Pulse wave measurement device

Abstract

To stable arrange a pulse wave sensor in the vicinity of the radial artery of the subject.SOLUTION: A pulse wave measuring device capable of being attached to a subject includes: a pulse wave sensor having a strain gauge; a sensor arrangement part in which the pulse wave sensor is arranged; a first bent part having one end connected to the sensor arrangement part; a second bent part having one end connected to the sensor arrangement part; and a belt-like body connected to the other end of the first bent part and to the other end of the second bent part. The first bent part and the second bent part are connected at an opposite side with the sensor arrangement part interposed therebetween in plane view, and the first bent part and the second bent part have different curvatures.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a pulse wave measuring device.

Background Art

[0002] A pulse wave sensor for detecting a pulse wave generated as the heart pumps blood is known. As an example, there is a pulse wave sensor provided with a pressure receiving plate serving as a strain generating body that is supported so as to be bendable by the action of an external force, and piezoelectric conversion means for converting the bending of the pressure receiving plate into an electric signal. This pulse wave sensor is formed in a dome shape in which the flexible region of the pressure receiving plate is a convex curved surface facing outward, and a pressure detection element is provided on the inner surface of the top of the pressure receiving plate as the piezoelectric conversion means (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A pulse wave sensor needs to detect a minute signal. Therefore, in a pulse wave measuring device using a pulse wave sensor, in order to improve the measurement accuracy, it is necessary to stably arrange the pulse wave sensor near the radial artery of the subject.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a pulse wave measuring device capable of stably arranging a pulse wave sensor near the radial artery of a subject.

Means for Solving the Problems

[0006] A pulse wave measuring device according to one embodiment of the present disclosure is a pulse wave measuring device that can be worn on a subject, comprising: a pulse wave sensor having a strain gauge; a sensor placement section on which the pulse wave sensor is arranged; a first curved section with one end connected to the sensor placement section; a second curved section with one end connected to the sensor placement section; and a strip-shaped body connected to the other end of the first curved section and the other end of the second curved section, wherein the first curved section and the second curved section are connected on opposite sides of the sensor placement section in a plan view, the first curved section and the second curved section have different curvatures, the first curved section is longer than the second curved section, and the center of the pulse wave sensor is positioned at the center of the subject's wrist. A straight line parallel to the axial direction of the sensor arrangement portion passing through it. It is offset to the side of the second curved section. [Effects of the Invention]

[0007] According to the disclosed technology, a pulse wave measurement device can be provided that allows the pulse wave sensor to be stably positioned near the radial artery of a subject. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view illustrating a pulse wave measuring device according to the first embodiment. [Figure 2] This is a surface-side perspective view illustrating a pulse wave measuring device according to the first embodiment. [Figure 3] This is a rear-side perspective view illustrating a pulse wave measuring device according to the first embodiment. [Figure 4] This is a side view illustrating a pulse wave measuring device according to the first embodiment. [Figure 5] This is a cross-sectional view of the sensor section. [Figure 6] This is a disassembled perspective view of the sensor unit. [Figure 7] This is a disassembled perspective view of the sensor unit. [Figure 8] This is a perspective view illustrating a pulse wave sensor according to the first embodiment. [Figure 9] This is a plan view illustrating a pulse wave sensor according to the first embodiment. [Figure 10]It is a cross-sectional view illustrating the pulse wave sensor according to the first embodiment. [Figure 11] It is a plan view illustrating the strain gauge according to the first embodiment. [Figure 12] It is a cross-sectional view (Part 1) illustrating the strain gauge according to the first embodiment. [Figure 13] It is a cross-sectional view (Part 2) illustrating the strain gauge according to the first embodiment.

Modes for Carrying Out the Invention

[0009] Hereinafter, modes for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components, and redundant descriptions may be omitted.

[0010] 〈First Embodiment〉 [Pulse Wave Measuring Device 1] FIG. 1 is a perspective view illustrating the pulse wave measuring device according to the first embodiment, showing the state where the pulse wave measuring device is worn on the wrist of a subject. FIG. 2 is a front-side perspective view illustrating the pulse wave measuring device according to the first embodiment. FIG. 3 is a back-side perspective view illustrating the pulse wave measuring device according to the first embodiment. FIG. 4 is a side view illustrating the pulse wave measuring device according to the first embodiment.

[0011] As shown in FIG. 1, the pulse wave measuring device 1 is a wristwatch-type wearable device that can be worn on the wrist of a subject. The pulse wave measuring device 1 mainly includes a sensor unit 10 and a belt unit 90.

[0012] Referring to FIGS. 2 to 4, the sensor unit 10 includes at least a base 20 and a pulse wave sensor 40. The base 20 has a sensor placement portion 21, a first curved portion 22, and a second curved portion 23. For example, a lid portion 80 is provided on the sensor placement portion 21. The detailed configuration of the sensor unit 10 will be described later.

[0013] Incidentally, as long as the pulse wave measuring device 1 has a sensor arrangement section 21, a first curved section 22, a second curved section 23, a pulse wave sensor 40, and a belt section 90, other configurations can be arbitrary.

[0014] In the base section 20, the sensor arrangement section 21 is a section where the pulse wave sensor 40 is arranged. One end of the first curved section 22 is connected to the sensor arrangement section 21. Also, one end of the second curved section 23 is connected to the sensor arrangement section 21. The first curved section 22 and the second curved section 23 are connected to opposite sides of the sensor arrangement section 21 in a plan view. Here, the plan view means viewing from the normal direction of the upper surface of the lid section 80 (the N direction shown in FIGS. 5 and 6 described later).

