load cell

Abstract

To provide a small-sized load cell that can measure a heavy load and can also withstand high stress, in which wiring is prevented from peeling off.SOLUTION: A load cell R comprises: a strain body 10 having elasticity; a force transmission member 13 for transmitting a force to the strain body 10, formed protruding from the top face 11(first principal plane) of the strain body 10; a fixed part 14 surrounding the entire peripheral part of the strain body 10 protrudingly in the circumference direction on the top face side; and a strain gauge part 20 composed of a conductive member having an isotropic gauge factor, with the member formed extendedly in the circumferential direction on the underside plane 12(second principal plane) opposite to the top face 11 of the strain body 10. The strain body 10 and the fixed part 14 are integrally formed.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a load cell, and more particularly to a load cell that can be miniaturized.

Background Art

[0002] The efficiency improvement of production equipment by IoT emphasizes three technologies: sensing, information communication, information processing, and their reaction. Conventionally, on-site sensing relying on human hands has been required to have the ability to handle various and diverse environments. Among the scenarios where sensing is desired, the measurement of stress, which is a physical change, is important. In stress measurement, a load cell has generally been used. In the future development of sensing functions, the stress measurement of minute spaces and minute objects, which has been difficult to measure conventionally, is particularly important.

[0003] Small load cells have been developed so far, but there has been a problem that as they are miniaturized, the measurable stress also becomes smaller. A load cell uses a strain gauge, and a strain detection part is provided at the strain generating part. Due to the strain generated by applying stress to the strain generating part, the strain detection part is also strained, resulting in a change in resistance value. This change in resistance value is inversely converted to calculate load, pressure, etc. When the load cell is miniaturized, the strain generating part also becomes smaller, and the stress that can be endured also becomes smaller. If the strain generating part is made highly rigid so that it can endure stress, the amount of strain becomes smaller, and thus stress cannot be detected. That is, there has been an essential problem that when trying to miniaturize a load cell, the measurable stress (load) also becomes smaller.

[0004] When miniaturizing a load cell, the electrodes attached to the strain gauge also become smaller, and it becomes difficult to attach wiring to the electrodes. Further, when a high load is applied to the miniaturized load cell, the load cell is likely to be distorted, and since it is a movable part, even if wiring is attached to the electrodes, it is likely to peel off. The demand for miniaturization of load cells is high, and various technologies have been used to address this so far.

[0005] Patent Document 1 describes a multi-axial force load cell characterized by having two identical load cell halves, each supported by four square-section spoke columns arranged in a cross shape at the center of a cylindrical holder, with the ends of the holder facing each other and arranged symmetrically vertically. In this technology, if only one side is supported, the cylindrical portion that forms the side wall will deform under load, and repeated use will result in residual strain and deterioration of hysteresis. However, by connecting the same structure vertically, this deterioration of hysteresis is resolved. The technology in Patent Document 1 avoids the increase in load on the housing that occurs with miniaturization.

[0006] Patent Document 2 describes a technique for forming a load cell by attaching a strain gauge (corresponding to the strain gauge in Japanese Patent Application Publication No. 2014-074661) made of a Cr-N thin film formed on an insulating ceramic substrate with a thickness of 80 μm or less to the area that is most heavily deformed in an integrally molded, roughly Z-shaped housing. In response to the problem that conventional low-sensitivity commercially available strain gauges could not provide a sufficient signal and thus measurement was impossible due to the increased apparent rigidity in the strain-generating area caused by miniaturization, the above technique is said to enable further miniaturization of load cells made of roughly Z-shaped housings by using a highly sensitive Cr-N thin film strain gauge.

[0007] Patent document 3 describes a technique for miniaturizing a load cell by connecting (bridging) an inner circular tube and an outer circular tube with a strain detection unit equipped with strain gauges. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2007-163405 [Patent Document 2] Japanese Patent Publication No. 2014-077673 [Patent Document 3] Japanese Patent Publication No. 2012-063266 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The technology described in Patent Document 1 addresses the issue of distortion occurring in identical structures by combining two structures. While this reduces distortion, it does not provide a fundamental solution. Furthermore, when creating a small load cell, how to implement the electrodes other than the gauge portion and the wiring from them is crucial, but this aspect is not explained. As load cells are miniaturized, the housing and gauge portion become smaller, but the associated electrodes and wiring tend to become relatively larger. It is easy to surmise that attaching electrodes to the ends of strain gauges arranged on spoke-shaped columns and then attaching wiring to them will affect other spoke-shaped columns and reduce accuracy.

