Sweat volume sensor

Abstract

This sweat volume sensor comprises: a sensor unit in which a heater is provided on a flexible substrate; and a calculation unit. The calculation unit measures the volume of sweat flowing on a region where radiant heat of the heater reaches, on the basis of the temperature of the heater when the power of the heater is controlled so as to become consistent, the power of the heater when the temperature of the heater is controlled so as to become consistent, or the temperature difference around the heater.

Description

Sweat rate sensor

[0001] The present disclosure relates to a sweat rate sensor.

[0002] JP 2023-132965 A states, "The fluid sensor system 1A shown in FIG. 1 estimates (detects) the flow direction Df of a fluid flowing through a fluid flow path 10. Such a fluid sensor system 1A is applied to various machines and facilities that have a fluid flow path 10, such as steam turbines, gas turbines, compressors, and wind tunnel facilities. The fluid sensor system 1A can also be applied to pipes, ducts, and the like that form a fluid flow path. The fluid sensor system 1A can also be applied to cases where, as a moving body such as the wing or body of an aircraft, the hull of a ship, or the body of a vehicle moves, a relative speed difference occurs between the surrounding gas (e.g., air) or liquid (e.g., water), and the surrounding gas or liquid can be considered to flow relative to the moving body. The fluid whose flow direction Df is estimated by the fluid sensor system 1A may be, for example, a gas such as air, or a liquid such as water."

[0003] In recent years, various wearable devices have been developed for the purpose of monitoring health status and exercise volume, and wearable devices capable of measuring heart rate and blood oxygen concentration have been realized. Here, quantitative monitoring of sweat rate could lead to early detection of dehydration and heatstroke. Conventionally, techniques for estimating the flow direction of a fluid flowing through a flow path have been known (e.g., JP 2023-132965 A). However, the fluid sensor in JP 2023-132965 A is intended exclusively for industrial applications, and the sensor unit is rigid and embedded in the flow path surface. Such fluid sensors intended for industrial applications have the problem that they cannot be applied to sweat rate sensors in the first place, or even if they were applied, they cannot accurately monitor sweat rate.

[0004] The present disclosure has been made in view of the above circumstances, and aims to provide a sensor suitable for monitoring the amount of sweat.

[0005] The sweat rate sensor according to the first aspect of the present disclosure comprises a sensor unit having a heater mounted on a flexible substrate, and a calculation unit, and the calculation unit measures the amount of sweat flowing within the range of the radiant heat of the heater based on the temperature of the heater when the heater's power is controlled to be constant, the heater's power when the heater's temperature is controlled to be constant, or the temperature difference around the heater.

[0006] A sweat rate sensor according to a second aspect of the present disclosure is the sweat rate sensor according to the first aspect, wherein the sensor section has an elastic member on which the flexible substrate is laminated, and the elastic member has a flow path through which the sweat flows.

[0007] A sweat rate sensor according to a third aspect of the present disclosure is the sweat rate sensor according to the second aspect, wherein the elastic member has an opening formed on the surface opposite to the surface on which the flexible substrate is laminated, and the opening is connected to the flow path.

[0008] A fourth aspect of the present disclosure is a sweat rate sensor according to the third aspect, wherein the sensor unit has a tape member on which the elastic member is laminated, and the tape member has an exposed portion that exposes the opening, and the calculation unit measures the amount of sweat that flows into the flow path through the exposed portion and the opening when the sensor unit is attached to the skin.

[0009] A sweat rate sensor according to a fifth aspect of the present disclosure is a sweat rate sensor according to any one of the first to fourth aspects, wherein the calculation unit is capable of switching between a first mode in which the amount of sweat is measured based on the temperature of the heater or the power of the heater, and a second mode in which the amount of sweat is measured based on the temperature difference around the heater.

[0010] A sixth aspect of the present disclosure relates to a sweat rate sensor, wherein in the fifth aspect of the sweat rate sensor, the calculation unit switches from the first mode to the second mode when the change in the heater temperature or the heater power does not satisfy a predetermined threshold.

[0011] A sweat rate sensor according to a seventh aspect of the present disclosure is the sweat rate sensor according to any one of the first to sixth aspects, wherein the calculation unit removes noise caused by backflow of the sweat.

