load cell

Abstract

To provide a high-accuracy load cell configured to be less subjected to stresses other than weight.SOLUTION: A strain element 11 is cut out of an integral metal block. An annular frame body part 13 is arranged around a weight receiving part 12. A first movable beam part 14 with a strain gauge 17 bonded thereto is provided between the weight receiving part 12 and the frame body part 13. One end of the first movable beam part 14 is coupled to the weight receiving part 12 while the other end thereof is coupled via a second movable beam part 21 provided on the frame body part 13 to the frame body part 13. The second movable beam part 21 is arranged so that a longer direction is perpendicular to the first movable beam part 14 and is connected to the first movable beam part 14 at a center part 23. The second movable beam part 21 is connected to the frame body part 13 at end edges 22 on both sides. Gaps between the center part 23 and the end edges 22 on both sides are bridged by two plate bodies 24a, 24b, respectively so that a groove part 25 vertically penetrating is provided. As a result, a flexible bending mechanism is achieved.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a load cell that is low in height, thin, easy to process, and has high precision.

Background Art

[0002] In Patent Document 1, for example, as shown in the perspective view of FIG. 4, the strain generating body 11 of the load cell is cut out from a metal block by cutting. An annular frame body 13 is arranged around a columnar load receiving portion 12 located at the center of the strain generating body 11, and between the load receiving portion 12 and the frame body 13, for example, three prismatic movable beam portions 14 are radially spanned.

[0003] One end of each movable beam portion 14 is directly connected to the load receiving portion 12, and the other end is joined to the frame body 13 through a wall portion 15 provided on the frame body 13. The wall portion 15 is arranged on the frame body 13 in a direction perpendicular to the movable beam portion 14, and is integrated with the frame body 13 at the lower portions of both side edges thereof, and the wall portion 15 has flexibility in the direction of the movable beam portion 14.

[0004] An elliptical hole portion 16 that crosses horizontally is drilled in the movable beam portion 14, and a Roberval mechanism is constituted. Strain gauges 17 are respectively attached to the thin-walled beam portions on the upper and lower surfaces of the hole portion 16. In addition, a screw hole 18 for connecting to a load load is drilled in the load receiving portion 12.

[0005] When a load load is applied to the load receiving portion 12 in the vertical direction, the load is divided into three equal parts, and in each movable beam portion 14, the load can be measured by the strain gauges 17 that constitute a Wheatstone bridge circuit, so the outputs of the respective strain gauges 17 may be added. In this case, in the movable beam portion 14, deformation due to tension other than bending strain that occurs in proportion to the load occurs. This deformation affects hysteresis, but since the wall portion 15 provided on the frame body 13 flexes in the direction of the movable beam portion 14, this extra deformation is absorbed, so the output of the strain gauge 17 can measure the load without being affected by this hysteresis. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent Publication No. 2962703 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in this conventional load cell, as shown in Figure 5, when a load Fa from above is applied to the load receiving section 12, both lower ends of the wall section 15 are fixed and the middle section is flexible. As a result, compressive stress is generated in the upper central part of the wall section 15 in the direction of the movable beam section 14, and tensile stress is generated in the lower part, creating a rotational moment Ma as indicated by the arrow, centered on the longitudinal axis of the wall section 15. Also, as shown in Figure 6, when a load Fb from below is applied to the load receiving section 12, a rotational moment Mb as indicated by the arrow is similarly generated in the wall section 15. These rotational moments M are added to the output of the strain gauge 17, causing a decrease in measurement accuracy.

