JP3853170B2 - Load sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a load sensor that detects a load by a bending state of a plate-like strain generating body on which a strain element is mounted, and particularly relates to an attachment structure for supporting the strain generating body on a fixed shaft body such as a bolt.
[0002]
[Prior art]
FIG. 9 is an explanatory view showing a conventional example of this type of load sensor. In the figure, reference numeral 1 is a strain element made of a thick film resistor, and 2 is a strain plate made of a metal plate having a shaft hole 2 a and mounting the strain element 1. A load point 2b to which a load from the measurement object is applied is provided. Reference numeral 3 denotes a bolt inserted through the shaft hole 2a. The bolt 3 is fixed to a frame 4 or the like as an installation member using a nut 9 or the like. Reference numerals 5 and 6 denote flat washers that are externally attached to the bolt 3, and the peripheral portion of the shaft hole 2 a of the strain generating body 2 is disposed between the pair of washers 5 and 6. Reference numerals 7 and 8 are nuts screwed to the bolt 3, and the washer 6, the strain body 2 and the washer 5 are sandwiched and fixed between the pair of nuts 7 and 8 in a laminated state.
[0003]
That is, when attaching the strain body 2 to the bolt 3, after the nut 8 is screwed onto the bolt 3, the washer 6, the strain body 2 and the washer 5 are sequentially extrapolated to the bolt 3, and then the nut 7 is attached. The nuts 7 and 8 are tightened by screwing onto the bolts 3. As a result, the pair of washers 5 and 6 sandwiching the peripheral portion of the shaft hole 2a of the strain generating body 2 is sandwiched between the pair of nuts 7 and 8 along the axial direction of the bolt 3, so the washer The strain generating body 2 can be firmly fixed to the bolt 3 via 5 and 6.
[0004]
[Problems to be solved by the invention]
In this type of load sensor, the strain body 2 is a metal plate made of, for example, SUS having a thickness of about 2 mm. However, it is difficult to bring the strain body 2 and the washers 5 and 6 into full surface contact. A place where the pressurizing force from the washers 5 and 6 acts strongly and a place where the pressure force acts weakly are generated at the peripheral portion of the shaft hole 2a of the strain body 2. In particular, as shown in FIG. 10, when the nut 7 (or 8) is screwed at an angle with respect to the bolt 3, excessive stress is concentrated on one side of the washer 5 (or 6). The other side portion is lifted away from the strain generating body 2 with the point P as a supporting point. As a result, in the peripheral portion of the shaft hole 2 a of the strain generating body 2, stress concentration points applied to the washers 5 and 6 are extremely unevenly distributed, and there is a distortion that adversely affects the characteristics of the strain element 1. It will occur in the strain body 2. A load sensor in which such distortion is likely to occur in the strain generating body 2 during mounting is difficult to obtain high reliability because the output value of the strain element 1 is likely to vary from product to product even when an equivalent load is applied to the load point 2b. Become. Note that the inclination of the nut 7 (or 8) as shown in FIG. 10 may occur to some extent due to the tolerance of the thread grooves formed in the nuts 7 and 8 and the bolt 3.
[0005]
The present invention has been made in view of such a state of the art, and its purpose is to provide a highly reliable structure in which a strain generating body can be easily and reliably attached to a fixed shaft body without adversely affecting the characteristics of the strain element. It is in providing a load sensor.
[0006]
[Means for Solving the Problems]
In order to achieve the above-described object, the load sensor of the present invention includes a plate-like strain body having a shaft hole provided at a position away from a load point at which a load acts, and the load point of the strain body. A strain element mounted between the shaft hole, a spacer member disposed opposite to a peripheral portion of the shaft hole of the strain body, and the strain body through the shaft hole and the spacer member. A fixed shaft body to be supported; and a pressure member that is fixed to the fixed shaft body and pressurizes the spacer member in a plate thickness direction of the strain-generating body, the seat being in contact with the pressure member among the spacer members The surface was set to have a smaller diameter than the pressure member.