[0012] The sweat rate sensor according to an eighth aspect of the present disclosure is the sweat rate sensor according to the seventh aspect, wherein when the direction of the sweat flow reverses and fluctuates within a predetermined period, the calculation unit removes the fluctuation as noise.

[0013] A sweat rate sensor according to a ninth aspect of the present disclosure is a sweat rate sensor according to any one of the first to eighth aspects, in which a pair of temperature sensors are provided on the flexible substrate and arranged opposite each other across the heater, and the calculation unit uses the difference in temperatures detected by the pair of temperature sensors as the temperature difference around the heater.

[0014] A sweat rate sensor according to a tenth aspect of the present disclosure is a sweat rate sensor according to any one of the first to ninth aspects, in which a temperature compensation sensor is provided on the flexible substrate, and the calculation unit corrects the temperature of the heater using the difference between the temperature detected by the temperature compensation sensor and the temperature of the heater, and measures the amount of sweat using the corrected heater temperature.

[0015] The sweat rate sensor of the present disclosure can provide a sensor suitable for monitoring the amount of sweat.

[0016] FIG. 1 is a diagram showing an example of a schematic configuration of a sensor system 10 according to the present embodiment; FIG. 2 is a diagram showing an example of a cross-sectional view of a sensor unit 200 according to the present embodiment; FIG. 3 is a diagram showing an example of a hardware configuration of an arithmetic processing device 300 according to the present embodiment; FIG. 4 is a diagram showing an example of a functional configuration of the arithmetic processing device 300 according to the present embodiment; FIG. 5 is a diagram for explaining the measurement principle of a sweat rate sensor 100 according to the present embodiment; FIG. 6 is a diagram showing an example of measurement sensitivity according to a flow rate; FIG. 7 is a diagram showing an example of body movement noise; and FIG. 8 is a diagram showing an example of the amount of sweat measured by the sweat rate sensor 100 according to the present embodiment.

[0017] An example of an embodiment of the present disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components and parts are designated by the same reference numerals. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0018] 1 is a diagram showing an example of a schematic configuration of a sensor system 10 according to this embodiment. In the sensor system 10, a perspiration rate sensor 100 is used to measure the amount of sweat produced by a subject 50.

[0019] The subject 50 is an object for measuring the amount of sweating. In this figure, the subject 50 is shown as a human being as an example, but is not limited to this. The subject 50 may be another animal such as a horse or cow, or may be a plant. In other words, the term "sweating" here may be defined as a term that also includes "transpiration."

[0020] The sweat rate sensor 100 includes a sensor unit 200 and an arithmetic processing device 300. The sensor unit 200 is attached to the subject 50 and detects physical quantities associated with sweat produced by the subject 50. Since the sensor unit 200 is attached to the subject 50, it is preferable that it is lightweight and small. Therefore, as shown in the figure, the sensor unit 200 and the arithmetic processing device 300 are preferably configured as separate units. In this case, the sensor unit 200 and the arithmetic processing device 300 may be connected to each other so as to be able to communicate with each other via a wire or wirelessly. However, this is not a limitation, and the sensor unit 200 and the arithmetic processing device 300 may be configured as an integrated unit.

[0021] 2 is a diagram showing an example of a cross-sectional view of the sensor unit 200 according to this embodiment. As shown in this diagram, the sensor unit 200 may be formed by laminating a tape member 210, an elastic member 220, a flexible substrate 230, and a protective member 240 in this order.

[0022] The tape member 210 has adhesive properties. More specifically, the tape member 210 may be a nonwoven fabric substrate with adhesive applied to both sides. One adhesive may be attached to the skin of the subject 50. The other adhesive may be attached to the elastic member 220. In this manner, the sensor unit 200 may have the tape member 210 on which the elastic member 220 is laminated. Here, the tape member 210 may have an exposed portion 211 that exposes an opening 221, which will be described later.

