JP7623065B2 - Pulse wave measuring device - Google Patents

Description

The present invention relates to a pulse wave measuring device.

Pulse wave sensors are known that detect pulse waves generated when the heart pumps blood. One example is a pulse wave sensor that is provided with a pressure-receiving plate that is a strain-generating body supported so that it can flex when subjected to an external force, and a piezoelectric conversion means that converts the flexure of the pressure-receiving plate into an electrical signal. In this pulse wave sensor, the flexible area of the pressure-receiving plate is formed in a dome shape that is a convex curved surface facing outward, and a pressure detection element is provided on the inner surface of the apex of the pressure-receiving plate as the piezoelectric conversion means (see, for example, Patent Document 1).

JP 2002-78689 A

Because the pulse wave sensor needs to detect minute signals, in a pulse wave measuring device that uses a pulse wave sensor, the pulse wave sensor needs to be placed in close contact with the subject to improve measurement accuracy.

The present invention has been made in consideration of the above points, and aims to provide a pulse wave measuring device that allows adjustment of the degree of contact between the subject and the pulse wave sensor.

The pulse wave measuring device is a pulse wave measuring device that can be worn by a subject, and includes a cylindrical holding portion and a strain body on which a strain gauge is arranged, the strain body being at least partially inserted inside the holding portion and held so as to be movable in the axial direction of the holding portion, the strain body being exposed from the holding portion so as to be contactable with the subject, a biasing portion that is arranged inside the holding portion on the opposite side of the pulse wave sensor from the strain body and biases the pulse wave sensor towards the subject, and an adjustment portion that is arranged on the opposite side of the pulse wave sensor across the biasing portion and is capable of adjusting the biasing force of the biasing portion , the adjustment portion having at least a portion that fits inside the holding portion and is screwed into the holding portion, and the biasing force of the biasing portion can be adjusted depending on the degree of screwing .

The disclosed technology provides a pulse wave measuring device that allows adjustment of the degree of contact between the subject and the pulse wave sensor.

1 is a perspective view (part 1) illustrating a pulse wave measuring device according to a first embodiment; FIG. 2 is a second perspective view illustrating the pulse wave measuring device according to the first embodiment; FIG. 3 is a front side perspective view of the main body and its vicinity in FIG. 2 . 3 is a rear perspective view of the main body and its vicinity in FIG. 2 . FIG. 4 is an exploded perspective view of FIG. 3 . 1 is a perspective view illustrating a pulse wave sensor according to a first embodiment; 1 is a plan view illustrating a pulse wave sensor according to a first embodiment. FIG. 1 is a cross-sectional view illustrating a pulse wave sensor according to a first embodiment. FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. FIG. 1 is a perspective view (part 1) illustrating a pulse wave measuring device according to a first modified example of the first embodiment. FIG. 2 is a perspective view (part 2) illustrating a pulse wave measuring device according to a second modified example of the first embodiment. 13 is a rear perspective view of the vicinity of the pulse wave sensor shown in FIG. 12 .

Below, a description will be given of a mode for carrying out the invention with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated explanations may be omitted.

First Embodiment
[Pulse wave measuring device 1]
FIG. 1 is a perspective view (part 1) illustrating a pulse wave measuring device according to the first embodiment. FIG. 2 is a perspective view (part 2) illustrating a pulse wave measuring device according to the first embodiment. FIG. 3 is a front side perspective view of the vicinity of the main body of FIG. 2. FIG. 4 is a rear side perspective view of the vicinity of the main body of FIG. 2. FIG. 5 is an exploded perspective view of FIG. 3. FIG. 1 shows a state in which the pulse wave measuring device shown in FIG. 2 is worn on the wrist of a subject. Also, the arrow N in FIG. 3 and FIG. 5 indicates the normal direction of the upper surface of the adjustment unit 70.

Referring to Figures 1 to 5, the pulse wave measuring device 1 is a wristwatch-type wearable device that can be worn by a subject, and mainly comprises a main body 10, a belt 40, a pulse wave sensor 50, a biasing unit 60, and an adjustment unit 70.

The pulse wave measuring device 1 is worn on the subject's wrist, for example, so that the pulse wave sensor 50 is positioned near the subject's radial artery. A pulse wave is a waveform that captures changes in the volume of blood vessels that occur when the heart pumps blood, and the pulse wave measuring device 1 can monitor changes in the volume of blood vessels.

The main body 10 has a lower member 20 and an upper member 30. For example, a battery and electronic components are mounted on the main body 10. The electronic components mounted on the main body 10 may include, for example, a semiconductor for signal processing that processes the signal measured by the pulse wave sensor 50, and a semiconductor for wireless communication that transmits the results of the signal processing to the outside.

The lower member 20 is a member that is located on the subject side when the pulse wave measuring device 1 is worn by the subject. The upper member 30 is a member that is located on the opposite side to the subject when the pulse wave measuring device 1 is worn by the subject. The lower member 20 and the upper member 30 can be formed, for example, from resin, rubber, metal, etc. The lower member 20 and the upper member 30 can be joined by an appropriate method such as screwing or press fitting. It is preferable that the lower member 20 and the upper member 30 are joined in a removable manner.