[0007]
In this way, if the seating surface of the spacer member that contacts the pressure member is made smaller than the pressure member, it is assumed that pressure is applied to the spacer member while the pressure member is inclined with respect to the fixed shaft body. However, since only the inner peripheral portion of the spacer member is directly pushed into the pressure member, a phenomenon that a part of the spacer member is lifted and separated from the strain generating body does not occur. Therefore, when attaching the strain body to the fixed shaft body, there is no concern that the stress concentration points of the strain body due to the spacer member will be extremely unevenly distributed around the shaft hole, and the characteristics of the strain element will be adversely affected. Therefore, the strain body can be securely attached to the fixed shaft body. In addition, it is preferable that the fixed shaft body is made of a bolt in which a screw is engraved and the pressure member is made of a nut fastened to the bolt, because the attaching work of the strain generating body can be easily performed.
[0008]
Further, in this configuration, the spacer member is composed of a pair of washers in which a flange portion projects from the substantially central cylindrical portion to the outside in the radial direction, and the cylindrical portions of both washers are laminated to form a strain generating body. If the end surface of the cylindrical portion located outside the shaft hole is used as the seat surface, the interval between the collar portions of both washers can be accurately defined. The axial hole peripheral portion of the strain generating body can be arranged without difficulty between the flanges. Then, the gap between the flanges is set to be larger than the plate thickness of the strain-generating body, and a gap is formed between the axial hole peripheral portion of the strain-generating body and the flange, and this gap is filled with an adhesive fixing agent. In this case, the pressure applied by both washers is dispersed by the adhesive fixing agent and applied to the strain generating body, which is preferable because excessive stress concentration on the strain generating body can be suppressed.
[0009]
Alternatively, in this configuration, the spacer member is a tube spacer disposed in the shaft hole of the strain body, and a pair of convex washers whose one end surface is the seating surface and the other end surface is in contact with the tube spacer. It is also possible that these both convex washers are pressed against the pressure member to pinch the tube spacer. Also in this case, the axial dimension of the tube spacer is set to be larger than the plate thickness of the strain-generating body, and a gap is formed between the axial hole peripheral portion of the strain-generating body and the convex washer. Is preferably filled with an adhesive fixing agent.
[0010]
Alternatively, in this configuration, a concave or convex pressed portion is provided at a predetermined location around the shaft hole of the strain generating body, the pressed portion is pressed by a spacer member, and the covered It is also possible to keep the surface of the strain generating body excluding the pressing portion in non-contact with the spacer member. In this case, since the pressurizing force of the spacer member is always applied only to the specific portion (the pressed portion) at the peripheral portion of the shaft hole of the strain generating body, the stress concentration portion of the strain generating body by the spacer member is around the shaft hole. A uniform distribution can be obtained.
[0011]
Moreover, in each structure mentioned above, if the plate | board thickness of a shaft hole peripheral part is set larger than the plate | board thickness of the part which mounts a distortion element among strain generating bodies, a load will be added to a load point. When the strain generating body is bent, the starting point of the deformation is limited to the boundary between the portion where the plate thickness is small and the portion where the plate thickness is large and does not vary, so that the detection accuracy can be improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of the main part of a load sensor according to a first embodiment, and FIG. 2 is an overall perspective view of the load sensor shown in FIG. 3 is a plan view of the strain generating body shown in FIGS. 1 and 2, FIG. 4 is a cross-sectional view of the main part of the load sensor according to the second embodiment, and FIG. 5 is the main part of the load sensor according to the third embodiment. FIG. 6 is a sectional view of a principal part of a load sensor according to a fourth embodiment, FIG. 7 is a plan view of a principal part of a load sensor according to a fifth embodiment, and FIG. It is sectional drawing which follows a line, and the same code | symbol is attached | subjected to the part corresponding to FIG.
