Figure 24] FIG. 24 is a plan view schematically showing gauge patterns and wiring patterns of a first sensor sheet and a second sensor sheet in a strain gauge sensor device according to a fourth embodiment. [Figure 25]FIG. 25 is a plan view schematically showing gauge patterns and wiring patterns of a first sensor sheet and a second sensor sheet in a strain gauge sensor device according to a fifth embodiment. [Figure 26] FIG. 26 is a plan view schematically showing gauge patterns and wiring patterns of a first sensor sheet and a second sensor sheet in a strain gauge sensor device according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[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 easily conceivable by those skilled in the art while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings may be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0008] (First embodiment) As an example of a strain detection device, a strain gauge sensor device according to a first embodiment will be described in detail. Fig. 1 is a perspective view of the strain gauge sensor device according to the first embodiment. As shown in the figure, the strain gauge sensor device 10 according to the first embodiment constitutes a single-sided strain gauge sensor. The strain gauge sensor device 10 includes a long, thin, flexible base substrate 44, a sensor sheet 20 attached to one side of the base substrate 44, and an intermediate substrate (drive circuit board) 12 connected to the sensor sheet 20 via a flexible printed circuit (FPC) 14. In one example, the base substrate 44 is made of a resin such as polyethylene terephthalate (PET) or polyimide, and has a thickness of approximately 0.3 to 0.5 mm. The sensor sheet 20 has a flexible, elongated sheet substrate 22 and a conductor pattern provided on one side of the sheet substrate 22. The conductor pattern includes a plurality of strain gauges G1 to Gn. The plurality of strain gauges G1 to Gn are arranged in a row in the longitudinal direction X at predetermined intervals from one end to the other end of the sheet substrate 22 in the longitudinal direction X. In the drawing, the longitudinal direction X and the width direction Y of the sensor sheet 20 are two directions that intersect at right angles to each other. These directions may intersect at an angle other than 90 degrees.

[0009] 2 is a plan view schematically showing the strain gauges and wiring pattern of the sensor sheet 20. As shown in the figure, the conductor pattern of the sensor sheet 20 has a plurality of strain gauges G1 to Gn. The plurality of strain gauges G1 to Gn are arranged in a row at intervals in the longitudinal direction X of the sensor sheet 20. Each of the strain gauges G1 to Gn extends in a bellows-like shape in the width direction Y, and has one end and the other end in the width direction Y. Each of the strain gauges G1 to Gn produces a resistance change in response to strain.

[0010] The conductor pattern has a power supply line VL, a ground line GNL, a first signal line SG1, and a second signal line SG2 that extend in the longitudinal direction X along the row of the strain gauges G1 to Gn. The first signal line SG1 and the power supply line VL are located on one end side of the strain gauges G1 to Gn, and the power supply line VL is located outside the first signal line SG1 in the width direction Y and spaced apart. The second signal line SG2 and the ground line GNL are located on the other end side of the strain gauges G1 to Gn, and the ground line GNL is located outside the second signal line SG2 in the width direction Y and spaced apart. One end of each of the strain gauges G1 to Gn is connected to a power supply line VL via a first switch SW1. The other end of each of the strain gauges G1 to Gn is connected to a ground line GNL via a second switch SW2. Furthermore, one end of each of the strain gauges G1 to Gn is connected to a first signal line SG1 via a third switch SW3. The other end of each of the strain gauges G1 to Gn is connected to a second signal line SG2 via a fourth switch SW4.

[0011] The sensor sheet 20 includes a first selector SEL1 for switching the first and second switches SW1 and SW2 of each of the strain gauges G1 to Gn, and a second selector SEL2 for switching the third and fourth switches SW3 and SW4 of each of the strain gauges G1 to Gn. The first selector SEL1 includes a plurality of shift registers (S / R) SR1 arranged side by side in the longitudinal direction X on the side of the ground line GNL and corresponding to the strain gauges G1 to Gn, three signal lines SGL1 for inputting signals (RSTa, CLKa, STVa) to the plurality of shift registers SR1, and a gate line GL1 for inputting the output signal of each shift register SR1 to the corresponding first and second switches SW1 and SW2.

[0012] The second selector SEL2 has a plurality of shift registers (S / R) SR2 arranged side by side in the longitudinal direction X on the side of the power supply line VL and corresponding to the strain gauges G1 to Gn, three signal lines SGL2 for inputting signals (RSTb, CLKb, STVb) to the plurality of shift registers SR2, and a gate line GL2 for inputting the output signals of each shift register SR2 to the corresponding third open / close switch SW3 and fourth open / close switch SW4.

[0013] The wiring structure of the sensor sheet will now be described in detail. 3 is a plan view showing the wiring structure of the sensor sheet in more detail, FIG. 4 is a cross-sectional view of the sensor sheet taken along line AA in FIG. 3, and FIG. 5 is a cross-sectional view of the sensor sheet taken along line BB in FIG. As shown in FIGS. 3 and 4, in the sensor sheet 20, gate lines GL1 and GL2 are provided on the surface of the sheet substrate 22. An interlayer film 24 is laminated on the surface of the sheet substrate 22, overlapping the gate lines GL1 and GL2. A semiconductor layer SC and a conductive layer are formed on the interlayer film 24. The conductive layer forms the wiring patterns of the strain gauges G1 to Gn, the power line VL, and the ground line GNL. Each semiconductor layer SC faces the gates formed by the gate lines GL1 and GL2, sandwiching the interlayer film 24 between them. Branch wiring that branches from the power line VL and connects to one end of the strain gauge G is separated along the way, and the separated ends of each branch wiring are positioned overlapping the semiconductor layer SC, forming source and drain electrodes, respectively. In this way, the gates, semiconductor layers SC, source electrodes, and drain electrodes form thin-film transistors (TFTs). These TFTs form the first on-off switch SW1, the second on-off switch SW2, the third on-off switch SW3, and the fourth on-off switch SW4.

[0014] An interlayer film 26 is laminated on the interlayer film 24, overlapping the conductive layer. First and second signal lines SG1 and SG2 are formed on the interlayer film 26, and a protective film 28 is laminated on the interlayer film 26, overlapping the first and second signal lines SG1 and SG2. Branch lines branching from multiple locations on the first signal line SG1 are connected to one end of the strain gauge G via contact holes CH1. That is, the first signal line SG1 is connected to one end of the strain gauge G via the contact holes CH1, the branch lines, and the third switch SW3. Similarly, branch lines branching from multiple locations on the second signal line SG2 are connected to the other end of the strain gauge G via contact holes CH2. That is, the second signal line SG2 is connected to the other end of the strain gauge G via the contact holes CH2, the branch lines, and the fourth switch SW4.

[0015] Next, we will explain the drive circuit (controller) that drives the sensor sheet 20 configured as above. Fig. 6 is a block diagram that schematically shows the drive circuit (controller) of the strain gauge sensor device 10, and Fig. 7 is a circuit diagram of the difference detection circuit in the analog front end. As shown in FIG. 6, a drive circuit 40 provided on a relay board (drive circuit board) 12 includes an analog front end (AFE: signal conditioning circuit) 30, a signal generator 32, a timing controller 34, a communication interface 36, and the like.

[0016] 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 detected data (data) to the host controller 38. The timing controller 34 outputs a drive signal to the signal generator 32 and the analog front end 30 in response to the drive signal (setting). The signal generator 32 generates a clock signal CLKa, a reset signal RSTa, and a data signal STVa in response to a drive signal from the timing controller 34, and inputs the signals CLKa, RSTa, and STVa to the shift register SR1. At the same time, the signal generator 32 generates a clock signal CLKb, a reset signal RSTb, and a data signal STVb, and inputs the signals CLKb, RSTb, and STVb to the shift register SR2.

