JP2018141538A - Fastening bolt device for detecting axial force - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection sensitivity without deteriorating stability and reliability of detection as much as possible, in a fastening bolt device for detecting axial force.SOLUTION: A fastening bolt 3 has a head part 21 with a recessed part 31. An inclined surface 37 inclined relative to a central axis 39 is provided at an inside surface of a peripheral wall 44 of the recessed part 31. Two strain gauges 47 are fixedly attached in two positions corresponding to the minimum thickness part of the peripheral wall 44 while mutually facing on the inclined surface 37. Each of the strain gauges 47 responds to strain in an inclination direction or circumferential direction of the inclined surface 37.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fastening bolt device for detecting an axial force of a fastening bolt, that is, a fastening force.

  An apparatus having a fastening bolt and a circuit for automatically measuring a force applied to a shaft portion of the bolt is known. Such a fastening bolt device is useful for grasping the state of a machine or facility and realizing timely and accurate maintenance.

  An apparatus disclosed in Patent Document 1 includes a fastening bolt having a head and a shaft, a cylindrical cavity formed in the shaft of the bolt along the central axis, and a strain gauge bonded to the inner surface of the cavity. And a detection circuit for measuring the axial force from the electrical resistance of the strain gauge.

  An apparatus disclosed in Patent Document 2 includes a fastening bolt having a head portion and a shaft portion, a strain gauge attached to the outer surface of the head portion of the bolt, and a detector that detects an axial force from the electrical resistance of the strain gauge. And have.

  The device disclosed in Patent Document 3 includes a fastening bolt having a head portion and a shaft portion, a concave portion provided in the head portion of the bolt, a strain sensor attached in the concave portion, and an electric resistance of the strain sensor. And a circuit for detecting looseness of the bolt. The strain sensor is disposed on a gap formed at the bottom of the recess, and the center thereof is floating from the bottom of the recess.

The device disclosed in Patent Document 4 includes a fastening bolt having a head portion and a shaft portion, a concave portion provided in the head portion of the bolt, a strain gauge bonded to the inner bottom surface of the concave portion, and the strain gauge. And a circuit for measuring axial force from electric resistance.

JP 2010-185809 A JP 2010-53927 A Japanese Patent Laid-Open No. 2002-236064 International Publication No. WO 2015/075823

  In the configuration in which the strain gauge is provided in the cavity formed in the shaft portion as described in Patent Document 1, the deformation of the shaft portion due to the axial force is directly reflected in the deformation of the strain gauge. On the other hand, in the configuration in which the strain gauge is provided on the head as described in Patent Literature 2-4, the deformation of the head is reflected in the deformation of the strain gauge, not the deformation of the shaft portion. Therefore, it is considered that the former configuration will have a larger deformation amount of the strain gauge under the same axial force than the latter configuration, and therefore the detection sensitivity will be better.

  However, from the viewpoint of the fastening performance of the bolt, in which a larger fastening force is obtained with the bolt of the same size, the configuration described in Patent Literature 2-4 is provided from the configuration in which a hollow is provided in the shaft portion as described in Patent Literature 1. Thus, it can be said that the configuration without the cavity in the shaft portion is superior.

  Next, when the configuration described in Patent Document 2-4 is compared, the configuration described in Patent Document 3 or 4 is based on the configuration in which a strain gauge is arranged on the outer surface of the head as described in Patent Document 2. The configuration in which the strain gauge is disposed in the concave portion of the portion is superior in the function of protecting the strain gauge from collision with an external object, erosion and corrosion due to wind and rain, and the like.

  Furthermore, when the configurations described in Patent Documents 3 and 4 are compared, the latter is superior to the former in the practically important performances of detection stability and reliability.

  That is, in the configuration of Patent Document 3, the strain sensor is arranged in a state of floating from the bottom surface of the recess through the gap. Such a configuration is presumably devised for the purpose of increasing the detection sensitivity by increasing the deformation amount of the strain gauge. However, as a side effect, the strain sensor itself may be deformed without depending on the deformation of the bolt head, and erroneous detection may occur. For example, when a bolt vibrates, the strain sensor itself vibrates due to inertial force and deforms unnecessarily. In addition, when an external force is applied from the upper opening side of the recess due to a change in external air pressure or contact with an external foreign object, the strain sensor itself is deformed by the external force.

  On the other hand, in the configuration of Patent Document 4, since the strain sensor is fixed to the bottom surface of the concave portion of the head and the strain sensor is deformed only by deformation of the head, detection is highly stable and reliable. .

  However, in the configuration of Patent Document 4, it is difficult to obtain detection sensitivity as high as the configuration described in Patent Document 1. This is because the deformation amount of the bottom surface of the concave portion of the head under the same axial force is smaller than the deformation amount of the shaft portion.

  An object of the present invention is to increase the detection sensitivity of an axial force while maintaining the fastening performance and the stability and reliability of axial force detection as much as possible in a fastening bolt that detects the axial force.

  A fastening bolt device according to an embodiment of the present invention includes a fastening bolt having a head portion and a shaft portion, and one or more stress sensors that are used to detect axial force of the fastening bolt and respond to stress or strain generated in the head portion. With. The head has a recess recessed downward from an upper surface thereof, and an annular peripheral wall surrounding the recess. The peripheral wall has an inclined surface that faces the concave portion and is inclined with respect to the central axis of the shaft portion on the inner side surface thereof. One or more stress sensors are disposed on the inclined surface and configured to respond to stress or strain on the inclined surface.