[0015] The belt section 90 is a belt-like body for attaching the sensor section 10 to the wrist of the subject, and is configured to be wound around the wrist of the subject from the outside. The belt section 90 is connected to the other end of the first curved section 22 and the other end of the second curved section 23.

[0016] The belt section 90 has, for example, a belt main body 91, a first connection section 92, and a second connection section 93. The belt main body 91 is formed of, for example, resin, rubber, cloth, etc., and has elasticity. The first connection section 92 and the second connection section 93 are members for connecting the belt main body 91 to the first curved section 22 and the second curved section 23. The first connection section 92 and the second connection section 93 can be formed of, for example, resin, rubber, etc.

[0017] In the illustrated example, one end of the belt main body 91 is inserted into and fixed to a groove provided at one end of the first connection section 92. The other end of the first connection section 92 is attached to an attachment section 22x provided on the first curved section 22 so as to be swingable uniaxially. Also, the other end of the belt main body 91 is inserted into and fixed to a groove provided at one end of the second connection section 93. The other end of the second connection section 93 is attached to an attachment section 23x provided on the second curved section 23 so as to be swingable uniaxially.

[0018] The first connecting portion 92 and the second connecting portion 93 can be provided as needed. That is, the belt portion 90 may consist only of the belt body 91, with one end of the belt body 91 pivotably attached directly to the mounting portion 22x of the first curved portion 22, and the other end of the belt body 91 pivotably attached directly to the mounting portion 23x of the second curved portion 23.

[0019] The belt body 91 may be a single continuous structure as shown in the illustrated example, but it may also be composed of multiple structures. For example, it may be provided with a first belt-shaped body with one end fixed to a first connecting portion 92 and a second belt-shaped body with one end fixed to a second connecting portion 93, and the other end of the first belt-shaped body and the other end of the second belt-shaped body may be detachably connected by hook-and-loop fasteners or the like.

[0020] The first curved section 22 and the second curved section 23 are curved such that when the pulse wave measuring device 1 is attached to the subject's wrist, their respective centers roughly point towards the center P1 of the wrist (see Figure 4). The first curved section 22 and the second curved section 23 have different curvatures. The radius of curvature of the first curved section 22 is larger than the radius of curvature of the second curved section 23. In other words, the curvature of the first curved section 22 is smaller than the curvature of the second curved section 23. The preferred curvatures of the first curved section 22 and the second curved section 23 may differ between the male pulse wave measuring device 1 and the female pulse wave measuring device 1. For example, it is preferable for the curvature of the first curved section 22 to be about 70-90 mm and the curvature of the second curved section 23 to be about 20-30 mm.

[0021] Furthermore, the first curved portion 22 and the second curved portion 23 have different lengths. The first curved portion 22 is longer than the second curved portion 23. The lengths of the first curved portion 22 and the second curved portion 23 are compared by the lengths of the parts of the first curved portion 22 and the second curved portion 23 closest to the center P1 in the side view shown in Figure 4. For example, it is preferable that the length of the first curved portion 22 be about 70 to 90 mm and the length of the second curved portion 23 be about 8 to 10 mm. However, it is preferable that the sum of the lengths of the first curved portion 22 and the second curved portion 23 is less than or equal to half the circumference of the wrist.

[0022] As shown in Figure 4, in the pulse wave measurement device 1, the center of the pulse wave sensor 40 (the center of the strain generating body 42, described later) is offset by L1 from the center P1 of the subject's wrist. Although there are individual differences in the position of the center P1 of the subject's wrist, the pulse wave measurement device 1 is designed so that L1 is approximately 15 mm to 20 mm. L1 is the amount of offset from the center P1 in a direction perpendicular to the normal to the upper surface of the lid 80 (the N direction shown in Figures 5 and 6, described later).

[0023] The pulse wave measuring device 1 is attached to the subject's wrist using a belt portion 90, for example, so that the pulse wave sensor 40 is positioned near the subject's radial artery. A pulse wave is a waveform that captures the change in blood vessel volume that occurs as the heart pumps blood, and the pulse wave measuring device 1 can monitor the change in blood vessel volume.

[0024] Furthermore, because the first curved section 22 and the second curved section 23 of the pulse wave measuring device 1 have different curvatures, it is easy to attach the pulse wave measuring device 1 along the subject's wrist even when the center of the pulse wave sensor 40 is offset from the center of the subject's wrist. This allows the pulse wave sensor 40 to be stably positioned near the subject's radial artery, thereby enabling stable measurement of the subject's pulse wave.

[0025] Furthermore, if the lengths of the first curved section 22 and the second curved section 23 are different, it becomes even easier to attach the pulse wave measuring device 1 along the subject's wrist. This allows the pulse wave sensor 40 to be positioned more stably closer to the subject's radial artery, thereby enabling more stable measurement of the subject's pulse wave.

[0026] Figure 5 is a cross-sectional view of the sensor section. Figure 6 is an exploded perspective view of the sensor section. Figure 7 is an exploded perspective view of the sensor unit. As shown in Figures 5 to 7, the sensor section 10 includes, for example, a base 20, a sensor unit 30, a biasing section 70, and a cover 80. The sensor unit 30 also includes, for example, a pulse wave sensor 40, a housing section 50, and a holding section 60.