[0017] The analog front end 30 includes a readout circuit, an AD converter, a digital filter, etc. As shown in Fig. 7, according to this embodiment, the analog front end 30 includes a difference detection circuit (subtraction circuit) 30a. The analog front end 30 performs signal conditioning (amplification, AD conversion, filtering) on ​​the detection signals RXa and RXb sent from each of the strain gauges G1 to Gn in response to the drive signal, and outputs the signals 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 difference between the detection values ​​Rxa and Rxb of each of the strain gauges G1 to Gn is calculated by the difference detection circuit 30a and output as a signal. The host controller 38 reads the output signal (data) sent from the communication interface 36, performs arithmetic processing such as data shaping and curved surface calculation, and calculates the distortion, curved surface shape, etc. of the subject detected by the sensor sheet 20.

[0018] Next, the operation mode of the strain gauge sensor device 10 will be described. FIG. 8 is a timing chart showing signal outputs when operating in sleep mode (first operation mode), and FIG. 9 is a timing chart showing signal outputs when operating in active mode (second operation mode). As shown in FIG. 8, in sleep mode, the power supply and signal lines are scan-driven to sequentially supply potential to the strain gauges G1-Gn and sequentially read the detected values ​​of the strain gauges G1-Gn. Specifically, in response to instructions from the host controller 38, the drive circuit 40 inputs a clock signal CLKa to all shift registers SR1. The drive circuit 40 also inputs a reset signal RSTa to all shift registers SR1 in synchronization with the clock signal CLKa. This resets all shift registers SR1 of the first selector SEL1. The drive circuit 40 then inputs a data signal STVa, which serves as a shift register start pulse, to the first-stage shift register SR1 (the shift register corresponding to strain gauge G1). This causes the first-stage shift register SR1 to output an ON signal to the first open / close switch SW1 and the second open / close switch SW2 for a certain period of time, turning the first open / close switch SW1 and the second open / close switch SW2 ON (closed) for a certain period of time. After a certain time has passed, the ON signal is turned OFF, and the first ON / OFF switch SW1 and the second ON / OFF switch SW2 are switched OFF (open). While the first ON / OFF switch SW1 and the second ON / OFF switch SW2 are ON, the strain gauge G1 is connected to the power line VL and the ground line GNL, and the power supply voltage is applied. This causes a current to flow through the strain gauge G1 for a certain time.

[0019] After that, an input signal is input from the first-stage shift register SR1 to the second-stage shift register SR1 (the shift register corresponding to strain gauge G2). This input signal corresponds to the data signal STVa input to the first-stage shift register SR1, and as a result, the second-stage shift register SR1 outputs an ON signal to the first open / close switch SW1 and the second open / close switch SW2 for a certain period of time, turning the first open / close switch SW1 and the second open / close switch SW2 ON (closed) for the certain period of time. While the first open / close switch SW1 and the second open / close switch SW2 are ON, a power supply voltage is applied to the strain gauge G2, and a current flows through the strain gauge G2 for a certain period of time. Thereafter, in the same manner as above, over one frame (the period until the next reset signal RSTa is input), the input signals as described above are input sequentially to the first to nth stage shift registers SR1, the first open / close switch SW1 and the second open / close switch SW2 are turned on sequentially, and the power supply voltage is applied sequentially to the strain gauges G3 to Gn.

[0020] Furthermore, the drive circuit 40 inputs a clock signal CLKb, a reset signal RSTb synchronized with the clock signal, and a data signal STVb to the second selector SEL2 in synchronization with the scan drive of the power supply. More specifically, the drive circuit 40 inputs the clock signal CLKb to all shift registers SR2. The clock signal CLKb is substantially the same signal as the clock signal CLKa. The drive circuit 40 also inputs a reset signal RSTb to all shift registers SR2 in synchronization with the clock signal CLKb. The reset signal RSTb is synchronized with the reset signal RSTa and is supplied to all shift registers SR2 at the same timing as the reset signal RSTa. This resets all shift registers SR2. Thereafter, the drive circuit 40 inputs a data signal STVb to the first-stage shift register SR2 (the shift register corresponding to the strain gauge G1). The data signal STVb is synchronized with the data signal STVa and is supplied to the first-stage shift register SR2 at the same timing as the data signal STVa. As a result, the first-stage shift register SR2 outputs an ON signal to the third switch SW3 and the fourth switch SW4 for a certain period of time, at the same timing as the first-stage shift register SR1, turning the third switch SW3 and the fourth switch SW4 ON (closed) for the certain period of time. After the certain period of time has elapsed, the ON signal turns OFF, and the third switch SW3 and the fourth switch SW4 are switched OFF (open). While the third switch SW3 and the fourth switch SW4 are ON, one end and the other end of the strain gauge G1 are connected to the first signal line SG1 and the second signal line SG2, and for a certain period of time, the detection signal (voltage value) RXa from one end of the strain gauge G1 and the detection signal (voltage value) RXb from the other end are output to the first and second signal lines SG1 and SG2. The detection signals RXa and RXb are sent to the analog front end 30 of the drive circuit 40 via the first and second signal lines SG1 and SG2.

[0021] Then, an input signal is input from the first-stage shift register SR2 to the second-stage shift register SR2 (the shift register corresponding to strain gauge G2). This input signal corresponds to the data signal STVb input to the first-stage shift register SR2, and as a result, the second-stage shift register SR2 outputs an ON signal to the third switch SW3 and the fourth switch SW4 for a certain period of time at the same timing as the second-stage shift register SR1, turning the third switch SW3 and the fourth switch SW4 ON (closed) for a certain period of time. While the third switch SW3 and the fourth switch SW4 are ON, one end and the other end of the strain gauge G2 are connected to the first signal line SG1 and the second signal line SG2, and the detection signal (voltage value) RXa at one end of the strain gauge G2 and the detection signal (voltage value) RXb at the other end are output to the first and second signal lines SG1 and SG2 for a certain period of time. The detection signals RXa and RXb are sent to the analog front end 30 of the drive circuit 40 via first and second signal lines SG1 and SG2.

[0022] Thereafter, in the same manner as above, the input signals as described above are input sequentially to the first-stage to n-th-stage shift registers SR2 over one frame. As a result, the first open / close switch SW1 and the second open / close switch SW2 are sequentially switched on, and the third open / close switch SW3 and the fourth open / close switch SW4 are sequentially switched on by the shift register SR2. As a result, the detection signals RXa and RXb of the strain gauges G3 to Gn are sequentially output to the first and second signal lines SG1 and SG2.

[0023] The detection signals RXa, RXb are sequentially sent to the analog front end 30, where they are adjusted and the difference is detected. All of the adjusted and difference-detected detection signals RXa, RXb are sent together to the communication interface 36, and further sent via the communication interface 36 to the host controller 38. Note that the above phrase "the same timing" not only means exactly the same timing, but also includes timing that is slightly shifted to the extent that it can be considered the same timing in terms of driving in this embodiment.

[0024] In the sleep mode described above, current flows only through the strain gauge G to be scanned, so the power consumption of the sensor during strain detection can be reduced compared to when the power of all strain gauges G1 to Gn is always on.

[0025] On the other hand, as shown in FIG. 9, in active mode (second operating mode), after all strain gauges G1 to Gn are turned on, only signal lines SG1 and SG2 are scan-driven. This allows the detection values ​​of strain gauges G1 to Gn to be read sequentially. Specifically, in response to an instruction from host controller 38, drive circuit 40 outputs clock signal CLKa to each shift register SR1. Furthermore, drive circuit 40 outputs reset signal RSTa synchronized with clock signal CLKa to all shift registers SR1. This resets all shift registers SR1 of first selector SEL1. Thereafter, data signal STVa is input to first-stage shift register SR1 (shift register corresponding to strain gauge G1). This data signal STVa keeps first-stage shift register SR1 at an ON level during the frame (until the next reset signal is input). As an input signal equivalent to the data signal STVa is sequentially supplied to the next-stage shift register SR1, each shift register SR1, from the first-stage shift register SR1 to the final-stage shift register SR1, sequentially outputs an ON signal to the first ON / OFF switch SW1 and the second ON / OFF switch SW2, and maintains the ON signal output state. As a result, the first ON / OFF switch SW1 and the second ON / OFF switch SW2 connected to each shift register SR1 are sequentially turned ON (closed), and the ON state is maintained. While the first ON / OFF switch SW1 and the second ON / OFF switch SW2 are ON, each strain gauge G1 to Gn is connected to the power line VL and the ground line GNL, and a power supply voltage is applied. As a result, a current flows through the strain gauges G1 to Gn.

