Pulse wave measurement device

Abstract

To provide a pulse wave measuring device capable of adjusting adhesion between a subject and a pulse wave sensor.SOLUTION: A pulse wave measuring device that can be mounted on a subject includes: a pulse wave sensor having a strain gauge; a sensor fixing part for fixing the pulse wave sensor; and a belt-like body, one end of which is swingably connected to one end side of the sensor fixing part by a first shaft, and the other end of which is swingably connected to the other end side of the sensor fixing part by a second shaft. The first shaft and the second shaft are positioned on a side opposite to the subject with respect to the surface that comes in contact with the subject of the pulse wave sensor.SELECTED DRAWING: Figure 4

Description

Technical Field

[0004] ,

[0006] , , , , , ,

[0005] , , , , , ,

[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 that serves as a strain body supported so as to be bendable by the action of an external force, and a piezoelectric conversion means for converting the bending of the pressure receiving plate into an electric signal. This pulse wave sensor has a dome shape in which the flexible region of the pressure receiving plate is formed as 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

[0007] According to the disclosed technology, a pulse wave measurement device can be provided in which the contact between the subject and the pulse wave sensor can be adjusted. [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 an exploded perspective view of the pulse wave measuring device according to the first embodiment. [Figure 6] This is a perspective view illustrating a pulse wave sensor according to the first embodiment. [Figure 7] This is a plan view illustrating a pulse wave sensor according to the first embodiment. [Figure 8] This is a cross-sectional view illustrating a pulse wave sensor according to the first embodiment. [Figure 9] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 10] This is a cross-sectional view illustrating a strain gauge according to the first embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0010] <First Embodiment> [Pulse wave measurement device 1] Figure 1 is a perspective view illustrating a pulse wave measurement device according to the first embodiment, showing the device attached to the wrist of a subject. Figure 2 is a front-side perspective view illustrating a pulse wave measurement device according to the first embodiment. Figure 3 is a back-side perspective view illustrating a pulse wave measurement device according to the first embodiment. Figure 4 is a side view illustrating a pulse wave measurement device according to the first embodiment. Figure 5 is an exploded perspective view of the pulse wave measurement device according to the first embodiment. Note that arrow N in Figure 4 indicates the normal direction of the detection surface (bottom surface in Figure 4) of the pulse wave sensor 10.

[0011] Referring to Figures 1 to 5, the pulse wave measurement device 1 is a wristwatch-type wearable device that can be worn by a subject, and mainly consists of a pulse wave sensor 10, a sensor fixing part 20, and a belt 80.

[0012] The pulse wave measuring device 1 is attached to the subject's wrist, for example, so that the pulse wave sensor 10 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 this change in blood vessel volume.

[0013] The pulse wave sensor 10 is fixed to one side (the subject side) of the sensor fixing portion 20. Specifically, for example, a plurality of screw holes 10y are provided on the back side of the pulse wave sensor 10. Also, for example, the sensor fixing portion 20 is provided with a plurality of insertion holes 20y through which screws are inserted so as to penetrate the sensor fixing portion 20. For example, two screws 90 are inserted into the respective insertion holes 20y, and the tip portions protrude from the respective insertion holes 20y and are screwed into the respective screw holes 10y, so that the pulse wave sensor 10 is fixed to one side of the sensor fixing portion 20. A positioning hole such as a cylindrical shape for positioning the pulse wave sensor 10 may be provided on one side of the sensor fixing portion 20.

[0014] A through hole 10x through which a cable for extracting an electrical signal from the inside of the pulse wave sensor 10 passes may be provided on the side surface of the pulse wave sensor 10. By passing the cable through the through hole 10x, the signal detected by the pulse wave sensor 10 can be wired-connected to an external circuit. For example, a notch 20x is provided in the sensor fixing portion 20, and the through hole 10x is exposed within the notch 20x.

[0015] The belt 80 is a belt-like body for attaching the pulse wave sensor 10 and the sensor fixing portion 20 to the wrist or the like of the subject, and is configured to be wound around the wrist or the like of the subject from the outside. The belt 80 is formed of, for example, resin, rubber, cloth, etc., and has flexibility.