The lower member 20 has a bottom 21, side walls 22, and a holding portion 23. The bottom 21 is, for example, substantially rectangular when viewed from the N direction. The bottom 21 may be bent or curved into a shape that is easy to wear on the subject's wrist, etc. The bottom 21 is provided with, for example, two attachment portions 21x on each side in the longitudinal direction for attaching a belt 40. A frame-shaped side wall portion 22 is provided so as to be continuous with the outer edge of the bottom 21.

A cylindrical holder 23 for holding the pulse wave sensor 50 is provided on the same side of the bottom 21 as the side wall 22, penetrating the bottom 21. The holder 23 (i.e., the pulse wave sensor 50) is preferably positioned offset from the center of the main body 10 (the center of the bottom 21). This makes it easy to position the pulse wave sensor 50 near the subject's radial artery.

The holding portion 23 is, for example, cylindrical, but it does not have to be cylindrical as long as it can hold the pulse wave sensor 50 inside. The height of the holding portion 23 is approximately equal to the height of the side wall portion 22. The holding portion 23 may have a portion that protrudes from the main body 10 as long as at least a portion of the holding portion 23 is disposed within the main body 10.

The holding part 23 has a groove 23x that opens toward the adjustment part 70 in order to position the pulse wave sensor 50 in the rotational direction. For example, two grooves 23x can be provided at positions facing each other across the center of the holding part 23 when viewed from the N direction.

The upper member 30 has a top 31, a side wall 32, and a protrusion 33. When viewed from the N direction, the upper member 30 has a shape that substantially overlaps with the lower member 20. When viewed from the N direction, the top 31 is, for example, substantially rectangular. The top 31 may be bent or curved in a similar shape to the bottom 21. A frame-shaped side wall 32 is provided so as to be continuous with the outer edge of the top 31. The side wall 32 is sized and shaped so that the entire circumference of the lower end surface can contact the entire circumference of the upper end surface of the side wall 22 of the lower member 20.

A cylindrical protrusion 33 into which the adjustment part 70 is inserted is provided on the side opposite the side wall part 32 of the top part 31 so as to penetrate the top part 31. The inner diameter of the protrusion 33 is approximately equal to the inner diameter of the holding part 23. The protrusion 33 is positioned so as to overlap with the holding part 23 when viewed from the N direction when the upper member 30 is joined to the lower member 20.

The belt 40 is a band for attaching the main body 10 to the subject's wrist or the like, and is configured so that it can be wrapped around the subject's wrist or the like from the outside. The belt 40 includes, for example, a first band 41 and a second band 42. The first band 41 and the second band 42 are made of, for example, resin, rubber, cloth, etc., and are flexible.

One end of the first band 41 is attached to the mounting portion 21x on one side of the lower member 20 so as to be freely swingable. One end of the second band 42 is attached to the mounting portion 21x on the other side of the lower member 20 so as to be freely swingable. The other end of the first band 41 and the other end of the second band 42 can be detachably connected, for example, by a hook-and-loop fastener or the like. Note that the belt 40 may be formed integrally with the first band 41 and the second band 42 without distinction.

The pulse wave sensor 50 is a substantially cylindrical member, and is formed to a size that allows it to be inserted into the holding portion 23. The pulse wave sensor 50 has a positioning protrusion 50x on its side. The pulse wave sensor 50 is positioned by fitting the protrusion 50x into the groove 23x of the holding portion 23, and is held in the holding portion 23 in a state in which it can move in the axial direction of the holding portion 23. The axial direction of the holding portion 23 is, for example, the central axial direction of the cylinder if the holding portion 23 is cylindrical.

When the pulse wave sensor 50 is inserted into the holding portion 23, the surface of the pulse wave sensor 50 facing the biasing portion 60 is, for example, located lower than the upper end of the holding portion 23. The pulse wave sensor 50 may have a portion that protrudes from the holding portion 23 as long as at least a portion of the pulse wave sensor 50 is inserted inside the holding portion 23. Details of the pulse wave sensor 50 will be described later.

The biasing unit 60 is disposed inside the holding unit 23, on the opposite side of the pulse wave sensor 50 from the strain generating body 52 (described later). The biasing unit 60 can bias the pulse wave sensor 50 in the N direction. That is, when the pulse wave measuring device 1 is worn by a subject, the biasing unit 60 can bias the pulse wave sensor 50 toward the subject. The biasing unit 60 is, for example, a coil spring, but may also be a leaf spring or the like. The biasing unit 60 can be formed, for example, from metal, resin, rubber, or the like. The biasing unit 60 may also be an air pump that utilizes an electric motor.

The adjustment unit 70 is disposed on the opposite side of the biasing unit 60 from the pulse wave sensor 50. The adjustment unit 70 has, for example, a substantially cylindrical insertion unit 71 and a substantially disk-shaped lid unit 72 with one end of the insertion unit 71 having an expanded diameter. The insertion unit 71 is sized so that it can be inserted into the protrusion 33 and the holding unit 23, while the lid unit 72 is sized so that it cannot be inserted into the protrusion 33. The insertion unit 71 is inserted into the protrusion 33, and the tip side reaches the holding unit 23.