[0026] After turning on all of the first and second switches SW1 and SW2, the drive circuit 40 inputs a clock signal CLKb to all of the shift registers SR2. The drive circuit 40 also inputs a reset signal RSTb, synchronized with the clock signal, to all of the shift registers SR2. The drive circuit 40 then inputs a data signal STVb to the first-stage shift register SR2. As a result, each shift register SR2 sequentially outputs an ON signal to the third and fourth switches SW3 and SW4, switching the third and fourth switches SW3 and SW4 ON (closed) for a fixed period of time. Using the data signal STVb as a start pulse, the strain gauges G1 to Gn are sequentially connected to the first and second signal lines SG1 and SG2, and output the detection values ​​(detection signals) RXa and RXb of both ends of the strain gauge G to the first and second signal lines SG1 and SG2 at regular intervals. The detection signals RXa and RXb are sent to the analog front end 30 of the drive circuit 40 via the first and second signal lines SG1 and SG2. The detection signals RXa and RXb are conditioned by the analog front end 30 and then sent to the host controller 38 via the communication interface 36. In the active mode described above, all of the first and second switches SW1 and SW2 remain on while the drive circuit 40 receives detection signals from the strain gauges G1 to Gn. This reduces the fluctuation in parasitic capacitance in the power supply line VL and ground line GNL compared to the sleep mode, increasing the response speed of the strain gauge sensors.

[0027] Next, a method for calculating the radius of curvature of a test object using a single-sided strain gauge sensor will be described. FIG. 10 is a schematic diagram illustrating a portion of a strain gauge sensor device in a curved state installed on the peripheral surface of a test object. As shown in the figure, in the curved state, the neutral plane of the base substrate 44 is curved with the same radius of curvature r as the peripheral surface of the test object. Here, the neutral plane is a plane where the strain gauge sensor does not expand or contract before or after bending (i.e., where there is zero strain even after bending), and is assumed to be spaced a distance h from the outer peripheral surface (top surface) of the base substrate 44. Note that, when considering only the base substrate 44, the neutral plane would be located at a position equal to half the thickness of the base substrate 44. However, in this embodiment, the sensor sheet 20 is installed on one side of the base substrate 44, and the neutral plane is set taking the sensor sheet 20 into consideration, so the neutral plane is also closer to the sensor sheet installation side.

[0028] In Figure 10 and the formula below, W0: initial width of the strain gauge, Wa: width of the strain gauge on the outer periphery, ΔW: change in strain gauge width, θ: opening angle of the strain gauge, r: radius of curvature of the neutral plane, k: gauge factor, R0: reference resistance of the strain gauge, and ΔR: change in strain gauge resistance.

[0029] If the width of the strain gauge G on the neutral plane of the base substrate 44 is the initial width W0 of the strain gauge, then W0 = rθ. The strain gauge G on the outer periphery is deformed into an elongated state by bending, and this causes the strain gauge resistance value to change by ΔR from the reference resistance R0. Here, the gauge width Wa after deformation is

number

number

[0030] FIG. 11 is a diagram schematically showing an equivalent circuit of the sensor sheet 20. As shown in FIG. As shown in the figure, when strain is detected, a voltage drop is measured at one end and the other end of each strain gauge G. If the reference resistance value of strain gauge G before deformation is R0, the resistance value of strain gauge G after deformation is Ra, the voltage values ​​at one end and the other end of strain gauge G are V1 and V2, the change in resistance of strain gauge G is ΔR, and the current flowing through strain gauge G is I, then the voltage drop V12 between one end and the other end of strain gauge G is:

number

[0031] Here, if Ra is expressed using the change in gauge resistance as follows, the rate of change in strain resistance can be found.

number

[0032] Therefore, when the above relational expression is applied to the above-mentioned calculation formula (1) for the radius of curvature r, the radius of curvature r is calculated by the following formula.

number

[0033] The strain gauge sensor device 10 configured as described above can detect the strain state of the subject by detecting the detection values ​​of each strain gauge G1-Gn with the base substrate 44, on which the sensor sheet 20 is laminated, attached to the surface of the subject. Furthermore, by calculating the detection values ​​of each strain gauge G1-Gn with the sensor sheet 20 attached to a curved surface or with the base substrate 44, on which the sensor sheet 20 is laminated, wrapped around a cylindrical peripheral surface, the curved shape of the surface or the peripheral shape can be detected or quantified. According to the strain gauge sensor device 10 of this embodiment, open / close switches are provided between the power supply line and the strain gauge, and between the ground line and the strain gauge, and by selectively opening and closing these open / close switches, it is possible to sequentially drive (scan drive) the power supplies of multiple strain gauges. This allows current to flow only through the strain gauge G to be scanned, and reduces the power consumption of the sensor during strain detection compared to when the power supplies of all strain gauges G1 to Gn are always on.

[0034] According to the strain gauge sensor device 10 of this embodiment, by providing an ON / OFF switch between the signal line and the strain gauge and selectively opening and closing the ON / OFF switch, it is possible to sequentially drive (scan drive) the signal line for each strain gauge. When the signal lines are driven sequentially, no charging or discharging of the wiring parasitic capacitance occurs, and therefore the response speed of the strain gauge sensor is increased. Furthermore, according to the strain gauge sensor device 10 of this embodiment, an open / close switch is provided between each strain gauge G and the wiring, allowing selective connection between each strain gauge G and the wiring. Therefore, a common power supply line, a common ground line, and a common signal line can be used for the multiple strain gauges G1 to Gn. This reduces the number of wires and the area occupied by the wires, making it possible to miniaturize the sensor. As described above, according to this embodiment, it is possible to provide a strain gauge sensor device that can reduce power consumption and size.

[0035] Next, a strain gauge sensor device according to another embodiment will be described. In the other embodiments described below, the same parts as those in the first embodiment described above will be given the same reference numerals as those in the first embodiment, and detailed descriptions thereof may be simplified or omitted. (Second embodiment) Figure 12 is a plan view showing the wiring structure of the sensor sheet in the strain gauge sensor device of the second embodiment, Figure 13 is a cross-sectional view of the sensor sheet taken along line CC in Figure 12, and Figure 14 is a cross-sectional view of the sensor sheet taken along line DD in Figure 12. The second embodiment differs from the first embodiment in that the wiring structure of the sensor sheet 20 is configured as a two-layer structure consisting of a so-called gate line layer and a signal line layer.

[0036] 12, 13, and 14, in the sensor sheet 20, gate lines GL1 and GL2 and bridge wirings BR1 and BR2 in the same layer are provided on the surface of the sheet base material 22. The bridge wirings BR1 and BR2 each extend a predetermined length in the width direction Y and are provided at positions facing the first signal line SG1 and the second signal line SG2, respectively. An interlayer film (gate insulating film) 24 is laminated on the surface of the sheet substrate 22, overlapping the gate lines GL1, GL2 and bridge wirings BR1, BR2. A semiconductor layer SC and a conductive layer are formed on the interlayer film 24. The conductive layer forms the wiring patterns of the strain gauges G1 to Gn, the power supply line VL, the ground line GND, the first signal line SG1, and the second signal line SG2. Each semiconductor layer SC faces the gates formed by the gate lines GL1, GL2, with the interlayer film 24 sandwiched between them. A protective film 28 is laminated on the interlayer film 24, overlapping the conductive layer.

[0037] As shown in Figures 12 and 13, the branch wiring that branches off from the power line VL and connects to one end of the strain gauge G is separated by a predetermined length where it intersects with the first signal line SG1, and both ends of the separated side face the first signal line SG1 with a gap between them. Both ends of the separated side are connected to the underlying bridge wiring BR1 via contact holes CH1 and CH2, respectively. Furthermore, a portion of the branch wiring overlaps the semiconductor layer SC, forming the source electrode and drain electrode. In this way, the gate, semiconductor layer SC, source electrode, and drain electrode form a thin-film transistor (TFT), i.e., the first open / close switch SW1. As a result, the power line VL is connected to one end of the strain gauge G via the branch wiring, bridge wiring BR1, and first open / close switch SW1.