[0008] The object of the present invention is to solve the above-mentioned problems and provide a load cell that can obtain high-precision output by employing a deflection mechanism using a flexible plate to reduce the rotational moment applied to the first movable beam to which the strain gauge is attached, and to effectively absorb excess deformation hysteresis. [Means for solving the problem]

[0009] To achieve the above objective, the load cell according to the present invention has a strain generating body formed by processing a single metal block, the strain generating body has a load receiving portion in the center and an annular frame portion on its outer circumference, a plurality of rectangular prismatic first movable beam portions having holes and to which strain gauges are attached, projecting horizontally and radially outward from the load receiving portion, a second movable beam portion is arranged on the frame portion in a direction perpendicular to the longitudinal direction of the first movable beam portion, and the end of the first movable beam portion is connected to the center of the longitudinal direction of the second movable beam portion, the second movable beam portion has a rectangular cross-section, and a deflection mechanism is provided between the end edges on both sides joined to the frame portion and the central portion. The bending mechanism comprises two plates placed parallel to each other between the central portion and the edges on both sides, and a slit-shaped groove that penetrates vertically between the two plates. It is characterized by the following. [Effects of the Invention]

[0010] The load cell according to the present invention has a second movable beam positioned between a first movable beam and a frame, and accurate measurement values ​​can be obtained through the function of the second movable beam. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view of the load cell in the example. [Figure 2] Plan view. [Figure 3] This is an explanatory diagram of the second movable beam section when a load is applied. [Figure 4] This is a perspective view of a conventional load cell. [Figure 5] This is an explanatory diagram showing a conventional load cell with a load applied from above. [Figure 6] This is an explanatory diagram showing a conventional load cell with a load applied from below. [Modes for carrying out the invention]

[0012] The present invention will be described in detail based on the embodiments shown in Figures 1 to 3. Figure 1 is a perspective view of the load cell in this embodiment, and Figure 2 is a plan view. Note that the same reference numerals as in the conventional example indicate the same parts.

[0013] The strain generating body 11 is formed by cutting a single metal block made of steel, aluminum, etc., using a lathe, milling machine, etc. An annular frame portion 13 is arranged at a distance from a cylindrical load-receiving portion 12 positioned vertically at the center of the strain generating body 11, and for example, three rectangular prism-shaped first movable beam portions 14 are radially spanned between the load-receiving portion 12 and the frame portion 13.

[0014] One end of each first movable beam section 14 is directly connected to the load-receiving section 12, while the other end is connected to the frame section 13 via a second movable beam section 21. The second movable beam section 21 is a rectangular member with a square cross-section, positioned perpendicular to the longitudinal direction of the first movable beam section 14 and provided at three locations on the frame section 13.

[0015] The lower parts of the edges 22 on both sides of the second movable beam section 21 are integrally joined to the frame section 13, the intermediate section including the central section 23 between the edges 22 is separated upward from the frame section 13, and the other end of the first movable beam section 14 is joined to the central section 23 of the second movable beam section 21.

[0016] A deflection mechanism is configured between the central part 23 and the edges 22 on both sides of the second movable beam section 21. In this deflection mechanism, two parallel plates 24a and 24b, which are flexible in the thickness direction, are arranged opposite each other with a gap between them. In other words, a slit-shaped groove 25 that penetrates in the vertical direction is formed between the two plates 24a and 24b.

[0017] A total of four strain gauges 17 are attached to the thin-walled beam sections on the upper and lower surfaces of the holes 16 that constitute the Roberval mechanism of the first movable beam section 14. Lead wires (not shown) connected to the strain gauges 17 are routed along the first movable beam section 14, and the four strain gauges 17 constitute a Wheatstone bridge circuit, although the lower strain gauge 17 is not shown.

[0018] Note that the load receiving portion 12 is drilled with a screw hole 18 for connecting to a load load, and the frame body portion 13 is formed with a plurality of through holes 19 for fixing the strain generating body 11 to other members.

[0019] Illustrating the dimensions of the second movable beam portion 21 of the embodiment, the diameter of the frame body portion 13 is 84 mm, the horizontal length of the second movable beam portion 21 is 46 mm, the horizontal thickness is 5 mm, the vertical height is 8 mm, the lengths of the plate bodies 24a and 24b are 12.5 mm, the thickness is 1 mm each, and the inner width of the groove portion 25 which is the gap between the plate bodies 24a and 24b is 3 mm.

[0020] Note that the length of the wall portion 15 of the conventional example shown in FIG. 4 is 46 mm, the thickness is 2 mm, and the vertical height is 8 mm.