For example, the outer surface of the insertion portion 71 is male threaded, and the inner surface of the holding portion 23 is female threaded. A groove 72x is provided on the top surface of the lid portion 72. When the tip of a screwdriver or the like is inserted into the groove 72x and the adjustment portion 70 is rotated, at least a part of the insertion portion 71 of the adjustment portion 70 enters the inside of the holding portion 23 and is screwed into the holding portion 23, and the adjustment portion 70 and the holding portion 23 are fixed. The biasing force of the biasing portion 60 can be adjusted by the degree of screwing. In other words, the biasing force of the biasing portion 60 can be adjusted by adjusting the amount of rotation of the adjustment portion 70 (the amount of insertion of the insertion portion 71 into the holding portion 23).

In this way, when the pulse wave measuring device 1 is worn by a subject, the adjustment unit 70 can be rotated to move and bias the pulse wave sensor 50 toward the subject, thereby applying an appropriate initial pressure to the subject's radial artery. In other words, the pulse wave measuring device 1 can adjust the contact between the subject's radial artery and the pulse wave sensor 50 to an appropriate value, thereby improving the accuracy of pulse wave measurement.

In addition, in the pulse wave measuring device 1, the pulse wave sensor 50 can move in the axial direction of the holding part 23, but if an appropriate gap is provided between the holding part 23 and the side of the pulse wave sensor 50, it can swing within the holding part 23 around the protrusion 50x. In this structure, the pulse wave sensor 50 can tilt around the protrusion 50x depending on how the pulse wave measuring device 1 is attached to the subject, improving the adhesion between the subject's radial artery and the pulse wave sensor 50 and making it easier to keep applying a constant pressure.

In addition, when playing sports, the adjustment unit 70 can be rotated a lot to apply a relatively strong initial pressure, and when there is no need to measure the pulse wave, such as when sleeping, the adjustment unit 70 can be rotated less to apply no initial pressure, improving the freedom of use according to the situation.

In addition, by obtaining highly accurate pulse waves using the pulse wave measuring device 1, blood sugar levels, blood pressure, etc. can be monitored. It also makes it possible to predict arteriosclerosis, etc.

[Pulse wave sensor 50]
Fig. 6 is a perspective view illustrating the pulse wave sensor according to the first embodiment. Fig. 7 is a plan view illustrating the pulse wave sensor according to the first embodiment. Fig. 8 is a cross-sectional view illustrating the pulse wave sensor according to the first embodiment, showing a cross section along line A-A in Fig. 7. Note that Figs. 6 to 8 are viewed from a different direction than Fig. 5, and the bottom surface of pulse wave sensor 50 in Fig. 5 is the top surface in Figs. 6 to 8.

Referring to Figures 6 to 8, the pulse wave sensor 50 has a housing 51, a strain body 52, and a strain gauge 100. The pulse wave sensor 50 is held in the holding part 23 with the strain body 52 exposed from the lower member 20 side of the holding part 23 and in a state where it can come into contact with the subject (see Figure 4). The pulse wave sensor 50 may protrude from the lower member 20 towards the subject.

The flexure body 52 has a base 52a, a beam 52b, a load portion 52c, and an extension 52d. The flexure body 52 has, for example, a four-fold symmetric shape in a plan view. The material of the flexure body 52 can be, for example, SUS (stainless steel), copper, or aluminum. The flexure body 52 has, for example, a flat plate shape, and each component is integrally formed, for example, by a press processing method. The flexure body 52 may be flat, or may have a dome-like protruding shape so that the subject side is convex. The thickness t of the flexure body 52 excluding the load portion 52c is, for example, constant. The thickness t is, for example, 0.01 mm or more and 0.25 mm or less.

In the description of the pulse wave sensor 50 in Figures 6 to 8, for convenience, the side on which the load portion 52c of the flexure body 52 is provided is referred to as the upper side or one side, and the side on which the load portion 52c is not provided is referred to as the lower side or the other side. Also, the surface on which the load portion 52c of each part is provided is referred to as the one side or upper side, and the surface on which the load portion 52c is not provided is referred to as the other side or lower side. However, the pulse wave sensor 50 can be used upside down or placed at any angle. Also, a planar view refers to viewing an object from the normal direction of the top surface of the flexure body 52, and a planar shape refers to the shape of the object viewed from the normal direction of the top surface of the flexure body 52.

In the pulse wave sensor 50, the housing 51 is a portion that holds the strain body 52. The housing 51 is cylindrical, with the bottom side closed and the top side open. The housing 51 can be made of, for example, metal or resin. The roughly disk-shaped strain body 52 is fixed with an adhesive or the like so as to close the opening on the top side of the housing 51. The strain body 52 has a strain gauge 100 arranged therein, and is a portion that detects the pulse wave.

In the flexure body 52, the base 52a is a circular frame-shaped (ring-shaped) region outside the circular dashed lines shown in Figures 7 and 8. The region inside the circular dashed lines may be referred to as a circular opening. In other words, the base 52a of the flexure body 52 has a circular opening. The width _w1 of the base 52a is, for example, 1 mm or more and 5 mm or less. The inner diameter d of the base 52a (i.e., the diameter of the circular opening) is, for example, 5 mm or more and 40 mm or less.