[0023] The elastic member 220 is laminated between the tape member 210 and the flexible substrate 230. In this manner, the sensor unit 200 may have the elastic member 220 on which the flexible substrate 230 is laminated. Here, an opening 221 may be formed in the elastic member 220 on a surface opposite to the surface on which the flexible substrate 230 is laminated. Furthermore, the elastic member 220 may have a flow path 222 through which sweat flows, formed, for example, parallel to the laminated surface. Here, the opening 221 may be in communication with the flow path 222. As a result, sweat produced by the subject 50 flows through the flow path 222 via the exposed portion 211 and the opening 221. The amount of sweat flowing through the flow path 222 can be adjusted by the size of the exposed portion 211.

[0024] The elastic member 220 may be formed of, for example, an elastomer. An elastomer is a soft polymer that has elasticity like rubber. Examples of elastomers include silicone elastomers such as PDMS (Polydimethylsiloxane). The flow channel 222 may be, for example, a micro-flow channel finely formed in such PDMS.

[0025] The flexible substrate 230 is a printed circuit board that is flexible and can be repeatedly deformed while maintaining its electrical characteristics even when deformed. The flexible substrate 230 is provided with a heater 231, an upstream temperature sensor 232U, a downstream temperature sensor 232D (collectively referred to as "temperature sensors 232"), and a temperature compensation sensor 233.

[0026] The heater 231 locally increases the temperature of the sweat flowing through the flow path 222. The heater 231 may be disposed on the flexible substrate 230 at a position directly above the flow path 222.

[0027] The temperature sensor 232 detects distortion caused by the temperature rise caused by the heater 231 and the flow of sweat. The upstream temperature sensor 232U and the downstream temperature sensor 232D are a pair of temperature sensors 232 arranged in positions close to the heater 231, specifically, in positions facing each other across the heater 231, within the range of the radiant heat from the heater 231. More specifically, the upstream temperature sensor 232U and the downstream temperature sensor 232D may be arranged directly above the flow path 222 on the flexible substrate 230, facing each other across the heater 231. In this case, the upstream temperature sensor 232U may be arranged closer to the opening 221 than the downstream temperature sensor 232D, i.e., upstream in the flow of sweat. The upstream temperature sensor 232U and the downstream temperature sensor 232D each output a value (e.g., a voltage value) corresponding to the detected temperature as a detection signal to the arithmetic processing device 300.

[0028] The temperature compensation sensor 233 detects a temperature to compensate for the effects of body temperature and outside air temperature. The temperature compensation sensor 233 outputs a value corresponding to the detected temperature as a detection signal to the arithmetic processing device 300. The temperature compensation sensor 233 may be provided at a position on the flexible substrate 230 away from the heater 231, preferably at a position where it can be assumed that the radiant heat from the heater 231 does not reach the sensor. Note that the temperature compensation sensor 233 may not necessarily be provided, as it may not be used depending on the usage scenario.

[0029] The protective member 240 is laminated on the flexible substrate 230 to protect the elements provided on the flexible substrate 230. The protective member 240 may be made of PDMS or the like, similar to the elastic member 220. In this manner, the sensor unit 200 may be configured by laminating flexible members. This allows the sensor unit 200 to be in close contact with the skin, thereby achieving a high wearing comfort and high measurement accuracy.

[0030] 3 is a diagram showing an example of the hardware configuration of the arithmetic processing device 300 according to this embodiment. The arithmetic processing device 300 performs arithmetic processing on the detection signal input from the sensor unit 200 and outputs a measurement result according to the amount of sweat. The arithmetic processing device 300 may be a computer. More specifically, the arithmetic processing device 300 may include a processor 301, a ROM (Read Only Memory) 302, a RAM (Random Access Memory) 303, a storage 304, a communication interface 305, and a user interface 306. These components are connected to each other via a bus 309 so as to be able to communicate with each other.

[0031] The processor 301 executes various programs and controls each component. Here, the processor 301 is assumed to be a CPU (Central Processing Unit). The ROM 302 stores various programs and various data. The RAM 303 temporarily stores programs or data as a working area. The storage 304 is configured with an HDD (Hard Disk Drive) or an SSD (Solid State Drive) and stores various programs including an operating system and various data.