[0038] The branch wiring, which branches off from the ground line GNL and connects to the other end of the strain gauge G, is separated by a predetermined length where it intersects with the second signal line SG2, and both ends of the separated section face the second signal line SG2 with a gap between them. Both ends of the separated section are connected to the underlying bridge wiring BR2 via contact holes CH3 and CH4, respectively. Furthermore, a portion of the branch wiring overlaps the semiconductor layer SC, forming the source electrode and drain electrode. The gate, semiconductor layer SC, source electrode, and drain electrode form a thin-film transistor (TFT), i.e., the second open-close switch SW2. The ground line GNL is thus connected to the other end of the strain gauge G via the branch wiring, bridge wiring BR2, and second open-close switch SW2.

[0039] 13 and 14, the branch wiring that branches off from the first signal line SG1 and connects to one end of the strain gauge G is separated along the way, and the separated ends of each branch wiring are positioned overlapping the semiconductor layer SC, forming a source electrode and a drain electrode, respectively. In this way, the gate, semiconductor layer SC, source electrode, and drain electrode form a thin-film transistor (TFT), i.e., a third open / close switch SW3. The first signal line SG1 is connected to one end of the strain gauge G via the branch wiring and the third open / close switch SW3.

[0040] Similarly, the branch wiring that branches off from the second signal line SG2 and connects to the other end of the strain gauge G is separated along the way, and the separated ends of each branch wiring are positioned overlapping the semiconductor layer SC, forming a source electrode and a drain electrode, respectively. In this way, the gate, semiconductor layer SC, source electrode, and drain electrode form a thin film transistor (TFT), i.e., a fourth open / close switch SW4. The second signal line SG2 is connected to the other end of the strain gauge G via the branch wiring and the fourth open / close switch SW4. According to the second embodiment configured as described above, the wiring pattern of the sensor sheet 20 has a two-layer structure, thereby making it possible to further reduce the thickness of the sensor sheet 20. Furthermore, the strain gauge sensor device according to the second embodiment can also achieve the same effects as the strain gauge sensor device according to the first embodiment described above.

[0041] (Third embodiment) FIG. 15 is a perspective view of a strain gauge sensor device according to a third embodiment, and FIG. 16 is a perspective view schematically showing a base end portion of a sensor sheet and a relay board in the strain gauge sensor device. As shown in the figure, the strain gauge sensor device 10 according to the second embodiment constitutes a double-sided strain gauge sensor. The strain gauge sensor device 10 includes a long, thin, flexible base substrate 44, 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 (rear surface) of the base substrate 44, and an interconnect substrate (drive circuit board) 12 connected to the first sensor sheet 20A and the second sensor sheet 20B via a flexible printed circuit (FPC) 14. In one example, the base substrate 44 is made of a resin such as polyethylene terephthalate (PET) or polyimide, and has a thickness of approximately 0.3 to 0.5 mm.

[0042] Each of the first sensor sheet 20A and the second sensor sheet 20B has a long, thin, flexible sheet substrate 22 and a conductive pattern provided on one side of the sheet substrate 22. The conductive pattern includes a plurality of strain gauges G1 to Gn. The plurality of strain gauges G1 to Gn are arranged side by side in the longitudinal direction X at predetermined intervals from one end to the other end of the sheet substrate 22 in the longitudinal direction X. The strain gauges G1 to Gn of the first sensor sheet 20A face the strain gauges G1 to Gn of the second sensor sheet 20B, with the base substrate 44 sandwiched between them.

[0043] FIG. 17 is a plan view schematically showing the strain gauges and wiring patterns of the first sensor sheet 20A and the second sensor sheet 20B. As shown in the figure, each of the first sensor sheet 20A and the second sensor sheet 20B is configured similarly to the sensor sheet 20 in the first embodiment described above. That is, the first sensor sheet 20A has a flexible, strip-shaped sheet substrate 22 and a conductor pattern provided on one side of the sheet substrate 22. The conductor pattern of the first sensor sheet 20A has a plurality of strain gauges G1 to Gn. The strain gauges G1 to Gn are arranged in a row at intervals in the longitudinal direction X of the first sensor sheet 20A. Each of the strain gauges G1 to Gn extends in a bellows-like manner in the width direction Y and has one end and the other end in the width direction Y. Each of the strain gauges G1 to Gn generates a resistance change in response to strain.

[0044] The conductor pattern has a power supply line VL, a ground line GNL, and two signal lines SG1 and SG2 that extend in the longitudinal direction X along the rows of the strain gauges G1 to Gn. The first signal line SG1 and the power supply line VL are located on one end side of the strain gauges G1 to Gn, and the power supply line VL is located outside and spaced apart from the first signal line SG1 in the width direction Y. The second signal line SG2 and the ground line GNL are located on the other end side of the strain gauges G1 to Gn, and the ground line GNL is located outside and spaced apart from the second signal line SG2 in the width direction Y.

[0045] One end of each of the strain gauges G1 to Gn is connected to a power supply line VL via a first switch SW1. The other end of each of the strain gauges G1 to Gn is connected to a ground line GNL via a second switch SW2. Furthermore, one end of each of the strain gauges G1 to Gn is connected to a first signal line SG1 via a third switch SW3. The other end of each of the strain gauges G1 to Gn is connected to a second signal line SG2 via a fourth switch SW4. The first to fourth on-off switches SW1 to SW4 are each configured by a switching element, for example, a thin film transistor (TFT).

[0046] The first sensor sheet 20A includes a first selector SEL1 for switching the first and second open / close switches SW1 and SW2 of each of the strain gauges G1 to Gn, and a second selector SEL2 for switching the third and fourth open / close switches SW3 and SW4 of each of the strain gauges G1 to Gn. The first selector SEL1 includes a plurality of shift registers (S / R) SR1 arranged side by side in the longitudinal direction X on the side of the ground line GNL and corresponding to the strain gauges G1 to Gn, three signal lines SGL1 for inputting signals (RSTa, CLKa, STVa) to the plurality of shift registers SR1, and a gate line GL1 for inputting the output signal of each shift register SR1 to the corresponding first and second open / close switches SW1 and SW2.

[0047] The second selector SEL2 has a plurality of shift registers (S / R) SR2 arranged side by side in the longitudinal direction X on the side of the power supply line VL and corresponding to the strain gauges G1 to Gn, three signal lines SGL2 for inputting signals (RSTb, CLKb, STVb) to the plurality of shift registers SR2, and a gate line GL2 for inputting the output signals of each shift register SR2 to the corresponding third open / close switch SW3 and fourth open / close switch SW4.

[0048] The second sensor sheet 20B is configured in the same manner as the first sensor sheet 20A. The same parts are given the same reference numerals, and detailed descriptions thereof will be omitted. The first sensor sheet 20A and the second sensor sheet 20B configured as described above are attached to the base substrate 44 by attaching the sheet substrate 22 sides to the front and back surfaces of the base substrate 44, and are opposed to each other with the base substrate 44 in between. Here, it is preferable that the strain gauges G1-Gn of the first sensor sheet 20A and the strain gauges G1-Gn of the second sensor sheet 20B at least partially overlap each other in a plan view. Alternatively, it is preferable that the strain gauges G1-Gn of the sensor sheets 20A and 20B overlap each other while allowing for at least some misalignment in the longitudinal direction X, without any misalignment in the width direction Y. Alternatively, it is preferable that the strain gauges G1-Gn of the sensor sheets 20A and 20B overlap each other without any misalignment in either the longitudinal direction X or the width direction Y.

[0049] As shown in FIG. 16 , the ground line GNL of the first sensor sheet 20A extends to the relay board 12 through the FPC 14. The power line VL of the second sensor sheet 20B extends to the relay board 12 through the FPC 14. The ground line GNL and the power line VL are electrically connected to each other at the relay board 12 via a connection line, for example, a plated through hole SH, formed in the relay board 12. This allows each strain gauge G1-Gn of the first sensor sheet 20A to be connected in series to the corresponding strain gauge G1-Gn of the second sensor sheet 20B. In this embodiment, the ground line GNL of the first sensor sheet 20A functions as a power line that supplies voltage to the power line VL of the second sensor sheet 20B, and therefore, hereinafter, the ground line GNL may be referred to as the relay power line of the first sensor sheet 20A. Alternatively, the ground line GNL of the first sensor sheet 20A, the power line VL of the second sensor sheet 20B, and the connection line connecting them may be collectively referred to as the relay power line IVL. Furthermore, the connecting wires are not limited to plated through holes SH, but may be wiring patterns on a relay board or the like.