  According to this fastening bolt device, the stress sensor is disposed on the inclined surface provided on the inner surface of the peripheral wall surrounding the concave portion of the head. From the stress analysis of the fastening bolt conducted by the inventors, it was found that a relatively large level of stress is generated on the inclined surface when an axial force is applied to the fastening bolt. Therefore, providing a stress sensor on the inclined surface is effective in obtaining good detection sensitivity.

  At least one of the one or more stress sensors may be disposed at an angular position θ corresponding to a location where the radial thickness of the peripheral wall is minimum. For example, in the case of a bolt having a hexagonal head, within the range of the angle position θ of “θ = 30 degrees × odd number” ± 10 degrees with the origin of the outer surface of the hexagonal head as the origin, more desirably ± 5 At least one stress sensor may be disposed within the range of the angular position θ of degrees. Since such an angular position θ on the inclined surface generates a larger stress than other angular positions θ, it is effective to arrange a stress sensor at that position.

  Two stress sensors may be arranged on the inclined surface. The two stress sensors may be arranged in an axially symmetric positional relationship with respect to the central axis.

  Both of the two stress sensors may be tilt direction stress sensors that respond to the stress in the tilt direction of the tilted surface. Alternatively, both of the two stress sensors may be circumferential stress sensors that respond to the circumferential stress on the inclined surface. Alternatively, one of the two stress sensors may be a tilt direction stress sensor and the other may be a circumferential stress sensor.

  When two stress sensors are used, the measurement circuit can be configured such that the absolute values of the response values of the two stress sensors are added and reflected in the output value of the axial force detection.

  Furthermore, you may arrange | position four stress sensors on an inclined surface. The measurement circuit can be configured such that the absolute values of the response values of the four stress sensors are added and reflected in the output value of the axial force detection.

  The fastening bolt device can further include an electronic device electrically connected to the stress sensor, and a protective container in which at least a part of the electronic device is accommodated. And a protective container may be combined with a head and it may be constituted so that the upper end opening of the crevice of a head may be plugged up watertight.

  A fastening bolt device according to another embodiment of the present invention includes a fastening bolt having a head portion and a shaft portion, and one or more stresses that are used to detect an axial force of the fastening bolt and respond to stress or strain generated in the head portion. A sensor. The head has a recess recessed downward from an upper surface thereof, and an annular peripheral wall surrounding the recess. The peripheral wall has a vertical surface on its inner surface that faces the recess and is parallel to the central axis of the shaft portion. One or more stress sensors are then disposed on the vertical surface and configured to respond to stress or strain on the vertical surface.

  According to the fastening bolt stress analysis conducted by the inventors, when an axial force is applied to the fastening bolt, a relatively large level of stress (particularly, axial stress parallel to the central axis) is generated on the vertical surface. It turns out that there is a possibility. Therefore, it can be said that providing a stress sensor on the vertical surface (in particular, an axial stress sensor that mainly responds to axial stress) is effective in obtaining good detection sensitivity.

The exploded view which shows the cross-section structural example of the volt | bolt of the fastening bolt apparatus which concerns on the 1st Embodiment of this invention, and the structural example of a detection apparatus. The top view of the bolt head which shows the example of arrangement | positioning of the strain gauge in the fastening bolt apparatus which concerns on 1st Embodiment. The circuit diagram which shows the structural example of the Wheatstone bridge using the two strain gauges in the fastening bolt which concerns on 1st Embodiment. Stress distribution diagram showing the magnitude of the stress generated in various parts of the cross section along the central axis of the fastening bolt according to the first embodiment, obtained by stress analysis using finite element analysis software, in five levels. . The figure which shows the dimensional condition of the volt | bolt employ | adopted by the same stress analysis. The stress distribution diagram which showed the magnitude | size of the stress of the circumferential direction which arises in the inclined surface of the fastening bolt based on 1st Embodiment obtained by the same stress analysis as a function of angle position (theta). The stress distribution diagram which showed the magnitude | size of the stress of the inclination direction which arises in the inclined surface of the fastening bolt based on 1st Embodiment obtained by the same stress analysis as a function of angle position (theta). The top view of the bolt head which shows the example of arrangement | positioning of a strain gauge in the fastening bolt apparatus which concerns on the 2nd Embodiment of this invention. The circuit diagram which shows the structural example of the Wheatstone bridge using the two strain gauges in the fastening bolt which concerns on 2nd Embodiment. The top view of the bolt head which shows the example of arrangement | positioning of the strain gauge in the fastening bolt apparatus which concerns on the 3rd Embodiment of this invention. The circuit diagram which shows the structural example of the Wheatstone bridge using the two strain gauges in the fastening bolt which concerns on 3rd Embodiment. The top view of the bolt head which shows the example of arrangement | positioning of a strain gauge in the fastening bolt apparatus which concerns on the 4th Embodiment of this invention. The circuit diagram which shows the structural example of the Wheatstone bridge using the four strain gauges in the fastening volt | bolt which concerns on 4th Embodiment. The top view of the bolt head which shows the example of arrangement | positioning of a strain gauge in the fastening bolt apparatus which concerns on the 5th Embodiment of this invention. The top view of the bolt head which shows the example of arrangement | positioning of a strain gauge in the fastening bolt apparatus which concerns on the 6th Embodiment of this invention. The figure which shows the result of having analyzed how the stress state of an inclined surface changes according to the diameter D of the bottom face of a recessed part obtained by the stress analysis using a finite element analysis software. Sectional drawing along the center axis | shaft of a volt | bolt in the fastening bolt apparatus which concerns on the 7th Embodiment of this invention. FIG. 20 is a cross-sectional view along the central axis of a bolt in a fastening bolt device according to an eighth embodiment of the present invention. FIG. 20 is a cross-sectional view along the central axis of a bolt in a fastening bolt device according to a ninth embodiment of the present invention. FIG. 16 is a cross-sectional view along the central axis of a bolt in a fastening bolt device according to a tenth embodiment of the present invention. FIG. 25 is a cross-sectional view along the central axis of the bolt in the fastening bolt device according to the eleventh embodiment of the present invention.

