JPH0674942U - Load cell - Google Patents

Abstract

(57) [Abstract] [Purpose] In a strain gauge type load cell having a fixed beam structure at both ends, a highly accurate and stable load cell can be easily realized while keeping the outer shape small and thin. [Structure] An outer peripheral fixing portion 1 and a center applying portion 2 are connected by a plurality of beam strain-generating portions 3 ', and two strain gauges are provided above and below the middle portion of each strain-generating portion 3', a total of four strain gauges. 4 is attached, and the cross section of the beam straining portion 3 ′ is formed as a curved surface such that a portion near the outer periphery fixing portion and the center applying portion is thick and a middle portion is thin, so that the outer periphery fixing portion and the center applying portion are formed. It was constructed so that high precision could be obtained by reducing the influence of stress inflow from the.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a strain gauge type thin load cell having a beam structure fixed at both ends.

[0002]

[Prior art]

 As a conventional strain gauge type load cell of this type, there are one having a structure shown in FIGS. 5A, 5B, 6 and 7 and one disclosed in JP-A-2-272336. In FIG. 5, reference numeral 1 denotes an outer peripheral fixing portion of a pressure plate, 2 is a central load applying portion, and 3 is a rectangular beam structure having a uniform thickness connecting the outer peripheral fixing portion 1 and the central applying portion 2. The strain gages 4 and 4 are strain gauges attached to the beams 3 of the strain gage 3 at two positions above and below, respectively. The strain gages are detected by detecting the load W applied to the central application part. It is designed to be converted into a signal and taken out. FIG. 6 is a stress distribution diagram of the load cell, in which the outer peripheral fixed portion side is a and the central application portion side is b, and the center of the beam is zero and linearly increases in the outer peripheral direction and the central direction. In this conventional load cell, the gauge distance L must be increased in order to obtain a necessary and sufficient value for stress detection, but the gauge sticking position is close to the outer peripheral fixing portion 1 and the center applying portion 2. It is inevitable to do it. Moreover, in this case, when the necessary stress is detected by the gauge, the outer peripheral fixing portion 1 is easily affected by the mounting surface state, and the central application portion 2 is easily affected by the applied load on the contact surface stress. Further, it becomes easy to be affected by stress concentration at the joint between the rectangular beam 3 and the rigid bodies 1 and 2. That is, the stresses 5 and 6 flowing in from the outer peripheral fixed portion 1 and the central application portion 2 are more likely to affect the characteristics, and the balance of the stress distribution detected by each strain gauge is upset, so that the straight line in the load-output characteristic is affected. As a result, it was not possible to realize a highly accurate load cell.

Further, as shown in FIG. 7, there is a conventional technique in which the strain-flexing part structure has a uniform thickness and a curved surface in the width direction as shown in FIG. 7, but in this structure, the maximum stress is the beam 7 Although the influence of stress that occurs from the central application part and leads to a decrease in accuracy from the outer peripheral fixed part and the load contact surface is reduced, the width of the strain generating part becomes extremely narrow in the small capacity load cell, and the space for attaching the strain gauge is reduced. There was a limit to miniaturization.

[0004]

[Problems to be solved by the device]

 In the strain gauge type load cell having the fixed beam structure at both ends, in the above-mentioned conventional structure, the stress distribution is linear as shown in FIG. 6, and it is necessary to lengthen the inter-gauge distance L in order to obtain necessary and sufficient stress. Therefore, the gauge position is located very close to the outer circumference fixed part and the center applied part, so the balance of the detected stress distribution is lost due to the stress flowing from the fixed part and the applied part side, and the output characteristics It was impossible to manufacture high-precision products because the linearity was obstructed. Therefore, in order to eliminate these adverse effects, consideration should be given to making the outer circumference fixed part stronger than necessary or to place the strain gauge away from the part that causes the error factor by increasing the overall height and outer shape. Therefore, it was difficult to realize a compact, lightweight and thin load cell. Therefore, the present invention intends to provide a small and thin high-precision load cell by removing the error factor by changing the structure of the beam straining portion.

[0005]

[Means for Solving the Problems]

 In this invention, in a strain gauge type load cell having a beam structure fixed at both ends, the cross section of a plurality of beam strain portions connecting the outer fixed portion and the central application portion is made thicker in the portion near the outer fixed portion and the central application portion. However, the curved surface that makes the middle part thinner reduces the flow of stress from the outer fixed part and the center applying part to the beam strain part, so that high accuracy can be realized while keeping the outer size small and thin. It is characterized by being formed.