[0016] One end of the belt 80 is connected to one end side of the sensor fixing portion 20 so as to be swingable about a single axis, and the other end of the belt 80 is connected to the other end side of the sensor fixing portion 20 so as to be swingable about a single axis. Specifically, one end of the belt 80 is inserted into a groove provided in the belt fixing portion 30 and fixed to the belt fixing portion 30. Protruding portions 30a protruding on both sides in the width direction of the belt 80 are provided at the end portion of the belt fixing portion 30 on the sensor fixing portion 20 side. The protruding portions 30a are inserted into through holes of the mounting portion 20a provided in the sensor fixing portion 20.

[0017] As a result, as shown in Figure 4, the sensor fixing part 20 and the belt fixing part 30 to which one end of the belt 80 is fixed are connected so as to be able to swing freely on one axis in the direction of the arrow, with UA1 as the axis. The belt fixing part 30 and the belt 80 move as a single unit. In other words, axis UA1 becomes the axis when one end of the belt 80 swings.

[0018] The other end of the belt 80 is inserted into a through hole provided in the belt insertion section 40. The end of the belt insertion section 40 on the sensor fixing section 20 side is provided with projections 40a that protrude on both sides in the width direction of the belt 80. The projections 40a are inserted into through holes in the mounting section 20b provided in the sensor fixing section 20. In other words, the other end of the belt 80 is pivotably connected to the other end of the sensor fixing section 20 via the belt insertion section 40 by shaft UA2.

[0019] As a result, the sensor fixing part 20 and the belt insertion part 40 into which the other end of the belt 80 is inserted are connected so as to be able to swing freely on one axis with UA2 as the axis, in the direction of the arrow. The belt insertion part 40 and the belt 80 move as a single unit. In other words, axis UA2 is the axis when the other end of the belt 80 swings. The direction of the arrow in Figure 4 is the direction in which the tightening force of the belt 80 is increased or decreased.

[0020] The other end of the belt 80, which is inserted into the through-hole of the belt insertion section 40, can pass through the through-hole of the belt insertion section 40 and be detachably connected to the outer surface of the portion of the belt 80 that is not inserted into the belt insertion section 40, for example, by a hook-and-loop fastener. By changing the position to which the other end of the belt 80 is connected in the longitudinal direction of the belt 80, the tightening strength when attaching the pulse wave measuring device 1 to the subject can be changed.

[0021] When the pulse wave measuring device 1 is attached to a subject, the sensor fixing part 20 and the belt 80 swing around axes UA1 and UA2, allowing the entire pulse wave measuring device 1 to follow the shape of the subject's wrist, etc. At the same time, by changing the tightening strength of the belt 80, the pulse wave sensor 10 can be pressed in the N direction, so the degree of contact between the subject and the pulse wave sensor 10 can be adjusted. This makes it possible to bring the strain-generating body 12 side of the pulse wave sensor 10 into close contact with the subject's radial artery.

[0022] Furthermore, in Figure 4, the lower surface of the pulse wave sensor 10 is the detection surface for detecting pulse waves, while axes UA1 and UA2 are located above the detection surface of the pulse wave sensor 10, that is, on the opposite side of the pulse wave sensor 10 from the subject. The detection surface of the pulse wave sensor 10 is the surface of the pulse wave sensor 10 that is in contact with the subject, and specifically, it is the surface of the strain generating body 12, which will be described later, that is on the subject side.

[0023] Because axes UA1 and UA2 are positioned on the opposite side of the subject from the detection surface of the pulse wave sensor 10, the detection surface of the pulse wave sensor 10 can be easily pressed against the subject's wrist by changing the tightness of the belt 80. In particular, it is preferable that the lower surface of the pulse wave sensor 10 protrudes toward the subject from the sensor fixing part 20. This makes it even easier to press the detection surface of the pulse wave sensor 10 against the subject's wrist by changing the tightness of the belt 80.

[0024] It is preferable that shafts UA1 and UA2 extend in a direction perpendicular to the longitudinal direction of the belt 80 when the belt 80 is extended in the left-right direction of Figure 4 (the depth direction of Figure 4).