  Hereinafter, some embodiments of the present invention will be described with reference to the drawings.

  In any of the embodiments introduced below, as a stress sensor for detecting the stress (or strain) generated in the fastening bolt, a resistance strain gauge (in which electric resistance changes according to the stress (or strain)) ( Hereinafter, it is referred to as “strain gauge”, but this is merely an illustrative example, and is not intended to limit the use of other types of stress sensors. In any of the embodiments, a screw bolt having a hexagonal head and a washer part integrated with the head is used as the fastening bolt, but this is merely an example for explanation, and other types of fastening are used. It is not intended to limit the use of bolts.

  FIG. 1 shows a structural example of a fastening bolt device according to a first embodiment of the present invention.

  As shown in FIG. 1, the fastening bolt device 1 includes a fastening bolt 3 (hereinafter referred to as “bolt”) and a detection device 5. The detection device 5 includes a hollow protective container 7 made of a sufficiently strong non-conductive material such as a certain synthetic resin and having an opening at the lower end, and an electronic device 9 accommodated in the protective container 7. As shown in the drawing, a part of the electronic device 9 may protrude from the lower end opening of the protective container 7, or the entire electronic device 9 may be accommodated in the protective container 7. The protective container 7 containing the electronic device 9 is coupled to the head 21 of the bolt 3 by, for example, screwing.

  The gap between the electronic device 9 in the protective container 7 and the inner surface of the protective container 7 is filled or cross-linked with a flexible material having vibration absorption performance such as silicon rubber, so that the electronic device 9 is protected. 7 is protected from mechanical shock or vibration applied from the outside.

  The electronic device 9 includes a measurement circuit (not shown) for measuring the axial force of the bolt 3, a storage circuit (not shown) for storing measured axial force data, and axial force data stored in the storage circuit. And a power supply circuit (not shown) for obtaining power from the outside and supplying power to each of the above circuits. The measurement circuit described above is electrically connected to two strain gauges 47 attached to the bolt 3 described later, for example, by an electric wire 49.

  The protective container 7 has a cylindrical coupling cylinder 11 for coupling with the head 21 of the bolt 3 around the opening at the lower end thereof. The coupling cylinder 11 has a male screw on its outer peripheral surface, and this male screw is screwed together with a female screw on a coupling surface 33 of the head 21 of the bolt 3 to be described later. An O-ring 13 is fitted on the outer periphery of the coupling cylinder 11. When the bolt 3 and the protective container 7 are coupled, the O-ring 13 seals the boundary between the two in a watertight manner.

  The bolt 3 has a substantially regular hexagonal columnar head (so-called “hexagonal head”) 21 and a long cylindrical shaft portion 23 extending downward from the head 21. Further, a circular washer 25 is integrally formed at the lower end of the head 21. A portion where the washer portion 25 and the shaft portion 23 are connected is referred to as a neck portion 27 in this specification.

  The head 21 of the bolt 3 has a recess 31 that is recessed downward from the upper surface thereof. The recess 31 can be formed by forging or cutting, for example.

  The recess 31 is surrounded by an annular peripheral wall 44 of the head 21. The inner side surface of the peripheral wall 44 facing the recess 31 has a coupling surface 33 near the upper end opening and an inclined surface 35 below the coupling surface 33. In the present specification, of the peripheral walls 44, the wall having the coupling surface 33 is referred to as a coupling wall 41, and the wall having the inclined surface 37 is referred to as an inclined wall 43.

  The lower end of the recess 31 is closed by the low wall 45 of the head 21. The low wall 45 has a bottom surface 35 that faces the recess 31.

  The coupling surface 33 is a surface for closely coupling with the coupling cylinder 11 of the protective container 7. The coupling surface 33 is, for example, an annular surface, in which a female screw is formed, and the female screw is screwed with the male screw of the coupling cylinder 11 of the protective container 7. As a result, the recess 31 and the inner space of the protective container 7 are hermetically sealed, and the surfaces 35 and 37 defining the inner space and the objects 9 and 47 accommodated in the inner space are connected to the outside air, wind and rain, or foreign matter. Isolated and protected from.

  The inclined surface 37 is, for example, an annular surface that is inclined with respect to the central axis 39 at an angle greater than 0 degree and less than 90 degrees. The bottom surface 35 is a circular plane perpendicular to the central axis 39, for example.

  For example, two strain gauges 47 are closely attached to the surface of the inclined surface 37 of the head 21. As each strain gauge 47, a commercially available general thin plate-shaped strain gauge having an insulating substrate film and a resistive metal pattern provided on the film can be adopted. In this case, the strain gauge 47 is firmly fixed to the inclined surface 37 by, for example, an adhesive on the entire surface of one side thereof.

  Alternatively, as each strain gauge 47, for example, a strain gauge formed directly on the surface of the inclined surface 37 by a printing method (that is, closely adhered) and having an insulating layer and a resistive metal pattern layer is adopted. Also good. In that case, when high temperature treatment is required in the formation process of each layer, the influence of heat on the metal crystal of the bolt 3 can be suppressed by selectively treating only each layer with a laser beam, for example.

  Each of the two strain gauges 47 is configured such that its electrical resistance changes mainly in response to stress (that is, strain) in the direction of inclination of the inclined surface 37 (that is, radial direction in plan view). This can be realized by matching the direction of the metal pattern of each strain gauge 47 with the direction of the inclined direction of the inclined surface 37.

