JPH027415B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure for removing tare from an electronic scale using a load cell.

Recently, electronic scales, that is, scales using a load cell such as a resistance wire strain type or a capacitance change type in a weighing structure, have come into widespread use. Among them, there is one called the parallelogram system, as shown in Figure 1. In the figure, 1 is the load cell body, 2 is the upper beam part, 3 is the lower beam part,
4 is a load application part, 5 is a fixed base, 6, 7, 8, 9
1 is a strain gauge; 10, 11, 12, and 13 are thin-walled portions forming elastic fulcrums; and 14 is a platform including a belt conveyor. However, according to this structure, the weight of the part to be measured W and the weight of the platform 14 are all applied to the load cell. Originally, it is only necessary to measure the weight of the part to be measured W, but now the tare weight is also measured, so it is necessary to use a load cell with a large capacity that includes the tare weight. Moreover, when the weight of the part to be weighed W is smaller than the tare weight (weight of the mounting table 14), the output voltage of the load cell is small and it is difficult to take out the signal effectively, resulting in poor accuracy of the scale. .

Therefore, it is an object of the present invention to provide a scale having a structure that allows the tare value to be easily removed.

A feature of the present invention is that in a parallelogram type load cell, an auxiliary beam is formed by extending from one or both of the vertically parallel beam portions to the side opposite to the load application portion. The point is that a counterweight is provided to eliminate part or all of the tare weight.

In general, strain gauges 6, 7, 8, and 9 provided at thin-walled portions 10, 11, 12, and 13 of a load cell as shown in FIG. . Gauges 6 and 9 detect compressive strain, and gauges 7 and 8 detect tensile strain. The bending stress of each elastic fulcrum is selected at the design stage according to the weight load of the object to be weighed, but the shear stress at this part will be about 1/30th of the bending stress if properly designed.
This invention focuses on this point, and by forming an auxiliary beam extending from one or both of the beam parts 2 and 3 of the load cell and providing a counterweight to this, the moment acting on the load cell due to the mounting base 14 is reversed. It is designed to give a moment in the direction and cancel it out. Therefore, the bending stress due to the tare of the bending stress applied to the strain gauge can be partially or completely canceled out by the bending stress in the opposite direction by the counterweight. The weight increase of this auxiliary beam and counterweight is
However, as mentioned above, this shear stress is very small, so there is no problem.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 shows a first embodiment, in which parts equivalent to those in FIG. 1 are designated by the same reference numerals. The main points different from the one in FIG. 1 are the auxiliary beam 20,
21 and counterweights 22 and 23 are provided.

The auxiliary beam 20 has one end attached to the upper beam part 2 with a screw 2.
4, and the other end extends to the opposite side from the load application section 4, and a counterweight 22 is attached thereto. The auxiliary beam 21 has one end connected to the lower beam part 3 by a screw 25, and the other end extends to the opposite side from the load application part 4 and is connected to a counterweight 23.
is attached. The weight of the counterweights 22, 23 and the auxiliary beams 20, 21
The position where it is attached is such that the bending stress in the direction opposite to the bending stress generated in the thin wall portions 10, 11, 12, 13 due to the weight of the platform 14 applied to the load applying part 4 of the load cell, that is, the tare weight, is applied to the load applying section 4 of the load cell. By adjusting the weight of the weights 20 and 21 or adjusting the mounting position of the weights,
It is predetermined to erase part or all of the tare.

As an example, a case will be explained in which all tare weights are erased. The scale configured in this way has thin parts 10, 11, 1 of the parallelogram type load cell.
2, 13, that is, at the elastic fulcrum, the bending stress caused by the tare weight is canceled out by the bending force in the opposite direction caused by the auxiliary beams 20, 21 and the counterweights 22, 23, and is reduced. Therefore,
When there is no article W to be weighed on the platform 14, no bending strain occurs in the thin wall portions 10, 11, 12, 13, so the strain gauges 6, 7, 8, 9 all detect compressive strain or tensile strain. No, article to be weighed W
When placed on the platform 14, the thin parts 10, 11,
12 and 13 are subjected to bending strain according to the weight of the article to be weighed, and the strain gauges 6, 7, 8, and 9 detect this as compressive strain or tensile strain. Accordingly, if the gauge has a well-known bridge circuit configuration, an electrical signal corresponding to the weight of the article to be weighed can be obtained and the weight can be detected.