[0027] In this embodiment, for convenience, the side of the sensor unit 10 facing the lid 80 is referred to as the "upper side," and the side facing the base 20 is referred to as the "lower side." Furthermore, the surface located above each part is referred to as the "upper surface," and the surface located below each part is referred to as the "lower surface." However, the sensor unit 10 can also be used upside down. Furthermore, the sensor unit 10 can be positioned at any angle. Moreover, a planar view refers to viewing the object in the direction normal to the upper surface of the lid 80 from top to bottom (direction N shown in Figures 5 and 6). And the planar shape refers to the shape of the object when viewed in the aforementioned normal direction.

[0028] In the base portion 20, the sensor placement portion 21 is the part in which the sensor unit 30 is housed. As will be described later, the biasing portion 70 is housed in the holding portion 60 that constitutes the sensor unit 30, so it can also be said that the sensor placement portion 21 houses both the sensor unit 30 and the biasing portion 70.

[0029] The sensor unit 10 has, for example, a cover portion 80 on the side opposite to the direction in which the strain-generating body 42, described later, is exposed in the sensor placement portion 21. For example, the cover portion 80 is attached to the sensor placement portion 21, which houses the sensor unit 30 and the biasing portion 70, from above the biasing portion 70. The cover portion 80 may be attached to the sensor placement portion 21 by appropriate means such as screws.

[0030] A marker portion 80x may be provided on the lid portion 80. Preferably, the center of the marker portion 80x coincides with the center of the strain generating body 42 described later in a plan view. The marker portion 80x can be provided, for example, in a position that overlaps with the load portion 42c of the strain generating body 42 described later in a plan view, but does not overlap with the base portion 42a in a plan view. The marker portion 80x is, for example, a projection that protrudes from the upper surface of the lid portion 80. A non-penetrating groove or through hole may be provided in the center of the projection. By providing a marker portion 80x on the upper surface of the lid portion 80 with a center that coincides with the center of the strain generating body 42 described later in a plan view, the marker portion 80x can be used as a marker when positioning the pulse wave measuring device 1 near the radial artery of the subject.

[0031] The inner surface of the sensor placement section 21 is provided with grooves 21x for positioning the sensor unit 30 on the base 20. In the illustrated example, three grooves 21x, with the thickness direction of the sensor placement section 21 as the longitudinal direction, are provided at approximately equal intervals in the circumferential direction of the sensor placement section 21. However, the shape and number of grooves 21x are not limited to the illustrated example, as long as the sensor unit 30 can be positioned on the base 20. On the lower end of the inner surface of the sensor placement section 21, a receiving portion 21y, which is approximately ring-shaped in plan view, is provided so as to protrude from the inner surface toward the center. The receiving portion 21y acts as a stopper for the sensor unit 30. The center side of the receiving portion 21y is open.

[0032] As shown in Figure 7, the pulse wave sensor 40 is a substantially cylindrical member and is formed to a size that can be housed in the housing 50. The top and bottom sides of the pulse wave sensor 40 are closed. Connection parts 40x for connecting cables, etc., may be provided on the outer surface of the pulse wave sensor 40. The pulse wave sensor 40 can transmit and receive electrical signals with external circuits, etc. via a wired connection, for example, through a cable, etc., connected to the connection parts 40x. Alternatively, the pulse wave sensor 40 may be configured to transmit and receive electrical signals with external circuits, etc. wirelessly without providing connection parts 40x. The detailed structure of the pulse wave sensor 40 will be described later.

[0033] The housing section 50 houses the pulse wave sensor 40. The housing section 50 is a substantially cylindrical member, with its top closed and bottom open. Multiple projections 50x are provided on the upper end of the outer surface of the housing section 50, projecting outward from the outer surface of the housing section 50 in order to engage with the retaining section 60. In the illustrated example, three projections 50x are provided at substantially equal intervals in the circumferential direction of the housing section 50. However, the shape and number of projections 50x are not limited to the illustrated example, as long as they can engage with the retaining section 60. Although not shown in the illustration, the outer surface of the housing section 50 is provided with an opening for the connection section 40x of the pulse wave sensor 40 to project outward. The pulse wave sensor 40 is housed in the housing section 50 from the bottom side, but the bottom side of the pulse wave sensor 40 protrudes from the housing section 50.

[0034] The holding portion 60 holds the pulse wave sensor 40 housed in the housing portion 50. The holding portion 60 is a substantially cylindrical member with openings on its top and bottom sides. An opening 60x for engaging with the projection 50x of the housing portion 50 is provided on the outer surface of the holding portion 60 at a position where it can engage with the projection 50x. When the projection 50x of the housing portion 50 engages with the opening 60x of the holding portion 60, the pulse wave sensor 40 housed in the housing portion 50 is held in the holding portion 60.

[0035] When held by the holding portion 60, a portion of the pulse wave sensor 40 and a portion of the housing portion 50 protrude from the lower side of the holding portion 60. Also, when held by the holding portion 60, the upper surface of the housing portion 50 does not reach the very top of the holding portion 60. That is, a recess is formed by the upper surface of the housing portion 50 and a portion of the inner surface of the holding portion 60. The biasing portion 70 is housed in this recess.