  The two strain gauges 47 are electrically connected to a measurement circuit (not shown) in the electronic device 9 by, for example, an electric wire 49 to constitute a Wheatstone bridge circuit to be described later. The bridge circuit generates an output voltage having a value corresponding to a stress (strain) mainly in the radial direction of the inclined surface 37. From the output voltage, the axial force of the bolt 3 is measured.

  The fastening bolt device 1 is configured by coupling the detection device 5 and the bolt 3 described above. The fastening bolt device 1 operates by obtaining driving power from an external device (not shown), for example, by a non-contact power feeding method, measures the axial force of the bolt 3, and uses the measured axial force data as, for example, It transmits to the external device by wireless communication.

  FIG. 2 is a plan view of the bolt head showing an arrangement example of the strain gauges 47 in the first embodiment.

  As shown in FIG. 2, the two strain gauges 47 are respectively disposed at two positions on the inclined surface 37 that are in axial symmetry with respect to the central axis 39 of the shaft portion 23.

  Further, as shown in FIG. 2, each strain gauge 47 is used by using the angular position θ around the central axis 39 with the apex ridge 51 of the outer surface of the polygonal column (for example, hexagonal column) head 21 as the origin. In other words, the angular position of each strain gauge 47 (particularly the position of its center line) corresponds to “θ = 30 degrees × odd number”. That is, each strain gauge 47 (its center line) is arranged at a position of θ = 30 degrees, 90 degrees, 150 degrees 180 degrees, 210 degrees, 270 degrees, or 330 degrees. In the illustrated example, the angular positions of the two strain gauges 47 are θ = 30 degrees and 210 degrees, which are in an axially symmetric relationship.

  Such an angular position θ of each strain gauge 47 can be said to be a position corresponding to the center of one of the straight planes 53 on the outer surface of the head 21. Alternatively, it can be said that the angular position θ of each strain gauge 47 corresponds to the position where the thickness in the radial direction of the peripheral walls 44 (41, 43) surrounding the recess 31 of the head 21 is the smallest (thinnest). Such selection of the angular position of the strain gauge 47 is effective for obtaining as high a detection sensitivity as possible, as will be described later.

  FIG. 3 is a circuit diagram showing a configuration example of a Wheatstone bridge using two strain gauges 47 in the first embodiment.

  The example shown in FIG. 3 is commonly referred to as the opposite side 2 active gauge method. That is, two strain gauges 47 are wired on two opposite sides of the bridge. Two fixed resistors 61 are wired on the other two opposite sides. When the resistance value of each strain gauge 47 is Rg1, and the resistance value of each fixed resistor 61 is R, the output voltage Vout is as follows.

  Vout = (Vin ・ Ks ・ ε1) / 2

Here, Vin is an input voltage, Ks is a gauge factor, and ε1 is a response value to the strain of each strain gauge 47 (change rate of the length (resistance value Rg1) of the metal pattern).

  In this circuit example, when the shaft portion 23 of the bolt 3 is slightly tilted to the right or left from the head 21 (for example, when the upper surface and the lower surface of the member to be fastened are not parallel), it depends on the inclination of the shaft portion 23. The stress imbalance of the inclined surface 37 of the head 21 can be compensated by the difference in resistance value between the two strain gauges 47.

  Further, by wiring the two strain gauges 47 that respond to the stress in the tilt direction to the opposite sides of the bridge, the absolute values of the response values of the two strain gauges 47 are added together and reflected in the output voltage Vout. Thereby, better detection sensitivity can be obtained as compared with the case where only one strain gauge described below is used.

  In the first embodiment described above, two strain gauges 47 are used. However, it is possible to omit one of them and use only one strain gauge 47. In that case, one of the two strain gauges 47 in the bridge circuit shown in FIG. 3 is replaced with a fixed resistor. In this case, the output voltage Vout is, for example, as follows.

  Vout = (Vin ・ Ks ・ ε1) / 4

  Therefore, the sensitivity is lower than that of the circuit example using the two strain gauges 47 shown in FIG. 3, but there is an advantage that only one strain gauge 47 needs to be used.

  FIG. 4 shows the distribution of the magnitude of the stress generated in the cross-sectional areas along the central axis of the bolt 3 having the configuration shown in FIG. 1 at five levels (the greater the level number, the greater the stress).

  The stress distribution shown in FIG. 4 is obtained by stress analysis using the finite element analysis software “ABAQUS”. FIG. 5 shows specific dimensional conditions of the bolt 3 used in the stress analysis, and the numbers in the figure are dimensional values in millimeters.

  In this stress analysis, as shown in FIG. 4, the shaft portion 23 of the bolt 3 is inserted into the vertical hole of the fastened member (cuboid block) 63 under the dimensional conditions shown in FIG. A tensile axial force of 120 kN was applied to the tip of the wire. As material characteristics of the bolt 3, the Young's modulus was set to 206 kN / mm2, and the Poisson's ratio was set to 0.29. A thin plate shell element for stress evaluation as shown in FIG. 5 (hatched portion (in FIG. 5, the thickness is shown enlarged for the sake of clarity)) is pasted on the inclined surface of the bolt head. It was.

  As shown in FIG. 4, a moderate level 3 stress is generated in the upper thick portion 23A of the shaft portion 23 of the bolt 3, and a larger level 4 is present in the lower screw diameter portion 23A. This causes stress. Also, the stress on the inclined surface 37 of the head portion 21 is approximately the same as or close to that of the screw lower diameter portion 23A, that is, a level 4 stress. Incidentally, the portion where the highest level 5 stress is generated is in the vicinity of the outer surface of the neck portion 27.