[0013]
First, the first embodiment will be described with reference to FIGS. 1 to 3. Reference numeral 1 in the figure denotes a strain element made of a thick film resistor, and 2 denotes a strain element 1 having a shaft hole 2a. A strain gauge is constituted by the strain element 1 and the strain body 2. As shown in FIG. 2, the load sensor according to the present embodiment is for detecting the weight of the passenger incorporated in the seat of the automobile, and is a load point provided at the tip of the strain body 2. A passenger's load acts on 2b via the arm 17 fixed to the seat side. Reference numeral 3 denotes a bolt as a fixed shaft body, and the bolt 3 is fixed to a seat frame 4 as an installation member using a nut 9. Reference numerals 7 and 8 are nuts screwed to the bolt 3 as pressure members. Reference numerals 10 and 11 denote convex washers that are extrapolated to the bolt 3 as spacer members, and the pair of convex washers 10 and 11 are opposed to the front and back surfaces of the peripheral portion of the shaft hole 2a of the strain body 2. And clamped and fixed by a pair of nuts 7 and 8. However, the seating surface 10a of the convex washer 10 in contact with the nut 7 and the seating surface 11a of the convex washer 11 in contact with the nut 8 are set to have a smaller diameter than the nuts 7 and 8, The outer peripheral portions of the nuts 7 and 8 are not brought into contact with the convex washers 10 and 11.
[0014]
In this embodiment, as shown in FIG. 3, the strain elements 1 are arranged at four positions on the upper surface of the strain generating body 2, and the Wheatstone bridge formed by connecting these four strain elements 1. Four terminals 1a of the circuit are gathered at the end of the strain body 1 on the shaft hole 2a side.
[0015]
In the configuration described above, when the strain generating body 2 (strain gauge) on which the strain element 1 is mounted is attached to the bolt 3, the nut 8 is screwed onto the bolt 3, and then the convex washer 11 is removed from the bolt 3. Further, the peripheral portion of the shaft hole 2 a of the strain generating body 2 is extrapolated to the bolt 3. Thereafter, the convex washer 10 is extrapolated to the bolt 3, and the nut 7 is screwed onto the bolt 3 to tighten both nuts 7 and 8. Thus, the convex washers 10 and 11 are sandwiched between the pair of nuts 7 and 8 along the plate thickness direction of the strain generating body 2 (the axial direction of the bolt 3). The peripheral edge portion of the shaft hole 2a is sandwiched between the convex washers 10 and 11. That is, the strain body 2 is supported by the bolt 3 via the convex washers 10 and 11.
[0016]
As described above, in the present embodiment, the small-diameter seating surfaces 10a and 11a of the convex washers 10 and 11 holding the strain body 2 are in contact with the nuts 7 and 8, so that the nuts 7 and 8 are Even when tightened while being tilted with respect to the bolt 3, the clamping pressure is directly applied from the nuts 7 and 8 only to the inner peripheral portions of the convex washers 10 and 11. The hook-shaped portions 10b and 11b are not lifted up and separated from the strain generating body 2. That is, when the strain body 2 is attached to the bolt 3, there is no fear that the stress concentration portions of the strain body 2 by the convex washers 10 and 11 are extremely unevenly distributed around the shaft hole 2a. Therefore, the strain generating body 2 can be easily and reliably attached to the bolt 3 without adversely affecting the characteristics of the strain element 1, and a highly reliable load sensor can be obtained.
[0017]
In the second embodiment shown in FIG. 4, as a spacer member sandwiched between the nuts 7 and 8, a pair of flange portions 12b and 13b projecting radially outward from the substantially central cylindrical portions 12c and 13c. Washers 12 and 13 are used, and the cylindrical portions 12c and 13c of both washers 12 and 13 are laminated and disposed in the shaft hole 2a of the strain generating body 2. When such washers 12 and 13 are used, the interval between the flange portions 12b and 13b can be accurately defined. Therefore, the peripheral portion of the shaft hole 2a of the strain body 2 is interposed between the flange portions 12b and 13b. Can be arranged without difficulty. However, in FIG. 4, the interval between the flanges 12b and 13b is set to be slightly larger than the plate thickness of the strain-generating body 2, so that the peripheral edges of the laminated washer 12 and 13 and the shaft hole 2a of the strain-generating body 2 A gap is formed between the portions, and the gap is filled with an anaerobic adhesive 14 that hardly shrinks even when cured. Further, the upper end surface of the cylindrical portion 12c of the washer 12 is formed as a seat surface 12a that contacts the nut 7, and the lower end surface of the cylindrical portion 13c of the washer 13 is configured as a seat surface 13a that contacts the nut 8. These seat surfaces 12 a and 13 a are set to have a smaller diameter than the nuts 7 and 8.
