Strain sensor and strain measurement method

Abstract

The strain sensor (100) disposed inside a measured object comprises: a flat strain generating plate (F); a strain gauge (112) attached to the strain generating plate; and a pair of protrusions (P1, P2) protruding from the strain generating plate to both sides along the in-plane direction of the strain generating plate. The strain gauge is attached to a region (SC) of the strain generating plate sandwiched by the pair of protrusions.

Description

Technical Field

[0001] The invention relates to a strain sensor and a strain measurement method. Background Art

[0002] There is known a technique in which a strain sensor is arranged in a structure of a machine tool, for example, a press machine, to measure a machining force.

[0003] Patent Document 1 discloses a load cell composed of a bolt and a strain gauge attached to the bolt. Patent Document 1 also discloses that the load cell is regularly arranged on a plate of a press machine to obtain the distribution of stress generated on the plate due to the load from the punch.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6370005 Summary of the invention

[0007] Problems to be solved by the invention

[0008] An object of the present invention is to provide a strain sensor and a strain measurement method capable of measuring the strain generated in a measured object with high precision.

[0009] Solutions for solving problems

[0010] According to a first aspect of the present invention, there is provided a strain sensor disposed inside a measured object, the strain sensor comprising:

[0011] A flat plate-shaped strain generating plate;

[0012] A strain gauge is attached to the strain generating plate; and

[0013] A pair of protrusions protruding from the strain generating plate to both sides along the in-plane direction of the strain generating plate,

[0014] The strain gauge is attached to a region of the strain generating plate sandwiched by the pair of protrusions.

[0015] It may be that the strain sensor of the first scheme further comprises: a cylindrical cover having an inner circumferential surface, wherein the cylindrical cover accommodates the strain generating plate and the pair of protrusions in a state where the tops of the pair of protrusions abut against the inner circumferential surface, and the cylindrical cover is configured so that the outer diameter of the cylindrical cover becomes larger by being pressed by the pair of protrusions.

[0016] In the strain sensor according to the first aspect, the pair of protrusions and the cylindrical cover may be relatively moved in the axial direction of the cylindrical cover, thereby increasing the outer diameter of the cylindrical cover.

[0017] In the strain sensor according to the first aspect, the cylindrical cover may be formed with a slit extending in an axial direction of the cylindrical cover.

[0018] In the strain sensor according to the first aspect, the pair of protrusions may be formed symmetrically with respect to an axis of the cylindrical cover.

[0019] In the strain sensor according to the first aspect, top portions of the pair of protrusions may be tapered and inclined relative to an axial direction of the cylindrical cover.

[0020] In the strain sensor according to the first aspect, an inner peripheral surface of the cylindrical cover may be inclined in a tapered shape with respect to an axial direction of the cylindrical cover.

[0021] The strain sensor according to the first aspect may further include a connection portion that connects the strain generating plate and the cylindrical cover so that the strain generating plate and the cylindrical cover can move relative to each other in the axial direction of the cylindrical cover.

[0022] The strain sensor according to the first aspect may further include: an orientation adjustment assisting portion that assists in orientation adjustment of the strain generating plate inside the measured object.

[0023] It may be that in the strain sensor of the first scheme, the strain gauge comprises: two first-direction strain sensitive elements for measuring the strain generated in a first direction, the first direction being the direction in which the pair of protrusions protrude from the strain generating plate; and two second-direction strain sensitive elements for measuring the strain generated in a second direction within the plane of the strain generating plate, the second direction being a direction orthogonal to the first direction, and it may be that the two first-direction strain sensitive elements and the two second-direction strain sensitive elements constitute a Wheatstone bridge circuit.

[0024] According to a second aspect of the present invention, a method is provided for measuring the strain generated in a measuring direction of a measured object, wherein the method comprises:

[0025] forming a hole in the measured object extending in a direction orthogonal to the measuring direction;

[0026] inserting the strain sensor of the first aspect into the interior of the hole; and

[0027] The outer diameter of the cylindrical cover is increased so that the outer peripheral surface of the cylindrical cover abuts against the inner peripheral surface of the hole.

[0028] Effects of the Invention

[0029] According to the strain sensor and the strain measuring method of the present invention, the strain generated in the measured object can be measured with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is an exploded perspective view of a strain sensor according to an embodiment of the present invention.

[0031] Figure 2 It is a perspective view of a strain sensor according to an embodiment of the present invention.

[0032] Figure 3 It is a top view of the plate.

[0033] Figure 4 In the figure, (a) is a top view showing an example of a strain gauge, and (b) is a top view showing another example of a strain gauge.

[0034] Figure 5 In the figure, (a) and (b) are cross-sectional views along the central axis of the strain sensor according to the embodiment of the present invention. (a) shows a normal state, and (b) shows a state in which the cylindrical cover is expanded and the diameter of the cylindrical cover is increased.

[0035] Figure 6 This is a schematic diagram of a press machine equipped with a strain sensor.

[0036] Figure 7 : is a flowchart showing the steps of the strain measurement method according to the embodiment of the present invention.

[0037] Figure 8 , (a) to (c) are explanatory diagrams for explaining the steps of the strain measurement method. (a) shows a state where a measurement hole is formed in the template, (b) shows a state where a strain sensor is inserted into the measurement hole, and (c) shows a state where the outer peripheral surface of the strain sensor is in close contact with the inner peripheral surface of the measurement hole.