[0025] Furthermore, in Figure 4, i.e., in a side view, it is preferable that the straight line connecting the center of axis UA1 and the center of axis UA2 is parallel to the detection surface of the pulse wave sensor 10. In this case, the distance between the straight line connecting the center of axis UA1 and the center of axis UA2 and the detection surface of the pulse wave sensor 10 is, for example, 2 mm or more and 8 mm or less. Note that parallelism here includes the case where the angle between the two straight lines is within ±5 degrees. By having the straight line connecting the center of axis UA1 and the center of axis UA2 parallel to the detection surface of the pulse wave sensor 10, the detection surface of the pulse wave sensor 10 can be pressed evenly against the subject when the belt 80 is tightened.

[0026] If the detection surface of the pulse wave sensor 10 is a curved surface that protrudes toward the subject, the tangent to the tip of the detection surface of the pulse wave sensor 10 closest to the subject shall be interpreted as the detection surface of the pulse wave sensor 10 as described above.

[0027] Furthermore, in Figure 4, i.e., in a side view, it is preferable that the line connecting the midpoint of the line connecting the center of axis UA1 and the center of axis UA2 and the midpoint of the detection surface of the pulse wave sensor 10 is perpendicular to the line connecting the center of axis UA1 and the center of axis UA2. Here, perpendicular includes the case where the angle between the two lines is within 90 ± 5 degrees. When the belt 80 is tightened, the detection surface of the pulse wave sensor 10 can be pressed evenly against the subject by the line connecting the midpoint of the line connecting the center of axis UA1 and the center of axis UA2 and the midpoint of the detection surface of the pulse wave sensor 10 being perpendicular to the line connecting the center of axis UA1 and the center of axis UA2.

[0028] Furthermore, a biasing mechanism may be provided between the sensor fixing part 20 and the pulse wave sensor 10 to bias the pulse wave sensor 10 toward the subject. The biasing mechanism may consist of, for example, only a spring, or it may include a spring and an adjustment part for adjusting the biasing force of the spring, or it may have any other configuration. By having a biasing mechanism that biases the pulse wave sensor 10 toward the subject, the detection surface of the pulse wave sensor 10 can be stably pressed against the subject's wrist.

[0029] [Pulse wave sensor 10] Figure 6 is a perspective view illustrating a pulse wave sensor according to the first embodiment. Figure 7 is a plan view illustrating a pulse wave sensor according to the first embodiment. Figure 8 is a cross-sectional view illustrating a pulse wave sensor according to the first embodiment, showing a cross-section along line AA in Figure 7. Note that Figures 6 to 8 are viewed from a different direction than Figure 5, and the bottom surface (back surface) of the pulse wave sensor 10 in Figure 5 is the top surface in Figures 6 to 8.

[0030] Referring to Figures 6 to 8, the pulse wave sensor 10 comprises a housing 11, a strain generating body 12, and a strain gauge 100. The pulse wave sensor 10 is held in the sensor fixing part 20 such that the strain generating body 12 is exposed from the sensor fixing part 20 toward the subject and can contact the subject (see Figure 3). The pulse wave sensor 10 may also protrude from the sensor fixing part 20 toward the subject.

[0031] The strain generating body 12 has a base portion 12a, a beam portion 12b, a load portion 12c, and an extension portion 12d. The strain generating body 12 has a shape that is four-fold symmetrical in plan view, for example. As the material of the strain generating body 12, for example, stainless steel (SUS), copper, and aluminum can be used. The strain generating body 12 is for example a flat plate, and each component is integrally formed by, for example, a press working method. The strain generating body 12 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 12, excluding the load portion 12c, is for example constant. The thickness t is for example 0.01 mm or more and 0.25 mm or less.

[0032] In the explanation of the pulse wave sensor 10 in Figures 6 to 8, for convenience, the side of the strain generating body 12 on which the load portion 12c is provided will be referred to as the upper side or one side, and the side on which the load portion 12c is not provided will be referred to as the lower side or the other side. Also, the surface on which the load portion 12c is provided for each part will be referred to as one surface or the upper surface, and the surface on which the load portion 12c is not provided will be referred to as the other surface or the lower surface. However, the pulse wave sensor 10 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 12, 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 12.