[0050] Next, a drive circuit (controller) for driving the first sensor sheet 20A and the second sensor sheet 20B configured as described above will be described. Fig. 18 is a block diagram showing a schematic diagram of the drive circuit (controller) of the strain gauge sensor device 10, and Fig. 19 is a circuit diagram of the difference detection circuit in the analog front end. As shown in FIG. 18, a drive circuit 40 provided on a relay board (control circuit board) 12 includes an analog front end (AFE: signal conditioning circuit) 30, a signal generator 32, a timing controller 34, a communication interface 36, and the like.

[0051] 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 detected data (data) to the host controller 38. The timing controller 34 outputs a drive signal to the signal generator 32 and the analog front end 30 in response to the drive signal (setting). The signal generator 32 generates a clock signal CLKa, a reset signal RSTa, and a data signal STVa in response to a drive signal from the timing controller 34, and inputs the signals CLKa, RSTa, and STVa to the first selector SEL1 of the first sensor sheet 20A and the first selector SEL1 of the second sensor sheet 20B. The signal generator 32 also generates a clock signal CLKb, a reset signal RSTb, and a data signal STVb, and inputs the signals CLKb, RSTb, and STVb to the second selector SEL2 of the first sensor sheet 20A and the second selector SEL2 of the second sensor sheet 20B. That is, the same signals are input to corresponding signal lines in both sensor sheets 20A and 20B.

[0052] The analog front end 30 includes a readout circuit, an AD converter, a digital filter, etc. As shown in FIG. 19 , according to this embodiment, the analog front end 30 includes a differential detection circuit (subtraction circuit) 30a that processes the detection signal of the first sensor sheet 20A, and a differential detection circuit (subtraction circuit) 30b that processes the 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 and RXb sent from each strain gauge G1 to Gn in response to the drive signal, and outputs the signals 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 and 30b calculate the difference between the detection values ​​Rxa and Rxb of each strain gauge G1 to Gn and the difference between the detection values ​​Rxc and Rxd of each strain gauge G1 to Gn, and output the results as signals. The host controller 38 reads the output signal (data) sent from the communication interface 36, performs arithmetic processing such as data shaping and curved surface calculation, and calculates the distortion, curved surface shape, etc. of the subject detected by the sensor sheets 20A and 20B.

[0053] Next, the operation mode of the strain gauge sensor device 10 will be described. FIG. 20 is a timing chart showing output signals when operating in sleep mode (first operation mode), and FIG. 21 is a timing chart showing output signals when operating in active mode (second operation mode). As shown in Fig. 20, in sleep mode, the power supply and signal lines are scan-driven to sequentially supply potential to the strain gauges G1-Gn and sequentially read the detected values ​​of the strain gauges G1-Gn. Specifically, as shown in Fig. 20, in response to an instruction from the host controller 38, the drive circuit 40 inputs a clock signal CLKa to all shift registers SR1 of the first sensor sheet 20A and all shift registers SR1 of the second sensor sheet 20B. The drive circuit 40 also inputs a reset signal RSTa in synchronization with the clock signal CLKa to all shift registers SR1 of the first sensor sheet 20A and all shift registers SR1 of the second sensor sheet 20B. This resets all shift registers SR1 of the first selectors SEL1 of the first sensor sheet 20A and the second sensor sheet 20B. Then, the drive circuit 40 inputs a data signal STVa, which is a start pulse for the shift register, to the first-stage shift register SR1 (the shift register corresponding to strain gauge G1) of the first sensor sheet 20A, and also inputs the data signal STVa to the first-stage shift register SR1 (the shift register corresponding to strain gauge G1) of the first sensor sheet 20B. As a result, the first-stage shift registers SR1 of the first sensor sheet 20A and the second sensor sheet 20B output an ON signal to the first open-close switch SW1 and the second open-close switch SW2 for a certain period of time, turning the first open-close switch SW1 and the second open-close switch SW2 ON (closed) for the certain period of time. After the certain period of time has elapsed, the ON signal turns OFF, and the first open-close switch SW1 and the second open-close switch SW2 are switched OFF (open). While the first open / close switch SW1 and the second open / close switch SW2 are on, the strain gauge G1 of the first sensor sheet 20A is connected to the power line VL and the ground line GNL (relay power line IVL), and the strain gauge G1 of the second sensor sheet 20B is connected to the power line VL (relay power line IVL) and the ground line GNL. That is, during this fixed period, the drive circuit 40, the strain gauge G1 of the first sensor sheet 20A, and the strain gauge G1 of the second sensor sheet 20B are connected in series via the power line VL of the first sensor sheet 20A, the relay power line IVL, and the ground line GNL of the second sensor sheet 20B, and a power supply voltage is applied from the drive circuit 40 to the strain gauge G1 of both sensor sheets 20A and 20B.

[0054] Then, in the first sensor sheet 20A and the second sensor sheet 20B, an input signal is input from the first-stage shift register SR1 to the second-stage shift register SR1 (the shift register corresponding to strain gauge G2). This input signal corresponds to the data signal STVa input to the first-stage shift register SR1, and as a result, the second-stage shift register SR1 outputs an ON signal to the first open-close switch SW1 and the second open-close switch SW2 for a certain period of time, turning the first open-close switch SW1 and the second open-close switch SW2 ON (closed) for the certain period of time. While the first open-close switch SW1 and the second open-close switch SW2 are ON, the drive circuit 40, the strain gauge G2 of the first sensor sheet 20A, and the strain gauge G2 of the second sensor sheet 20B are connected in series via the power line VL of the first sensor sheet 20A, the relay power line IVL, and the ground line GNL of the second sensor sheet 20B, and the drive circuit 40 applies a power supply voltage to the strain gauges G2 of both sensor sheets 20A and 20B.

[0055] Thereafter, in the same manner as above, the input signals as described above are input sequentially to the third- to n-th-stage shift registers SR1 of the first sensor sheet 20A and the second sensor sheet 20B over one frame, and the first open / close switch SW1 and the second open / close switch SW2 are sequentially turned on. During this on period, the strain gauges G3 to Gn of both sensor sheets 20A and 20B are connected in series with each other, and a power supply voltage is applied sequentially to these strain gauges G3 to Gn.

[0056] The drive circuit 40 inputs a clock signal CLKb, a reset signal RSTb synchronized with the clock signal, and a data signal STVb to the second selector SEL2 of the first sensor sheet 20A and to the second selector SEL2 of the second sensor sheet 20B in synchronization with the scan drive of the power supply lines. More specifically, the drive circuit 40 inputs the clock signal CLKb to all shift registers SR2 of the first sensor sheet 20A and all shift registers SR2 of the second sensor sheet 20B. The clock signal CLKb is substantially the same signal as the clock signal CLKa. The drive circuit 40 also inputs a reset signal RSTb synchronized with the clock signal CLKb to all shift registers SR2 of the first sensor sheet 20A and all shift registers SR2 of the second sensor sheet 20B. The reset signal RSTb is synchronized with the reset signal RSTa and is supplied to all shift registers SR2 at the same timing as the reset signal RSTa. This resets all shift registers SR2. The drive circuit 40 then inputs a data signal STVb, which serves as a shift register start pulse, to the first-stage shift register SR2 (the shift register corresponding to strain gauge G1) of the first sensor sheet 20A and the second sensor sheet 20B. The data signal STVb is synchronized with the data signal STVa and is supplied to the first-stage shift register SR2 at the same timing as the data signal STVa. As a result, the first-stage shift register SR2 of the first sensor sheet 20A and the second sensor sheet 20B outputs an ON signal to the third open-close switch SW3 and the fourth open-close switch SW4 of strain gauge G1 for a certain period of time at the same timing as the first-stage shift register SR1, turning the third open-close switch SW3 and the fourth open-close switch SW4 ON (closed) for the certain period of time. After the certain period of time has elapsed, the ON signal turns OFF, and the third open-close switch SW3 and the fourth open-close switch SW4 are switched OFF (open). While the third opening / closing switch SW3 and the fourth opening / closing switch SW4 are on, one end and the other end of the strain gauge G1 of the first sensor sheet 20A are connected to the first signal line SG1 and the second signal line SG2, and the detection signal (voltage value) RXa at one end of the strain gauge G1 and the detection signal (voltage value) RXb at the other end are output to the first and second signal lines SG1 and SG2.At the same time, one end and the other end of the strain gauge G1 of the second sensor sheet 20B are connected to the first signal line SG1 and the second signal line SG2, and the detection signal (voltage value) RXc at one end of the strain gauge G1 and the detection signal (voltage value) RXd at the other end are output to the first and second signal lines SG1 and SG2. The detection signals RXa, RXb, RXc, and RXd are sent to the analog front end 30 of the drive circuit 40 via the first and second signal lines SG1 and SG2, respectively.