[0018]
Therefore, in this embodiment, when the nuts 7 and 8 are tightened and the washers 12 and 13 are clamped and fixed, the pressure applied by the washers 12 and 13 is applied to the shaft hole 2a of the strain generating body 2 via the adhesive 14. Therefore, excessive stress concentration on the strain generating body 2 can be suppressed. Moreover, since the small-diameter seat surfaces 12a and 13a are in contact with the nuts 7 and 8 as in the first embodiment, the nuts 7 and 8 are tightened while being inclined with respect to the bolts 3. Even in this case, the flanges 12b and 13b are not lifted and separated from the strain generating body 2, so that the stress concentration portions of the strain generating body 2 by the washers 12 and 13 tend to be almost uniformly distributed around the shaft hole 2a. . For this reason, the characteristics of the strain element 1 become extremely stable, and the reliability of the load sensor can be further enhanced.
[0019]
In the third embodiment shown in FIG. 5, as a spacer member sandwiched between nuts 7 and 8, a tube spacer 15 which is longer than the plate thickness of the strain generating body 2 and is disposed in the shaft hole 2a, and this tube A pair of convex washers 16 and 17 that are stacked on top and bottom of the spacer 15 are used. One convex washer 16 has an upper end surface as a small-diameter seat surface 16 a that abuts the nut 7, and an inner peripheral portion of the lower end surface abuts the tube spacer 15. Similarly, the other convex washer 17 has a lower end surface as a small-diameter seat surface 17 a that abuts the nut 8, and an inner peripheral portion of the upper end surface abuts the tube spacer 15. Therefore, when the nuts 7 and 8 are tightened, the bi-convex washers 16 and 17 pinch the pipe spacer 15, and the overall shape of the spacer member is substantially the same as that of the pair of washers 12 and 13 shown in FIG. Will be the same. In the case of this embodiment as well, the anaerobic adhesive 14 is provided in the gap between the spacer member composed of the tube spacer 15 and the convex washers 16 and 17 and the peripheral portion of the shaft hole 2a of the strain body 2. Is filled.
[0020]
In the fourth embodiment shown in FIG. 6, as spacer members sandwiched between the nuts 7 and 8, flanges 18b and 19b project from the substantially central cylindrical portions 18c and 19c to the outer side in the radial direction. A pair of washers 18 and 19 are used in which end portions on the seating surfaces 18a and 19a side of the shaped portions 18c and 19c are tapered surfaces. Both washers 18 and 19 are formed by stacking cylindrical portions 18c and 19c in the shaft hole 2a of the strain body 2, and the peripheral portion of the shaft hole 2a of the strain body 2 and the flange portion 18b, An anaerobic adhesive 14 is filled in a gap between the gap 19b. Further, in the present embodiment, the plate thickness in the vicinity of the shaft hole 2a in the strain generating body 2 is larger than the plate thickness of the extending portion on which the strain element 1 is mounted. In this way, if the plate thickness of the strain generating body 2 is increased at the base end opposite to the load point 2b, when the strain is applied to the load point 2b and the strain generating body 2 is bent, its deformation Since the starting point is limited to the boundary Q between the portion where the plate thickness is small and the portion where the plate thickness is large, the detection accuracy can be improved.
