JP2509226Y2 - Closed load cell - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] This invention is a hermetically sealed type used in a weight measuring device or the like for accommodating a load cell body in an enclosure and converting a load into an electric signal in a harmful atmosphere for measurement. It relates to the load cell.

[Conventional technology]

It is well known that the load cell main body is integrally formed of an elastic body, and a strain gauge is provided on a Roberval structure having a Roberval mechanism having thin elastic strain generating portions at four positions.
This structure has a simple structure, and it is easy to correct the error of the eccentric load applied to the plane of the load platform directly connected to the Roberval mechanism. Therefore, it is often used as a sensor for balances. However, when a coating is applied on the strain gauge in order to prevent the performance deterioration of the strain gauge due to the external atmosphere, there is a problem that mechanical interference of the coating material adversely affects the output of the load cell. Further, since the main body of the load cell is exposed to an external harmful atmosphere, there is a problem that it is easily corroded.

Therefore, as shown in FIG. 7, there is a configuration in which the load cell 1 is housed in the bellows 2 to protect it from harmful outside air. However, in this case, since it is necessary to make the load cell 1 small in order to house the load cell 1 in the bellows 2, when the load cell 1 is directly connected to the mounting table, the Roberval mechanism has a weak resistance to twisting, and the load cell 1 is twisted around the axis 3. There is a problem that the reaction force of the bellows 2 having a large resistance to the load causes an output error. For this reason, the mounting table cannot be directly connected, and the loading method is limited to the hanging type.
The load cell having the structure shown in FIG. 7 is mounted on the lever type Roberval mechanism 4 as shown in FIG. 8 or the elastic type integrated Roberval mechanism 4a as shown in FIG. 9 ( JP-A-58-73821). The former has a problem in that it has a movable part with the lever connected to the pin, which causes hysteresis and includes an element that hinders the characteristics of the weigher itself, while the latter prevents the elastic deformation part from hindering the performance of the load cell. Since it needs to be weakened, there is a problem that it is difficult to obtain sufficient strength as a whole. In any case, the load cell body 1 is covered with the bellows 2.

Separately, as shown in FIG. 10, the load cell main body 5 is housed in the housing 6 and the load acting shaft 8 is provided so as to penetrate the upper wall 7 of the housing upward as shown in FIG. There is one in which a mount 9 is provided on the upper end of the working shaft 8 and a bellows 10 is provided on the working shaft 8 (Japanese Utility Model Publication No. 2-5039).
In this configuration, when the load acts on the platform, the bellows 10 is displaced so as to compress the bellows in the axial direction, so that the reaction force acts on the platform and the action in the load detection direction also occurs due to the change in the internal pressure due to the temperature change. The force acts on the platform.

[Problems to be solved by the device]

The configuration shown in FIGS. 7 to 9 in which the load cell body is covered with the bellows has a problem that the load cell body cannot be made too large due to the relationship with the bellows, and the adjustment desired after being covered with the bellows is required. That is, the problem that the four corners cannot be adjusted by finely adjusting the dimensions of the strain-flexing part, and the first condition is that the elastic material of the load cell body has stable elastic characteristics. Since it is not possible to use a sufficient material having corrosion resistance, there is a problem in that the portion exposed from the bellows is corroded and the airtightness is lost, resulting in corrosion inside.

The bellows 10 alone cannot remove the reaction force or cancel the action force generated by the change in the internal pressure, and it is necessary to provide another solution for sufficient accuracy, which complicates the configuration. I had a problem with.

For this reason, the present invention can be used for a long time in a harmful atmosphere by using a load cell body having a strain gauge provided on a Roberval structure made of a conventional elastic body with many advantages, and can be used as a hanging type. An object of the present invention is to provide a hermetically-sealed load cell that does not have to have a sufficient accuracy as a platform is fixedly coupled to the load cell body side.