[0036] As shown in Figure 5, when the cover portion 80 is attached to the sensor placement portion 21, which houses the sensor unit 30 and the biasing portion 70, from above the biasing portion 70, the biasing portion 70 can bias the pulse wave sensor 40 in the N direction. The holding portion 60 of the sensor unit 30 is fixed to the sensor placement portion 21. Therefore, the biasing by the biasing portion 70 causes the pulse wave sensor 40 and the housing portion 50 to move together. In other words, the pulse wave sensor 40 and the housing portion 50 are held in the sensor placement portion 21 in a state where they can move in the axial direction of the sensor placement portion 21 (the N direction in Figure 5).

[0037] In other words, the biasing unit 70 can bias the pulse wave sensor 40 toward the subject when the pulse wave measuring device 1 is attached to the subject. The biasing unit 70 is, for example, a coil spring, but may also be a leaf spring or the like. The biasing unit 70 can be made of, for example, metal, resin, or rubber. The biasing unit 70 may also be an air pump using an electric motor or the like.

[0038] When the biasing portion 70 is a coil spring, it is preferable that the biasing portion 70 is a conical coil spring. When the biasing portion 70 is a conical coil spring, the height when compressed can be reduced compared to when it is a cylindrical coil spring, thus enabling a lower profile for the sensor placement portion 21. When the biasing portion 70 is a conical coil spring, it is preferable to position the portion of the conical coil spring with a smaller coil diameter toward the lid portion 80 in order to stably position the biasing portion 70.

[0039] Thus, the sensor unit 10 of the pulse wave measuring device 1 has a biasing mechanism that biases the pulse wave sensor 40 toward the subject by the biasing unit 70, thereby applying an appropriate initial pressure to the subject's radial artery. As a result, the pulse wave measuring device 1 achieves good contact between the subject and the pulse wave sensor 40, improving the accuracy of pulse wave measurement.

[0040] [Pulse wave sensor 40] Figure 8 is a perspective view illustrating a pulse wave sensor according to the first embodiment. Figure 9 is a plan view illustrating a pulse wave sensor according to the first embodiment. Figure 10 is a cross-sectional view illustrating a pulse wave sensor according to the first embodiment, showing a cross-section along line AA in Figure 9. Note that Figures 8 to 10 are viewed from a different direction than Figures 5 to 7, and the lower surface of the pulse wave sensor 40 in Figures 5 to 7 is the upper surface in Figures 8 to 10.

[0041] Referring to Figures 8 to 10, the pulse wave sensor 40 comprises a housing 41, a strain generating body 42, and a strain gauge 100. Referring to Figures 8 to 10, as well as Figure 4, etc., the pulse wave sensor 40 is held in the holding part 60 in a state where the strain generating body 42 is exposed from the sensor placement part 21 of the base part 20 and can come into contact with the subject.

[0042] It is preferable that the pulse wave sensor 40 protrudes toward the subject from the sensor placement portion 21 of the base portion 20. When the pulse wave sensor 40 protrudes toward the subject from the sensor placement portion 21, it is preferable that the protrusion amount be about 3 mm to 7 mm. In this case, for example, if the spring constant of the biasing portion 70 is 0.33 N / mm, a load of about 100 g can be applied to the subject. This provides good contact between the subject and the pulse wave sensor 40, and improves the accuracy of pulse wave measurement.

[0043] Thus, the pulse wave sensor 40 includes a strain generating body 42 on which the strain gauge 100 described later is arranged. The pulse wave sensor 40 is held so as to be movable in the axial direction of the sensor mounting section 21, with at least a portion of it inserted inside the sensor mounting section 21, and the strain generating body 42 is exposed from the sensor mounting section 21 and can contact the subject. Furthermore, by having the pulse wave sensor 40 protrude towards the subject from the sensor mounting section 21, an appropriate initial pressure can be applied to the subject's radial artery.

[0044] The strain generating body 42 has a base portion 42a, a beam portion 42b, a load portion 42c, and an extension portion 42d. The strain generating body 42 has a shape that is four-fold symmetrical in plan view, for example. As the material of the strain generating body 42, for example, stainless steel (SUS), copper, and aluminum can be used. The strain generating body 42 is for example a flat plate, and each component is integrally formed by, for example, a press working method. The strain generating body 42 may be flat, or it may have a shape that protrudes in a dome shape or the like so that the side facing the subject is convex. The thickness t of the strain generating body 42, excluding the load portion 42c, is for example constant. The thickness t is for example 0.01 mm or more and 0.25 mm or less.

[0045] In the explanation of the pulse wave sensor 40 in Figures 8 to 10, for convenience, the side of the strain generating body 42 on which the load portion 42c is provided will be referred to as the upper side or one side, and the side on which the load portion 42c is not provided will be referred to as the lower side or the other side. Also, the side of each part on which the load portion 42c is provided will be referred to as one side or the upper surface, and the side on which the load portion 42c is not provided will be referred to as the other side or the lower surface. However, the pulse wave sensor 40 can be used upside down or positioned at any angle. Furthermore, "plan view" refers to viewing the object from the direction normal to the upper surface of the strain generating body 42, and "planar shape" refers to the shape of the object when viewed from the direction normal to the upper surface of the strain generating body 42.

[0046] In the pulse wave sensor 40, the housing 41 is the part that holds the strain generating body 42. The housing 41 is cylindrical, with the bottom side closed and the top side open. The housing 41 can be made of, for example, metal or resin. A roughly disc-shaped strain generating body 42 is fixed to the housing 41 with adhesive or the like so as to close the opening on the top side. The strain generating body 42 is the part that detects pulse waves and has a strain gauge 100 positioned on it.