[0021]
In the fifth embodiment shown in FIGS. 7 and 8, a plurality of concave pressed portions 2c and 2d (for example, four each) are provided on both the front and back surfaces of the strain generating body 2 in the vicinity of the shaft hole 2a. The pair of convex washers 20 and 21 that are externally attached to the bolt 3 and face each other via the strain body 2 have the small-diameter seating surfaces 20a and 21a abutted against the nuts 7 and 8, respectively. The convex washers 20 and 21 are provided with a plurality of pressing protrusions 20b and 21b inserted into the pressed portions 2c and 2d of the strain generating body 2, respectively. These convex washers 20 and 21 are clamped by the nuts 7 and 8 and fixed to the bolt 3 with the pressing protrusions 20b and 21b inserted into the corresponding pressed parts 2c and 2d. The strain body 2 is pinched by the convex washers 20 and 21 at a plurality of pressed portions 2c and 2d. However, the front and back surfaces of the strain generating body 2 excluding the pressed parts 2c and 2d are kept in non-contact with the convex washers 20 and 21.
[0022]
That is, in this embodiment, the location (pressed portion 2c, 2d) where the strain body 2 is clamped is specified in advance, and the stress concentration location of the strain body 2 by the convex washers 20, 21 is determined. A uniform distribution can be obtained around the shaft hole 2a. Since the small-diameter seating surfaces 20a and 21a of the convex washers 20 and 21 are brought into contact with the nuts 7 and 8, even when the nuts 7 and 8 are tightened while being inclined with respect to the bolt 3, The protrusions 20b and 21b are not lifted up and separated from the strain generating body 2. In this embodiment, a convex pressed portion may be provided in the vicinity of the shaft hole 2a of the strain body 2 so as to be clamped.
[0023]
In each of the above-described embodiments, the case where the bolt 3 is used as the fixed shaft body and the nuts 7 and 8 are screwed and tightened to the bolt 3 is illustrated, but a screw groove is provided like a rivet. When the strain body 2 is attached to a fixed shaft body that is not present, a spacer member such as a washer may be pressed by a technique such as caulking.
[0024]
【The invention's effect】
The present invention is implemented in the form as described above, and has the following effects.
[0025]
A load sensor that attaches a strain body to a fixed shaft body by pressurizing a spacer member such as a washer with a pressure member such as a nut. The seating surface of the spacer member that contacts the pressure member has a smaller diameter than the pressure member. Therefore, even when pressure is applied to the spacer member while the pressure member is tilted with respect to the fixed shaft body, a phenomenon in which a part of the spacer member is lifted away from the strain body does not occur. . Therefore, when attaching the strain generating body to the fixed shaft body, there is no concern that the stress concentration portion of the strain generating body due to the spacer member will be extremely unevenly distributed around the shaft hole, and the characteristics of the strain element are adversely affected. It is possible to easily and reliably attach the strain generating body to the fixed shaft body without affecting, and a highly reliable load sensor can be obtained.
[0026]
Further, in this configuration, the spacer member is composed of a pair of washers in which a flange portion projects from the substantially central cylindrical portion to the outside in the radial direction, and the cylindrical portions of both washers are laminated to form a strain generating body. If the end surface of the cylindrical portion located outside the shaft hole is used as the seat surface, the interval between the collar portions of both washers can be accurately defined. The axial hole peripheral portion of the strain generating body can be arranged without difficulty between the flanges. Then, the gap between the flanges is set to be larger than the plate thickness of the strain-generating body, and a gap is formed between the axial hole peripheral portion of the strain-generating body and the flange, and this gap is filled with an adhesive fixing agent. If so, the applied pressure of the spacer member is dispersed by the adhesive fixing agent and applied to the strain generating body, so that excessive stress concentration on the strain generating body can be suppressed.
[0027]
In addition, a concave or convex pressed portion is provided at a predetermined location around the shaft hole of the strain generating body, the pressed portion is not pressed by the spacer member, and the pressed portion is excluded. If the surface of the strain body is configured so as to be kept in non-contact with the spacer member, the peripheral edge of the shaft hole of the strain body is always subjected to the pressing force of the spacer member only at a specific location (pressed portion). Therefore, the stress concentration portion of the strain generating body by the spacer member can be made to be uniform around the shaft hole.