[0010] Furthermore, while the electrodes on the smaller strain gauges are also smaller, there is no explanation as to how the wiring connected to them will be connected. Also, although the strain gauge portion is exposed to the outside, due to its structure, the spoke-like column portion is visible from the outside, and depending on the installation environment, the accumulation of dust and other debris may become a problem. In particular, when miniaturizing the load cell, it is conceivable that maintenance after installation may become impossible to access. In addition, the presence of corrosive dust and gases at the site is also a concern. In future sensing in the IoT field, it will be necessary to anticipate installation in locations that were previously unimaginable. Furthermore, when miniaturizing load cells, it is important to see how small the strain gauge portion can be made. However, this point is not described in detail in Patent Document 1. In the load cell of Patent Document 1, the rectangular portion is used as the strain gauge portion, and it is presumed that strain is detected in the direction in which the rectangle expands and contracts. However, if the length of this rectangle is long, the circular tube will be larger, making miniaturization difficult.

[0011] In the technology described in Patent Document 2, although the width of the strain-generating body is narrow at 4 mm, it has an approximately Z-shaped structure, which results in a long height and hinders miniaturization. The load cell shown as an example has a width of 4 mm, a length of 11 mm, and a height of 14 mm. While the width is small, the length (depth) and height are not small when aiming for overall miniaturization. Furthermore, because the substrate with the strain gauges is attached to the strain-generating body, there is a possibility of problems improving measurement accuracy from the perspective of creep and strain transmission. This problem is mainly due to the configuration in which the strain gauges are placed inside the approximately Z-shaped structure, which can only be installed by attachment, making further miniaturization and increased capacity (enabling high-load measurement) difficult.

[0012] In the technology described in Patent Document 3, compared to creating a diaphragm structure by methods such as machining, connecting two circular pipes with multiple bridges requires maintaining an even balance. It is difficult to create a structure in which the inner circular pipe, the outer circular pipe, and the deformable portion between them are integrated. Miniaturizing the load cell makes it even more difficult to create the structure. Furthermore, if the circular pipes are connected only by a component with a strain detection unit, it will not be able to withstand high loads. In addition, the strain detection unit is a meander line, resulting in a long overall length. While it is required to minimize the distance between the inner and outer circular pipes, such a long detection unit limits the miniaturization of the load cell.

[0013] This invention has been made in view of the above problems, and the object of this invention is to provide a load cell that is small in size, capable of measuring high loads, can withstand high stress, and has reduced risk of wiring peeling. [Means for solving the problem]

[0016] beforeThe problem described above is solved by the load cell of the present invention, which comprises: an elastic strain generating body; a force transmitting member formed protruding from a first main surface of the strain generating body and transmitting force to the strain generating body; a fixing part surrounding the peripheral edge of the strain generating body so as to protrude toward the first main surface side over its entire circumference; and a strain gauge part made of a conductive member having an isotropic gauge ratio formed to extend circumferentially on a second main surface of the strain generating body opposite to the first main surface, wherein the strain generating body and the fixing part are integrally formed, and further comprises a cylindrical housing member covering the strain generating body, the fixing part and the strain gauge part from the outside, an electrode part formed on the second main surface of the strain generating body and constituting a strain detection circuit together with the strain gauge part, and a wiring member connected to the electrode part, wherein the wiring member is a flexible substrate on which wiring is formed, and from a connection part connected to the electrode part In the folded section Turned back After reversing Extending to the outside of the housing member Furthermore, the portion of the wiring member extending from the folded portion to the outside of the housing member extends in the opposite direction to the direction in which the wiring member moves from the connection portion to the folded portion. This will resolve the issue. In this way, by creating a diaphragm structure in which the strain generating body is integrated with a fixing part surrounding its periphery, it is possible to ensure structural strength and reduce the height of the load cell. Therefore, the problems that existed in conventional technology when miniaturizing load cells are resolved, and it becomes possible to provide an ultra-compact load cell of 5 mmφ or less that can measure high capacity (large load). In addition, because the wiring member, which is a flexible printed circuit board, is folded back and then inverted before being taken out of the housing member, when a load is applied to the force transmission member and the strain generating body moves up and down, the up and down movement is absorbed at the folded part of the wiring member. When miniaturizing a load cell, the area of ​​the connection point between the wiring member and the electrode part becomes smaller, making the wiring member more prone to peeling off the electrode part. However, because the wiring member, which is a flexible printed circuit board, is folded back, the peeling of the wiring member from the electrode part is suppressed. Furthermore, it is preferable that the second main surface of the strain generating body is further provided with a cover member that covers the opening of the housing member.

