JPS6118128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a strain gauge type load cell. In particular, the aim is to realize a high-precision load cell with a sheet metal structure that facilitates instrumental error adjustment.

BACKGROUND ART Conventionally, for example, a load cell having a shape as shown in FIG. 1 has been put into practical use. The illustrated device is based on the invention described in US Pat. No. 2,866,059, and is said to be particularly effective when measuring minute loads. The principle will be explained below with reference to FIGS. 1 and 2. FIG. 1 shows the longitudinal direction of a rectangular parallelepiped load cell, which is mounted on a fixed base (not shown) using mounting holes 14 and 15 provided at the left end, and mounted on the right end, for example. A load is applied as shown by arrow 13. Holes 5 and 6 are provided in the center of the load cell, thereby forming minimum cross-sectional portions 7, 8, 9, and 10 at four locations in the longitudinal direction of the load cell. Well-known strain gauges 1, 2, 3, and 4 are attached to the outer surface of the load cell in opposition to this minimum portion. As shown in Fig. 2, the strain gauge is connected to a bridge circuit, input signals are applied from terminals 16 and 17, and output signals corresponding to the magnitude of load 13 applied to terminals 18 and 19 are obtained. The invention is characterized by the fact that:

Furthermore, in recent years, inventions have been emerging that allow a weighing pan to be attached directly to a load cell, thereby allowing the load cell itself to cancel out the influence of an unbalanced load moment caused by the position of the object to be measured placed on the weighing pan.

However, the biggest drawback of the load cells found in these conventional inventions is that they all use rod-shaped or cast metals, and are finished into the above-mentioned special shapes by cutting. In this case, there are the following three problems.

1. The load cell base material and its processing costs are high.

2. It is difficult to adjust the error (instrumental error) due to unbalanced load on the load cell.

3 For example, a constant elastic material cannot be used as the material for the load cell (the material can only be made in the form of a plate); other materials require temperature compensation.

In contrast, the present invention aims to solve the above problem by realizing a load cell having a structure mainly made of sheet metal.

1. Realize a low-cost load cell using sheet metal and press processing.

2. Realize a high-precision load cell that can easily adjust errors caused by unbalanced loads.

3. By using sheet metal, which is easily available as a constant elastic material, as the load cell material, a load cell with extremely stable characteristics against temperature changes can be realized.

FIG. 3 is a diagram illustrating the basic structure of the present invention.

The basic principle of the present invention will be explained below with reference to FIGS. 3, 4, and 5. FIG. 3 is a longitudinal front view of the load cell of the present invention, and its overall appearance is a beam, similar to that of FIG. 1. board 25,
Two plates 26 are arranged in parallel, and at both ends of each plate are blocks 27 and 2 blocks made of pipe-shaped square timber.
8 is intervening. The two plates and the two blocks are firmly fixed to each other at their contact portions by, for example, welding. On the left side of the figure, two holes (not shown) are provided symmetrically with respect to the longitudinal centers of the plates 25 and 26, passing through them in the vertical direction.
and bolts 36a, 37a, and nuts 36b, 37
b is fixed to the base 29. Further, on the right side of the figure, a through hole similar to the above is provided, and sleeve-shaped washers 45, 46 and bolts 34 are provided.
Plate 42 by a, 35b and nuts 34b, 35b
is fixed.

The plates 25 and 26 have the same shape,
As shown in FIG. 4, two holes 30, 31, 32, 33 are arranged symmetrically with respect to the longitudinal center line.
are provided in the thickness direction of the plate, forming minimum sections of section modulus at two locations in the longitudinal direction of the plate.
As shown in the figure, four strain gauges 21, 22, 23, and 24 are attached to the surfaces of the smallest sections of the two plates. Also, bolts 34a, 35a, 36
a, 37a have nuts 34c, 34d, 35c,
35d, 36c, 36d, 37c, and 37d are attached, and by adjusting the nuts, the cross-sectional shape of the pipe-shaped square material is deformed, and the spacing between the plates 25 and 26 is adjusted.