[0038] Fig. 9 Among them, (a) and (b) are explanatory diagrams for explaining the meaning of the protrusions of the plate. (a) shows a case where a load X is applied to a plate of a comparative scheme without a protrusion, and (b) shows a case where a load X is applied to a plate with a protrusion.

[0039] Fig.10 In the drawings, (a) to (c) are plan views showing modified examples of the protrusions provided on the plate portion. DETAILED DESCRIPTION

[0040] <Implementation Method>

[0041] The strain sensor 100 ( Figure 1 , Figure 2 ) is embedded in the stamping machine 500 ( Figure 6) is used as an example to describe the strain sensor 100 according to the embodiment of the present invention.

[0042] like Figure 1 , Figure 2 As shown, the strain sensor 100 of the embodiment mainly includes a main body 10 and a cover 20. The cover 20 includes a cylindrical cover 21, and most of the main body 10 is accommodated inside the cylindrical cover 21.

[0043] In the following description, the central axis of the cylindrical cover 21 is set as the central axis AX of the strain sensor 100, and the direction in which the central axis AX extends is called the axial direction. The side where a part of the main body 10 (the small-diameter cylindrical portion 122 described later) protrudes from the cylindrical cover 21 is called the axial rear side, and the opposite side is called the axial front side. In addition, the radial direction and circumferential direction of the cylindrical cover 21 are called the radial direction and circumferential direction of the strain sensor 100.

[0044] The main body 10 mainly includes a strain detection portion 11 and a main body-side connection portion 12 connected to the axial rear side of the strain detection portion 11 .

[0045] The strain detection unit 11 includes a plate portion 111 and a strain gauge 112 attached to the plate portion 111 .

[0046] As an example, the plate portion 111 is a substantially cross-shaped flat plate formed of a metal such as stainless steel. As an example, the thickness of the plate portion 111 can be set to about 0.5 mm to 1.5 mm, but is not limited thereto and can be any value. Figure 3 As shown, the plate portion 111 includes: a strain generating portion F, which generates strain when receiving an external load during strain measurement; and a pair of protrusions P1 and P2, which transmit the external load to the strain generating portion F during strain measurement.

[0047] The strain generating part F is rectangular, its long dimension direction coincides with the axial direction of the strain sensor 100, and its short dimension direction coincides with the radial direction of the strain sensor 100. The central axis AX passes through the center of the strain generating part F in the short dimension direction and the thickness direction.

[0048] An opening A is formed at one end in the longitudinal direction of the strain occurrence portion F. The opening A communicates with the space around the plate portion 111 via the short side of the strain occurrence portion F.

[0049] The protrusion P1 protrudes in a trapezoidal shape from the long side of one side of the strain generating portion F in the short side direction of the strain generating portion F (i.e., the in-plane direction of the strain generating portion F). The protrusion P2 protrudes in a trapezoidal shape from the other long side of the strain generating portion F in the short side direction of the strain generating portion F. The protrusion P1 and the protrusion P2 have the same shape as each other and are provided to be line-symmetrical with respect to the central axis AX.

[0050] The tops P1t and P2t of the protrusions P1 and P2 extend in the axial direction at a predetermined inclination angle relative to the central axis AX, respectively, in a manner that the distance from the strain generating portion F increases as the strain sensor 100 approaches the axial front side. Thus, the tops P1t and P2t of the protrusions P1 and P2 form a symmetrical cone with respect to the central axis AX.

[0051] On each radial surface of the strain generating portion F ( Figure 3 The area sandwiched by the protrusion P1 and the protrusion P2 (the surface facing the direction perpendicular to the paper surface) is marked as a strain concentration area (stress concentration area) SC. The strain concentration area SC is an area where a particularly large strain (and stress) will be generated even in the strain generating part F when a load from the outside is applied to the plate part 111 (details will be described later).

[0052] like Figure 4 As shown in (a), the strain gauge 112 mainly includes a rectangular flexible substrate B and two first-direction strain sensitive elements SE1 and two second-direction strain sensitive elements SE2 formed on the flexible substrate B. The first-direction strain sensitive element SE1 is configured to sense strain generated in a specified first direction (here, the long dimension direction of the flexible substrate B), and the second-direction strain sensitive element SE2 is configured to sense strain generated in a second direction orthogonal to the first direction (here, the short dimension direction of the flexible substrate B).

[0053] The two first-directional strain sensitive elements SE1 and the two second-directional strain sensitive elements SE2 are connected by a printed wiring PW so as to form a Wheatstone bridge circuit WSB.

[0054] The strain gauge 112 is adhered to the strain concentration area SC on one side of the strain generating part F of the plate part 111 in such a way that the first direction is consistent with the short dimension direction of the strain generating part F (the radial direction of the strain sensor 100) and the second direction is consistent with the long dimension direction of the strain generating part F (the axial direction of the strain sensor 100).

[0055] The main body-side connection portion 12 cooperates with a cover-side connection portion 22 (described later) of the cover portion 20 to connect the main body 10 and the cover portion 20 so that the main body 10 and the cover portion 20 can move relative to each other in the axial direction.

[0056] As an example, the main body side connection portion 12 is formed of a metal such as stainless steel, and includes: a large diameter cylindrical portion 121; and a small diameter cylindrical portion 122, which is coaxially connected to the large diameter cylindrical portion 121 and is connected to the axial rear side of the large diameter cylindrical portion 121. The outer diameter of the small diameter cylindrical portion 122 is smaller than the outer diameter of the large diameter cylindrical portion 121. The central axes of the large diameter cylindrical portion 121 and the small diameter cylindrical portion 122 coincide with the central axis AX of the strain sensor 100.