[0033] In the pulse wave sensor 10, the housing 11 is the part that holds the strain generating body 12. The housing 11 is cylindrical, with the bottom side closed and the top side open. The housing 11 can be made of, for example, metal or resin. A roughly disc-shaped strain generating body 12 is fixed to the housing 11 with adhesive or the like so as to close the opening on the top side. The strain generating body 12 is the part that detects pulse waves and has a strain gauge 100 arranged on it.

[0034] In the strain-generating body 12, the base portion 12a is the circular frame-shaped (ring-shaped) region outside the circular dashed line shown in Figures 7 and 8. The region inside the circular dashed line is sometimes referred to as the circular opening. In other words, the base portion 12a of the strain-generating body 12 has a circular opening. The width w1 of the base portion 12a is, for example, 1 mm or more and 5 mm or less. The inner diameter d of the base portion 12a (i.e., the diameter of the circular opening) is, for example, 5 mm or more and 40 mm or less.

[0035] The beam section 12b is provided to bridge the inside of the base section 12a. The beam section 12b 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 7, 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 orthogonal. It is preferable that each of the two orthogonal beams is located inside the inner diameter d (diameter of the circular opening) of the base section 12a 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 12b, 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.

[0036] The load-bearing section 12c is provided on the beam section 12b. The load-bearing section 12c is provided, for example, in the region where two beams constituting the beam section 12b intersect. The load-bearing section 12c protrudes from the upper surface of the beam section 12b. The amount of protrusion of the load-bearing section 12c relative to the upper surface of the beam section 12b is, for example, about 0.1 mm. The beam section 12b is flexible and undergoes elastic deformation when a load is applied to the load-bearing section 12c.

[0037] The four extensions 12d are fan-shaped portions that extend from the inside of the base 12a toward the beam 12b in a plan view. A gap of about 1 mm is provided between each extension 12d and the beam 12b. If this gap is set to, for example, 0.05 to 0.2 mm, it is possible to prevent contamination from entering the inside of the housing 11 from the outside. The extensions 12d do not contribute to the sensing of the pulse wave sensor 10 and therefore do not need to be provided. The pulse wave sensor 10 has a shielded cable, a flexible circuit board, etc. (not shown) for inputting and outputting electrical signals to and from the outside.

[0038] The strain gauge 100 is provided on the strain generating body 12. The strain gauge 100 can be provided, for example, on the lower surface of the beam portion 12b. Since the beam portion 12b 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.

[0039] 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 12c (towards the center of the circular opening), facing each other in a plan view, with the load section 12c 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 12a, facing each other in a plan view, with the load section 12c in between. This arrangement allows for effective detection of compressive and tensile forces, enabling greater output from the full bridge.

[0040] The pulse wave sensor 10 is used by fixing it to the subject's arm so that the load portion 12c is in contact with the subject's radial artery. When a load is applied to the load portion 12c in response to the subject's pulse wave, causing the beam portion 12b to elastically deform, the resistance value of the resistor of the strain gauge 100 changes. The pulse wave sensor 10 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 12b. 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.

[0041] [Strain Gauge 100] Figure 9 is a plan view illustrating a strain gauge according to the first embodiment. Figure 10 is a cross-sectional view illustrating a strain gauge according to the first embodiment, showing a cross-section along line BB in Figure 9. Referring to Figures 9 and 10, the strain gauge 100 includes a base material 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. In Figure 9, for convenience, only the outer edge of the cover layer 160 is shown with a dashed line. The cover layer 160 may be provided as needed.

[0042] In the explanation of the strain gauge 100 in Figures 9 and 10, for convenience, the side of the base material 110 on which the resistor 130 is provided will be referred to as the upper side or one side, and the side on which the resistor 130 is not provided will be referred to as the lower side or the other side. Also, the side of each part on which the resistor 130 is provided will be referred to as one side or the upper surface, and the side on which the resistor 130 is not provided will be referred to as the other side or the lower surface. However, the strain gauge 100 can be used upside down or positioned at any angle. For example, in Figure 8, the strain gauge 100 is attached to the beam section 12b in an inverted state compared to Figure 10. That is, the base material 110 in Figure 10 is attached to the lower surface of the beam section 12b with adhesive or the like. Furthermore, "plan view" refers to viewing the object from the direction normal to the upper surface 110a of the base material 110, and "planar shape" refers to the shape of the object when viewed from the direction normal to the upper surface 110a of the base material 110.