The beam portion 52b is provided so as to bridge the inside of the base portion 52a. The beam portion 52b has, for example, two beams that cross in a cross shape in a plan view, and the crossing region of the two beams includes the center of the circular opening. In the example of FIG. 7, one beam constituting the cross has the X direction as its longitudinal direction, and the other beam constituting the cross has the Y direction as its longitudinal direction, and the two beams are perpendicular to each other. Each of the two perpendicular beams is preferably located inside the inner diameter d (diameter of the circular opening) of the base portion 52a 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 constituting the beam portion 52b, the width _w2 other than the crossing 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 in that the strain can be detected linearly.

The load portion 52c is provided on the beam portion 52b. The load portion 52c is provided, for example, in the region where the two beams that make up the beam portion 52b intersect. The load portion 52c protrudes from the upper surface of the beam portion 52b. The amount of protrusion of the load portion 52c based on the upper surface of the beam portion 52b is, for example, about 0.1 mm. The beam portion 52b is flexible, and elastically deforms when a load is applied to the load portion 52c.

The four extensions 52d are sector-shaped portions that extend from the inside of the base 52a toward the beam 52b in a plan view. A gap of about 1 mm is provided between each extension 52d and the beam 52b. If the gap is set to, for example, about 0.05 to 0.2 mm, it is possible to prevent contamination from entering the inside of the housing 51 from the outside. The extensions 52d do not contribute to the sensing of the pulse wave sensor 50, so they do not need to be provided. The pulse wave sensor 50 has a shielded cable, a flexible board, etc. (not shown) that inputs and outputs electrical signals from the outside.

The strain gauge 100 is provided on the strain generating body 52. The strain gauge 100 can be provided, for example, on the underside of the beam portion 52b. Since the beam portion 52b is flat, the strain gauge can be easily attached. One or more strain gauges 100 may be provided, but in this embodiment, four strain gauges 100 are provided. By providing four strain gauges 100, strain can be detected by a full bridge.

Two of the four strain gauges 100 are arranged on the side closer to the load section 52c of the beam with the longitudinal direction in the X direction (towards the center of the circular opening) so as to face each other across the load section 52c in a plan view. The other two of the four strain gauges 100 are arranged on the side closer to the base section 52a of the beam with the longitudinal direction in the Y direction so as to face each other across the load section 52c in a plan view. This arrangement makes it possible to effectively detect compressive and tensile forces and obtain a large output from the full bridge.

The pulse wave sensor 50 is fixed to the subject's arm so that the load portion 52c contacts the subject's radial artery. When a load is applied to the load portion 52c in response to the subject's pulse wave and the beam portion 52b elastically deforms, the resistance value of the resistor in the strain gauge 100 changes. The pulse wave sensor 50 can detect the pulse wave based on the change in the resistance value of the resistor in the strain gauge 100 that accompanies the deformation of the beam portion 52b. 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.

[Strain gauge 100]
Fig. 9 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 10 is a cross-sectional view illustrating the strain gauge according to the first embodiment, showing a cross section along line B-B in Fig. 9. With reference to Figs. 9 and 10, the strain gauge 100 has a substrate 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. For convenience, only the outer edge of the cover layer 160 is shown by a dashed line in Fig. 9. The cover layer 160 may be provided as necessary.

9 and 10, for the sake of convenience, the side of the strain gauge 100 on which the resistor 130 of the substrate 110 is provided is referred to as the upper side or one side, and the side on which the resistor 130 is not provided is referred to as the lower side or the other side. In addition, the surface on which the resistor 130 of each part is provided is referred to as the one side or upper surface, and the surface on which the resistor 130 is not provided is referred to as the other side or lower surface. However, the strain gauge 100 can be used upside down or placed at any angle. For example, in FIG. 8, the strain gauge 100 is attached to the beam 52b in a state in which it is upside down compared to FIG. 10. In other words, the substrate 110 in FIG. 10 is attached to the lower surface of the beam 52b with an adhesive or the like. Additionally, a planar view refers to viewing the object from the normal direction of the upper surface 110a of the substrate 110, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 110a of the substrate 110.

The substrate 110 is a flexible member that serves as a base layer for forming the resistor 130 and the like. There are no particular limitations on the thickness of the substrate 110, and it can be selected appropriately depending on the purpose, but it can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transmission of strain from the surface of the strain generator that is joined to the lower surface of the substrate 110 via an adhesive layer or the like, and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation.

The substrate 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, polyolefin resin, etc. Note that a film refers to a flexible material with a thickness of about 500 μm or less.

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

Examples of materials other _than resin for the base material 110 include crystalline materials _such as _SiO2 , _ZrO2 (including YSZ), Si, _Si2N3 , _Al2O3 (including sapphire), ZnO, perovskite ceramics ( _CaTiO3 , _BaTiO3 ), and amorphous glass. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the base material 110. In this case, for example, an insulating film is formed on the metal base material 110.