[0047] In the strain generating body 42, the base portion 42a is the circular frame-shaped (ring-shaped) region outside the circular dashed line shown in Figures 8 and 9. The region inside the circular dashed line is sometimes referred to as the circular opening. In other words, the base portion 42a of the strain generating body 42 has a circular opening. The width w1 of the base portion 42a is, for example, 1 mm or more and 5 mm or less. The inner diameter d of the base portion 42a (i.e., the diameter of the circular opening) is, for example, 5 mm or more and 40 mm or less.

[0048] The beam section 42b is provided to bridge the inside of the base section 42a. The beam section 42b has, for example, two beams that intersect in a cross shape in a plan view, and the region where the two beams intersect includes the center of the circular opening. In the example of Figure 9, one beam forming the cross has its longitudinal direction in the X direction, and the other beam forming the cross has its longitudinal direction in the Y direction, and the two are perpendicular to each other. It is preferable that each of the two perpendicular beams is located inside the inner diameter d (diameter of the circular opening) of the base section 42a and is as long as possible. In other words, it is preferable that the length of each beam is approximately equal to the diameter of the circular opening. In each beam forming the beam section 42b, the width w2 outside the intersecting region is constant, for example, 1 mm or more and 5 mm or less. It is not essential that the width w2 is constant, but it is preferable that the width w2 is constant so that strain can be detected linearly.

[0049] The load-bearing portion 42c is provided on the beam portion 42b. The load-bearing portion 42c is provided, for example, in the region where two beams constituting the beam portion 42b intersect. The load-bearing portion 42c protrudes from the upper surface of the beam portion 42b. The amount of protrusion of the load-bearing portion 42c relative to the upper surface of the beam portion 42b is, for example, about 0.1 mm. The beam portion 42b is flexible and elastically deforms when a load is applied to the load-bearing portion 42c.

[0050] The four extensions 42d are fan-shaped portions that extend from the inside of the base 42a toward the beam 42b in a plan view. A gap of about 1 mm is provided between each extension 42d and the beam 42b. If this gap is set to, for example, 0.05 to 0.2 mm, it is possible to prevent contamination from entering the housing 41 from the outside. The extensions 42d do not contribute to the sensing of the pulse wave sensor 40 and therefore do not need to be provided. The pulse wave sensor 40 has a shielded cable, a flexible circuit board, etc. (not shown) for inputting and outputting electrical signals to and from the outside.

[0051] The strain gauge 100 is provided on the strain generating body 42. The strain gauge 100 can be provided, for example, on the lower surface of the beam portion 42b. Since the beam portion 42b is flat, the strain gauge can be easily attached to it. One or more strain gauges 100 are sufficient, but in this embodiment, four strain gauges 100 are provided. By providing four strain gauges 100, strain can be detected by full bridge.

[0052] Two of the four strain gauges 100 are positioned on the side of the beam with its longitudinal direction in the X direction that is closer to the load section 42c (towards the center of the circular opening), facing each other in a plan view, with the load section 42c in between. The other two of the four strain gauges 100 are positioned on the side of the beam with its longitudinal direction in the Y direction that is closer to the base section 42a, facing each other in a plan view, with the load section 42c in between. This arrangement allows for effective detection of compressive and tensile forces, enabling greater output from the full bridge.

[0053] The pulse wave sensor 40 is used by fixing it to the subject's arm so that the load portion 42c is in contact with the subject's radial artery. When a load is applied to the load portion 42c in response to the subject's pulse wave, causing the beam portion 42b to elastically deform, the resistance value of the resistor of the strain gauge 100 changes. The pulse wave sensor 40 can detect the pulse wave based on the change in the resistance value of the resistor of the strain gauge 100 accompanying the deformation of the beam portion 42b. The pulse wave is output, for example, as a periodic change in voltage from a measurement circuit connected to the electrodes of the strain gauge 100.

[0054] [Strain Gauge 100] Figure 11 is a plan view illustrating a strain gauge according to the first embodiment. Figure 12 is a cross-sectional view illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 11. Referring to Figures 11 and 12, the strain gauge 100 includes a base material 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. In Figure 11, for convenience, only the outer edge of the cover layer 160 is shown with a dashed line. The cover layer 160 can be provided as needed.

[0055] In the explanation of the strain gauge 100 in Figures 11 and 12, for convenience, the side of the base material 110 on which the resistor 130 is provided will be referred to as the "upper side," and the side on which the resistor 130 is not provided will be referred to as the "lower side." Also, the surface located on the upper side of each part will be referred to as the "upper surface," and the surface located on the lower side of each part will be referred to as the "lower surface." However, the strain gauge 100 can also be used upside down. Furthermore, the strain gauge 100 can be positioned at any angle. For example, in Figure 10, the strain gauge 100 is attached to the beam section 42b in an inverted state compared to Figure 12. That is, the base material 110 in Figure 12 is attached to the lower surface of the beam section 42b with adhesive or the like. Also, a plan view refers to viewing the object in the direction of the normal from the top to the bottom with respect to the upper surface 110a of the base material 110. Furthermore, the planar shape refers to the shape of the object when viewed in the direction of the normal vector.