[0057] Thereafter, in the first sensor sheet 20A and the second sensor sheet 20B, an input signal is input from the first-stage shift register SR2 to the second-stage shift register SR2 (the shift register corresponding to strain gauge G2). This input signal corresponds to the data signal STVb input to the first-stage shift register SR2, and as a result, in the first sensor sheet 20A and the second sensor sheet 20B, the second-stage shift register SR2 outputs an ON signal to the third open-close switch SW3 and the fourth open-close switch SW4 for a certain period of time at the same timing as the second stage of the shift register SR1, turning the third open-close switch SW3 and the fourth open-close switch SW4 on (closed) for a certain period of time. While the third open / close switch SW3 and the fourth open / close switch SW4 are on, one end and the other end of the strain gauge G2 of the first sensor sheet 20 are connected to the first signal line SG1 and the second signal line SG2, and a detection signal (voltage value) RXa from one end of the strain gauge G2 and a detection signal (voltage value) RXb from the other end are output to the first and second signal lines SG1 and SG2. At the same time, one end and the other end of the strain gauge G2 of the second sensor sheet 20B are connected to the first signal line SG1 and the second signal line SG2, and a detection signal (voltage value) RXc from one end of the strain gauge G2 and a detection signal (voltage value) RXd from the other end are output to the first and second signal lines SG1 and SG2. The detection signals RXa, RXb, RXc, and RXd are sent to the analog front end 30 of the drive circuit 40 via the first and second signal lines SG1 and SG2, respectively.

[0058] Thereafter, in the same manner as above, the input signals as described above are input sequentially to the third to nth shift registers SR2 of the first sensor sheet 20A and the second sensor sheet 20B over one frame. As a result, the first switch SW1 and the second switch SW2 of the shift register SR1 are sequentially turned on, and accordingly the third switch SW3 and the fourth switch SW4 of the shift register SR2 are sequentially turned on. As a result, the detection signals RXa and RXb of the strain gauges G3 to Gn of the first sensor sheet 20A are sequentially output to the first and second signal lines SG1 and SG2, and the detection signals RXc and RXd of the strain gauges G3 to Gn of the second sensor sheet 20B are sequentially output to the first and second signal lines SG1 and SG2. The detection signals RXa, RXb, RXc, and RXd are sent in sequence to the analog front end 30, where they are conditioned and differentially detected. All of the conditioned and differentially detected detection signals RXa, RXb, RXc, and RXd are sent together to a communication interface 36, and further to a host controller 38 via the communication interface 36.

[0059] As described above, by driving the first sensor sheet 20A and the second sensor sheet 20B for scanning in synchronization with each other, the two strain gauges G1 to Gn positioned opposite each other simultaneously detect strain at the same location. In the sleep mode described above, current flows only through the strain gauge G to be scanned, so the power consumption of the sensor during strain detection can be reduced compared to when the power of all strain gauges G1 to Gn is always on.

[0060] On the other hand, as shown in FIG. 21, in the active mode (second operating mode), a potential is supplied to all strain gauges G1-Gn on the first sensor sheet 20A and the second sensor sheet 20B, and then only the signal lines SG1 and SG2 are simultaneously scanned and driven on both sensor sheets 20A and 20B, thereby sequentially reading the detected values ​​of the strain gauges G1-Gn on both sensor sheets 20A and 20B. Specifically, as shown in FIG. 21, in response to an instruction from the host controller 38, the drive circuit 40 outputs a clock signal CLKa to each shift register SR1 on the first sensor sheet 20A and each shift register SR1 on the second sensor sheet 20B. The drive circuit 40 also outputs a reset signal RSTa synchronized with the clock signal CLKa to all shift registers SR1 on the first sensor sheet 20A and all shift registers SR1 on the second sensor sheet 20B. This resets all shift registers SR1 of the first selectors SEL1 on the first sensor sheet 20A and the second sensor sheet 20B. The drive circuit 40 then inputs a data signal STVa, which serves as a shift register start pulse, to the first-stage shift register SR1 (the shift register corresponding to strain gauge G1) of the first sensor sheet 20A. At the same time, the drive circuit 40 also inputs a similar data signal STVa to the first-stage shift register SR1 (the shift register corresponding to strain gauge G1) of the second sensor sheet 20B. The data signal STVa causes the first-stage shift registers SR1 of both sensor sheets 20A and 20B to maintain an ON level for the current frame period (until the next reset signal is input). As an input signal equivalent to the data signal STVa is sequentially supplied to the next-stage shift register SR1, each shift register SR1 in the first and second sensor sheets 20A and 20B, from the first-stage shift register SR1 to the final-stage shift register SR1, sequentially outputs an ON signal to the first open / close switch SW1 and the second open / close switch SW2. The ON signal is maintained until a reset signal is input in the next frame.

[0061] As a result, during the frame period, the strain gauges G1-Gn of the first sensor sheet 20A and the strain gauges G1-Gn of the second sensor sheet 20B are sequentially connected in parallel. More specifically, first, the strain gauge G1 of the first sensor sheet 20A and the strain gauge G1 of the second sensor sheet 20B are connected in series via the relay power line IVL. Next, the strain gauges G1 and G2 of the first sensor sheet 20A and the strain gauges G1 and G2 of the second sensor sheet 20B are connected in parallel via the relay power line IVL. Subsequently, the number of strain gauges connected in parallel increases with time until the end of the frame period. It goes without saying that the strain gauges G1-Gn of the first sensor sheet 20A are connected to the drive circuit 40 via the power line VL, and the strain gauges G1-Gn of the second sensor sheet 20B are connected to the drive circuit 40 via the ground line GNL. As a result, current flows through all of the strain gauges G1-Gn.

[0062] After turning on all of the first and second switches SW1 and SW2, the drive circuit 40 inputs a clock signal CLKb to all of the shift registers SR2 of the first sensor sheet 20A and all of the shift registers SR2 of the second sensor sheet 20B. The drive circuit 40 also inputs a reset signal RSTb, synchronized with the clock signal CLKb, to all of the shift registers SR2 of the first sensor sheet 20A and all of the shift registers SR2 of the second sensor sheet 20B. The drive circuit 40 then inputs a data signal STVb, which serves as a shift register start pulse, to the first-stage shift register SR2 of the first sensor sheet 20A and simultaneously to the first-stage shift register SR2 of the second sensor sheet 20B. As a result, the shift registers SR2 of both sensor sheets 20A and 20B sequentially output ON signals to the third and fourth switches SW3 and SW4, switching the third and fourth switches SW3 and SW4 on (closed) for a certain period of time. As a result, in the first sensor sheet 20A, the strain gauges G1 to Gn are sequentially connected to the first and second signal lines SG1 and SG2, and the detection values ​​(detection signals) RXa and RXb at both ends of the strain gauge G are output to the first and second signal lines SG1 and SG2 at regular intervals.