[0043] The base material 110 is a member that serves as a base layer for forming the resistor 130, etc., and is flexible. The thickness of the base material 110 is not particularly limited and can be appropriately selected depending on the purpose, but for example it can be about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm for the base material 110 is preferable in terms of the transmission of strain from the surface of the strain-generating body joined to the lower surface of the base material 110 via an adhesive layer, etc., and dimensional stability against the environment, and a thickness of 10 μm or more is even preferable in terms of insulation.

[0044] The base material 110 can be 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. Note that "film" refers to a flexible component with a thickness of approximately 500 μm or less.

[0045] Here, "formed from an insulating resin film" does not prevent the base material 110 from containing fillers or impurities in the insulating resin film. For example, the base material 110 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0046] Other materials for the substrate 110 besides resin include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3), as well as amorphous glass. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 110. In this case, an insulating film is formed on the metallic substrate 110.

[0047] The resistor 130 is a thin film formed on the substrate 110 in a predetermined pattern, and is a sensitive part that undergoes a change in resistance when strained. 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. In Figure 9, for convenience, the resistor 130 is shown with a dark, textured pattern.

[0048] 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 direction of the BB line in Figure 9), and the ends of adjacent elongated sections are connected alternately, resulting in an overall zigzag folding 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 direction perpendicular to the BB line in Figure 9).

[0049] The longitudinal ends of the two elongated portions located on the outermost side in the grid width direction are bent in the grid width direction, forming the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction. Each of the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction is electrically connected to the electrode 150 via the wiring 140. In other words, the wiring 140 electrically connects each of the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction to each of the electrode 150.

[0050] 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).

[0051] Here, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0052] The thickness of the resistor 130 is not particularly limited and can be appropriately selected depending on the purpose, but for example, it can be about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more of the resistor 130 is preferable because it improves the crystallinity of the crystals constituting the resistor 130 (for example, the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less of the resistor 130 is even preferable because it can reduce cracks in the film caused by internal stress in the film constituting the resistor 130 and warping from the substrate 110. The width of the resistor 130 can be optimized for the required specifications such as resistance value and lateral sensitivity, and also takes into account measures to prevent wire breakage, for example, it can be about 10 μm to 100 μm.

[0053] 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. Furthermore, 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 higher, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Here, "main component" means that the substance in question accounts for 50% by weight or more of the total substances 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, and more preferably 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0054] 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 at 20% by weight or less, the decrease in gauge factor can be suppressed.

[0055] Furthermore, the proportion of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the proportion of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes even more pronounced due to the semiconducting properties of Cr2N. In addition, brittle fracture is reduced by reducing the ceramicization.

[0056] On the other hand, if trace amounts of N2 or atomic N are mixed into the film, external environmental factors (such as high temperatures) can cause them to escape from the film, resulting in changes in film stress. By creating chemically stable CrN, the generation of the aforementioned unstable N is avoided, and a stable strain gauge can be obtained.

[0057] The wiring 140 is formed on the substrate 110 and is electrically connected to the resistor 130 and the electrode 150. The wiring 140 has a first metal layer 141 and a second metal layer 142 laminated on the upper surface of the first metal layer 141. 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 9, the wiring 140 and the electrode 150 are shown with a matte finish that is thinner than the resistor 130.

[0058] The electrode 150 is formed on the substrate 110 and is electrically connected to the resistor 130 via the wiring 140. For example, it is wider than the wiring 140 and formed in a roughly 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, and for example, lead wires for external connection are joined to it.

[0059] The electrode 150 has a pair of first metal layers 151 and a second metal layer 152 laminated on the upper surface of each first metal layer 151. The first metal layers 151 are electrically connected to the ends 130e1 and 130e2 of the resistor 130 via the first metal layers 141 of the wiring 140. The first metal layers 151 are formed in a substantially rectangular shape in plan view. The first metal layers 151 may be formed to the same width as the wiring 140.