  On the other hand, the stress generated in the region near the outer periphery of the coupling wall 41 and the inclined wall 43 of the head 21, the low wall 45, the washer 25, and the region near the central axis of the neck 27 is a relatively small level 2. Or it turned out to be level 1.

  Therefore, measuring the stress (strain) of the inclined surface 37 with the configuration shown in FIG. 1 is the same as measuring the stress (strain) of the shaft portion 23 (especially the screw lower diameter portion 23A) or It is possible to obtain detection sensitivity close to that.

  6 and 7 show the magnitude of the stress in the circumferential direction and the tilt direction generated on the inclined surface 37 of the bolt 3, respectively, as a function of the angular position θ. The results of FIGS. 6 and 7 are also the stress values obtained by the stress evaluation shell element (hatched portion) as a result of performing the stress analysis under the conditions described above with reference to FIG. The angular position θ in FIGS. 6 and 7 is an angular position around the central axis 39 with the vertex 51 of the outer surface of the head 21 as the origin, as shown in FIG.

  As shown in FIG. 6, stress having a negative polarity, that is, compressive stress is generated in the circumferential direction of the inclined surface 37. On the other hand, as shown in FIG. 7, stress having a positive polarity, that is, tensile stress is generated in the direction of inclination of the inclined surface 37.

  Both the circumferential and radial stresses vary according to the angular position θ. Both the circumferential stress and the radial stress are maximized at the angular position θ corresponding to “θ = 30 degrees × odd number” and minimized at the angular position θ corresponding to “θ = 30 degrees × even number”. Become.

  Therefore, as shown in FIG. 1, the arrangement of each strain gauge 47 (its center line) at the angular position θ corresponding to “θ = 30 degrees × odd number” is effective for obtaining high detection sensitivity. It is.

  Further, as can be seen from FIG. 6 and FIG. 7, both the circumferential stress and the tilt stress are within the fluctuation range of ± 10 degrees around the angle position θ of “θ = 30 degrees × odd number”. Among them, a stress that falls within about 30% can be obtained, and in the same range of ± 5 degrees, a stress that falls within about 10% in the vicinity of the maximum value can be obtained.

  Therefore, the arrangement of the strain gauges 47 (it is practically difficult to make “θ = 30 degrees × odd number” strictly) an angle of ± 10 degrees centered on the angle position θ of “θ = 30 degrees × odd number” It is desirable to be within the position range, and it is even more desirable to be within the angular position range of ± 5 degrees.

  Based on the above knowledge, there may be various variations in the arrangement of the strain gauges 47 in addition to the arrangement shown in FIG. Some of these variations will be described below as second to sixth embodiments.

  FIG. 8 is a plan view of a bolt head showing an example of arrangement of strain gauges in the fastening bolt device according to the second embodiment of the present invention.

  The main difference from the first embodiment shown in FIG. 1 in the second embodiment shown in FIG. 8 is that two circumferential strain gauges 71 responding mainly to circumferential stress on the inclined surface 37. Is used. That is, the two circumferential strain gauges 71 are arranged on the inclined surface 37 with the orientation of the metal pattern along the circumferential direction of the inclined surface 37.

  The angular position θ of each of the two circumferential strain gauges 71 corresponds to “θ = 30 degrees × odd number” (for example, within a range of ± 5 degrees centered on “θ = 30 degrees × odd number”), and More preferably, they are in an axially symmetric positional relationship with respect to the central axis 39 (see FIG. 1) of the shaft portion 23.

  Regarding other configurations, the second embodiment is basically the same as the first embodiment except for the Wheatstone bridge configuration described below.

  FIG. 9 shows a configuration example of the Wheatstone bridge in the second embodiment.

  As shown in FIG. 9, two circumferential strain gauges 71 are wired on two opposite sides of the bridge. Two fixed resistors 61 are wired on the other two opposite sides. When the resistance value of each strain gauge 71 is Rg2, and the resistance value of each fixed resistor 61 is R, the output voltage Vout is as follows.

  Vout = (Vin ・ Ks ・ ε2) / 2

Here, Vin is an input voltage, Ks is a gauge factor, and ε2 is a response value to the strain of each strain gauge 71 (the rate of change of the length (resistance value Rg2) of the metal pattern).

  FIG. 10 is a plan view of a bolt head showing an arrangement example of strain gauges in the fastening bolt device according to the third embodiment of the present invention.

  The main difference from the first embodiment shown in FIG. 1 in the third embodiment shown in FIG. 10 is that the inclined strain gauge 47 responds mainly to the stress in the inclined direction of the inclined surface 37, and The inclined surface 37 is mainly used in combination with a circumferential strain gauge 71 that responds mainly to circumferential stress. The tilt direction strain gauge 47 is disposed on the tilted surface 37 with the orientation of the metal pattern along the tilt direction of the tilted surface 37. On the other hand, the circumferential strain gauge 71 is disposed on the inclined surface 37 with the orientation of the metal pattern along the circumferential direction of the inclined surface 37.

  Each angular position θ of the strain gauges 47 and 71 corresponds to “θ = 30 degrees × odd number” (for example, within a range of ± 5 degrees centered on “θ = 30 degrees × odd number”), and Desirably, they are in an axially symmetric positional relationship with respect to the central axis 39 (see FIG. 1) of the shaft portion 23.

  With respect to other configurations, the third embodiment is basically the same as the first embodiment except for the configuration of the Wheatstone bridge described below.

  FIG. 11 shows a configuration example of the Wheatstone bridge in the third embodiment.