[0017] Furthermore, the aforementioned problem is solved by the load cell of the present invention, which comprises: an elastic strain-generating body; a force-transmitting member formed protruding from a first main surface of the strain-generating body and transmitting force to the strain-generating body; a fixing portion surrounding the peripheral edge of the strain-generating body so as to protrude toward the first main surface over its entire circumference; and a strain gauge portion made of a conductive member having an isotropic gauge ratio formed to extend circumferentially on a second main surface of the strain-generating body opposite to the first main surface, wherein the strain-generating body and the fixing portion are integrally formed, and the strain gauge portion is formed by the linear conductive member. ,beforeAn electrode portion is formed on the second main surface of the strain generating body and constitutes a strain detection circuit together with the strain gauge portion. The conductive member includes a first conductive member arranged to extend annularly at a position surrounding the force transmission member, and a second conductive member arranged to extend annularly at a position around the fixing portion. The electrode portion extends along the circumferential direction of the conductive member and is disposed between the first conductive member and the second conductive member in the radial direction of the conductive member, thereby solving the problem.

[0018] At this time, before A wiring portion connected to the electrode portion Material It is preferable to further include. In this way, by forming the electrode portion on the second main surface (back surface) of the strain generating body and connecting the wiring member, it becomes easier to lead out the wiring to the outside of the load cell.

[0019] At this time, The system further comprises a cylindrical housing member that covers the strain generating body, the fixing portion, and the strain gauge portion from the outside, The wiring member is a flexible substrate on which wiring is formed, and it is preferable that the wiring member is folded back from a connection portion connected to the electrode portion and extends to the outside of the housing member. In this way, the wiring member, which is a flexible printed circuit board, is folded back and taken out to the outside of the housing member after being once inverted. When a load is applied to the force transmission member and the strain generating body moves up and down, the up and down movement is absorbed at the folded portion of the wiring member. When miniaturizing the load cell, the area of the connection portion between the wiring member and the electrode portion becomes small, so the wiring member is likely to be peeled off from the electrode portion. However, since the wiring member, which is a flexible printed circuit board, is folded back, the wiring member is prevented from being peeled off from the electrode portion.

[0020] At this time, it is preferable that the electrode portion is formed on the second main surface of the strain generating body, between the force transmission member and the fixing portion, or on the back side of the force transmission member. In this way, by forming the electrode portion between the periphery of the force transmission member and the fixing portion, or on the back side of the force transmission member, where the + strain and - strain are maximum, it becomes possible to appropriately detect the load.

[0022] At this time, it is preferable that the conductive member is composed of a Cr-N thin film made of Cr, N, and inevitable impurities. When using existing strain gauges made of Cu-Ni or Ni-Cr alloys, their transverse sensitivity (sensitivity when the longitudinal direction of the sensing part, which is the direction in which the current for measurement flows, is arranged perpendicular to the strain direction) is very small. Therefore, in order to detect radial strain with a large amount of strain, it is necessary to use a radial arrangement using longitudinal sensitivity (sensitivity when the longitudinal direction of the sensing part, which is the direction in which the current for measurement flows, is arranged parallel to the strain direction). That is, it is necessary to arrange the longitudinal direction in which the current of the strain gauge flows along the radial direction, so it is required to secure a long radial strain region. For this reason, the width between the force transmission member and the fixing part of the diaphragm structure serving as the strain generating part must be widened, and thus it is difficult to miniaturize the diaphragm.

[0023] On the other hand, the Cr-N thin film, different from conventional strain gauge materials, has a transverse sensitivity as large as the longitudinal sensitivity, that is, it shows isotropic sensitivity (Japanese Patent Laid-Open No. 2014-35239). Therefore, even if the longitudinal direction in which the current flows in the circumferential direction (perpendicular to the radial direction) of the diaphragm is arranged, it is possible to detect radial strain using the transverse sensitivity. Moreover, it is possible to detect circumferential strain together with the longitudinal sensitivity. Therefore, when the Cr-N thin film is installed at a position where these strains have the same sign, it is possible to detect a larger strain amount obtained by adding the radial strain and the circumferential strain. By arranging a linear Cr-N thin film in a ring shape in the circumferential direction, it only occupies a very narrow region corresponding to the line width in the radial direction, so the strain region can be narrow, and it is possible to narrow the width between the force transmission member and the fixing part of the diaphragm structure serving as the strain generating part. Thus, it is possible to miniaturize the diaphragm (Japanese Patent Laid-Open No. 2020-153791).