[0006]

[Action]

 The cross-sectional shape of the beam strain section that connects the outer fixed section and the center application section has a curved surface that thickens the section near the outer fixation section and the center application section and thins the middle section. The flow of stress from the center can be reduced, and a highly accurate, stable, compact and thin load cell can be realized.

[0007]

【Example】

 A first embodiment is shown in FIGS. 1A, 1B and 2. In the load cell of the present invention, the same portion as the load cell described in FIG. 5 described above is attached to the pressure plate-shaped outer peripheral fixing portion of 1, the center load applying portion of 2 and each beam strain portion. Is a strain gauge of. The different part is the structure of the beam straining part. As shown in the figure, the beam is changed to the conventional rectangular cross-section beam 3, the part near the outer peripheral fixing part 1 and the center applying part 2 is thickened, and the middle part is thinned. The beam strained portion 3 ′ having such a curved surface is formed. Therefore, as shown in FIG. 2, assuming that the outer peripheral fixed portion side is a and the center applied portion side is b, a non-linear stress distribution exhibiting the maximum stress near the middle portion of the beam straining portion 3 ′. Can be obtained. That is, the strain gauge sticking position 4 described above can also be arranged closer to the middle portion of the beam straining portion 3 ', so that the gauge gap 1 is shorter than L in FIG. 5 shown in the conventional example. Therefore, it is possible to secure a long distance of the strain gauge 4 from each of the outer periphery fixing portion 1 and the center applying portion 2, and the linearity in the characteristics due to the stresses 5 and 6 flowing from the outer periphery fixing portion 1 and the center applying portion 2 can be ensured. The influence can be reduced as much as possible. Although the number of beam strained portions is four in the figure, the number is not limited as long as it is plural.

A second embodiment is shown in FIGS. 3A and 3B. In this embodiment, the outer peripheral fixing portion of the first embodiment described above is formed into a thick-walled rectangular shape 1'instead of being formed into a thick-walled disc shape. Therefore, the central application portion 2'is also formed into a rectangular shape. Has become.

Further, a third embodiment is shown in FIGS. 4A and 4B. In this embodiment, as shown in the above-mentioned first and second embodiments, the outer circumference is changed to a circular shape or a rectangular shape to have a simple fixed shape at both ends 8 and 8 ', and a load is applied to the central applying portion 2'. However, the characteristics of the load cell are similar to those of the above-mentioned embodiment.

[0010]

[Effect of device]

 According to this invention, since the strain gauge can be arranged away from the outer fixing part and the center applying part that adversely affect the accuracy, it is possible to reduce the influence of the stress flowing from the outer fixing part and the center applying part. Furthermore, since the distance between the gauges can be shortened, the length of the beam straining portion can be shortened, which has the effect of realizing a highly accurate load cell with a small and thin shape.

[Brief description of drawings]

FIG. 1 is a plan view A and X- according to a first embodiment of the present invention.
It is an X sectional view B.

FIG. 2 is a stress distribution diagram of a beam straining portion of the present invention.

FIG. 3 is a plan view A and Y- according to a second embodiment of the present invention.
It is a Y sectional view B.

FIG. 4 is a plan view A and Z- according to a third embodiment of the present invention.
It is Z sectional drawing B.

FIG. 5 is a plan view A and a cross-sectional view X'-X 'of a conventional load cell.

FIG. 6 is a stress distribution diagram of a beam strain portion in a conventional load cell.

FIG. 7 is a plan view of a load cell according to another conventional example.

[Explanation of symbols]

 1, 1'outer peripheral fixing part 2, 2'center applying part 3, 3'beam strain part 4 strain gauge 5 stress inflow from outer peripheral fixing part 6 stress inflow from central applying part 7 beam of another conventional example Deflection part 8, 8'Simple end fixing part

Claims (2)

[Scope of utility model registration request] 1. A strain gauge type load cell having a circular or rectangular outer periphery, a load applying portion having the same shape as the outer periphery being formed in the center, and the outer periphery and the central applying portion being connected by a plurality of beam straining portions, The cross section of the strain generating section is a curved surface with a thicker portion near the outer peripheral fixing section and the central load applying section, and a thinner intermediate section, and the influence of the stress flow from the outer peripheral fixing section and the load applying section to the beam strain section. Strain gauge type load cell characterized by high accuracy with less load. 2. A strain gauge type load cell, wherein the outer peripheral fixing portion in claim 1 has a simple fixed shape at both ends instead of a circular shape or a rectangular shape.