[0021] When a load to be measured is applied to this strain generating body 11 via the load receiving portion 12, the load is divided into three equal parts, and the first movable beam portion 14 intervening between the load receiving portion 12 and the frame body portion 13 has a thin-walled beam portion deformed, and the load applied by the attached strain gauge 17 can be measured. What is necessary is just to add the outputs by the strain gauges 17 of the three first movable beam portions 14.

[0022] At this time, as exaggeratedly shown in FIG. 3, when a load F is applied to the load receiving portion 12, the second movable beam portion 21 can effectively bend the central portion 23 in the direction of the first movable beam portion 14 by a bending mechanism by the two plate bodies 24a and 24b, and similar to the wall portion 15 of the conventional example, it is possible to absorb the influence of deformation due to tension other than bending strain due to the load.

[0023] In this case, the thicknesses of the plate bodies 24a and 24b of the second movable beam portion 21 are 1 mm each and the total is 2 mm, which is the same as the thickness of 2 mm of the conventional example. However, since the second movable beam portion 21 employs a bending mechanism by the plate bodies 24a and 24b with a plate thickness of 1 mm that is easy to bend, it has more flexibility than the conventional example and can sufficiently absorb extra tension.

[0024] Furthermore, in conventional load cells, as mentioned above, the wall portion 15 tends to rotate around its longitudinal axis, and this rotational moment M inevitably affects the output of the strain gauge 17 in synergy with the measured value. However, in the load cell according to this embodiment, the second movable beam portion 21 has a wall thickness of 5 mm in the direction of the first movable beam portion 14, which is significantly larger than the 2 mm wall thickness of the conventional example. Therefore, even if the aforementioned rotational moment M is generated, its magnitude decreases inversely proportional to the wall thickness, becoming about 2 / 5 of that of the conventional example.

[0025] Therefore, the second movable beam section 21 of this embodiment has greater flexibility than conventional examples due to the deflection mechanism, while the rotational moment M generated is smaller than in conventional examples, thus improving measurement accuracy.

[0026] In the strain-generating body 11, the first movable beam section 14 and the second movable beam section 21 are located above the frame section 13, so these movable beam sections 14 and 21 can be machined as needed without being obstructed by other parts.

[0027] In this embodiment, the first movable beam section 14 was described as having a Roberval structure. However, even without extending the hole 16 horizontally, the middle of the hole 16 can be made into a dead end, a strain gauge 17 can be attached to this dead end, and the shear stress in the first movable beam section 14 can be measured to determine the load.

[0028] Furthermore, the first movable beam section 14 can be spanned not only in three directions, but also in two opposing directions, four directions in a cross shape, or in other multiple directions. In these cases as well, a second movable beam section 21 will be provided for each first movable beam section 14. [Explanation of symbols]

[0029] 11 Strain body 12 Load-bearing section 13 Frame body part 14. First movable beam section 16 Hole 17 Strain Gauge 21 Second movable beam section 22 Duan Yu 23 Central Department 24a and 24b plates 25 ditch part

Claims

1. A load cell having a strain generating body formed by processing a single metal block, the strain generating body having a load receiving portion in the center and an annular frame portion around its outer circumference, with a plurality of rectangular prismatic first movable beam portions having holes and to which strain gauges are attached, projecting horizontally and radially outward from the load receiving portion, a second movable beam portion positioned on the frame portion in a direction perpendicular to the longitudinal direction of the first movable beam portion, and the end of the first movable beam portion connected to the center of the longitudinal direction of the second movable beam portion, The second movable beam section has a rectangular cross-section, and a bending mechanism is provided between the two end edges joined to the frame section and the central section. The aforementioned bending mechanism is a load cell characterized by having two plates placed parallel to each other between the central portion and the edges on both sides, and a slit-shaped groove that penetrates vertically between the two plates.

2. The load cell according to claim 1, characterized in that the first movable beam portion is made up of three portions and is arranged radially from the load receiving portion toward the frame portion.

3. The load cell according to claim 1, characterized in that the first movable beam portion is a Roberval mechanism and the strain gauges are attached to the thin-walled beam portions on the upper and lower surfaces.

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