[0024] Furthermore, with existing strain gauges made of Cu-Ni or Ni-Cr alloys, which have low sensitivity, resistance changes are difficult to obtain unless the amount of strain is large. Therefore, it was necessary to reduce the thickness between the force transmission member of the diaphragm structure, which is the strain-generating part, and the fixed part to generate the required resistance change. In contrast, since Cr-N thin films are highly sensitive (Japanese Patent Publication No. 2015-31633), even slight strain can cause a large change in resistance. This allows for an increase in the thickness between the force transmission member of the diaphragm structure, which is the strain-generating part, and the fixed part, thereby increasing the rigidity of the diaphragm and improving the strength of the structure, making it possible to provide a load cell that can withstand high stress and enable high load measurement.

[0025] In this case, it is preferable that the strain generating body is made of metal, the second main surface of the strain generating body is provided with an insulating layer, and the strain gauge portion is formed on the insulating layer. In this way, by applying an insulating layer to the metal strain-generating body and forming a strain gauge portion (conductive member) on top of it, the strain generated in the metal strain-generating body can be directly detected without the influence of the relatively soft adhesive layer present when using a bonded strain gauge, or the substrate which would be superfluous in transmitting the strain, thereby improving the accuracy of the load cell. [Effects of the Invention]

[0026] The load cell of the present invention utilizes a circumferential arrangement that takes advantage of the isotropic sensitivity of a Cr-N thin film, and by integrating the strain-generating body with a fixing part surrounding its periphery into a diaphragm structure, it is possible to achieve miniaturization and structural strength, while also reducing the height of the load cell. Therefore, the problems that existed in conventional technology when miniaturizing load cells are resolved, and it becomes possible to provide an ultra-compact load cell with an outer diameter of 5 mmφ or less and a height of 3 mm or less, capable of measuring high capacity (large load) over a wide range from 1 N to 400 N. [Brief explanation of the drawing]

[0027] [Figure 1] This is a schematic diagram showing the configuration of a load cell relating to one embodiment of the present invention. [Figure 2A] This is a perspective view of the diaphragm component of a load cell. [Figure 2B] This is a cross-sectional view AA of Figure 2A. [Figure 2C] This is a perspective view showing the back side of the diaphragm component. [Figure 3A] This is a perspective view of the housing and cover components of a load cell. [Figure 3B] This is a front view of the housing component. [Figure 3C] Figure 3B is a cross-sectional view of BB. [Figure 4] This is a cross-sectional view taken along line IV-IV in Figure 1. [Figure 5] This is a schematic diagram showing an example of the arrangement of the strain gauge and electrode sections on the back side of the diaphragm member. [Figure 6A] Figure 5 is a cross-sectional view of CC. [Figure 6B] This is a cross-sectional view of the electrode section (EE cross-section in Figure 5). [Figure 7A] This is a schematic diagram showing a flexible circuit board as a wiring component. [Figure 7B] This is a schematic diagram showing how a flexible substrate is connected to an electrode. [Figure 8] This is a schematic diagram illustrating the routing of a flexible circuit board. [Figure 9] This graph shows the structural analysis results, including the housing components. [Figure 10] This graph shows the results of the load application test. [Figure 11] This graph shows the results of a load application test, which involved 7 repetitions of load application ranging from 5N to 35N. [Figure 12] This is a graph plotting resistance values ​​against load. [Figure 13] This graph shows the results of load application tests up to 400N. [Modes for carrying out the invention]

[0028] Hereinafter, a load cell R according to one embodiment of the present invention will be described with reference to Figures 1 to 13.

[0029] In this embodiment, the load cell R is configured with a diaphragm member D, which serves as a strain detection unit, housed in a housing member H (Figure 1). For the purpose of describing the position and orientation of the components of the load cell R, the direction in which the force transmission member 13 protrudes from the strain generating body 10 will be referred to as the upper side (front side).

[0030] The diaphragm member D, which serves as the strain detection unit, comprises a strain generating body 10, a force transmission member 13 that transmits force to the strain generating body 10, a fixing part 14 that supports the peripheral edge of the strain generating body 10, a strain gauge part 20, and an electrode part 30 (Figures 2A and 2B).

[0031] The elastic strain-generating body 10 has an upper surface 11 (first main surface, front surface) and a lower surface 12 (second main surface, back surface). Specifically, the strain-generating body 10 has a thickness direction in the vertical direction, and is formed in a substantially disc shape with an upper surface 11 and a lower surface 12 that are perpendicular to the vertical direction as a pair of main surfaces. The thickness of the strain-generating body 10 may be uniform, or it may be non-uniform, such as when there are locally thinner regions.