[0057] like Figure 5 As shown in (a), the inner hole 121h of the large diameter cylindrical portion 121 and the inner hole 122h of the small diameter cylindrical portion 122 have the same diameter and communicate with each other to form the inner hole 12h.

[0058] The outer thread MS is formed on the entire area of ​​the outer peripheral surface 122c of the small-diameter cylindrical portion 122. In addition, a D-shaped cut portion DC is formed at the rear end of the small-diameter cylindrical portion 122, and the D-shaped cut surface DCs extends in a plane parallel to the central axis AX. Alternatively, a D-shaped cut portion opposite to the D-shaped cut portion DC in the radial direction may be formed at the rear end of the small-diameter cylindrical portion 112, and a D-shaped cut surface parallel to the D-shaped cut surface DCs is formed.

[0059] The strain detection part 11 and the main body side connection part 12 are connected to each other as a whole in a state where the rear edge of the plate part 111 of the strain detection part 11 is fixed to the front surface of the large diameter cylindrical part 121 of the main body side connection part 12. The plate part 111 is connected to the large diameter cylindrical part 121 in a manner that passes through the central axis of the large diameter cylindrical part 121. In this state, the opening A of the strain generating part F of the plate part 111 is connected to the inner hole 12h of the main body side connection part 12.

[0060] The strain detection portion 11 and the main body side connection portion 12 are connected so that the radial surface of the plate-shaped strain generating portion F (i.e., the surface defining the strain concentration region SC) and the D-shaped cut surface DCs face the same direction, i.e., are parallel to each other.

[0061] The plate portion 111 of the strain detection portion 11 and the main body-side connection portion 12 may be integrally formed by cutting a metal round bar such as stainless steel, for example.

[0062] The cover portion 20 mainly includes a cylindrical cover 21 and a cover-side connecting portion 22 rotatably inserted in the vicinity of a rear end 21 r of the cylindrical cover 21 .

[0063] like Figure 2 and Figure 5 As shown in (a), the cylindrical cover 21 is arranged on the radially outer side of the main body 10, covering the entire strain detection part 11 and most of the main body side connection part 12. In other words, the entire strain detection part 11 of the main body 10 and most of the main body side connection part 12 are accommodated inside the cylindrical cover 21.

[0064] As an example, the cylindrical cover 21 is formed of metal such as stainless steel. As an example, the outer diameter of the cylindrical cover can be set to about 5 mm to 30 mm.

[0065] like Figure 5As shown in (a), the cylindrical cover 21 is divided into three regions, namely, a first region AR1, a second region AR2, and a third region AR3, from the rear end 21r to the front end 21f, and the inner diameters of the regions are different.

[0066] In each of the first area AR1 and the second area AR2, the inner diameter is constant, and the inner diameter in the first area AR1 is larger than the inner diameter in the second area AR2. The inner diameter in the third area AR3 gradually increases as it moves from the axial rear side to the front side. That is, in the third area, the inner peripheral surface 21i of the cylindrical cover 21 forms a cone that is symmetrical with respect to the central axis AX.

[0067] Slits SL extending rearward from the front end 21f are formed at equal intervals at three locations in the circumferential direction of the cylindrical cover 21. Each slit SL extends over the entire third area AR3 and substantially the front half of the second area AR2.

[0068] The cover-side connection portion 22 cooperates with the main body-side connection portion 12 of the main body 10 to connect the main body 10 and the cover 20 so that the main body 10 and the cover 20 can move relative to each other in the axial direction.

[0069] As an example, the cover side connection part 22 is formed of a metal such as stainless steel. The cover side connection part 22 includes: a small diameter cylindrical part 221; a large diameter cylindrical part 222, which is coaxially connected to the small diameter cylindrical part 221 at the axial rear side of the small diameter cylindrical part 221; and a snap-fitting cylindrical part 223, which is coaxially connected to the large diameter cylindrical part 222 at the axial rear side of the large diameter cylindrical part 222. The central axes of the small diameter cylindrical part 221, the large diameter cylindrical part 222, and the snap-fitting cylindrical part 223 are consistent with the central axis AX of the strain sensor 100.

[0070] The outer diameter of the small-diameter cylindrical portion 221 is smaller than the outer diameter of the large-diameter cylindrical portion 222 .

[0071] The engaging cylinder 223 is a substantially cylindrical shape in which a portion of the outer peripheral surface 223c is cut off by a plane parallel to the central axis to form a plane portion 223cf. A rectangular engaging protrusion EP protruding radially from the plane portion 223cf is provided at the rear end 223r of the engaging cylinder 223. In addition, a pair of D-shaped cut portions are formed near the rear end 223r of the engaging cylinder 223, and the D-shaped cut surfaces DC1s and DC2s extend in a plane parallel to the central axis AX in a manner parallel to each other and orthogonal to the plane portion 223cf.

[0072] like Figure 5 As shown in (a), the inner hole 221h of the small diameter cylindrical part 221, the inner hole 222h of the large diameter cylindrical part 222 and the inner hole 223h of the engagement cylinder part 223 have the same diameter and are connected to form the inner hole 22h. An internal thread FS is formed on the inner peripheral surface defining the inner hole 22h.