[0056] The base material 110 is a component that serves as a base layer for forming the resistor 130, etc. The base material 110 is flexible. The thickness of the base material 110 is not particularly limited and may be appropriately determined according to the intended use of the strain gauge 100, etc. For example, the thickness of the base material 110 may be about 5 μm to 500 μm. However, from the viewpoint of strain transmission from the outer surface of the strain generating body 42 to the sensing part, and dimensional stability against environmental changes, the thickness of the base material 110 is preferably in the range of 5 μm to 200 μm. Furthermore, from the viewpoint of insulation, the thickness of the base material 110 is preferably 10 μm or more.

[0057] The base material 110 is formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, or polyolefin resin. The term "film" refers to a flexible material with a thickness of approximately 500 μm or less.

[0058] When the base material 110 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the base material 110 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0059] Other materials for the substrate 110 besides resin include, for example, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3). In addition to the aforementioned crystalline materials, amorphous glass or the like may also be used as the material for the substrate 110. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 110. When a metal is used, an insulating film is provided on the metallic substrate 110.

[0060] The resistor 130 is a thin film formed in a predetermined pattern on the upper side of the substrate 110. In the strain gauge 100, the resistor 130 is a sensitive part that receives strain and causes a change in resistance. The resistor 130 may be formed directly on the upper surface 110a of the substrate 110, or it may be formed on the upper surface 110a of the substrate 110 via another layer. For convenience, in Figure 11, the resistor 130 is shown with a dark, textured pattern.

[0061] The resistor 130 has a structure in which multiple elongated sections are arranged at predetermined intervals with their longitudinal directions aligned in the same direction (the X direction in the example of Figure 11), and the ends of adjacent elongated sections are connected alternately, so that the whole structure is folded in a zigzag pattern. The longitudinal direction of the multiple elongated sections becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the Y direction in the example of Figure 11).

[0062] In the resistor 130, the X-side end of the elongated portion located furthest to the Y+ side bends in the Y+ direction and reaches one end 130e1 in the grid width direction of the resistor 130. Similarly, the X-side end of the elongated portion located furthest to the Y- side bends in the Y- direction and reaches the other end 130e2 in the grid direction of the resistor 130. Each end 130e1 and 130e2 is electrically connected to the electrode 150 via the wiring 140. In other words, the wiring 140 electrically connects each end 130e1 and 130e2 in the grid width direction of the resistor 130 to each electrode 150.

[0063] The resistor 130 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 130 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0064] Here, a Cr multiphase film is a film in which Cr, CrN, and Cr2N are mixed together. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0065] The thickness of the resistor 130 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 100. For example, the thickness of the resistor 130 may be approximately 0.05 μm to 2 μm. In particular, when the thickness of the resistor 130 is 0.1 μm or more, the crystallinity of the crystal constituting the resistor 130 (for example, the crystallinity of α-Cr) is improved. Also, when the thickness of the resistor 130 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 110, caused by internal stress in the film constituting the resistor 130, are reduced.

[0066] Considering the need to minimize lateral sensitivity and prevent wire breakage, the width of the resistor 130 is preferably 10 μm or more and 100 μm or less. More specifically, the width of the resistor 130 is preferably 10 μm or more and 70 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0067] For example, if the resistor 130 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Also, for example, if the resistor 130 is a Cr multiphase film, by making α-Cr the main component of the resistor 130, the gauge factor of the strain gauge 100 can be set to 10 or more, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / ℃ to +1000 ppm / ℃. Here, "main component" means a component that accounts for 50% by weight or more of the total material constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 130 contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, it is even more preferable that the resistor 130 contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0068] Furthermore, if the resistor 130 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less, the decrease in the gauge factor of the strain gauge 100 can be suppressed.

[0069] Furthermore, in the Cr multiphase film, it is preferable that the ratio of CrN to Cr2N is such that the proportion of Cr2N is 80% or more and less than 90% by weight relative to the total weight of CrN and Cr2N. More preferably, the ratio is such that the proportion of Cr2N is 90% or more and less than 95% by weight relative to the total weight of CrN and Cr2N. Cr2N has semiconducting properties. Therefore, by setting the proportion of Cr2N to 90% or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes even more pronounced. Moreover, by setting the proportion of Cr2N to 90% or more and less than 95% by weight, the ceramicization of the resistor 130 can be reduced. Therefore, brittle fracture of the resistor 130 can be made less likely.

[0070] On the other hand, CrN also has the advantage of being chemically stable. By including more CrN in the Cr multiphase film, the possibility of unstable nitrogen generation can be reduced, thus enabling the creation of a stable strain gauge. Here, "unstable nitrogen" refers to trace amounts of N2 or atomic nitrogen that may be present in the Cr multiphase film. These unstable nitrogen atoms may escape from the film depending on the external environment (e.g., high temperature environment). When unstable nitrogen atoms escape from the film, the film stress of the Cr multiphase film may change.

[0071] The wiring 140 is provided on the base material 110. The wiring 140 is electrically connected to the resistor 130 and the electrode 150. The wiring 140 is not limited to a straight line and can be in any pattern. Also, the wiring 140 can have any width and any length. For convenience, in Figure 11, the wiring 140 is shown with a textured surface that is thinner than the resistor 130.