Next, as another example, a case will be described in which part of the tare weight is deleted. If the total weight of the tare and the object to be weighed exceeds the rated load of the load cell, or if it is larger than the rated load of the load cell, remove the tare weight so as not to exceed the rated load of the load cell, or It may also be operated to reduce the load value to a certain predetermined value. The elastic fulcrum parts 10, 11, 1 are supported by counterweights 22, 23 attached to the auxiliary beams 20, 21.
In order to eliminate the bending stress caused by the load in 2 and 13, either set the weight of the counterweight to a weight that cancels out all of the tare weight, or cancel part of the tare load by adjusting the mounting position of the weight. .
By doing this, it is possible to keep the total weight of the weight of the object to be measured and the tare weight within the rating of the load cell, and there is no need to use a load cell with a load rating one rank higher. This method also allows the rated load values of the object to be measured and the load cell to be close to each other, allowing highly accurate measurement.

As mentioned above, with this scale, even though the tare weight is large including the conveyor,
Since the strain gauges 6, 7, 8, and 9 are placed in a state in which the tare weight is substantially removed, the load cell can have a capacity that corresponds to the weight of the article to be weighed, allowing for highly accurate weighing. . That is, it is not necessary to use a large-capacity load cell that corresponds to the weight of the tare weight plus the weight of the article to be weighed.
In addition, when erasing the tare value using this method,
Depending on the design, it is possible to erase a tare value that is several times to ten times the weighed value.

In the above embodiment, a configuration was shown in which auxiliary beams 20 and 21 were provided on each of the upper and lower beam sections 2 and 3 and counterweights were attached to them, but this is a desirable configuration in view of the strength of the load cell. However, in some cases, for example when the tare value is not very large, the auxiliary beam 20a may be extended from only one beam section, for example the upper beam section 2, as in the second embodiment shown in FIG. Then place this on the counterweight 22 corresponding to the platform 14a.
You may also attach a. In the figure, 30 is a capacitive displacement detector which detects the displacement of the load applying section 4 with respect to the fixed base 5 to detect the weight. Also, parts of the same figure that are equivalent to those in FIG. 2 are designated by the same drawing symbols.

It is also possible to use a differential transformer type displacement detector in place of the detector 30 in the second embodiment.

As described above, according to the present invention, in a scale using a parallelogram type load cell, the weight of the simple platform or the platform including the conveyor and hopper, which can be considered as the tare weight, is eliminated, It is possible to provide a scale in which only the weight of the article to be weighed is taken out as an electrical output, and a load cell having an appropriate capacity corresponding to the weight of the article to be weighed can be used.

[Brief explanation of drawings]

FIG. 1 is a schematic side view showing an example of a scale using a conventional parallelogram type load cell, FIG. 2 is a schematic side view showing the configuration of a first embodiment of the present invention, and FIG. FIG. 3 is a schematic side view showing the configuration of a second embodiment of the invention. DESCRIPTION OF SYMBOLS 1...Load cell main body, 2...Upper beam part, 3...Lower beam part, 4...Load application part, 5...Fixed base, 6,
7, 8, 9...Strain gauge, 10, 11, 1
2, 13... Thin wall part (elastic fulcrum), 14, 14a...
Platform, 20, 21, 20a... Auxiliary arm, 22,
23, 22a... Counterweight, W... Article to be weighed.

Claims (1)

[Claims] 1 Upper and lower beam parts of equal length, elastic fulcrums provided at both ends of both beam parts, and both vertical beam parts that maintain a predetermined distance between both ends of the upper and lower beam parts via the elastic fulcrums. In a scale having a parallelogram-type load cell in which one of the vertical parts is a fixed base and the other is a load application part, one or both of the upper beam part or the lower beam part forming an auxiliary beam extending from the section to the side opposite to the load application section;
A scale characterized in that the auxiliary beam is provided with a counterweight corresponding to part or all of the tare weight acting on the load application section.