[0073] The cover side connection part 22 is coaxially inserted with the cylindrical cover 21 to the vicinity of the rear end 21r of the cylindrical cover 21, and is prevented from falling off by the notch ring R. When the cover side connection part 22 is inserted into the cylindrical cover 21, the entirety of the small diameter cylindrical part 221, the entirety of the large diameter cylindrical part 222, and the vicinity of the front end of the engaging cylindrical part 223 are accommodated inside the cylindrical cover 21, and the rear end 223r side of the engaging cylindrical part 223 protrudes to the rear side of the cylindrical cover 21.

[0074] Specifically, if Figure 5 As shown in (a), the small diameter cylindrical portion 221 is arranged in the second area AR2 of the cylindrical cover 21 in a state where the outer peripheral surface of the small diameter cylindrical portion 221 abuts against the inner peripheral surface 21i of the cylindrical cover 21. The large diameter cylindrical portion 222 is arranged in the first area AR1 of the cylindrical cover 21 in a state where the outer peripheral surface of the large diameter cylindrical portion 222 abuts against the inner peripheral surface 21i of the cylindrical cover 21. The notch ring R is arranged in the first area AR1 near the rear end 21r of the cylindrical cover 21 and is fixed to the cylindrical cover 21. Thus, the cover-side connecting portion 22 is held in the cylindrical cover 21 in a state where its axial movement is restricted and it can only move in rotation.

[0075] The small diameter cylindrical portion 122 of the main body side connection portion 12 of the main body 10 is inserted into the inner hole 22h of the cover side connection portion 22 of the cover portion 20 to thread the external thread MS with the internal thread FS, thereby the main body 10 and the cover portion 20 are coaxially connected in a manner that can move relative to each other in the axial direction through the action of the thread. In this way, the main body side connection portion 12 and the cover side connection portion 22 constitute a connection portion (connection mechanism) that connects the main body 10 and the cylindrical cover 21 in a manner that the main body 10 and the cylindrical cover 21 can move relative to each other in the axial direction.

[0076] In a state where the main body 10 and the cover 20 are connected and the plate 111 is accommodated in the cylindrical cover 21, Figure 5 As shown in FIG. 2( a ), the top portions P1 t and P2 t of the protrusions P1 and P2 are in contact with the inner peripheral surface 21 i of the cylindrical cover 21 in the third region AR3 of the cylindrical cover 21 .

[0077] When the cover-side connecting portion 22 is rotated in this state, the main body 10 moves in the axial direction. When the main body 10 moves axially rearward, the protrusions P1 and P2 press and expand the cylindrical cover 21 radially outward, and the outer diameter of the cylindrical cover 21 increases ( Figure 5 (b)).

[0078] The wiring W ( Figure 8 (b) Figure 8 (c)) passes through the opening A and the inner hole 12h and is pulled out to the rear of the strain sensor 100. It should be noted that the wiring W is Figure 8(b) Figure 8 Illustration is omitted in figures other than (c).

[0079] Next, a method of measuring the strain generated in the die plate DP of the press working machine 500 using the strain sensor 100 according to the embodiment will be described.

[0080] like Figure 6 As shown, the punching machine 500 comprises: a template DP; a template holder DH, which holds the template DP; a punch PN; a punch holder PH, which holds the punch PN; and a plurality of guide pins GP, which support the punch holder PH so that it can move up and down relative to the template holder DH. When the punching machine 500 is used for punching, the pressure of the punch PN is applied to the workpiece on the template DP in order to perform plastic working and cutting of the workpiece.

[0081] like Figure 7 As shown, the strain measurement method of this embodiment includes: a measuring hole forming step S1, forming a measuring hole H in a template DP, the interior of the measuring hole H is used to set the strain sensor 100; a sensor setting step S2, fixedly setting the strain sensor 100 inside the measuring hole H; and a measuring step S3, using the strain sensor 100 inside the measuring hole H to measure the strain generated in the template DP.

[0082] In the measurement hole forming step S1 , a measurement hole H is formed in the template DP using an electric drill or the like. In the present embodiment, the cylindrical cover 21 is a cylinder, and therefore the measurement hole H is preferably a circular hole having an inner diameter slightly larger than the outer diameter of the strain sensor 100 .

[0083] like Figure 8 As shown in (a), the measuring hole H is formed to extend in a manner perpendicular to the direction (measuring direction MD) in which the strain as the measurement object is generated. In this embodiment, the strain in the moving direction (i.e., the vertical direction) of the punch PN generated in the template DP is set as the measurement object, and the measuring hole H extending in the horizontal direction is formed in the template DP.

[0084] The position where the measuring hole H is formed and the number of the measuring holes H can be arbitrarily set according to the purpose of measurement. Generally speaking, by forming the measuring hole H at a position where a larger strain as the measurement object is generated, the strain sensor 100 can be arranged at a position where a larger strain as the measurement object is generated, and the accuracy of strain measurement can be improved. In the die plate DP of the stamping machine 500, the position where the largest strain is generated is usually directly below the position where the punch PN presses the die plate DP.

[0085] In the sensor installation step S2 , first, the strain sensor 100 is inserted from the front side to the vicinity of the entrance of the measurement hole H, and the orientation of the plate portion 111 is adjusted in consideration of the measurement direction MD.