[0063] Similarly, in the second sensor sheet 20B, the strain gauges G1 to Gn are sequentially connected to first and second signal lines SG1 and SG2, and output the detection values ​​(detection signals) RXc and RXd from both ends of the strain gauge G to the first and second signal lines SG1 and SG2 at regular intervals. That is, the first sensor sheet 20A and the second sensor sheet 20B are provided on the front and back sides of the base substrate 44, but the detection values ​​of the strain gauges G1 to Gn that are arranged opposite each other are simultaneously output to the drive circuit 40. More specifically, when the detection values ​​RXa and RXb are detected by the strain gauge G1 of the first sensor sheet 20A, the detection values ​​RXc and RXd are simultaneously detected by the strain gauge G1 of the second sensor sheet 20B, and this continues for the strain gauge G2 and onwards. The detection signals RXa, RXb, RXc, and RXd are sent to the analog front end 30 of the drive circuit 40 via the first and second signal lines SG1 and SG2. The detection signals RXa, RXb, RXc, and RXd are conditioned by the analog front end 30 and then sent to the host controller 38 via the communication interface 36.

[0064] As described above, by driving the first sensor sheet 20A and the second sensor sheet 20B in synchronization with each other, the two strain gauges G1 to Gn positioned opposite each other simultaneously detect strain at the same location. In the active mode described above, all of the first open / close switches SW1 and second open / close switches SW2 remain on, so the fluctuations in parasitic capacitance in the power supply line VL and ground line GNL are smaller than in the sleep mode, and the response speed of the strain gauge sensor is faster than in the sleep mode.

[0065] Next, a method for calculating the shape of a curved surface, for example, the radius of curvature, using a double-sided strain gauge sensor device will be described. 22 is a schematic diagram showing a portion of a strain gauge sensor device installed on the peripheral surface of a subject. As shown in the figure, when installed on the peripheral surface, the neutral plane of the base substrate 44 is curved with the same radius of curvature r as the peripheral surface. Here, the neutral plane is a plane where the strain gauge sensor does not expand or contract before or after bending (i.e., where there is zero strain even after bending). In this embodiment, since the same sensor sheet is provided on both sides of the base substrate 44, the neutral plane may be provided at a position that is ½ the thickness of the base substrate 44. The strain gauge Ga of the first sensor sheet 20A located on the outer periphery and the strain gauge Gb of the second sensor sheet 20B located on the inner periphery face each other in the radial direction.

[0066] In Figure 22 and the formula below, W0: initial width of the strain gauge, Wa: width of the strain gauge on the outer periphery, Wb: width of the strain gauge on the inner periphery, ΔW: change in width of the strain gauge, d: thickness of the base substrate, θ: opening angle of the strain gauge, r: radius of curvature of the neutral plane, k: gauge factor, R0: reference resistance of the strain gauge, and ΔR: change in resistance of the strain gauge.

[0067] If the width of the strain gauge G on the neutral plane of the base substrate 44 is the initial width W0 of the strain gauge, then W0 = rθ. The strain gauge Ga on the outer periphery is deformed by bending and stretched in the width direction, and its gauge width Wa is

number

number

number

[0068] FIG. 23 is a diagram schematically showing the equivalent circuits of the first sensor sheet 20A and the second sensor sheet 20B. As shown in the figure, in this embodiment, the ground line GNL of the first sensor sheet 20A is connected to the power line VL of the second sensor sheet 20B via a connecting line, and these lines form a relay power line IVL (see FIG. 17). This connects the outer strain gauge Ga and the inner strain gauge Gb in series. When strain is detected, a voltage drop is measured at one end and the other end of each strain gauge Ga and Gb.

[0069] Let R0 be the initial resistance value of each strain gauge Ga, Gb before deformation, Ra be the resistance value of the outer peripheral strain gauge Ga after deformation, Rb be the resistance value of the inner peripheral strain gauge Gb after deformation, V1 and V2 be the voltage values ​​at one end and the other end of the outer peripheral strain gauge Ga, V3 and V4 be the voltage values ​​at one end and the other end of the inner peripheral strain gauge Gb, ΔR be the change in resistance of the strain gauge, and I be the current flowing through each strain gauge Ga, Gb. Then, the voltage drop V12 between one end and the other end of strain gauge Ga and the voltage drop V34 between one end and the other end of strain gauge Gb are given by:

number

number

number

number

[0070] Applying the above relational expression to the aforementioned formula (3) for calculating the radius of curvature r, we get the following:

number

[0071] The strain gauge sensor device 10 detects the voltage values ​​at one end and the other end of each strain gauge G1 to Gn, and calculates the radius of curvature r of the peripheral surface of the object by using the difference between these voltage values ​​(V12, V34) and the above equation (4). By sequentially calculating the radii of curvature at multiple points on the peripheral surface, the curved surface shape of the entire peripheral surface can be detected. According to the strain gauge sensor device 10 of this embodiment, by arranging strain gauges facing each other on both the front and back sides and detecting the curved surface shape based on the difference between the side constant voltages, it is possible to detect only the resistance changes of the strain gauges without being affected by the wiring resistances (Re1 to Re5) of the wiring routed on the sheet sensor or relay board. Also, it is not necessary to input the initial value R0 of the strain resistance of each strain gauge G1 to Gn, which makes it possible to easily calculate the radius of curvature.

[0072] The strain gauge sensor device 10 configured as described above can detect the strain state of a test object by detecting the detection values ​​of each strain gauge G1-Gn with either sensor sheet 20A or 20B attached to the surface of the test object. Furthermore, by calculating the detection values ​​of each strain gauge G1-Gn with sensor sheet 20A or 20B attached to a curved surface or wrapped around a cylindrical surface, the curved shape or circumferential shape of the surface can be detected or quantified. When detecting strain on a curved surface using the double-sided strain gauge sensor device 10, the inner and outer strain gauges G1-Gn have different radii of curvature. The detection values ​​of the two strain gauges located opposite each other at the same position on the inner and outer sides also differ. Therefore, the curved shape of the test object can be detected more accurately by calculating the difference between the detection values ​​of the two opposing strain gauges.

[0073] If the temperature differs partially at the detection position, the detected value of the strain gauge will fluctuate, but by detecting simultaneously using two opposing strain gauges and taking the difference between the detected values, the effects of temperature changes can be cancelled out. Also, even if noise is present in the power supply, the same noise is applied to both the front and back strain gauges, so by taking the difference between the two detected values, the effects of the noise can be cancelled out. This improves the detection accuracy of the sensor. Furthermore, in the third embodiment, the same effects as those in the first embodiment can be obtained.

[0074] (Fourth embodiment) FIG. 24 is a plan view schematically showing a sensor sheet of the strain gauge sensor device according to the fourth embodiment. As shown in the figures, the double-sided strain gauge sensor device 10 according to the fourth embodiment includes a first sensor sheet 20A and a second sensor sheet 20B. The wiring structure of the first sensor sheet 20A and the second sensor sheet 20B and the array structure of the strain gauges G1 to Gn themselves are configured identically to the sensor sheet 20 according to the first embodiment. In the fourth embodiment, the first selector SEL1 and the second selector SEL2 of one sensor sheet, for example, the second sensor sheet 20B, are provided at positions that are mirror-inverted relative to the first selector SEL1 and the second selector SEL2 of the other first sensor sheet 20A.

[0075] In detail, in the first sensor sheet 20A, the multiple shift registers SR1 and signal line SGL1 constituting the first selector SEL1 are arranged on the side of the ground line GNL (relay power line IVL) relative to the row of strain gauges G1 to Gn, and the multiple shift registers SR2 and signal line SGL2 constituting the second selector SEL2 are arranged on the side of the power line VL relative to the row of strain gauges G1 to Gn. In contrast, in the second sensor sheet 20B, the multiple shift registers SR1 and signal line SGL1 that constitute the first selector SEL1 are arranged on the side of the power supply line VL relative to the row of strain gauges G1 to Gn, and the multiple shift registers SR2 and signal line SGL2 that constitute the second selector SEL2 are arranged on the side of the ground line GNL relative to the row of strain gauges G1 to Gn.