  As shown in FIG. 11, strain gauges 47 and 71 are wired on two adjacent sides sharing one output point of the bridge. Two fixed resistors 61 are wired on the other two sides. When the resistance value of the tilt direction strain gauge 47 is Rg1, the resistance value of the circumferential direction strain gauge 71 is Rg2, and the resistance value of each fixed resistor 61 is R, the output voltage Vout is as follows.

  Vout = (Vin ・ Ks ・ (ε1 + ε2)) / 4

Here, Vin is the input voltage, Ks is the gauge factor, ε1 is the response value to the strain of the tilt direction strain gauge 47 (change rate of the length (resistance value Rg1) of the metal pattern), and ε2 is the strain of the circumferential strain gauge 71 Is the response value (the rate of change of the length (resistance value Rg1) of the metal pattern).

  By wiring the inclination direction strain gauge 47 and the circumferential direction strain gauge 71 on adjacent sides sharing the output point of the bridge, the absolute values of the response values (one is positive and the other is negative) of the two strain gauges 47 and 71. Are added together and reflected in the output voltage Vout. Thereby, a better detection sensitivity can be obtained as compared with the case where only one strain gauge is used.

  FIG. 12 is a plan view of a bolt head showing an arrangement example of strain gauges in the fastening bolt device according to the fourth embodiment of the present invention.

  The main difference from the first embodiment shown in FIG. 1 in the fourth embodiment shown in FIG. 12 is that two inclined strain gauges 47 responding mainly to the stress in the inclined direction of the inclined surface 37. In addition, a total of four strain gauges of the two circumferential strain gauges 71 responding mainly to the stress in the circumferential direction of the inclined surface 37 are used in combination. The two tilt direction strain gauges 47 are arranged on the tilted surface 37 with the orientation of the metal pattern being along the tilt direction of the tilted surface 37. On the other hand, the two circumferential strain gauges 71 are arranged on the inclined surface 37 with the orientation of the metal pattern along the circumferential direction of the inclined surface 37.

  The angular position θ of each of these four strain gauges 47 and 71 corresponds to “θ = 30 degrees × odd number” (for example, within a range of ± 5 degrees centered on “θ = 30 degrees × odd number”). is there). More preferably, the two inclined strain gauges 47 are in an axially symmetric positional relationship with respect to the central axis 39 (see FIG. 1) of the shaft portion 23, and the two circumferential strain gauges 71 are also center axes. 39 is in an axially symmetric positional relationship with each other.

  Regarding the other configurations, the fourth embodiment is basically the same as the first embodiment except for the Wheatstone bridge configuration described below.

  FIG. 13 shows a configuration example of the Wheatstone bridge in the fourth embodiment.

  As shown in FIG. 13, two inclined strain gauges 47 are wired to two opposite sides of the bridge, and two circumferential strain gauges 71 are wired to two other opposite sides. . When the resistance value of the inclination direction strain gauge 47 is Rg1, and the resistance value of the circumferential direction strain gauge 71 is Rg2, the output voltage Vout is as follows.

  Vout = (Vin ・ Ks ・ (ε1 + ε2)) / 2

Here, Vin is the input voltage, Ks is the gauge factor, ε1 is the response value to the strain of the tilt direction strain gauge 47 (change rate of the length (resistance value Rg1) of the metal pattern), and ε2 is the strain of the circumferential strain gauge 71 Is the response value (the rate of change of the length (resistance value Rg1) of the metal pattern).

  According to the fourth embodiment, two inclination strain gauges and two circumferential strain gauges are combined and used so that the response values of the four strain gauges are added together and reflected in the output voltage Vout. As a result, it is possible to obtain higher detection sensitivity than in the case of using two strain gauges as in the first to third embodiments.

  FIG. 14 is a plan view of a bolt head showing an example of the arrangement of strain gauges in the fastening bolt device according to the fifth embodiment of the present invention.

  The main difference from the fourth embodiment shown in FIG. 12 in the fifth embodiment shown in FIG. 14 is that one inclined strain gauge 47 and one circumferential strain gauge 71 are inclined surfaces 37. It is a point arranged side by side in the tilt direction at the same upper angular position θ (for example, within the range of the same angular position θ ± 5 degrees). Another tilt direction strain gauge 47 and another circumferential direction strain gauge 71 are also arranged in the tilt direction at another same angular position θ (for example, within the range of the same angular position θ ± 5 degrees) on the tilted surface 37. It is arranged with.

  Regarding other configurations, the fifth embodiment is the same as the fourth embodiment.

  FIG. 15 is a plan view of a bolt head showing an example of the arrangement of strain gauges in the fastening bolt device according to the sixth embodiment of the present invention.

  The main difference from the fifth embodiment shown in FIG. 14 in the sixth embodiment shown in FIG. 15 is that they are arranged at the same angular position θ (for example, within the range of the same angular position θ ± 5 degrees). One tilt strain gauge 47 and one circumferential strain gauge 71 are arranged side by side in the circumferential direction. Another strain gauge 47 in the inclined direction and another strain gauge 71 in the second direction arranged at another same angular position θ (for example, within the range of the same angular position θ ± 5 degrees) are also arranged in the circumferential direction. It is arranged with.

  Regarding other configurations, the sixth embodiment is the same as the fifth embodiment.

  FIG. 16 shows how the stress state of the inclined surface 37 changes according to the diameter D of the bottom surface 35 of the recess 31.

  That is, FIG. 16 shows the circumferential stress S1 obtained by the stress evaluation shell element on the inclined surface 37 and the inclination when only the diameter D of the bottom surface 35 is increased or decreased under the dimensional conditions shown in FIG. It shows how the directional stress S2 (both maximum values obtained with “θ = 30 degrees × odd number”) changes. This is a result obtained by the stress analysis described above.