[0086] Specifically, the orientation of the plate portion 111 is adjusted so that the radial surface of the strain generating portion F (the surface where the strain concentration area is drawn), that is, the surface where the strain gauge 112 is attached, is parallel to the measuring direction MD. By configuring the plate portion 111 in this way, the protrusions P1 and P2 are arranged on both sides of the strain generating portion F in the measuring direction MD, and the strain gauge 112 attached to the strain concentration area SC of the strain generating portion F can be used to detect the strain generated in the measuring direction MD with higher accuracy (details will be described later). It should be noted that even if the surface of the strain generating portion F where the strain gauge 112 is attached is inclined by about 10° relative to the measuring direction MD, strain detection can be performed with sufficient accuracy.

[0087] The orientation of the plate portion 111 can be easily adjusted using the D-shaped cut surface DCs formed at the rear end of the small-diameter cylindrical portion 122 of the main body side connection portion 12. As described above, the strain detection portion 11 and the main body side connection portion 12 are connected in such a manner that the radial surface of the strain generating portion F (the surface that defines the strain concentration area SC) and the D-shaped cut surface DCs are parallel to each other. Therefore, by making the D-shaped cut surface DCs parallel to the measurement direction MD, the radial surface of the strain generating portion F can be made parallel to the measurement direction MD. That is, the D-shaped cut portion DC functions as an orientation adjustment auxiliary portion that assists the orientation adjustment of the plate portion 111 and the strain generating portion F.

[0088] After adjusting the orientation of the plate portion 111, the strain sensor 100 is pushed into the predetermined installation position in the measurement hole H. The double-layer cylindrical insert 50 ( Figure 8 (b)).

[0089] The insert 50 includes: an outer cylinder 51 whose top end is formed as a snap-fitting protrusion EP that can be snap-fitted to the cover-side connecting portion 22 of the strain sensor 100; and an inner cylinder 52 whose top end is formed as a D-shaped cut portion DC that can be snap-fitted to the main body-side connecting portion 12 of the strain sensor 100.

[0090] When the strain sensor 100 is pushed in using the insert 50, first, the wiring W extending from the strain gauge 112 is passed through the inner hole of the inner cylinder 52 (or between the inner cylinder 52 and the outer cylinder 51). Then, the insert 50 is inserted into the measurement hole H, and the strain sensor 100 is pushed into the measurement hole H, with the top end of the inner cylinder 52 and the top end of the outer cylinder 51 being engaged with the D-shaped cut portion DC and the engagement protrusion EP, respectively.

[0091] After the strain sensor 100 is pushed into the predetermined installation position and the inner cylinder 52 is fixed, only the outer cylinder 51 is rotated. As a result, the cover-side connecting portion 22 rotates while the rotation of the main body 10 is restricted, and the main body 10 moves backward relative to the cylindrical cover 21. At this time, the protrusions P1 and P2 of the plate portion 111 of the strain detection portion 11 press the inner peripheral surface 21i of the cylindrical cover 21 radially outward, thereby increasing the outer diameter of the cylindrical cover 21 ( Figure 5 (b)), the outer peripheral surface 21c of the cylindrical cover 21 is in close contact with the inner peripheral surface Hi of the measuring hole H ( Figure 8 (c)). Since the rotation of the main body 10 is restricted, the orientation of the adjusted plate 111 is maintained.

[0092] The strain sensor 100 is fixedly arranged inside the measuring hole H by the outer peripheral surface 21c of the cylindrical cover 21 being in close contact with the inner peripheral surface Hi of the measuring hole H. In addition, in this state, the top surfaces P1t and P2t of the protrusions P1 and P2 of the plate portion 111 are in close contact with the inner peripheral surface 21i of the cylindrical cover 21, and the outer peripheral surface 21c of the cylindrical cover 21 is in close contact with the inner peripheral surface Hi of the measuring hole H, so the strain generated in the template DP is well transmitted to the strain generating portion F. Therefore, the accuracy of strain detection is improved.

[0093] After the strain sensor 100 is fixedly arranged in the measuring hole H, the insert 50 is removed and the wiring W is connected to the control device CONT ( Figure 8 (c) connection.

[0094] When a plurality of strain sensors 100 are arranged, the measurement hole forming step S1 and the sensor setting step S2 are repeated in the same manner.

[0095] In the measurement step S3, the strain generated in the measurement direction MD of the template DP is measured mainly using the strain detection unit 11 of the main body 10 and the control device CONT. Specifically, the following steps are performed.

[0096] When strain in the measuring direction MD is generated in the template DP, the diameter of the setting hole H becomes smaller, and the protrusions P1 and P2 are pressed toward the strain generating portion F via the cylindrical case 21. As a result, the strain generating portion F is compressed in the measuring direction MD, and strain is generated in the strain generating portion F. Specifically, the strain generated in the strain generating portion F is a compressive strain generated in the measuring direction MD (the radial direction of the strain sensor 100) and a tensile strain generated in a direction orthogonal to the measuring direction MD (the axial direction of the strain sensor 100).

[0097] The strain gauge 112 attached to the strain concentration region SC of the strain generating portion F uses two first-direction strain sensitive elements SE1 and two second-direction strain sensitive elements SE2 to detect the strain generated in the strain concentration region SC. Specifically, the resistance values ​​of the two first-direction strain sensitive elements SE1 change due to the compressive strain generated in the measuring direction MD, and the resistance values ​​of the two second-direction strain sensitive elements SE2 change due to the tensile strain generated in the direction orthogonal to the measuring direction MD.