The resistor 130 is a thin film formed in a predetermined pattern on the substrate 110, and is a sensing part that generates a resistance change when strained. The resistor 130 may be formed directly on the upper surface 110a of the substrate 110, or may be formed on the upper surface 110a of the substrate 110 via another layer. For convenience, the resistor 130 is shown in FIG. 9 with a dark matte pattern.

The resistor 130 has multiple elongated portions arranged at regular intervals with their longitudinal direction in the same direction (the direction of line B-B in FIG. 9), and the ends of adjacent elongated portions are alternately connected, resulting in a zigzag fold-over structure as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction perpendicular to line B-B in FIG. 9).

One end in the longitudinal direction of the two elongated portions located at the outermost sides in the grid width direction is bent in the grid width direction to form terminal ends _130e1 and _130e2 in the grid width direction of the resistor 130. The terminal ends _130e1 and _130e2 in the grid width direction of the resistor 130 are electrically connected to the electrodes 150 via the wiring 140. In other words, the wiring 140 electrically connects the terminal ends _130e1 and _130e2 in the grid width direction of the resistor 130 to the electrodes 150.

The resistor 130 can be formed, for example, from 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 mixed phase 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).

Here, the Cr mixed phase film is a film in which Cr, CrN, Cr ₂ N, etc. are mixed together. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

The thickness of the resistor 130 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable in that the crystallinity of the crystals constituting the resistor 130 (for example, the crystallinity of α-Cr) is improved. Furthermore, a thickness of 1 μm or less is even more preferable in that film cracks caused by internal stress of the film constituting the resistor 130 and warping from the substrate 110 can be reduced. The width of the resistor 130 can be optimized for the required specifications such as resistance value and lateral sensitivity, and can be, for example, about 10 μm to 100 μm, taking into consideration measures against disconnection.

For example, when the resistor 130 is a Cr mixed phase film, the stability of the gauge characteristics can be improved by making the main component α-Cr (alpha chromium), which is a stable crystal phase. In addition, by making the resistor 130 mainly composed of α-Cr, the gauge factor of the strain gauge 100 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm/°C to +1000 ppm/°C. Here, the main component means that the target substance accounts for 50% by weight or more of the total substance constituting the resistor, but from the viewpoint of improving the gauge characteristics, it is preferable that the resistor 130 contains α-Cr at 80% by weight or more, and more preferably at 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

Furthermore, when the resistor 130 is a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr ₂ N. By containing the Cr mixed-phase film with 20% by weight or less of CrN and Cr ₂ N, a decrease in the gauge factor can be suppressed.

In addition, the ratio 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 ratio 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 more significant due to the _Cr2N having semiconducting properties. Furthermore, by reducing the ceramicization, brittle fracture is reduced.

On the other hand, if a small amount of _N2 or atomic N is mixed in or present in the film, it will escape to the outside of the film due to the external environment (for example, a high temperature environment), causing a change in the film stress. By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

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 being linear, and can be in any pattern. The wiring 140 can also be of any width and length. For convenience, in FIG. 9, the wiring 140 and the electrode 150 are shown with a matte pattern that is thinner than the resistor 130.

The electrodes 150 are formed on the substrate 110 and are electrically connected to the resistor 130 via the wiring 140, and are formed, for example, in a substantially rectangular shape wider than the wiring 140. The electrodes 150 are a pair of electrodes for outputting to the outside the change in resistance value of the resistor 130 caused by strain, and for example, lead wires for external connection are joined to the electrodes 150.

The electrode 150 has a pair of first metal layers 151 and a second metal layer 152 laminated on the upper surface of each of the first metal layers 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 a plan view. The first metal layers 151 may be formed to have the same width as the wiring 140.

Note that although the resistor 130, the first metal layer 141, and the first metal layer 151 are given different reference numbers for convenience, they can be formed integrally 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. Also, although the second metal layer 142 and the second metal layer 152 are given different reference numbers for convenience, they can be formed integrally 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.

The second metal layers 142 and 152 are formed from a material with a lower resistance than the resistor 130 (the first metal layers 141 and 151). There are no particular limitations on the material of the second metal layers 142 and 152, as long as it is a material with a lower resistance than the resistor 130, and it can be appropriately selected according to the purpose. For example, when the resistor 130 is a Cr mixed phase 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, and compounds are appropriately laminated. There are no particular limitations on the thickness of the second metal layers 142 and 152, and it can be appropriately selected according to the purpose, but it can be, for example, about 3 μm to 5 μm.

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 may be formed on the entire upper surface of the first metal layers 141 and 151. One or more other 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 the upper surface 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 the upper surface of the copper layer. By making the top layer of the electrode 150 a gold layer, the solder wettability of the electrode 150 can be improved.

In this way, the wiring 140 has a structure in which the second metal layer 142 is laminated on the first metal layer 141 made of the same material as the resistor 130. Therefore, the resistance of the wiring 140 is lower than that of the resistor 130, and the wiring 140 can be prevented from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 130 can be improved.

In other words, by providing wiring 140 with a lower resistance than resistor 130, the actual sensing area of strain gauge 100 can be limited to the local area where resistor 130 is formed. This improves the accuracy of strain detection by resistor 130.