[0028]
Also, if the plate thickness at the periphery of the shaft hole is set larger than the plate thickness of the portion where the strain element is mounted, the strain body is deflected by applying a load to the load point. At this time, since the starting point of the deformation is limited to the boundary between the portion where the plate thickness is small and the portion where the plate thickness is large, the detection accuracy can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a load sensor according to a first embodiment of the present invention.
2 is an overall perspective view of the load sensor shown in FIG. 1. FIG.
FIG. 3 is a plan view of the strain generating body shown in FIGS.
FIG. 4 is a cross-sectional view of a main part of a load sensor according to a second embodiment of the present invention.
FIG. 5 is a cross-sectional view of a main part of a load sensor according to a third embodiment of the present invention.
FIG. 6 is a cross-sectional view of a main part of a load sensor according to a fourth embodiment of the present invention.
FIG. 7 is a plan view of an essential part of a load sensor according to a fifth embodiment of the present invention.
8 is a cross-sectional view taken along line AA in FIG.
FIG. 9 is a cross-sectional view of a main part of a load sensor according to a conventional example.
FIG. 10 is an explanatory diagram showing a problem of the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Strain element 2 Strain body 2a Shaft hole 2b Load point 2c, 2d Pressed part 3 Bolt (fixed shaft body)
7,8 Nut (Pressurizing member)
10-13, 16-21 Washer (spacer member)
10a to 13a, 16a to 21a Seat surface 12b, 13b, 18b, 19b Ridge part 12c, 13c, 18c, 19c Tubular part 14 Adhesive 15 Pipe spacer

Claims (8)

A plate-like strain generating body provided with a shaft hole at a position away from a load point on which a load acts, a strain element mounted between the load point of the strain generating body and the shaft hole, A spacer member disposed opposite to the peripheral edge portion of the shaft hole of the strain body, a fixed shaft body that passes through the shaft hole and supports the strain body through the spacer member, and is fixed to the fixed shaft body and A pressure member that pressurizes the spacer member in the plate thickness direction of the strain body, and a seating surface that contacts the pressure member among the spacer members is set to have a smaller diameter than the pressure member. Load sensor. 2. The load sensor according to claim 1, wherein the fixed shaft body is made of a bolt engraved with a screw, and the pressure member is made of a nut fastened to the bolt. The spacer member according to claim 1 or 2, wherein the spacer member includes a pair of washers formed by projecting a flange portion radially outward from a substantially central cylindrical portion, and the cylindrical portions of both washers are stacked. The load sensor is arranged in the shaft hole of the strain body and the end surface of the cylindrical portion located outside the shaft hole serves as the seat surface. 4. The shaft of the strain-generating body according to claim 3, wherein an interval between the flange portions of the pair of washers in which the cylindrical portions are stacked is set larger than a plate thickness of the strain-generating body. A load sensor characterized in that a gap is formed between a hole peripheral portion and the flange, and the gap is filled with an adhesive fixing agent. 3. The spacer according to claim 1, wherein the spacer member is a tube spacer disposed in the shaft hole of the strain body, and one end surface is used as the seat surface and the other end surface is brought into contact with the tube spacer. A load sensor comprising: a pair of convex washers, wherein both the convex washers are pressed by the pressure member to sandwich the tube spacer. The length of the tube spacer in the axial direction according to claim 5 is set to be larger than the plate thickness of the strain generating body, whereby the axial hole peripheral portion of the strain generating body and the convex washer A load sensor characterized in that a gap is formed between the gaps and an adhesive fixing agent is filled in the gap. 3. The concave or convex pressed portion is provided at a predetermined position on the peripheral edge portion of the shaft hole of the strain generating body according to claim 1 or 2, and the pressed portion is pressed by the spacer member. The load sensor is configured such that the surface of the strain generating body excluding the pressed portion is kept in non-contact with the spacer member. In any one of Claims 1-7, The plate | board thickness of the said shaft hole peripheral part among the said strain generating bodies was set larger than the plate | board thickness of the part which mounts the said strain element, It is characterized by the above-mentioned. Load sensor.

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