[0098] The change in these resistance values ​​causes the value of the output voltage outputted from the Wheatstone bridge WSB to change. Based on the change in the value of the output voltage received via the wiring W, the control device CONT obtains a measured value of the strain generated in the die DP using a predetermined calculation formula.

[0099] Here, in the strain sensor 100 of the present embodiment, the reason why the plate portion 111 of the strain detection portion 11 includes the protrusions P1 and P2 protruding from the strain generating portion F is as follows.

[0100] First, if Fig. 9 As shown in (a), the side surface of the long side of the strain generating portion F0 of the rectangular plate is considered to have a contact area A0 [mm 2 ] is in contact with the inner circumference Hi of the measuring hole H. In this scheme, when the template DP generates strain in the measuring direction MD and the load X [N] is applied to the strain generating portion F0, the magnitude of the compressive stress generated in the strain generating portion F0 is σ0 = X / A0 [N / mm 2 ].

[0101] Then, if Fig. 9 As shown in (b), consider the top surfaces of a pair of protrusions P1 protruding from the long sides of the rectangular strain generating part F1 to have a contact area A1 [mm 2 ] is in contact with the inner peripheral surface Hi of the measuring hole H. In this scheme, when the template DP generates strain in the measuring direction MD and the load X [N] is applied to the strain generating part F1, the magnitude of the compressive stress generated in the region SC1 of the strain generating part F1 sandwiched by the pair of protrusions P1 is σ1 = X / A1 [N / mm 2 ].

[0102] Here, when the sizes of the contact areas are compared, A1<A0, so the size of the compressive stress is σ1>σ0. Furthermore, when the compressive strain generated in the strain generating portion F0 as a rectangular plate is set to ε0, and the compressive strain generated in the region SC1 of the strain generating portion F1 is set to ε1, according to Hooke's law, the size of the compressive strain generated in the member is proportional to the size of the compressive stress generated in the member, so the size of the strain ε1>ε0.

[0103] Thus, by providing the protrusions P1 and P2 as in the plate portion 111 of the present embodiment to reduce the contact area with the inner peripheral surface Hi of the measuring hole H, a portion (strain concentration portion, stress concentration portion) where a large strain is generated is generated between the protrusions P1 and P2. By attaching a strain gauge to such a strain concentration portion, the strain generated in the template DP (measured object) can be amplified to detect the strain with high sensitivity, so that the strain can be detected and measured more accurately.

[0104] The effects of the strain sensor 100 and the strain measurement method according to the present embodiment are summarized as follows.

[0105] The strain sensor 100 of this embodiment is provided with protrusions P1 and P2 on both radial sides of the strain generating portion F of the plate portion 111, and a strain gauge 112 is attached to the strain concentration region SC sandwiched by the protrusions P1 and P2 of the strain generating portion F. Therefore, the strain generated in the test object such as the template DP can be detected with high sensitivity through the larger strain (amplified strain) of the strain concentration portion SC generated by the strain, so that strain detection and strain measurement can be performed with high accuracy.

[0106] The strain sensor 100 of this embodiment can be set at a position where a large strain is generated inside a measurement hole H formed in a test object such as a template DP. In this way, by forming the measurement hole H and setting the strain sensor 100 at a position where a large strain is generated, that is, a position where strain detection can be performed with high sensitivity, the accuracy of strain detection and strain measurement can be further improved.

[0107] The strain sensor 100 of this embodiment is provided with a cylindrical cover 21 that can increase the outer diameter. Therefore, by using the protrusions P1 and P2 of the plate portion 111 to press the cylindrical cover 21 to increase the outer diameter, it is easy to achieve a state in which the protrusions P1 and P2 of the plate portion 111, the cylindrical cover 21, and the inner peripheral surface Hi of the measurement hole H are in close contact with each other. By setting the strain sensor 100 in such a state, the strain generated in the measured object such as the template DP is well transmitted to the strain generating portion F, so the accuracy of strain detection and strain measurement can be further improved.

[0108] In particular, in this embodiment, the tops P1t and P2t of the protrusions P1 and P2 are tapered, and the inner peripheral surface 21i of the cylindrical cover 21 is also tapered. Therefore, the protrusions P1 and P2 are in close contact with the inner peripheral surface 21i of the cylindrical cover 21.

[0109] In the strain sensor 100 of this embodiment, the plate portion 111 has a strain generating portion F, and the strain generating portion F is plate-shaped. Therefore, the following scheme can be used: four strain sensitive elements are provided in the strain generating portion F, two strain sensitive elements are used to detect the compressive strain generated in the measuring direction MD, and the remaining two strain sensitive elements are used to detect the tensile strain generated in the direction orthogonal to the measuring direction MD. With such a scheme, the accuracy of strain detection and strain measurement can be further improved by forming a Wheatstone bridge with the four strain sensitive elements.

[0110] <Modification>

[0111] In the strain sensor 100 of the above embodiment, the following modifications may also be used.

[0112] In the strain sensor 100 of the above embodiment, the protrusions P1 and P2 are respectively trapezoidal in plan view and are tapered through the tops P1t and P2t, but the present invention is not limited thereto. The shape of the protrusions can be any shape, for example, Fig.10 The plate portion 111a shown in (a) of FIG. 1 may include protrusions P1a and P2a that are rectangular in plan view on both sides of the strain generating portion Fa, or may be configured as follows: Fig.10 The plate portion 111b shown in (b) of FIG. 1 may include planar triangular protrusions P1b and P2b on both sides of the strain generating portion Fb, or may be configured as follows: Fig.10 Like the plate portion 111c shown in (c), the plate portion 111c includes substantially square protrusions P1c and P2c on both sides of the strain generating portion Fc.