[0076] When the first sensor sheet 20A and the second sensor sheet 20B configured as described above are attached to the front and back surfaces of the base substrate 44, the first selector SEL1 and the second selector SEL2 of the first sensor sheet 20A are arranged opposite the first selector SEL1 and the second selector SEL2 of the second sensor sheet 20B, respectively. That is, wiring of the same type is arranged opposite each other in the same position. This makes it possible to easily connect the wiring of the first sensor sheet 20A and the second sensor sheet 20B to the wiring of the relay substrate 12, and to route the wiring, etc. In addition, the fourth embodiment can also provide the same effects as the third embodiment described above.

[0077] (Fifth embodiment) FIG. 25 is a plan view schematically showing a sensor sheet of the strain gauge sensor device according to the fifth embodiment. As shown in the figure, the double-sided strain gauge sensor device 10 according to the fifth embodiment includes a first sensor sheet 20A and a second sensor sheet 20B. The wiring structure of the first sensor sheet 20A and the second sensor sheet 20B and the array structure of the strain gauges G1 to Gn themselves are configured identically to the first and second sensor sheets 20A and 20B of the strain gauge sensor device 10 according to the fourth embodiment. According to the fifth embodiment, in one of the first sensor sheet 20A and the second sensor sheet 20B, for example, the second sensor sheet 20B, the wiring is arranged so that the distance in the width direction Y between the first signal line SG1 and the second signal line SG2 and the distance in the width direction Y between the power line VL and the ground line GNL are both wider than the above-mentioned distances in the other first sensor sheet 20A.

[0078] In the above configuration, when the first sensor sheet 20A and the second sensor sheet 20B are attached to the front and back surfaces of the base substrate 44, at least one wire (four wires in this embodiment) of the power supply line VL, the ground line GNL, the first signal line SG1, and the second signal line SG2 of the second sensor sheet 20B does not overlap the corresponding wires of the first sensor sheet 20A but is shifted in the surface direction relative to the corresponding wires. This prevents parasitic capacitance from occurring between the wires on the front surface side and the wires on the back surface side, thereby improving the sensor response speed. In addition, the fifth embodiment can also provide the same effects as the third embodiment described above.

[0079] (Sixth embodiment) FIG. 26 is a plan view schematically showing a sensor sheet of the strain gauge sensor device according to the sixth embodiment. As shown in the figure, in the double-sided strain gauge sensor device 10 according to the sixth embodiment, in one of the first sensor sheet 20A and the second sensor sheet 20B, for example, the second sensor sheet 20B, only the power supply line VL and the ground line GNL are arranged so as to be shifted in the planar direction relative to the power supply line VL and the ground line GNL (relay power line IVL) of the other first sensor sheet 20A. The first signal line SG1 and the second signal line SG2 of the second sensor sheet 20B face the first signal line SG1 and the second signal line SG2 of the first sensor sheet 20A, respectively.

[0080] In the sixth embodiment having the above configuration, the parasitic capacitance generated between the wiring on the front side (power supply line VL, ground line GNL) and the wiring on the rear side (power supply line VL, ground line GNL) can be reduced, thereby improving the sensor response speed. In addition, in the sixth embodiment, the same effects as those of the third embodiment can be obtained.

[0081] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. The novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. The embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as defined in the claims. All configurations that can be implemented by a person skilled in the art by appropriately modifying the design based on the respective configurations described above as the embodiments of the present invention also fall within the scope of the present invention as long as they include the gist of the present invention. For example, the number of strain gauges arranged in the sensor sheet is not limited to the above-described embodiment and can be selected arbitrarily. The selector (scanner circuit) that selectively opens and closes the switches is not limited to a combination of multiple shift registers, and a multiplexer or the like may be used. The constituent materials, dimensions, and shape of the sensor sheet are not limited to the above-described embodiment and can be changed as appropriate.

Claims

1. a plurality of strain gauges each having one end and the other end and arranged in a line at intervals; a power supply line, a ground line, a first signal line, and a second signal line, each extending along the row of the plurality of strain gauges; a plurality of first open / close switches respectively connected between the one ends of the plurality of strain gauges and the power supply line; a plurality of second open / close switches connected between the other ends of the plurality of strain gauges and the ground line, a plurality of third open / close switches respectively connected between the one ends of the plurality of strain gauges and the first signal line; a plurality of fourth open / close switches respectively connected between the other ends of the plurality of strain gauges and the second signal line; A strain detection device comprising:

2. a first selector that selectively opens and closes the first open / close switch and the second open / close switch; a second selector that selectively opens and closes the third open / close switch and the fourth open / close switch; The strain detection device according to claim 1 , further comprising:

3. a first operation mode in which the first selector opens and closes the first open-close switch and the second open-close switch sequentially along the row of the strain gauges to connect the plurality of strain gauges to the power supply line and the ground line, and in synchronization therewith, the second selector opens and closes the third open-close switch and the fourth open-close switch sequentially along the row of the strain gauges to connect the one end and the other end of the plurality of strain gauges to the first signal line and the second signal line; a second operation mode in which the first selector switches the first open / close switch and the second open / close switch to close to connect all of the plurality of strain gauges to the power supply line and the ground line, and then the second selector opens and closes the third open / close switch and the fourth open / close switch sequentially along the row of the strain gauges to sequentially connect the one end and the other end of the plurality of strain gauges to the first signal line and the second signal line.

4. a flexible substrate having a first major surface and a second major surface opposite to the first major surface; a first sensor sheet attached to the first main surface; a second sensor sheet attached to the second main surface and facing the first sensor sheet across the base material; a controller connected to the first sensor sheet and the second sensor sheet; Each of the first sensor sheet and the second sensor sheet includes: a plurality of strain gauges, each having one end and the other end, arranged in a row with spaces between them; a power supply line, a ground line, a first signal line, and a second signal line, each extending along the row of the plurality of strain gauges; a plurality of first open / close switches, each connected between the one end of the plurality of strain gauges and the power supply line; a plurality of second open / close switches, each connected between the other end of the plurality of strain gauges and the ground line; a plurality of third open / close switches, each connected between the one end of the plurality of strain gauges and the first signal line; a plurality of fourth open / close switches, each connected between the other end of the plurality of strain gauges and the second signal line; a first selector, which selectively opens and closes the first open / close switch and the second open / close switch; and a second selector, which selectively opens and closes the third open / close switch and the fourth open / close switch, the plurality of strain gauges of the first sensor sheet face the plurality of strain gauges of the second sensor sheet, with the base material interposed therebetween; Distortion detection device.

5. The strain detector according to claim 4 , wherein the ground line of the first sensor sheet is electrically connected to the power supply line of the second sensor sheet.

6. The strain detection device of claim 5, wherein the controller includes a circuit board connected to the wiring of the first sensor sheet and the wiring of the second sensor sheet, and the circuit board has a connection line connecting the ground line of the first sensor sheet and the power line of the second sensor sheet.

7. The strain detection device according to claim 4 , wherein the first selector and the second selector of the first sensor sheet face the first selector and the second selector of the second sensor sheet, respectively, with the base material sandwiched therebetween.

8. 5. The strain detection device of claim 4, wherein at least one of the power supply line, ground line, first signal line, and second signal line of the first sensor sheet is positioned offset in the planar direction relative to the power supply line, ground line, first signal line, and second signal line of the second sensor sheet.

9. The controller a first operation mode in which the first selector opens and closes the first open-close switch and the second open-close switch sequentially along the row of the strain gauges to connect the plurality of strain gauges to the power supply line and the ground line, and in synchronization therewith, the second selector opens and closes the third open-close switch and the fourth open-close switch sequentially along the row of the strain gauges to connect the one end and the other end of the plurality of strain gauges to the first signal line and the second signal line; a second operation mode in which the first selector switches the first open / close switch and the second open / close switch to close to connect all of the plurality of strain gauges to the power supply line and the ground line, and then the second selector opens and closes the third open / close switch and the fourth open / close switch sequentially along the row of the strain gauges to sequentially connect the one end and the other end of the plurality of strain gauges to the first signal line and the second signal line, 5. The strain detector according to claim 4, wherein the first sensor sheet and the second sensor sheet are driven in the first operation mode or the second operation mode in synchronization with each other.

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