In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed-phase film as the resistor 130, making the wiring 140 lower in resistance than the resistor 130 and limiting the actual sensing area to the local area where the resistor 130 is formed has a significant effect on improving strain detection accuracy. In addition, making the wiring 140 lower in resistance than the resistor 130 also has the effect of reducing lateral sensitivity.

The cover layer 160 is formed on the substrate 110, covers the resistor 130 and the wiring 140, and exposes the electrode 150. A part of the wiring 140 may be exposed from the cover layer 160. By providing the cover layer 160 that covers the resistor 130 and the wiring 140, mechanical damage to the resistor 130 and the wiring 140 can be prevented. Furthermore, by providing the cover layer 160, the resistor 130 and the wiring 140 can be protected from moisture and the like. The cover layer 160 may be provided so as to cover the entire portion except for the electrode 150.

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 a filler or pigment. There is no particular limit to the thickness of the cover layer 160 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

To manufacture the strain gauge 100, first, a substrate 110 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 110a of the substrate 110. Metal layer A is a layer that will ultimately be patterned to become resistor 130, first metal layer 141, and first metal layer 151. Therefore, the material and thickness of metal layer A are the same as those of resistor 130, first metal layer 141, and first metal layer 151 described above.

Metal layer A can be formed, for example, by magnetron sputtering using a raw material capable of forming metal layer A as a target. Instead of magnetron sputtering, metal layer A may also be formed using reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

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

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

The insulating resin film constituting the substrate 110 contains oxygen and moisture, and since Cr forms a self-oxidized film, particularly when the metal layer A contains Cr, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A.

The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the 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 (bismuth), etc. Examples of the metal include one or more metals selected from the group consisting of ruthenium (Ru), iron (Fe), molybdenum (Mo), tungsten (W), ruthenium (Ru), rhodium (Rh), rhenium (Rhenium), osmium (Os), iridium (Ir), platinum (Pt), palladium (Pd), silver (Ag), gold (Au), cobalt (Co), manganese (Mn), and aluminum (Al), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

Examples of the alloy include FeCr, TiAl, FeNi, NiCr, CrCu, _etc. Examples of the compound include TiN, TaN, _Si3N4 , _TiO2 , _Ta2O5 , _{SiO2 ,} etc.

When the functional layer is made of 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. In this range, the crystal growth of α-Cr can be promoted, and a part of the current flowing through the resistor can be prevented from flowing through the functional layer, which would reduce the sensitivity of strain detection.

When the functional layer is made of a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer is 1/50 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and it is also possible to further prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby reducing the sensitivity of strain detection.

When the functional layer is made of a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer is 1/100 or less of the thickness of the resistor. In this range, it is possible to further prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in the strain detection sensitivity.

When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. This range promotes the crystal growth of α-Cr and allows the functional layer to be easily formed without cracking.

When the functional layer is made of an insulating material such as an oxide or nitride, it is more preferable that the thickness of the functional layer is 1 nm to 0.8 μm. This range promotes the crystal growth of α-Cr and makes it easier to form the functional layer without cracking.

When the functional layer is made of an insulating material such as an oxide or nitride, it is even more preferable that the thickness of the functional layer is between 1 nm and 0.5 μm. This range promotes the crystal growth of α-Cr and makes it easier to form the functional layer without cracking.

The planar shape of the functional layer is patterned to be approximately the same as the planar shape of the resistor shown in FIG. 9, for example. However, the planar shape of the functional layer is not limited to being approximately the same as the planar shape of the resistor. If the functional layer is formed from an insulating material, it does not have to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid shape at least in the area where the resistor is formed. Alternatively, the functional layer may be formed in a solid shape over the entire top surface of the substrate 110.

In addition, when the functional layer is made of an insulating material, the functional layer is formed relatively thick, at a thickness of 50 nm to 1 μm, and formed in a solid shape, thereby increasing the thickness and surface area of the functional layer, and therefore heat generated by the resistor can be dissipated to the substrate 110. As a result, the deterioration of measurement accuracy due to self-heating of the resistor can be suppressed in the strain gauge 100.

The functional layer can be formed in a vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 110a of the substrate 110 with Ar, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

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

There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A, and they can be selected appropriately depending on the purpose. For example, it is possible to use Ti as the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component as the metal layer A.

In this case, for example, the metal layer A can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber. In this case, the ratio of CrN and Cr ₂ N contained in the Cr mixed phase film and the ratio of Cr ₂ N in CrN and Cr ₂ N can be adjusted by changing the amount and pressure (nitrogen partial pressure) of the nitrogen gas introduced or by adjusting the heating temperature by providing a heating process.

In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film can be formed that is mainly composed of α-Cr, which has a stable crystal structure. In addition, the Ti that constitutes the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 100 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm/°C to +1000 ppm/°C. Note that when the functional layer is formed from Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

When metal layer A is a Cr mixed phase 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 due to oxygen and moisture contained in the base material 110, and improving adhesion between the base material 110 and metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystalline phase. As a result, the stability of the gauge characteristics of the strain gauge 100 can be improved. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 100.