[0113] Furthermore, the protrusions P1 and P2 do not necessarily need to be formed as a plate portion integral with the strain generating portion F, and may be cylindrical, prismatic, spherical, or other protrusions mounted on the plate-shaped strain generating portion F and protruding from the strain generating portion F.

[0114] In this way, the protrusions P1 and P2 may be any protrusion (i.e., any protrusion whose top area in the radial direction (in-plane direction of the strain generating plate, protruding direction of the protrusion) is smaller than the area of ​​the side surface of the strain generating plate in the radial direction (in-plane direction of the strain generating plate, protruding direction of the protrusion)) that is arranged to abut against the inner peripheral surface 21i of the cylindrical cover 21 with a smaller contact area than when the strain generating portion F is in direct contact with the inner peripheral surface 21i. In addition, the pair of protrusions on both sides of the strain generating portion F do not necessarily have the same shape as each other, and may not be symmetrical around the central axis AX.

[0115] In the strain sensor 100 of the above embodiment, the strain gauge 112 including two first-direction strain sensitive elements SE1 and two second-direction strain sensitive elements SE2 is attached to one side of the strain generating portion F, but the present invention is not limited thereto. Figure 4The strain gauge 112' shown in (b) and having a single first-direction strain sensitive element SE1 and a single second-direction strain sensitive element SE2 is pasted one by one on both sides of the strain generating part F in such a manner that the first-direction strain sensitive element SE1 and the second-direction strain sensitive element SE2 respectively detect radial and axial strains, and the two strain gauges 112' are connected to form a Wheatstone bridge.

[0116] In addition, it is not necessary to form a Wheatstone bridge only by strain sensitive elements provided in the strain generating part F. Any strain gauge such as a single-chip strain gauge having only a single first-direction strain sensitive element SE1 or a single second-direction strain sensitive element SE2 can also be pasted on one or both sides of the strain generating part F.

[0117] In the strain sensor 100 of the above embodiment, the cylindrical cover 21 is cylindrical, but the present invention is not limited thereto. The cylindrical cover 21 may be any cylindrical member such as a cylindrical member having a quadrilateral cross-sectional shape perpendicular to the axis or a polygonal cylindrical member.

[0118] In the strain sensor 100 of the above embodiment, a plurality of slits SL are provided in the cylindrical cover 21 to make the outer diameter of the cylindrical cover 21 variable. However, the present invention is not limited to this, and only a single slit SL may be provided.

[0119] The outer diameter of the cylindrical cover 21 may be variable without providing the slit SL. Specifically, for example, the cylindrical cover 21 may have an outer diameter that increases in accordance with the internal pressure applied from the main body 10 by making the thickness of the cylindrical cover sufficiently thin.

[0120] The strain sensor 100 of the above-mentioned embodiment is configured as follows: the tops P1t and P2t of the protrusions P1 and P2 of the main body 10 and the inner peripheral surface 21i of the cylindrical cover 21 of the cover 20 are respectively configured as a cone that expands as they approach the axial front side, and the outer diameter of the cylindrical cover 21 is increased by moving the main body 10 backward relative to the cylindrical cover 21. However, it is not limited to this, and the tops P1t and P2t of the protrusions P1 and P2 of the main body 10 and the inner peripheral surface 21i of the cylindrical cover 21 of the cover 20 may be respectively configured as a cone that expands as they approach the axial rear side. According to this structure, the outer diameter of the cylindrical cover 21 increases by moving the main body 10 forward relative to the cylindrical cover 21.

[0121] In the strain sensor 100 of the above embodiment, the strain detection part 11 and the cylindrical cover 21 are integrally connected to each other via the main body side connection part 12 of the main body 10 and the cover side connection part 22 of the cover 20 so as to be relatively movable, but the present invention is not limited thereto.

[0122] It is also possible to omit the main body side connection part 12 and the cover side connection part 22 and adopt a strain sensor in which the strain detection part 11 is housed in the cylindrical cover 21 in a state that it can be separated from the cylindrical cover 21. When such a strain sensor is set in the measurement hole H, for example, after the strain sensor is inserted into the measurement hole H, the strain detection part 11 is pulled forward while restricting the movement of the cylindrical cover 21 using a predetermined insert. As a result, the strain detection part 11 moves in the axial direction relative to the cylindrical cover 21, and the outer diameter of the cylindrical cover 21 increases.

[0123] In the strain sensor 100 of the above embodiment, the D-shaped cut portion DC formed on the main body side connection portion 12 of the main body portion 10 functions as an auxiliary portion for orientation adjustment, but is not limited thereto. The structure for assisting the orientation adjustment of the plate portion 111 and the strain generating portion F may be any structure, for example, it may be a convex portion, a pattern, or other mark provided at the rear end of the small diameter cylindrical portion 122 of the main body side connection portion 12.

[0124] The strain sensor 100 of the above-described embodiment does not necessarily need to include the cylindrical cover 21 , and for example, the strain sensor may be constituted by only the strain detection portion 11 of the main body 10 .