Now, on this load cell, the load shown in Fig. 4,
That is, for the torsional moment 50 in the width direction,
Outer portions 44, 4 of holes 30, 32, 33 formed symmetrically with respect to the longitudinal center of plate 25
6, 47, 49 and the minimum section modulus portion (not shown) of the plate 26 as a moment in the width direction.
5, 48 and the minimum cross-sectional portion of the plate 26 (not shown)
has almost no effect. In particular, the minimum cross-sectional portions of the plates 25 and 26 to which the strain gauges are attached serve as neutral points of deformation and are hardly affected.

Furthermore, a method of adjusting errors (instrumental errors) due to each position when a plate 42 is attached to this load cell and a vertical load is applied to positions 38, 39, 40, and 41 shown in FIG. 5 will be described.

First, to adjust the vertical load at positions 38 and 39 in the width direction, rotate the nuts 34c and 34d attached to the bolt 34a and the nuts 35c and 35d attached to the bolt 35a, and rotate the nuts 34c and 34d attached to the bolt 34a. This is done by changing the cross-sectional shape of the plate 27 and changing the interval between the plates 26 and 27. Also, the instrumental difference adjustment of the vertical load at positions 40 and 41 in the width direction is performed using the nut 36 attached to the bolt 36a.
This is done in the same manner as above using nuts 37c and 37d attached to bolts 37a and 36d.

Further, the instrumental difference adjustment of the longitudinal positions 38 and 40, 39 and 41 is adjusted by means of instrumental difference adjustment nuts attached to the respective bolts in the same manner as described above.

Therefore, for each vertical load at each position 38, 39, 40, 41, plate 25, plate 26
deforms into almost the same shape, causing strain in the attached strain gauge to correspond to the magnitude of the load. At this time, for example, if a downward load is applied as shown in FIG.
Compressive distortion is added to . The amount of strain applied to these strain gauges is converted into an electrical signal in the same manner as in the conventional method shown in FIGS. 1 and 2.

As can be seen from the above description, the present invention is characterized by being able to perform instrumental error adjustment for the vertical load at each position of the plate attached to the load cell, and is also characterized by being realized by a sheet metal structure.

Here, it is possible to obtain the same effect as described above even if the strain gauge shown in FIG. 3 is attached to the front and back of the two minimum section modulus parts of the plate 25 as shown in FIGS. 6 and 7. Of course.

As described above, the following effects can be obtained by the present invention.

1 By adjusting the nuts in the sheet metal structure, it is possible to form a load cell that can eliminate the effects of unbalanced loads, and it is possible to produce high-precision load cells in large quantities at an extremely low cost. be.

2. By using a constant modulus material such as Ni-SPAN as the sheet metal material, a load cell that is extremely stable against temperature changes can be realized.

[Brief explanation of the drawing]

1 and 2 are diagrams explaining the principle of a conventional load cell, FIG. 3 is a front view explaining the principle and an embodiment of the load cell of the present invention, and FIG. 4 is a plan view of the same,
Fig. 5 is a plan view illustrating how to adjust the instrumental error with the load cell plate of the present invention attached, and Fig. 6 is a front view illustrating the load cell of the present invention when the position where the strain gauge is attached is changed. , FIG. 7 is a plan view of the same. 25, 26... Long plate-like member, 27, 28...
Pipe-shaped square timber, 30-33...hole, 34a, 35
a, 36a, 37a... bolt, 34c, 34
d, 35c, 35d, 36c, 36d, 37c,
37d...Natsuto.

Claims (1)

[Scope of Claims] 1. Two long plate-like members arranged at equal intervals,
Both ends of the two plate-like members are fixed to the sides of two pipe-shaped square members facing each other in parallel to form a box shape, and for each of the two plates, the section modulus is minimized at two places between the fixed pieces in the longitudinal direction. 1. A load cell characterized in that a strain gauge is attached to the minimum section modulus section. 2 Holes are provided in two places in the vertical direction of each of the two pipe-shaped square members facing the two plate-shaped members, and the interval between the two plate-shaped members is adjusted using bolts and nuts, thereby achieving instrumental error. 2. The load cell according to claim 1, wherein the load cell adjusts the load cell according to claim 1. 3. The load cell according to claim 1, wherein each of the two plates has four holes symmetrically formed with respect to a center line parallel to the longitudinal direction.