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

Specifically, first, a seed layer is formed by, for example, sputtering or electroless plating so as to cover the upper surface of metal layer A. Next, a photosensitive resist is formed over the entire upper surface of the seed layer, and is exposed and developed to form openings that expose the areas in which second metal layer 142 and second metal layer 152 are to be formed. At this time, the pattern of second metal layer 142 can be formed 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.

Next, for example, the second metal layer 142 and the second metal layer 152 are formed on the seed layer exposed in the opening by electrolytic plating using the seed layer as a power supply path. The electrolytic plating method is advantageous in that it has high tact and can form low-stress electrolytic plating layers as the second metal layer 142 and the second metal layer 152. By making the thick electrolytic plating layer low-stress, it is possible to prevent warping of the strain gauge 100. The second metal layer 142 and the second metal layer 152 may also be formed by electroless plating.

Next, the resist is removed. For example, the resist can be removed by immersing it in a solution that can dissolve the resist material.

Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to be patterned into a planar shape similar to that of the resistor 130, wiring 140, and electrode 150 in FIG. 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 the seed layer exposed from the resist, forming the resistor 130, wiring 140, and electrode 150 in the planar shape of FIG. 9.

For example, unnecessary portions of the metal layer A and the seed layer can be removed by wet etching. If a functional layer is formed below the metal layer A, the functional layer is patterned by etching into the planar shape shown in FIG. 9, similar to the resistor 130, the wiring 140, and the electrode 150. At this point, a seed layer is formed on the resistor 130, the first metal layer 141, and the first metal layer 151.

Next, the second metal layer 142 and the second metal layer 152 are used as an etching mask to remove the unnecessary seed layer exposed from the second metal layer 142 and the second metal layer 152, thereby forming the second metal layer 142 and the second metal layer 152. Note that the seed layer directly below the second metal layer 142 and the second metal layer 152 remains. For example, the unnecessary seed layer can be removed by wet etching using an etching solution that etches the seed layer but does not etch the functional layer, resistor 130, wiring 140, and electrode 150.

Thereafter, as necessary, a cover layer 160 that covers the resistor 130 and wiring 140 and exposes the electrodes 150 is provided on the upper surface 110a of the substrate 110, thereby completing the strain gauge 100. The cover layer 160 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 110a of the substrate 110 so as to cover the resistor 130 and wiring 140 and expose the electrodes 150, and then heating and curing the film. The cover layer 160 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 110a of the substrate 110 so as to cover the resistor 130 and wiring 140 and expose the electrodes 150, and then heating and curing the resin.

First Modification of the First Embodiment
In the first modification of the first embodiment, an example in which the holding part is disposed apart from the main body is shown. Note that in the first modification of the first embodiment, the description of the same components as those in the embodiment already described may be omitted.

Fig. 11 is a perspective view (part 1) illustrating a pulse wave measuring device according to modified example 1 of the first embodiment. Fig. 12 is a perspective view (part 2) illustrating a pulse wave measuring device according to modified example 1 of the first embodiment. Fig. 13 is a rear perspective view of the vicinity of the pulse wave sensor in Fig. 12. Fig. 11 shows the pulse wave measuring device shown in Fig. 12 worn on the wrist of a subject.

Referring to Figures 11 to 13, the pulse wave measuring device 1A differs from the pulse wave measuring device 1 mainly in that the holding part 23 is disposed on the belt 40 away from the main body 10A. The main body 10A is substantially rectangular. The main body 10A is not bent or curved because its longitudinal length is shorter than that of the main body 10, but it may be bent or curved as necessary.

The holding portion 23 is fixed to the second band 42, for example. The holding portion 23 penetrates the second band 42, for example, and protrudes on both sides of the second band 42. The holding portion 23 further penetrates the first band 41, and the insertion portion 71 of the adjustment portion 70 can be inserted from the first band 41 side. The holding portion 23 is disposed in a position roughly opposite the main body 10A in the state shown in FIG. 12.

The pulse wave sensor 50 is inserted into the holding part 23 with the protrusion 50x fitted into the groove 23x of the holding part 23 and positioned. The strain body 52 side of the pulse wave sensor 50 may protrude from the holding part 23 toward the subject.

At least a portion of the insertion portion 71 of the adjustment portion 70 enters inside the holding portion 23 and is screwed into the holding portion 23, fixing the adjustment portion 70 and the holding portion 23. As in FIG. 5, the biasing portion 60 is disposed between the pulse wave sensor 50 and the insertion portion 71, and the biasing force of the biasing portion 60 can be adjusted by adjusting the degree of screwing. In other words, the biasing force of the biasing portion 60 can be adjusted by adjusting the amount of rotation of the adjustment portion 70 (the amount of insertion of the insertion portion 71 into the holding portion 23).

In this manner, the holding portion 23 and the pulse wave sensor 50 held by the holding portion 23 may be provided on the belt 40.