[0125] When such a strain sensor is disposed inside the measurement hole H, for example, the measurement hole H is formed into a tapered shape whose diameter decreases toward the inner side, and the strain sensor is pushed into the tapered hole.

[0126] The strain sensor and strain measurement method of the embodiment and variant scheme are described above by taking the application in the stamping machine 500 as an example, but are not limited thereto. The strain sensor and strain measurement method of the embodiment and variant scheme can be used for any machine tool different from the stamping machine, and can be used for any object to be measured different from the machine tool. The object to be measured is not limited to metal, but can be any material such as concrete, resin, etc.

[0127] Specifically, for example, if the strain sensor of the embodiment or the variant is pre-embedded in concrete or resin and the main body 10 and the cover 20 are relatively moved at a necessary time point to increase the outer diameter of the cylindrical cover to measure the preload value (reaction force) at this time, the hardness of the concrete or resin can be measured based on the measured value. Such hardness measurement can be applied not only to concrete and resin, but also to foods such as bread dough. In addition, by pre-embedding the strain sensor of the embodiment or the variant in a building or the like and regularly performing such hardness measurement, the aging of the building or the like can be monitored.

[0128] The strain sensor of the embodiment or the modified embodiment may be placed in water to measure the water pressure. In this case, it is preferable to adopt a structure in which the strain sensing part provided in the main body is sealed by a cylindrical cover.

[0129] If vibration occurs in the object to be measured, a small displacement inside the object to be measured will affect the output of the strain sensor. Therefore, the vibration generated in the object to be measured can also be measured by the strain sensor of the embodiment or the variation.

[0130] The strain sensor of the embodiment or the variation may be used to check the fit. Specifically, for example, a strain sensor having a cylindrical cover with a predetermined outer diameter may be inserted into a hole, and the appropriateness of the hole size may be determined based on whether the strain value measured at this time is appropriate.

[0131] The strain sensor of the embodiment or variant may also be used to measure the tension of a wire or cable. Specifically, for example, when laying a wire or cable, the strain sensor of the embodiment or variant is provided with a portion around which the wire or cable is wound, and the tension of the wire or cable is calculated based on the measurement value of the strain sensor.

[0132] As long as the characteristics of the present invention are maintained, the present invention is not limited to the above-described embodiments, and other embodiments that can be conceived within the technical concept of the present invention are also included in the scope of the present invention.

[0133] Description of Reference Numerals

[0134] 10: main body; 11: strain detection part; 111: plate; 112: strain gauge; 12: main body side connection part; 20: cover; 21: cylindrical cover; 22: cover side connection part; 500: stamping machine; DP: template; F: strain generating part; P1, P2: protrusions.

Claims

1. A strain sensor, arranged inside a measured object, characterized in that: have: A flat plate-shaped strain generating plate; A strain gauge is attached to the strain generating plate; a pair of protrusions protruding from the strain generating plate to both sides along the in-plane direction of the strain generating plate; as well as a cylindrical cover having an inner peripheral surface, wherein the cylindrical cover accommodates the strain generating plate and the pair of protrusions in a state where the tops of the pair of protrusions abut against the inner peripheral surface; The strain gauge is attached to the region of the strain generating plate sandwiched by the pair of protrusions. The cylindrical cover is provided so that the outer diameter of the cylindrical cover increases by being pressed by the pair of protrusions.

2. The strain sensor according to claim 1, characterized in that: The pair of protrusions and the cylindrical cover move relatively in the axial direction of the cylindrical cover, whereby the outer diameter of the cylindrical cover increases.

3. The strain sensor according to claim 1 or 2, characterized in that: The cylindrical cover is formed with a slit extending in the axial direction of the cylindrical cover.

4. The strain sensor according to claim 1 or 2, characterized in that: The pair of protrusions are formed symmetrically with respect to the axis of the cylindrical cover.

5. The strain sensor according to claim 1 or 2, characterized in that: The tops of the pair of protrusions are inclined in a tapered shape with respect to the axial direction of the cylindrical cover.

6. The strain sensor according to claim 1 or 2, characterized in that: The inner peripheral surface of the cylindrical cover is inclined in a tapered shape with respect to the axial direction of the cylindrical cover.

7. The strain sensor according to claim 1 or 2, characterized in that: The invention further includes a connection portion that connects the strain generating plate and the cylindrical cover so that the strain generating plate and the cylindrical cover can move relative to each other in the axial direction of the cylindrical cover.

8. The strain sensor according to claim 1 or 2, characterized in that: The device further includes an orientation adjustment assisting portion for assisting in the orientation adjustment of the strain generating plate inside the measured object.

9. The strain sensor according to claim 1 or 2, characterized in that: The strain gauge comprises: two first-direction strain sensitive elements for measuring strain generated in a first direction, wherein the first direction is a direction in which the pair of protrusions protrude from the strain generating plate; and two second-direction strain sensitive elements for measuring the strain generated in the second direction within the surface of the strain generating plate, wherein the second direction is a direction orthogonal to the first direction, The two first directional strain sensitive elements and the two second directional strain sensitive elements form a Wheatstone bridge circuit.

10. A method for measuring strain generated in a measuring direction of a measured object, characterized in that: include: forming a hole in the measured object extending in a direction orthogonal to the measuring direction; inserting a strain sensor according to any one of claims 1 to 7 into the interior of the hole; and The outer diameter of the cylindrical cover is increased so that the outer peripheral surface of the cylindrical cover abuts against the inner peripheral surface of the hole.

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