[0032] In the arithmetic processing device 300 according to this embodiment, an arithmetic processing program is stored in the ROM 302 or the storage 304. The processor 301 reads the arithmetic processing program from the ROM 302 or the storage 304 and executes it using the RAM 303 as a working area, thereby controlling each component and executing various arithmetic processing in accordance with the arithmetic processing program.

[0033] The communication interface 305 is an interface through which the arithmetic processing device 300 communicates with other devices (including the sensor unit 200). The user interface 306 is an input / output interface through which the arithmetic processing device 300 exchanges information with a user. The user interface 306 may include a mouse, keyboard, touch panel, microphone, etc. as input devices, and a monitor, speaker, etc. as output devices.

[0034] 4 is a diagram showing an example of the functional configuration of the arithmetic processing device 300 according to this embodiment. The arithmetic processing device 300 includes an acquisition unit 310, a calculation unit 320, and an output unit 330. These functional configurations are realized by the processor 301 reading and executing an arithmetic processing program stored in the ROM 302 or the storage 304.

[0035] The acquisition unit 310 acquires the detection signals output by the sensor unit 200. For example, the acquisition unit 310 may acquire the detection signals output by the upstream temperature sensor 232U, the downstream temperature sensor 232D, and the temperature compensation sensor 233. The acquisition unit 310 also acquires information on the current and voltage applied to the heater 231.

[0036] The calculation unit 320 measures the amount of sweat flowing within the range of the radiant heat of the heater 231 based on the temperature of the heater 231 when the power of the heater 231 is controlled to be constant, the power of the heater 231 when the temperature of the heater 231 is controlled to be constant, or the temperature difference around the heater 231. More specifically, the calculation unit 320 measures the amount of sweat flowing into the flow path 222 via the exposed portion 211 and the opening 221 when the sensor unit 200 is attached to the skin of the subject 50. This will be described in detail later.

[0037] The output unit 330 outputs a measurement result corresponding to the amount of sweat measured by the calculation unit 320. The output unit 330 may output the measurement result, for example, as a display on a monitor, as an audio output through a speaker, or as a transmission output to another device.

[0038] 5 is a diagram for explaining the measurement principle of the perspiration rate sensor 100 according to this embodiment. This diagram shows an example of the temperature distribution when focusing on only the lower part of the flexible substrate 230. The left side of this diagram shows the temperature distribution when no sweat is flowing through the flow path 222, and the right side of this diagram shows the temperature distribution when sweat is flowing through the flow path 222.

[0039] When sweat is flowing through the flow path 222, the amount of heat taken from the heater 231 by the flow of sweat increases. Therefore, when the power of the heater 231 is controlled to be constant, the temperature of the heater 231 decreases compared to when no sweat is flowing through the flow path 222. Furthermore, when the temperature of the heater 231 is controlled to be constant, the power of the heater 231 increases compared to when no sweat is flowing through the flow path 222. Therefore, the calculation unit 320 can measure the amount of sweat flowing within the range reached by the radiant heat of the heater 231 based on the temperature of the heater 231 when the power of the heater 231 is controlled to be constant, or based on the power of the heater 231 when the temperature of the heater 231 is controlled to be constant.

[0040] At this time, the calculation unit 320 can correct the temperature of the heater 231 using the difference with the temperature detected by the temperature compensation sensor 233, and measure the amount of sweat using the corrected temperature of the heater 231. This makes it possible to correct for the effects of body temperature and outside air temperature. The temperature of the heater 231 itself may be obtained by a conventional method, and may be derived from the relationship between the current and voltage applied to the heater 231, for example.

[0041] Furthermore, when sweat is flowing through the flow path 222, the upstream side of the heater 231 is less affected by the heat generated by the heater 231, whereas the downstream side of the heater 231 experiences a temperature rise due to the heat generated by the heater 231. Therefore, compared to when sweat is not flowing through the flow path 222, the difference (e.g., potential difference) between the value detected by the upstream temperature sensor 232U and the value detected by the downstream temperature sensor 232D becomes larger. In other words, a distortion occurs in the distribution of temperature rise around the heater 231. Therefore, the calculation unit 320 can measure the amount of sweat flowing within the range of the radiant heat of the heater 231 based on the temperature difference around the heater 231. In this case, the calculation unit 320 can use the difference in temperatures detected by a pair of temperature sensors 232 arranged opposite each other across the heater 231 as the temperature difference around the heater 231.