[0032] The load cell R includes a substantially columnar force transmission member 13 that protrudes from the upper surface 11 of the strain generating body 10 in the central region of the strain generating body 10. Preferably, the force transmission member 13 is integrally formed with the strain generating body 10, but it is sufficient that it abuts against the strain generating body 10, and it may also be mechanically connected to the strain generating body 10 by a mechanical method such as a bolt-nut system.

[0033] The strain generating body 10 is provided with an annular fixing portion 14 that protrudes upward around its entire circumference. The fixing portion 14 is preferably formed to protrude from the upper surface 11 of the strain generating body 10 in the same direction as the force transmission member 13, that is, upward (towards the upper surface 11). Alternatively, the fixing portion 14 can be formed to protrude from the lower surface 12 of the strain generating body 10 in the opposite direction to the force transmission member 13, that is, downward. Furthermore, the fixing portion 14 can be formed to protrude both upward and downward from the strain generating body 10. The strain generating body 10 and the fixing portion 14 are integrally formed by machining or casting. In addition, the thickness of the strain generating body 10 (the diaphragm portion of the diaphragm member D) and the thickness of the fixing portion 14 on the outer circumference may be equal in the vertical direction.

[0034] The strain generating body 10 is supported by a fixing portion 14 at its peripheral edge and has a force transmission member 13 protruding from the upper surface 11. When a force is applied to the strain generating body 10 via the force transmission member 13, the strain generating body 10 is subjected to deformation.

[0035] The strain generating body 10 is made of, for example, an elastic metal or synthetic resin, or a combination thereof. If the strain generating body 10 is made of a conductive material such as a metal, its lower surface 12 is covered with an insulating thin film at least in the region where the strain gauge portion 20 and the electrode portion 30 are formed. This electrically insulates the strain generating body 10 from the strain gauge portion 20 and the electrode portion 30.

[0036] The strain gauge portion 20 has a conductive member 21 and is formed to extend circumferentially on the lower surface 12 (second main surface, back surface) of the strain generating body 10 (Figure 2C). The conductive member 21 is composed of a Cr thin film made of Cr and unavoidable impurities, which are materials having an isotropic gauge ratio, or a Cr-N thin film made of Cr, N and unavoidable impurities. The Cr-N thin film is, for example, made of Cr, which has the general formula Cr 100-x N x It is expressed as follows, and the composition ratio x is in atomic percent, where 0.0001 ≤ x ≤ 30. Cr-N thin films are stable to temperature changes because they have an extremely small temperature coefficient of resistance (TCR) (<±50 ppm / °C).

[0037] Furthermore, electrode portions 30 are provided at both ends of the conductive member 21, which together with the strain gauge portion 20 constitute a strain detection circuit. A flexible substrate F, which serves as a wiring member, is connected to these electrode portions 30. In the load cell R of this embodiment, the electrode portions 30 are formed on the lower surface 12 (second main surface, back surface) of the strain generating body 10, and by connecting the flexible substrate F (wiring member), it is easier to route the wiring to the outside of the load cell R.

[0038] In this embodiment, the load cell R is formed by integrating a strain-generating body 10, which has a strain gauge portion 20 formed on its lower surface 12 opposite to the force transmission member 13, with a fixing portion 14 surrounding its peripheral edge, into a diaphragm member D (diaphragm structure). This ensures structural strength and allows for a lower height of the load cell R. Therefore, the problems that existed in conventional technology when miniaturizing the load cell R are resolved, and an ultra-compact element of 5 mmφ or less that can measure high capacity (large load) can be realized.

[0039] (Housing component H) As shown in Figures 3A to 3C, the housing member H mainly consists of a cylindrical member 40 having an outer wall 41 and an inner wall 42. The cylindrical member 40 has a stepped portion 43a in its upper opening 43 for housing the diaphragm member D. The cylindrical member 40 has a notch 45 formed near its lower opening 44 to allow a flexible substrate F, which serves as a wiring member, to pass through. A cover member 46 is placed in the lower opening 44 of the cylindrical member 40.

[0040] A housing member H, which includes a cylindrical member 40, covers the strain generating body 10, the fixing part 14, and the strain gauge part 20 from the outside. In this way, by covering and supporting the diaphragm member D (diaphragm structure), which integrates the strain generating body 10 with the fixing part 14, with the cylindrical housing member H (Figure 4), deformation of the diaphragm structure is suppressed, and deformation of the entire structure when it returns to an unloaded state is suppressed. Note that the outer shape of the fixing part 14 and the housing member H is not limited to a cylindrical shape, but can be any shape such as a square, hexagon, or octagon.