[0060] Although the resistor 130, the first metal layer 141, and the first metal layer 151 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 130, the first metal layer 141, and the first metal layer 151 have approximately the same thickness. Similarly, although the second metal layer 142 and the second metal layer 152 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the second metal layer 142 and the second metal layer 152 have approximately the same thickness.

[0061] The second metal layers 142 and 152 are formed from a material with lower resistance than the resistor 130 (first metal layers 141 and 151). The material of the second metal layers 142 and 152 is not particularly limited as long as it has lower resistance than the resistor 130, and can be appropriately selected according to the purpose. For example, if the resistor 130 is a Cr multiphase film, the material of the second metal layers 142 and 152 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, or compounds are appropriately stacked. The thickness of the second metal layers 142 and 152 is not particularly limited and can be appropriately selected according to the purpose, but can be, for example, about 3 μm to 5 μm.

[0062] The second metal layers 142 and 152 may be formed on a portion of the upper surface of the first metal layers 141 and 151, or on the entire upper surface of the first metal layers 141 and 151. One or more additional metal layers may be laminated on the upper surface of the second metal layer 152. For example, the second metal layer 152 may be a copper layer, and a gold layer may be laminated on top of the copper layer. Alternatively, the second metal layer 152 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on top of the copper layer. By making the uppermost layer of the electrode 150 a gold layer, the solder wettability of the electrode 150 can be improved.

[0063] Thus, the wiring 140 has a structure in which a second metal layer 142 is laminated on a first metal layer 141 made of the same material as the resistor 130. Therefore, since the wiring 140 has lower resistance than the resistor 130, it is possible to suppress the wiring 140 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 130 can be improved.

[0064] In other words, by providing wiring 140 with lower resistance than the resistor 130, the effective sensitive area of ​​the strain gauge 100 can be limited to the local region where the resistor 130 is formed. Therefore, the accuracy of strain detection by the resistor 130 can be improved.

[0065] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or higher using a Cr multiphase film as the resistor 130, reducing the resistance of the wiring 140 to that of the resistor 130 and limiting the effective sensitive area to the local region where the resistor 130 is formed has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the wiring 140 to that of the resistor 130 also has the effect of reducing lateral sensitivity.

[0066] The cover layer 160 is formed on the substrate 110 and covers the resistor 130 and wiring 140, while exposing the electrode 150. A portion of the wiring 140 may be exposed from the cover layer 160. By providing the cover layer 160 that covers the resistor 130 and wiring 140, mechanical damage to the resistor 130 and wiring 140 can be prevented. In addition, the cover layer 160 can protect the resistor 130 and wiring 140 from moisture and other elements. The cover layer 160 may be provided so as to cover the entire portion excluding the electrode 150.

[0067] The cover layer 160 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin, polyolefin resin). The cover layer 160 may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer 160, and it can be appropriately selected depending on the purpose, but for example, it can be about 2 μm to 30 μm.

[0068] 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, the first metal layer 141, and the first metal layer 151. Therefore, the material and thickness of metal layer A are the same as those of the resistor 130, the first metal layer 141, and the first metal layer 151.

[0069] 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, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0070] From the viewpoint of stabilizing gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as an underlayer on the upper surface 110a of the substrate 110, for example, by conventional sputtering, before depositing the metal layer A.

[0071] 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 and moisture contained in the substrate 110, and the function of improving the adhesion between the substrate 110 and the metal layer A. The functional layer may further have other functions.

[0072] Since the insulating resin film that makes up the base material 110 contains oxygen and moisture, and especially when the metal layer A contains Cr, Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the metal layer A.

[0073] The material of the functional layer is not particularly limited as long as it is a material that has the function of promoting crystal growth of at least the upper metal layer A (resistor 130), and can be appropriately selected according to the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bisulfite). Examples include one or more metals selected from the group consisting of M(Os), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of these metals, or a compound of any of these metals.

[0074] Examples of the alloys mentioned above include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds mentioned above include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0075] When the functional layer is formed from a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor can flow into the functional layer, preventing a decrease in strain detection sensitivity.

[0076] When the functional layer is formed from a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer be 1 / 50 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor flows into the functional layer, further preventing a decrease in strain detection sensitivity.