  As can be seen from FIG. 16, when the diameter D of the bottom surface 35 is increased, the circumferential stress S1 (maximum value) decreases, but the inclined direction stress S2 (maximum value) increases more rapidly. If the diameter D is a certain dimension (approximately 8.5 mm in the example shown), the stress in the tilt direction S2 (maximum value) is greater than the circumferential stress S1 (maximum value). The stress S1 (maximum value) is greater than the tilt direction stress S2 (maximum value).

  Based on this knowledge, the embodiment in which the diameter D of the bottom surface 35 is expanded to the maximum diameter of the recess 31 (for example, a seventh embodiment described later), or the embodiment in which the diameter D of the bottom surface 35 is zero (for example, An eighth embodiment described later) can also be employed.

  FIG. 17 shows a cross-sectional structure along the central axis of the bolt 3 in the fastening bolt device according to the seventh embodiment of the present invention.

  The main difference from the first embodiment shown in FIG. 1 in the seventh embodiment shown in FIG. 17 is that the diameter D of the bottom surface 35 of the recess 31 is the same as the maximum diameter of the recess 31. The concave portion 31 of the bolt 3 is defined by a flat bottom surface 35 perpendicular to the central axis 39 and a cylindrical vertical surface 81 parallel to the central axis 39. Further, two strain gauges (for example, two axial strain gauges mainly responding to axial stress) 83 are fixed in close contact with the vertical surface 81. Each axial strain gauge 83 is attached to the vertical surface 81 in such a posture that the metal pattern faces the direction along the central axis 39. The two axial strain gauges 83 are preferably arranged at an angular position θ corresponding to “θ = 30 degrees × odd number”, and more preferably at positions symmetrical with respect to the central axis 39. As the Wheatstone bridge, one obtained by replacing the slope direction strain gauge 47 of the bridge shown in FIG.

  With respect to other configurations, the seventh embodiment is basically the same as the first embodiment.

  Also with respect to the seventh embodiment, modifications that can be adopted in other embodiments can be appropriately selected and adopted. For example, a configuration using only one axial strain gauge 83, or a configuration in which not only one or two axial strain gauges 81 but also one or two circumferential strain gauges 71 are fixed to the vertical surface 81, etc. Can be adopted. As another modification, a strain gauge is also arranged on the bottom surface 35 as shown by a broken line in FIG. 17 (preferably, arranged at an angular position θ corresponding to “θ = 30 degrees × odd number”). The Wheatstone bridge may be configured by combining these strain gauges and the strain gauge 83 on the vertical surface 81.

  FIG. 18 shows a cross-sectional structure along the central axis of the bolt 3 in the fastening bolt device according to the eighth embodiment of the present invention.

  The main difference from the first embodiment shown in FIG. 1 in the eighth embodiment shown in FIG. 18 is that the diameter D of the bottom surface 35 of the recess 31 is zero, that is, the bottom surface 35 is inclined. This is a point replaced by the surface 37. On the inclined surface 37, two strain gauges (for example, circumferential strain gauges) 71 are firmly fixed. The two circumferential strain gauges 71 are preferably arranged at an angular position θ corresponding to “θ = 30 degrees × odd number”, and more preferably at positions symmetrical with respect to the central axis 39. As the Wheatstone bridge, the bridge shown in FIG. 9 can be adopted.

  With respect to other configurations, the eighth embodiment is basically the same as the first embodiment.

  Also with respect to the eighth embodiment, modifications that can be adopted in other embodiments can be appropriately selected and adopted.

  FIG. 19 shows a cross-sectional structure along the central axis of the bolt 3 in the fastening bolt device according to the ninth embodiment of the present invention.

  The main difference from the first embodiment shown in FIG. 1 in the ninth embodiment shown in FIG. 19 is that all the inner side surfaces of the peripheral wall 44 surrounding the convex portion 31 are inclined surfaces 37. It is a point. The bolt head 21 can be coupled to the protective container 7 by a method other than screwing on any surface of the head 21, for example, adhesion, pressure contact, or engagement. In that case, the cross-sectional shape of the recess 31 may be a shape other than a circle (for example, a polygon such as a hexagon).

  And one or more inclined strain gauges (not shown) and / or circumferential strain gauges (not shown) are secured on the inclined surface 37 in the arrangement described with respect to any other embodiment, and Built into the Wheatstone Bridge.

  Regarding other configurations, the ninth embodiment is basically the same as the first embodiment.

  Also with respect to the ninth embodiment, modifications that can be employed in other embodiments can be appropriately selected and employed.

  20 and 21 show cross-sectional structures along the central axis of the bolt 3 in the fastening bolt device according to the tenth and eleventh embodiments of the present invention, respectively.

  In the tenth and eleventh embodiments, the main difference from the first embodiment shown in FIG. 1 is that the inclined surface 37 surrounding the convex portion 31 has a plurality of different angles with respect to the central axis 39 (for example, 2 This is a point having sub-inclined surfaces 37A and 37B each having an inclination angle of 1). In the tenth embodiment shown in FIG. 20, the inclination of the first sub inclined surface 37 </ b> A closer to the opening of the recess 31 is steeper than the second sub inclined surface 37 </ b> B closer to the bottom surface 35. In the eleventh embodiment shown in FIG. 21, the slope of the first sub-inclined surface 37A is gentler than that of the second sub-inclined surface 37B.

  And one or more inclined strain gauges (not shown) and / or circumferential strain gauges (not shown) in the arrangement described with respect to any other embodiment, on the first inclined surface 37A and / or It is fixed on the second inclined surface 37B and incorporated into the Wheatstone bridge.