[0072] The electrode 150 is provided on the substrate 110. The electrode 150 is electrically connected to the resistor 130 via the wiring 140. In a plan view, the electrode 150 is wider than the wiring 140 and is formed in a substantially rectangular shape. The electrode 150 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 130 caused by strain. For example, lead wires for external connection are joined to the electrode 150. A layer of a metal with low resistance, such as copper, or a layer of a metal with good solderability, such as gold, may be laminated on the upper surface of the electrode 150. For convenience, the resistor 130, wiring 140, and electrode 150 are given different reference numerals, but they can all be formed integrally from the same material in the same process. In Figure 11, for convenience, the electrode 150 is shown with the same textured pattern as the wiring 140.

[0073] The cover layer 160 is provided on the substrate 110 as needed. The cover layer 160 is provided on the upper surface 110a of the substrate 110 so as to cover the resistor 130 and wiring 140 and expose the electrodes 150. Examples of materials for the cover layer 160 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin, polyolefin resin). The cover layer 160 may also contain fillers and pigments. The thickness of the cover layer 160 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the cover layer 160 can be about 2 μm to 30 μm. By providing the cover layer 160, mechanical damage to the resistor 130 can be suppressed. In addition, by providing the cover layer 160, the resistor 130 can be protected from moisture and the like.

[0074] In the strain gauge 100, using a Cr multiphase film as the material for the resistor 130 makes it possible to achieve both high sensitivity and miniaturization. For example, while the output of a conventional strain gauge was about 0.04mV / 2V, using a Cr multiphase film as the material for the resistor 130 makes it possible to obtain an output of 0.3mV / 2V or higher. Furthermore, while the size (gauge length × gauge width) of a conventional strain gauge was about 3mm × 3mm, using a Cr multiphase film as the material for the resistor 130 makes it possible to miniaturize the size (gauge length × gauge width) to about 0.3mm × 0.3mm.

[0075] Therefore, the strain gauge 100, which uses a Cr multiphase film as the material for the resistor 130, is particularly suitable for use in a pulse wave measuring device 1 that needs to be positioned in a narrow area of ​​the strain generating body 42 and that needs to detect extremely minute fluctuations occurring in the radial artery. Furthermore, the strain gauge 100, which uses a Cr multiphase film as the material for the resistor 130, has higher resistance than conventional strain gauges. Therefore, when powered by a battery, it is possible to reduce power consumption and extend battery life.

[0076] [Method of manufacturing strain gauges] The manufacturing method for the strain gauge 100 is described below. To manufacture the strain gauge 100, first, a base material 110 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 110a of the base material 110. Metal layer A is the layer that will ultimately be patterned to become the resistor 130, wiring 140, and electrode 150. Therefore, the material and thickness of metal layer A are the same as those of the resistor 130, wiring 140, and electrode 150 described above.

[0077] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, or pulsed laser deposition instead of magnetron sputtering.

[0078] Alternatively, a base layer may be formed on the upper surface 110a of the substrate 110 before forming the metal layer A. For example, a functional layer of a predetermined thickness may be vacuum-deposited on the upper surface 110a of the substrate 110 by conventional sputtering. By providing a base layer in this way, the gauge characteristics of the strain gauge 100 can be stabilized.

[0079] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of at least the upper metal layer A (resistor 130). Preferably, the functional layer further has the function of preventing oxidation of the metal layer A by oxygen or moisture contained in the substrate 110, and / or the function of improving the adhesion between the substrate 110 and the metal layer A. The functional layer may further have other functions.

[0080] The insulating resin film constituting the base material 110 may contain oxygen and moisture, and Cr may form an oxidized film. Therefore, especially when metal layer A contains Cr, it is preferable to form a functional layer that has the function of preventing oxidation of metal layer A.

[0081] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics of the strain gauge 100 is improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A improves the gauge characteristics of the strain gauge 100.

[0082] Figure 13 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. Figure 13 shows the cross-sectional shape of the strain gauge 100 when a functional layer 120 is provided as a base layer for the resistor 130, wiring 140, and electrode 150.

[0083] The planar shape of the functional layer 120 may be patterned to be substantially the same as the planar shapes of, for example, the resistor 130, the wiring 140, and the electrodes 150. However, the planar shapes of the functional layer 120 and the resistor 130, the wiring 140, and the electrodes 150 do not have to be substantially the same. For example, if the functional layer 120 is formed from an insulating material, the functional layer 120 may be patterned to be a different shape from the planar shapes of the resistor 130, the wiring 140, and the electrodes 150. In this case, the functional layer 120 may be formed as a solid in the region where the resistor 130, the wiring 140, and the electrodes 150 are formed. Alternatively, the functional layer 120 may be formed as a solid over the entire upper surface of the substrate 110.

[0084] Next, the metal layer A is patterned using photolithography to form a planar resistor 130, two wirings 140, and two electrodes 150 as shown in Figure 11.

[0085] After forming the resistor 130, wiring 140, and electrode 150, a cover layer 160 may be formed on the upper surface 110a of the base material 110. The cover layer 160 covers the resistor 130 and wiring 140, but the electrode 150 may be exposed from the cover layer 160. For example, the cover layer 160 can be formed by laminating a semi-cured thermosetting insulating resin film onto the upper surface 110a of the base material 110 so as to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing the insulating resin film. Through the above steps, the strain gauge 100 is completed.