[0077] When the functional layer is formed from a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer be 1 / 100 or less of the thickness of the resistor. Within this range, it is possible to further prevent a decrease in strain detection sensitivity due to some of the current flowing through the resistor flowing into the functional layer.

[0078] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be easily formed without cracking.

[0079] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.8 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be formed more easily without cracking.

[0080] When the functional layer is formed from an insulating material such as an oxide or nitride, it is even more preferable that the thickness of the functional layer be 1 nm to 0.5 μm. Within this range, the crystal growth of α-Cr can be promoted, and the film can be formed more easily without cracking in the functional layer.

[0081] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in Figure 9. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. When the functional layer is formed from an insulating material, it does not need to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed as a solid block at least in the region where the resistor is formed. Alternatively, the functional layer may be formed as a solid block over the entire upper surface of the substrate 110.

[0082] Furthermore, when the functional layer is formed from an insulating material, forming the functional layer relatively thick, such as 50 nm to 1 μm, and forming it in a solid form increases the thickness and surface area of ​​the functional layer, allowing the heat generated when the resistor heats up to be dissipated towards the base material 110. As a result, the decrease in measurement accuracy due to self-heating of the resistor can be suppressed in the strain gauge 100.

[0083] The functional layer can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming a functional layer and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer is deposited while etching the upper surface 110a of the substrate 110 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

[0084] However, this is just one example of a method for forming a functional layer, and the functional layer may be formed by other methods. For example, the upper surface 110a of the substrate 110 may be activated by plasma treatment using Ar or the like before forming the functional layer to improve adhesion, and then the functional layer may be formed in a vacuum by magnetron sputtering.

[0085] There are no particular restrictions on the combination of materials for the functional layer and the metal layer A, and they can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the metal layer A.

[0086] In this case, for example, metal layer A can be formed by targeting a raw material capable of forming a Cr multiphase film and using a magnetron sputtering method with Ar gas introduced into the chamber. Alternatively, metal layer A may be formed by targeting pure Cr and using a reactive sputtering method with an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, the ratio of CrN and Cr2N in the Cr multiphase film, as well as the ratio of Cr2N within CrN and Cr2N, can be adjusted by changing the amount and pressure (partial pressure of nitrogen) of nitrogen gas introduced or by adjusting the heating temperature by providing a heating step.

[0087] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, enabling the formation of a Cr multiphase film primarily composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of a strain gauge of 100 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that if the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0088] Furthermore, when metal layer A is a Cr multiphase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of metal layer A, preventing oxidation of metal layer A by oxygen and moisture contained in the substrate 110, and improving adhesion between the substrate 110 and metal layer A. The same applies when Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0089] 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 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A can improve the gauge characteristics of the strain gauge 100.

[0090] Next, a second metal layer 142 and a second metal layer 152 are formed on the upper surface of metal layer A. The second metal layer 142 and the second metal layer 152 can be formed, for example, by photolithography.

[0091] Specifically, first, a seed layer is formed to cover the upper surface of metal layer A, for example, by sputtering or electroless plating. Next, a photosensitive resist is formed over the entire upper surface of the seed layer, and exposure and development are performed to create openings that expose the areas for forming the second metal layer 142 and the second metal layer 152. At this time, the pattern of the second metal layer 142 can be made into any shape by adjusting the shape of the openings in the resist. For example, a dry film resist can be used as the resist.

[0092] Next, for example, a second metal layer 142 and a second metal layer 152 are formed on the seed layer exposed within the opening by an electroplating method using the seed layer as the power supply path. The electroplating method is preferable because it has a high cycle time and can form low-stress electroplated layers as the second metal layer 142 and the second metal layer 152. By making the thick electroplated layer low-stress, warping of the strain gauge 100 can be prevented. The second metal layer 142 and the second metal layer 152 may also be formed by an electroless plating method.

[0093] Next, remove the resist. The resist can be removed, for example, by immersing it in a solution that can dissolve the resist material.

[0094] Next, a photosensitive resist is formed on the entire upper surface of the seed layer, exposed and developed to pattern it into a planar shape similar to the resistor 130, wiring 140, and electrode 150 in Figure 9. For example, a dry film resist can be used as the resist. Then, the resist is used as an etching mask to remove the metal layer A and seed layer exposed from the resist, forming the resistor 130, wiring 140, and electrode 150 with the planar shape shown in Figure 9.