[0042] In the above description, it has been explained that the amount of sweat can be measured based on the temperature or power of the heater 231, and that it can be measured based on the temperature difference around the heater 231. However, the inventors have discovered that the flow rates suitable for each measurement are different. This will be explained in detail.

[0043] Figure 6 is a diagram showing an example of measurement sensitivity depending on the flow rate. The left side of the figure shows the temperature or power change characteristics of the heater 231 relative to the flow rate. The right side of the figure shows the temperature difference (here, downstream temperature - upstream temperature) around the heater 231 relative to the flow rate. In this figure, "r" indicates that the range is the same.

[0044] As shown on the left side of the figure, it can be seen that the temperature or power of the heater 231 is sensitive in the high flow rate range. Also, as shown on the right side of the figure, it can be seen that the temperature difference around the heater 231 is sensitive in the low flow rate range. Although not shown in the figure, the temperature difference around the heater 231 eventually reaches a peak as the flow rate increases and then gradually decreases. In this way, the flow rates suitable for each measurement are different. Based on this discovery, the inventors came up with the idea of ​​using each measurement in combination to accommodate a wide range of flow rates.

[0045] That is, the calculation unit 320 may be configured to be able to switch between a first mode in which the amount of sweat is measured based on the temperature of the heater 231 or the power of the heater 231, and a second mode in which the amount of sweat is measured based on the temperature difference around the heater 231. In this case, the calculation unit 320 may switch from the first mode to the second mode when the amount of change in the temperature of the heater 231 or the power of the heater does not satisfy a predetermined threshold.

[0046] In this way, the calculation unit 320 may, in principle, measure the amount of sweat using the first mode, which requires relatively simple calculations. Then, in the case of a low flow rate range where the first mode is difficult to measure, the calculation unit 320 may switch to the second mode, which requires relatively complex calculations, to measure the amount of sweat. This reduces the processing load. While the above description has been given as an example of a case where the calculation unit 320 switches between either the first mode or the second mode, the first mode and the second mode may also be combined. In this case, the calculation unit 320 may measure the amount of sweat by, for example, calculating a weighted average of the measurement results obtained in the first mode and the second mode.

[0047] As described above, the sensor unit 200 is used by being attached to the skin of the subject 50. Therefore, noise occurs due to body movement of the subject 50. Therefore, the calculation unit 320 may also have a function to remove body movement noise.

[0048] 7 is a diagram showing an example of body movement noise. This diagram shows, as an example, the output of heater 231 and the change over time in the temperature difference around heater 231. As shown in this diagram, the temperature difference around heater 231 may be inverted. This is thought to be because bending, twisting, stretching of the skin, etc., compresses flow path 222, causing backflow, and the temperature detected by upstream temperature sensor 232U rises above the temperature detected by downstream temperature sensor 232D. In other words, such fluctuations can be identified as body movement noise, rather than fluctuations in sweating.

[0049] Therefore, the calculation unit 320 may remove noise caused by such reverse flow of sweat. In this case, if the direction of sweat flow reverses and fluctuates within a predetermined period, the calculation unit 320 can remove the fluctuation as noise. Note that a low-pass filter or a digital filter may be used as the filter for removing such noise.

[0050] 8 is a diagram showing an example of the amount of sweat measured by the sweat rate sensor 100 according to this embodiment. This diagram shows an example of the change in the amount of sweat over time when the subject is resting for 15 minutes after exercising for 10 minutes.

[0051] As shown in this figure, body movement noise is significant during exercise. However, by using a filter to remove noise, it is possible to continuously monitor sweat rate regardless of whether exercise is occurring or not.

[0052] As described above, the perspiration rate sensor 100 according to this embodiment includes a sensor unit 200 having a heater 231 provided on a flexible substrate 230, and a calculation unit 320, and the calculation unit 320 measures the amount of perspiration flowing within the range of the radiant heat of the heater 231 based on the temperature of the heater 231 when the power of the heater 231 is controlled to be constant, the power of the heater 231 when the temperature of the heater 231 is controlled to be constant, or the temperature difference around the heater 231. As a result, the perspiration rate sensor 100 according to this embodiment can provide a sensor suitable for monitoring the amount of perspiration.