[0041] Furthermore, by providing a cover member 46 that covers the lower opening 44 of the cylindrical member 40 on the lower surface 12 side of the strain generating body 10 on which the strain gauge portion 20 having a conductive member 21 is formed, the adhesion of dust and other debris to the strain gauge portion 20 in the measurement environment is suppressed, and the overall strength of the load cell R (element) is improved.

[0042] The specific configuration of the strain gauge section 20 and the electrode section 30 will be described below. As shown in Figure 5, five electrode sections 30 are formed on the lower surface 12 (second main surface, back surface) of the strain generating body 10, between the force transmission member 13 and the fixing section 14. By forming the electrode sections 30 in this way, between the periphery of the force transmission member 13 and the fixing section 14 (Figure 10, which will be described later), where the positive and negative strains are maximum, it becomes possible to appropriately detect the load. Note that the electrode sections 30 may also be formed near the center of the lower surface 12 of the strain generating body 10, that is, near the back side of the force transmission member 13.

[0043] Furthermore, the strain gauge section 20 is formed by linear conductive members 21, 22, 23, and 24. The conductive members 21 and 22 are arranged to extend in an annular shape around the force transmission member 13, and the conductive members 21 and 22 are also arranged to extend in an annular shape around the fixing portion 14. More specifically, the strain gauge section 20 is arranged on the lower surface 12 (second main surface, back surface) of the strain generating body 10 such that the conductive members 21, 22, 23, and 24 extend in an annular shape centered on the center of the strain generating body 10 at positions surrounding the force transmission member 13 (within a few mm of the force transmission member 13) and around the fixing portion 14 (within a few mm of the fixing portion 14), or at and around the position where the positive strain and negative strain generated in the diaphragm member D are at their maximum absolute values.

[0044] In this way, by placing linearly formed conductive members 21, 22, 23, and 24 at positions surrounding the force transmission member 13 and around the fixing part 14 where the positive and negative strains are maximum, it is possible to reduce the area occupied by the strain gauge section 20. Furthermore, by arranging the conductive members 21, 22, 23, and 24 to extend in an annular shape at positions surrounding the force transmission member 13 and around the fixing part 14 where the positive and negative strains are maximum, the strain gauge section 20 can be formed, thereby realizing an ultra-compact load cell R that can sense minute strains while maintaining high structural strength.

[0045] In this case, it is preferable that the conductive member is made of a Cr-N thin film consisting of Cr, N, and unavoidable impurities. Conventional strain gauges with low sensitivity have very low lateral sensitivity, so radial strain cannot be detected when they are extended in an annular shape (arranged in the circumferential direction), and only relatively small circumferential strains are detected with low sensitivity, making it difficult to produce a change in resistance value. For this reason, a folded pattern along the radial direction was used to detect radial strain and produce a detectable change in resistance value. By making the strain gauge portion 20 (conductive members 21, 22, 23, 24) an isotropic and highly sensitive Cr-N thin film and forming it to extend in an annular shape around the force transmission member 13 and around the fixing portion 14, it becomes possible to detect even slight strain in the line width direction. Furthermore, because Cr-N is highly sensitive, even slight strain can cause a large change in resistance. This allows for a larger thickness between the force transmission member 13 and the fixing part 14 in the diaphragm member D (diaphragm structure), which is the strain-generating part. This improves the strength of the structure and makes it possible to realize a load cell R that can withstand high stress.

[0046] As shown in Figure 6A, the strain-generating body 10 is mainly formed from a metal substrate 10a (for example, SUS304 or SUS316L), and an insulating film 10b (for example, an SiO2 film, about 3 μm thick) is formed on its lower surface 12 (second main surface). The strain gauge portion 20 is formed on the insulating film 10b. At this time, a protective film P (thickness 1 to 15 μm) made of polyimide resin or solder resist may be provided on the upper surface of the insulating film 10b, and on the upper and side surfaces of the conductive members 21, 22, 23, and 24.

[0047] As shown in Figure 6B, the electrode portion 30 is constructed by sequentially laminating the following on an insulating film 10b: Cr-N thin films 23a, 24a (thickness 50-500 nm), first metal thin films 23b, 24b made of Ti or Cr (thickness 30-50 nm), second metal thin films 23c, 24c made of Ni (thickness 150-250 nm), and third metal thin films 23d, 24d made of Au (thickness 50-100 nm). At this time, a protective film P (thickness 1-15 μm) made of polyimide resin or solder resist may be provided on the upper surface of the insulating film 10b and on the side surfaces of the electrode portion 30.