[0095] For example, unwanted portions of metal layer A and seed layer can be removed by wet etching. If a functional layer is formed beneath metal layer A, etching will pattern the functional layer into the planar shape shown in Figure 9, similar to the resistor 130, wiring 140, and electrode 150. At this point, seed layers are formed on resistor 130, first metal layer 141, and first metal layer 151.

[0096] Next, the second metal layers 142 and 152 are used as etching masks, and the unwanted seed layers exposed from the second metal layers 142 and 152 are removed to form the second metal layers 142 and 152. Note that the seed layers directly beneath the second metal layers 142 and 152 remain. For example, the unwanted seed layers can be removed by wet etching using an etching solution that etches the seed layers but not the functional layers, resistors 130, wiring 140, and electrodes 150.

[0097] Subsequently, if necessary, a cover layer 160 is provided on the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, thereby completing the strain gauge 100. The cover layer 160 can be made, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing it. Alternatively, the cover layer 160 may be made by applying a liquid or paste-like thermosetting insulating resin to the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing it.

[0098] 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]

[0099] 1 Pulse wave measuring device, 10 Pulse wave sensor 10, 10x through hole, 10y screw hole, 11 Housing, 12 Strain generating body, 12a base, 12b beam, 12c load part, 12d extension part, 20 Sensor fixing part, 20a, 20b mounting part, 20x notch, 20y insertion hole, 30 Belt fixing part, 30a, 40a projection, 40 Belt insertion part, 80 Belt, 90 Screw, 100 Strain gauge, 110 Base material, 110a Top surface, 130 Resistor, 130e1, 130e2 termination, 140 Wiring, 150 Electrode, 160 Cover layer

Claims

1. A pulse wave measuring device that can be worn on a subject, A pulse wave sensor equipped with a strain generating body on which strain gauges are arranged, A sensor fixing part for fixing the pulse wave sensor, It has a strip-shaped body, one end of which is pivotably connected to one end of the sensor fixing part by a first axis, and the other end of which is pivotably connected to the other end of the sensor fixing part by a second axis, The first and second axes are located on the opposite side of the subject from the surface of the pulse wave sensor that contacts the subject, The strain generating body has a base portion with a circular opening, a beam portion bridging the inside of the base portion, and a load portion formed integrally with the base portion and the beam portion. The aforementioned beam section has two flat, plate-shaped beams that intersect in a cross shape in a plan view. The load-bearing portion is provided in the region where the beams intersect, protruding from the upper surface of the beams. The strain generating body is exposed from the sensor fixing portion, The load unit is a pulse wave measuring device that can come into contact with the subject.

2. The pulse wave measuring device according to claim 1, wherein the pulse wave sensor protrudes from the sensor fixing portion toward the subject.

3. The pulse wave measuring device according to claim 1 or 2, wherein the other end of the strip-shaped body is pivotably connected to the other end of the sensor fixing part via the strip-shaped body insertion part on the second axis.

4. The pulse wave measuring device according to claim 3, wherein the other end of the strip-shaped body can be detachably connected to the outer surface of the portion of the strip-shaped body that is not inserted into the strip-shaped body insertion portion by passing through the through hole of the strip-shaped body insertion portion.

5. A pulse wave measuring device according to any one of claims 1 to 4, further comprising a biasing mechanism between the sensor fixing portion and the pulse wave sensor for biasing the pulse wave sensor toward the subject.

6. A pulse wave measuring device according to any one of claims 1 to 5, which detects a pulse wave based on a change in the resistance value of the strain gauge accompanying the deformation of the strain body.

7. The pulse wave measuring device according to any one of claims 1 to 6, wherein the region where the beams intersect includes the center of the circular opening.

8. 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 face each other in a plan view, with the load portion in between. The pulse wave measuring device according to any one of claims 1 to 7, 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.

9. The pulse wave measuring device according to any one of claims 1 to 8, wherein the strain gauge has a resistor formed from a Cr multiphase film.

Images