JPH083439B2 - Load cell - Google Patents

Description

Description: TECHNICAL FIELD The disclosed technology relates to a load cell that outputs an electric signal proportional to a load, and particularly belongs to a structural technical field of a load cell in which the linearity of an output change with respect to a load change is improved.

(Prior art and its problems) A cantilever type parallel beam type load cell is widely used for weight detectors such as electronic scales and combination weighing devices, but recently, strain gauges are directly connected by a thin film forming process. A technique for forming on the beam surface has been developed, and accordingly, a mode in which four strain gauges are arranged on only one side of one beam and a bridge circuit is formed by these strain gauges has been adopted.

However, if such an aspect is adopted, when an unbalanced load is applied to the load cell, as described in detail in JP-A-60-244819, there is a linearity between the load change and the bridge output accompanying it. It has been pointed out that there will be no.

That is, in a cantilever type parallel beam type load cell L as shown in FIG. 5, when a vertical load W is applied to a point P deviated in the axial direction, the bridge output is as shown in FIG. It changes in such a way that it no longer exhibits linearity.

Therefore, in the above-mentioned open technology, the thin-walled parts on the left and right
By varying the thickness of the arm portion A connecting n, n, such non-linearity is compensated. However, since the thickness of the arm portion A is largely influenced by the shape and size of the load cell, it is necessary to design the thickness by making various sizes and repeating performance tests. It is annoying.

(Object of the Invention) An object of the present invention is to solve the problem of non-linearity of the output of the bridge circuit due to such an eccentric load, and it is not necessary to manufacture various load cells having different shapes and dimensions as in the conventional case. However, the non-linearity of the bridge circuit output can be easily compensated, and therefore an excellent load cell which can be easily manufactured and can be applied to various shapes and sizes is provided.

(Structure of the Invention) In a cantilever type parallel beam type load cell in which a thin wall portion is formed at each end portion of upper and lower beams of a flexure body formed in a parallelogram shape, an axial line extends from the central position of the thin wall portion. There is a region in which the average value of the strain amount with respect to the load change linearly changes at a position slightly outward in the direction. In the present invention, a gauge for detecting strain is attached to this region so as to compensate the non-linearity of the output change with respect to the load change.

(Embodiment of the Invention) Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a cantilever type parallel beam type load cell in which thin wall portions 4 ... 4 are formed at each end of the upper and lower beams 2 and 3 of a flexure element 1 formed in a parallelogram shape. There are two strain gauges 5 ... 5 on the upper surface of each thin portion 4, 4 of one beam 2, lead wires 6 for forming them into a bridge circuit, and for external connection. Terminals 7 are formed by a thin film process. And
In the strain gauges 5 ... 5, especially the center Co of the strain gauges 5 ...
It is arranged at a position slightly deviated to the outside from the center Cc in the direction along the axis. As shown in FIG. 2, such a position is a region where the strain changes linearly with respect to a load change, and the strain distribution is the same for various shapes and sizes. It has been confirmed by various human experiments. And the output sensitivity in this case is
Although the position where the gauge is provided is slightly displaced from the center position of the thin portion, the position is reduced, but this can be sufficiently dealt with by increasing the gain of the amplifier.

FIGS. 3 (a), (b), and (c) show the bridge circuit output when the load point P for the pan 8 is sequentially changed to the left side, the center, and the right side in the configuration arranged as described above. It is a graph showing the relationship with the load change, and as is clear from these, it can be seen that even if an eccentric load is applied, a linear output always appears with respect to the load from the bridge circuit with the above configuration. .

It should be noted that the embodiment of the present invention is not limited to the above embodiment, and various embodiments can be adopted. For example, as shown in FIG. 4, a parallel beam type load cell in which notches are formed on the outer surfaces of the upper and lower beams may be used, or a foil gauge may be attached to the beam surface with an adhesive or the like without using a thin film process. A mode of sticking can also be adopted. Furthermore, it is also possible to adopt a mode in which one strain gauge is arranged in each thin portion.

(Effects of the Invention) As described above, according to the present invention, the linearity of the bridge circuit output with respect to the unbalanced load is adjusted by shifting the attached position of the strain gauge slightly outward in the direction along the axis from the center position of the thin portion. Therefore, a high-accuracy weight sensor can be obtained very easily without manufacturing various load cells having different shapes and dimensions as in the conventional case. Moreover, since the linearity can be compensated without being restricted by the shape and size, there is an effect that it can be applied to various shapes and sizes.

In addition, since the manufacturing is easy, there is an advantage that an economical and inexpensive load cell can be obtained.

[Brief description of drawings]

1 to 4 are explanatory views of an embodiment of the present invention, FIG. 1 is a perspective view of a load cell to which the present invention is applied, FIG. 2 is a view showing strain distribution on a gauge bonding surface, and FIG. Fig. 4 is a graph showing the relationship between bridge circuit output and load when the load point applied to the pan is changed, and Fig. 4 is
FIG. 5 is a side view showing another embodiment of the load cell, FIG. 5 is a side view for explaining the prior art, and FIG. 6 is a view showing the relationship between the bridge circuit output and the load when an unbalanced load is applied to the pan. It is a graph. 1 ... Strain element, 2, 3 ... Beam 4 ... Thin part, 5 ... Strain gauge

Claims (1)

[Claims] 1. A cantilever type parallel beam type load cell in which a thin portion for attaching a strain gauge is formed at each end of the upper and lower beams of a parallelogram-shaped strain element, and the strain gauge attachment position. , At a position slightly offset from the center of the thin portion to the outside in the direction along the axis, respectively, the average value of the strain amount of the thin portion caused by the eccentric load along the axis of the beam, in the load change The load cell is characterized by having a linearly changing region.