[0048] In this way, by forming the strain-generating body 10 by applying an insulating film 10b to a metal substrate 10a and directly forming the strain gauge portion 20 (conductive members 21, 22, 23, 24) on it, the strain generated in the metal can be directly detected without the influence of a relatively soft adhesive layer or a substrate that would be superfluous in transmitting the strain, thereby improving the accuracy of the load cell R.

[0049] The following describes the specific arrangement of the flexible substrate F as a wiring component. Figure 7A is a schematic diagram showing the flexible substrate F as a wiring component. Figure 7B is a schematic diagram showing the connection of the flexible substrate F to the electrode portion 30 on the lower surface 12 of the strain generating body 10. Figure 8 is a schematic diagram showing the routing of the flexible substrate F as a wiring component.

[0050] The flexible substrate F is a flexible printed circuit board, also known as an FPC (Flexible Printed Circuits). The flexible substrate F is made by chemically etching a copper-clad laminate, which is a thin plastic film such as polyimide with copper foil attached to it, to form the circuit. The connection part Fa of the flexible substrate F is connected to the electrode part 30 via an anisotropic conductive film (ACF).

[0051] The flexible substrate F, on which five wires are formed, is folded back at the folding portion Fb from the connection portion Fa connected to the five electrode portions 30 (electrode pads), extends from the notch 45 to the outside of the cylindrical member 40 (housing member H), and is connected to the 5-pin FPC connector. When the flexible substrate F, as a wiring member, is folded back and then reversed before being taken out to the outside of the housing member H, the vertical movement is absorbed at the folding portion Fb when a load is applied to the force transmission member 13 and the strain generating body 10 moves up and down.

[0052] When the load cell R is miniaturized, the area of ​​the connection part Fa, which is the connection point between the flexible substrate F (wiring material) and the electrode part 30, becomes smaller, making it easier for the flexible substrate F (wiring material) to peel off from the electrode part 30. In the load cell R of this embodiment, the wiring material, which is the flexible substrate F (wiring material), is folded back at the folded part Fb, which suppresses peeling off from the electrode part 30. [Examples]

[0053] Figure 9 shows the results of a structural analysis including the housing member H (outer diameter 4.6 mmφ) (strain-generating body 10: outer diameter 4 mmφ). Based on the results of the structural analysis, two annular sensor films R-1, R-2, R-3, and R-4 (conductive members) were placed in the circumferential direction at the positive and negative strain positions, respectively, at the radial positions (vertical lines) shown in Figure 9.

[0054] A load cell was fabricated consisting of a strain-generating body (outer diameter 4 mmφ) and a housing member (outer diameter 4.6 mmφ) of the aforementioned dimensions, and conductive members and wiring members arranged in the aforementioned positions and configurations. A load application test was then performed on the load cell using a mechanical testing machine and a resistance measuring device. The load application was performed by first applying a load up to 5 N, then returning to zero load, then adding another 5 N to reach 10 N, and so on, increasing the maximum load by 5 N increments until the measurement reached 35 N.

[0055] The change in resistance value of each of the annular sensor films R-1, R-2, R-3, and R-4 (conductive members) was measured. The results of the load application test for R-4 are shown in Figures 10 to 12. As can be seen from the figures, a clear output signal was stably obtained with the load cell of the present invention, and the results showed good linearity and no hysteresis up to 35N, indicating that it is possible to detect loads of 10N or more without problems, which could not be detected with the aforementioned small-sized load cell. Similarly, the results of measurements up to a maximum load of 400N are shown in Figure 13. As shown in the figure, it was found that an output signal approximately proportional to the load was obtained. In other words, with the load cell R of the present invention, even when the outer diameter of the strain-generating body is miniaturized to 4mmφ, it is possible to detect a wide load range up to 400N.