[0086] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. [Explanation of Symbols]

[0087] 1 Pulse wave measuring device, 10 Sensor part, 20 Base part, 21 Sensor placement part, 21x Groove, 21y Receiving part, 22 First curved part, 22x Mounting part, 23 Second curved part, 23x Mounting part, 30 Sensor unit, 40 Pulse wave sensor, 40x Connection part, 41 Housing, 42 Strain generating body, 42a Base part, 42b Beam part, 42c Load part, 42d Stretching part, 50 Housing part, 50x Protrusion part, 60 Holding part, 60x Opening, 70 Biasing part, 80 Cover part, 80x Marking part, 90 Belt part, 91 Belt body, 92 First connection part, 93 Second connection part, 100 Strain gauge, 110 Base material, 110a Top surface, 130 Resistor, 130e1, 130e2 Ends, 140 Wiring, 150 electrodes, 160 cover layer

Claims

1. A pulse wave measuring device that can be worn on a subject, A pulse wave sensor having a strain gauge, The sensor arrangement section on which the pulse wave sensor is arranged, A first curved portion, one end of which is connected to the sensor placement portion, A second curved portion, one end of which is connected to the sensor placement portion, It has a strip-shaped body connected to the other end of the first curved portion and the other end of the second curved portion, The first curved portion and the second curved portion are connected on opposite sides of the sensor placement portion in a plan view. The first curved section and the second curved section have different curvatures. The first curved portion is longer than the second curved portion. A pulse wave measuring device in which the center of the pulse wave sensor is offset from a straight line parallel to the axial direction of the sensor placement portion passing through the center of the subject's wrist to the side of the second curved portion.

2. The pulse wave measuring device according to claim 1, further comprising a biasing unit for biasing the pulse wave sensor toward the subject.

3. The pulse wave measuring device according to claim 2, wherein the biasing part is a coil spring.

4. The pulse wave measuring device according to claim 3, wherein the biasing part is a cone-shaped coil spring.

5. The pulse wave measuring device according to any one of claims 1 to 4, wherein the band-shaped body is stretchable.

6. The pulse wave measuring device according to any one of claims 1 to 5, wherein the pulse wave sensor comprises a strain generating body on which the strain gauge is arranged, at least a portion of which is inserted inside the sensor arrangement portion and held so as to be movable in the axial direction of the sensor arrangement portion, and the strain generating body is exposed from the sensor arrangement portion so as to be able to contact the subject.

7. The sensor arrangement portion has a cover portion on the side opposite to the direction in which the strain-generating body is exposed, The pulse wave measuring device according to claim 6, wherein the lid portion is provided with a marking portion that coincides with the center of the strain generating body in a plan view.

8. The strain-generating body is A base with a circular opening, A beam section bridging the inside of the base, The beam portion has a load-bearing section, A pulse wave measuring device according to claim 6 or 7, which detects a pulse wave based on a change in the resistance value of the strain gauge accompanying the deformation of the strain-generating body.

9. The aforementioned beam section has two beams that intersect in a cross shape in a plan view. The region where the beams intersect includes the center of the circular opening, The pulse wave measuring device according to claim 8, wherein the load section is provided in the region where the beams intersect.

10. The aforementioned strain gauge is equipped with four of the above-mentioned strain gauges. Two of the four strain gauges are positioned on the side of the beam closest to the load portion, with the first direction being the longitudinal direction, so as to be opposite each other in a plan view, with the load portion in between. The pulse wave measuring device according to claim 9, wherein the other two of the four strain gauges are arranged on the side of the beam closer to the base, with the second direction perpendicular to the first direction as its longitudinal direction, so as to face each other in a plan view, sandwiching the load portion.

11. A pulse wave measuring device that can be worn on a subject, A pulse wave sensor having a strain gauge, The sensor arrangement section on which the pulse wave sensor is arranged, A first curved portion, one end of which is connected to the sensor placement portion, A second curved portion, one end of which is connected to the sensor placement portion, It has a strip-shaped body connected to the other end of the first curved portion and the other end of the second curved portion, The first curved portion and the second curved portion are connected on opposite sides of the sensor placement portion in a plan view. The first curved section and the second curved section have different curvatures. The pulse wave sensor comprises a strain generating body on which the strain gauge is arranged, at least a portion of which is held so as to be movable in the axial direction of the sensor arrangement portion, and the strain generating body is exposed from the sensor arrangement portion so as to be able to contact the subject. The strain-generating body is A base with a circular opening, A beam section bridging the inside of the base, The beam portion has a load-bearing section, A pulse wave is detected based on the change in the resistance value of the strain gauge accompanying the deformation of the strain-generating body. The aforementioned beam section has two beams that intersect in a cross shape in a plan view. The region where the beams intersect includes the center of the circular opening, The load-bearing section is provided in the region where the beams intersect. The aforementioned strain gauge is equipped with four of the above-mentioned strain gauges. Two of the four strain gauges are positioned on the side of the beam closest to the load portion, with the first direction being the longitudinal direction, so as to be opposite each other in a plan view, with the load portion in between. A pulse wave measuring device in which the other two of the four strain gauges are arranged on the side of the beam closer to the base, with the second direction perpendicular to the first direction as its longitudinal direction, so as to be opposite the load portion in a plan view.

12. The pulse wave measuring device according to any one of claims 1 to 11, wherein the pulse wave sensor protrudes toward the subject side from the sensor placement portion.

13. The pulse wave measuring device according to any one of claims 1 to 12, wherein the strain gauge has a resistor formed from a Cr multiphase film.

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