[0053] The above-described processing can also be realized by a dedicated hardware circuit. In this case, the processing may be performed by a single piece of hardware or by multiple pieces of hardware.

[0054] In the above description, the processor 301 refers to a processor in a broad sense, and includes a general-purpose processor (e.g., CPU: Central Processing Unit, etc.) and a dedicated processor (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.).

[0055] Furthermore, the operations of the processor 301 described above may not only be performed by a single processor, but may also be performed by multiple processors located at physically separate locations working together. Furthermore, the order of the operations of the processor 301 is not limited to the order described above, and may be changed as appropriate.

[0056] The above-mentioned arithmetic processing program may be provided by a computer-readable non-transitory recording medium such as a USB (Universal Serial Bus) memory, a flexible disk, or a CD-ROM (Compact Disc Read Only Memory), or may be provided online via a network such as the Internet. In this case, the arithmetic processing program recorded on the computer-readable non-transitory recording medium is usually transferred to and stored in a memory or storage. The arithmetic processing program may be provided as standalone application software, or may be incorporated into the software of each device as a function of the device.

[0057] The above-described arithmetic processing program can be provided as a program product. The program product includes any type of product for providing a program. For example, the program product includes a program provided via a network such as the Internet, and a non-transitory computer-readable recording medium such as a CD-ROM or DVD on which the program is stored.

[0058] The present disclosure is not limited to the above, and it goes without saying that various modifications can be made without departing from the spirit of the present disclosure.

[0059] The disclosure of Japanese Patent Application No. 2024-143481, filed on August 23, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A sweat rate sensor comprising: a sensor unit having a heater mounted on a flexible substrate; and a calculation unit, wherein the calculation unit measures the amount of sweat flowing within the range of the radiant heat of the heater based on the temperature of the heater when the heater's power is controlled to be constant, the heater's power when the heater's temperature is controlled to be constant, or the temperature difference around the heater.

2. The sweat rate sensor according to claim 1, wherein the sensor unit has an elastic member on which the flexible substrate is laminated, and the elastic member has a flow path formed therein through which the sweat flows.

3. The sweat rate sensor according to claim 2, wherein the elastic member has an opening formed on a surface opposite to the surface on which the flexible substrate is laminated, the opening communicating with the flow path.

4. The sweat rate sensor according to claim 3, wherein the sensor unit has a tape member on which the elastic member is laminated, the tape member has an exposed portion that exposes the opening, and the calculation unit measures the amount of sweat that flows into the flow path through the exposed portion and the opening when the sensor unit is attached to the skin.

5. A sweat rate sensor as described in any one of claims 1 to 4, wherein the calculation unit is capable of switching between a first mode in which the amount of sweat is measured based on the temperature of the heater or the power of the heater, and a second mode in which the amount of sweat is measured based on the temperature difference around the heater.

6. The sweat rate sensor according to claim 5, wherein the calculation unit switches from the first mode to the second mode when the amount of change in the heater temperature or the heater power does not satisfy a predetermined threshold.

7. The sweat rate sensor according to claim 1, wherein the calculation unit removes noise caused by backflow of the sweat.

8. The sweat rate sensor according to claim 7, wherein, when the direction of the sweat flow reverses and fluctuates within a predetermined period, the calculation unit removes the fluctuation as noise.

9. A sweat rate sensor as claimed in any one of claims 1 to 4, wherein a pair of temperature sensors are provided on the flexible substrate, arranged to face each other across the heater, and the calculation unit uses the difference in temperatures detected by the pair of temperature sensors as the temperature difference around the heater.

10. A sweat rate sensor as claimed in any one of claims 1 to 4, wherein a temperature compensation sensor is provided on the flexible substrate, and the calculation unit corrects the temperature of the heater using the difference between the temperature detected by the temperature compensation sensor and the actual temperature, and measures the amount of sweat using the corrected heater temperature.

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