[0056] Therefore, it has become clear that the present invention is a valuable technology that solves the fundamental and difficult-to-solve problem with conventional load cells: miniaturization itself is difficult, and attempting to miniaturize them also reduces the measurable stress (load). The present invention makes it possible to provide load cells that are even smaller and capable of detecting even larger loads. [Industrial applicability]

[0057] The load cell of the present invention can be used to measure loads and stresses in environments where miniaturization is required, such as extremely small spaces and narrow gaps. Conventional technology measures loads for the entire element, but the load cell of the present invention makes it possible to measure loads in fine areas, so it can be applied to situations where it is necessary to measure loads in narrow regions and various mechanical quantities and their distributions based on them. For example, using the load cell of the present invention makes it possible to measure the shape, properties and distribution of the surface and interior of various processed products including cloth, walls, living organisms (skin and mammography of breasts), and flexible materials (measurement of microstructure, small irregularities and hardness / softness), to perform pressure response testing of touch points of push input devices, touch sensors and touch pen input devices (measurement with high positional resolution), and to measure stress and its distribution at target contact points of gripping devices such as robot hands and similar devices (wide-range measurement that can handle impact and overload). [Explanation of Symbols]

[0058] R load cell D Diaphragm member (strain detection unit) 10 Strain body 10a substrate 10b Insulating film (insulating layer) 11 Top surface (first principal surface, surface) 12 Bottom surface (2nd main surface, back surface) 13 Force transmission member 14 Outer fixed part (fixed part) 20 Strain gauge section 21, 22, 23, 24 Conductive members 23a,24a Cr-N thin film (100~500nm) 23b, 24b First metal thin film, Ti or Cr (30~50 nm) 23c,24c Second metal thin film, Ni (150~250nm) 23d,24d Third metal thin film, Au (50~100nm) P protective film 30 Electrode section (conducting wire member) H Housing component 40 Cylindrical Member 41 Exterior Wall 42 Inner wall 43 Upper opening 43a Stepped section 44 Lower opening 45 Notches 46 Cover component F Flexible circuit board (wiring material) Fa connection (ACF) Fb Folded section

Claims

1. An elastic strain-generating body, A force transmission member is formed protruding from the first main surface of the strain generating body and transmits force to the strain generating body, A fixing portion surrounds the peripheral edge of the strain generating body so as to protrude towards the first main surface side over its entire circumference, The strain gauge portion comprises a conductive member having an isotropic gauge ratio formed on the second main surface opposite to the first main surface of the strain generating body so as to extend circumferentially, The strain-generating body and the fixing portion are integrally formed, The system further comprises a cylindrical housing member that covers the strain generating body, the fixing portion, and the strain gauge portion from the outside, An electrode portion formed on the second main surface of the strain generating body, which together with the strain gauge portion constitutes a strain detection circuit, The system further comprises a wiring member connected to the electrode portion, The wiring member is a flexible substrate on which wiring is formed, extending from the connection portion connected to the electrode portion, through a folded portion, and then inverted to the outside of the housing member. A load cell characterized in that the portion of the wiring member extending from the folded portion to the outside of the housing member extends in the opposite direction to the direction in which the wiring member moves from the connection portion to the folded portion.

2. An elastic strain-generating body, A force transmission member is formed protruding from the first main surface of the strain generating body and transmits force to the strain generating body, A fixing portion surrounds the peripheral edge of the strain generating body so as to protrude towards the first main surface side over its entire circumference, The strain gauge portion comprises a conductive member having an isotropic gauge ratio formed on the second main surface opposite to the first main surface of the strain generating body so as to extend circumferentially, The strain-generating body and the fixing portion are integrally formed, The strain gauge portion is formed by the linear conductive member, The strain-generating body is provided with an electrode portion formed on the second main surface and, together with the strain gauge portion, constitutes a strain detection circuit, The conductive member comprises a first conductive member arranged to extend in an annular shape at a position surrounding the force transmission member, and a second conductive member arranged to extend in an annular shape at a position around the fixing portion. The load cell is characterized in that the electrode portion extends along the circumferential direction of the conductive member and is positioned between the first conductive member and the second conductive member in the radial direction of the conductive member.

3. The load cell according to claim 1, further comprising a cover member that covers the opening of the housing member on the side of the second main surface of the strain generating body.

4. The load cell according to claim 2, further comprising a wiring member connected to the electrode portion.

5. The invention further comprises a cylindrical housing member that covers the strain generating body, the fixing portion, and the strain gauge portion from the outside, The load cell according to claim 4, characterized in that the wiring member is a flexible substrate on which wiring is formed, and is folded back from the connection portion connected to the electrode portion and extends to the outside of the housing member.

6. The load cell according to claim 4 or 5, characterized in that the electrode portion is formed on the second main surface of the strain-generating body between the force transmission member and the fixing portion, or on the back side of the force transmission member.

7. The load cell according to claim 1 or 2, characterized in that the conductive member is composed of a Cr-N thin film made of Cr, N and unavoidable impurities.

8. The strain-generating body is made of metal, The second main surface of the strain-generating body is provided with an insulating layer. The load cell according to any one of claims 1 to 7, characterized in that the strain gauge portion is formed on the insulating layer.

Images