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

1, 1A Pulse wave measuring device, 10, 10A Main body, 20 Lower member, 21 Bottom, 21x Mounting portion, 22 Side wall portion, 23 Holding portion, 23x Groove, 30 Upper member, 31 Top portion, 32 Side wall portion, 33 Protrusion portion, 40 Belt, 41 First band-shaped body, 42 Second band-shaped body, 50 Pulse wave sensor, 50x Protrusion portion, 51 Housing, 52 Strain generating body, 52a Base portion, 52b Beam portion, 52c Load portion, 52d Extension portion, 60 Pressing portion, 70 Adjustment portion, 71 Insertion portion, 72 Lid portion, 72x Groove

Claims (10)

A pulse wave measuring device that can be worn by a subject,
A cylindrical holding portion;
a pulse wave sensor including a strain gauge disposed on the strain gauge, the strain gauge being held by the holding part so as to be movable in the axial direction of the holding part with at least a portion of the strain gauge inserted inside the holding part, the strain gauge being exposed from the holding part and being contactable with the subject;
a biasing portion that is disposed inside the holding portion on the opposite side of the pulse wave sensor from the strain body and biases the pulse wave sensor toward the subject;
an adjustment unit that is disposed on the opposite side of the biasing unit from the pulse wave sensor and that is capable of adjusting the biasing force of the biasing unit ;
The adjustment portion is at least partially inserted inside the holding portion and screwed to the holding portion, and the biasing force of the biasing portion can be adjusted by the degree of screwing . A pulse wave measuring device that can be worn by a subject,
A cylindrical holding portion;
a pulse wave sensor including a strain gauge disposed on the strain gauge, the strain gauge being held by the holding part so as to be movable in the axial direction of the holding part with at least a portion of the strain gauge inserted inside the holding part, the strain gauge being exposed from the holding part and being contactable with the subject;
a biasing portion that is disposed inside the holding portion on the opposite side of the pulse wave sensor from the strain body and biases the pulse wave sensor toward the subject;
an adjustment unit that is disposed on the opposite side of the biasing unit from the pulse wave sensor and that is capable of adjusting the biasing force of the biasing unit ;
The retaining portion includes a groove.
The pulse wave sensor has a protrusion on a side surface,
The protrusion is fitted into the groove, and the pulse wave sensor is capable of swinging about the protrusion as an axis . A main body on which electronic components are mounted, and a band for attaching the main body to the subject,
The pulse wave measuring device according to claim 1 , wherein at least a portion of the holding portion is disposed inside the main body. The pulse wave measuring device according to claim 3 , wherein the holding portion is disposed at a position offset from the center of the main body. A main body on which electronic components are mounted, and a band for attaching the main body to the subject,
The pulse wave measuring device according to claim 1 , wherein the holding portion is disposed on the band-shaped body and spaced apart from the main body. The strain body is
a base having a circular opening;
A beam portion bridging the inside of the base portion;
A load portion provided on the beam portion,
6. The pulse wave measuring device according to claim 1 , wherein the pulse wave is detected based on a change in resistance value of the strain gauge accompanying a deformation of the strain body. The beam portion has two beams that intersect in a cross shape in a plan view,
the intersecting region of the beams includes a center of the circular opening;
The pulse wave measuring device according to claim 6 , wherein the load portion is provided in an area where the beams intersect. The strain gauge includes four strain gauges,
Two of the four strain gauges are arranged on a side of the beam having a longitudinal direction in the first direction that is closer to the load portion, so as to face each other across the load portion in a plan view,
8. The pulse wave measuring device according to claim 7, wherein other two of the four strain gauges are arranged on a side closer to the base of the beam, whose longitudinal direction is a second direction perpendicular to the first direction, so as to face each other across the load portion in a planar view. A pulse wave measuring device that can be worn by a subject,
A cylindrical holding portion;
a pulse wave sensor including a strain gauge disposed on the strain gauge, the strain gauge being held by the holding part so as to be movable in the axial direction of the holding part with at least a portion of the strain gauge inserted inside the holding part, the strain gauge being exposed from the holding part and being contactable with the subject;
a biasing portion that is disposed inside the holding portion on the opposite side of the pulse wave sensor from the strain body and biases the pulse wave sensor toward the subject;
an adjustment unit that is disposed on the opposite side of the biasing unit from the pulse wave sensor and that is capable of adjusting the biasing force of the biasing unit ;
The strain body is
a base having a circular opening;
A beam portion bridging the inside of the base portion;
A load portion provided on the beam portion,
The beam portion has two beams that intersect in a cross shape in a plan view,
the intersecting region of the beams includes a center of the circular opening;
The load portion is provided in the intersecting region of the beam,
The strain gauge includes four strain gauges,
Two of the four strain gauges are arranged on a side of the beam having a longitudinal direction in the first direction that is closer to the load portion, so as to face each other across the load portion in a plan view,
The other two of the four strain gauges are arranged on a side closer to the base of the beam having a longitudinal direction in a second direction perpendicular to the first direction, so as to face each other across the load portion in a plan view,
A pulse wave measuring device that detects a pulse wave based on a change in resistance value of the strain gauge accompanying deformation of the strain body . The pulse wave measuring device according to any one of claims 1 to 9, wherein the strain gauge has a resistor formed from a Cr mixed phase film.

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