  For example, in the tenth embodiment shown in FIG. 20, one or more strain direction strain gauges (not shown) are arranged on the first sub-inclined surface 37A having a steeper slope, and the second slope having a gentler slope. A configuration in which a circumferential strain gauge (not shown) is disposed on the sub-inclined surface 37B can be employed.

  Further, for example, in the eleventh embodiment shown in FIG. 21, one or more circumferential strain gauges (not shown) are arranged on the first sub-inclined surface 37A having a gentler slope, and the slope with a steeper slope is provided. A configuration in which an inclination direction strain gauge (not shown) is disposed on the second sub-inclined surface 37B can be employed.

  Regarding other configurations, the tenth and eleventh embodiments are basically the same as the first embodiment.

  Regarding these tenth and eleventh embodiments, modifications that can be adopted in other embodiments can be appropriately selected and adopted.

  The several embodiments of the present invention described above are merely examples for description, and are not intended to limit the scope of the present invention only to those embodiments. The present invention can be implemented in various forms different from the above-described embodiment.

  For example, the head 21 of the bolt 3 may have a shape other than the hexagonal head. Even in this case, the angular position where the strain gauge is arranged is the angular position corresponding to the position where the radial thickness of the peripheral wall 44 surrounding the recess 31 is the smallest (the cross-sectional shape of the bolt head 21 and the recess 31). It is desirable that the angular position changes.

  Further, for example, an embodiment in which one or more inclined surfaces and one or more vertical surfaces are provided on the inner surface of the peripheral wall 44 of the head 21, and a strain gauge is attached to each of the inclined surfaces and the vertical surfaces, or the axial direction Alternatively, an embodiment in which a plurality of vertical surfaces with different radial positions are provided, and strain gauges are attached to the respective vertical surfaces, or a strain gauge is attached to an inclined surface or a vertical surface and a strain gauge is attached to the bottom surface. Forms can also be adopted.

DESCRIPTION OF SYMBOLS 1 Fastening bolt apparatus 3 Fastening bolt 5 Detection apparatus 7 Protective container 9 Electronic device 21 Head 23 of fastening bolt 3 Shaft part 31 of fastening bolt 3 Recess 37 of head 21 Bottom surface 37 of recessed part 37 Inclined surfaces 37A and 37B of recessed part 31 Sub inclined surface 39 Center axis 44 of shaft portion 23 Peripheral wall 45 of head 21 Bottom wall 47 of head 21 Strain gauge (inclination direction strain gauge)
51 The top edge 53 of the outer surface of the head 21 53 The flat surface 71 of the outer surface of the head 21 Strain gauge (circumferential strain gauge)
81 Vertical surface of concave 31 83 Strain gauge (axial strain gauge)
θ Angular position around the central axis 39 with the top edge 51 as the origin

Claims (9)

A fastening bolt having a head and a shaft,
One or more stress sensors used to detect the axial force of the fastening bolt and responding to stress or strain generated in the head;
With
The head is
A recess recessed downward from the upper surface of the head;
An annular peripheral wall surrounding the recess,
The peripheral wall has, on its inner surface, an inclined surface that faces the recess and is inclined with respect to the central axis of the shaft portion,
The one or more stress sensors are disposed on the inclined surface and configured to respond to stress or strain on the inclined surface;
Fastening bolt device for detecting axial force. 2. The fastening bolt device according to claim 1, wherein at least one of the one or more stress sensors is disposed at an angular position θ around the central axis of the shaft portion corresponding to a portion where the radial thickness of the peripheral wall is minimum. . The head is a hexagonal head;
3. The at least one stress sensor is arranged within an angular position θ of “θ = 30 degrees × odd number” ± 10 degrees with an origin at the top of the outer surface of the hexagonal head. Fastening bolt device. Two stress sensors arranged on the inclined surface;
The fastening bolt device according to any one of claims 1 to 3, wherein the two stress sensors are arranged at an angular position θ around the central axis of the shaft portion that is in an axially symmetric positional relationship with respect to the central axis. . Two stress sensors arranged on the inclined surface;
Both the two stress sensors respond mainly to one of the stress in the inclined direction and the stress in the circumferential direction of the inclined surface,
The fastening bolt according to any one of claims 1 to 4, further comprising a measurement circuit configured such that absolute values of response values of the two stress sensors are added and reflected in an output value of axial force detection. . Two stress sensors arranged on the inclined surface;
One of the two stress sensors is a tilt direction stress sensor that responds mainly to stress in the tilt direction of the tilt surface,
The other of the two stress sensors is a circumferential stress sensor that responds mainly to circumferential stress on the inclined surface,
The fastening bolt according to any one of claims 1 to 4, further comprising a measurement circuit configured such that absolute values of response values of the two stress sensors are added and reflected in an output value of axial force detection. . An electronic device electrically connected to the stress sensor;
A protective container containing at least a part of the electronic device therein;
The fastening bolt according to any one of claims 1 to 6, wherein the protective container is coupled to the head portion and watertightly closes an upper end opening of the recess. A fastening bolt having a head and a shaft,
One or more stress sensors used to detect the axial force of the fastening bolt and responding to stress or strain generated in the head;
With
The head is
A recess recessed downward from the upper surface of the head;
An annular peripheral wall surrounding the recess,
The peripheral wall has a vertical surface on the inner surface thereof that faces the recess and is parallel to the central axis of the shaft portion;
The one or more stress sensors are disposed on the vertical surface and configured to respond to stress or strain on the vertical surface;
Fastening bolt device for detecting axial force. At least one of the one or more stress sensors is
An axial stress sensor responsive to stress in a direction along the central axis of the vertical plane;
The fastening bolt device according to claim 8.

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