[Means for solving the problem]

In this invention, a load cell main body provided with a Roberval structure having a large size and formed of an elastic body so that a sufficient torsional rigidity can be obtained against an unbalanced load, and the load cell main body is housed and the fixed side of the load cell main body is fixed. The enclosure and the load applying side of the load cell main body, which was projected outward at a right angle to the flexible direction due to the load of the Roberval structure, and exited through the hole formed in the enclosure with a margin. One beam having a large torsional rigidity with a loading platform fixed to the end, and one end of the beam provided so as to surround the portion of the beam protruding outside the housing, and the other end being outside the beam And a bellows connected to the end or the loading platform so as to partition the inside of the housing from the outside.

[Action]

The load cell main body and the beam provided between the load application side of the load cell main body and the load platform have a large torsional rigidity, so that when the load acts on the load platform in a biased manner, Also, a twisting force acts on the load cell body, which can be countered. That is, even if the torsional force acts, the strain in the acting direction hardly occurs. As a result, torsional displacement does not occur in the beam portion to which one end of the bellows is coupled, so that no torsional force acts on the bellows, and therefore the reaction force does not affect load detection. Since the load applying side of the load cell body is displaced in parallel to the acting direction of the load, the bellows is bent in the axial direction by this. Although the bellows generally has a large torsion resistance, but the bending resistance is small, the influence of the bending resistance on the load detection is extremely small. Therefore, even if an eccentric load is applied to the load platform, the load can be accurately detected by the load cell body.

The horizontal outward force acting on the end of the bellows inner hole due to the increase in atmospheric pressure due to the temperature rise in the casing acts on the beam and the load cell body, but is not detected because it is a horizontal force.

〔Example〕

One embodiment of this invention is shown in FIGS. In the figure, 20 is a load cell main body, 21 is a casing, 22 is a beam,
23 is a bellows.

The load cell main body 20 is formed by forming four circular holes parallel to the horizontal direction in a block made of a rectangular parallelepiped elastic material, and processing each of the holes so as to be continuous with one approximately square hole. A Roberval structure is formed by forming thin-walled portions at four positions corresponding to the circular holes, and strain gauges are attached to the respective thin-walled portions. This structure is a known structure in which the four thin parts are strain generating parts. However, in this embodiment, the torsional rigidity is made sufficiently large as compared with a normal load detecting part of the same degree. It has a large size. That is, as shown in FIGS. 1 and 3, the entire size of the load cell main body 20 is large, and in particular, the height and thickness in the direction perpendicular to the paper surface are large. In the figure, 30 is a fixed side, 31 is a load applying side, 32 and 33 are parallel and equal length arm parts, and 34 is an elastic strain part (thin part).

The housing 21 is of a size capable of accommodating the load cell main body 20 with a necessary allowance, and is formed of a corrosion-resistant material against a harmful atmosphere depending on the application, and accommodates the load cell main body 20 and its fixed side 30 is substantially L-shaped. It is fixedly supported on the bottom portion 35 via the metal fittings. The casing 21 has an upper opening airtightly closed by an upper lid 36, and has an airtight structure as a whole. 37 in the figure
Is a mounting part.

One beam 22 is provided, and a beam support 38 is fixed to the load application side 31 of the load cell main body 20, one end of which is fixed to the support 38, and the other end extends horizontally outward to form a housing. It penetrates the side wall of 21 and goes out of the housing 21, and is externally coupled to the mounting base mounting metal 39. The beam 22 has high rigidity with respect to torsion about the axis. The hole 40 through which the beam 22 passes is formed with a margin so as not to come into contact with the beam 22 due to a minute displacement of the load applying side 31 due to a load. In the figure, reference numeral 41 is a load platform which is attached to the metal fitting 39.

The bellows 23 is made of metal that surrounds the portion of the beam 22 outside the housing 21 with a margin, and is made of a material considering corrosion resistance. One end of the bellows 23 has a hole 40 in the housing 21.
Is airtightly coupled to the outer peripheral edge of the beam, and the other end is airtightly coupled to the outer circumference of the tip of the beam 22.

In the figure, 42 is a signal line that hermetically penetrates the enclosure wall, and 43 is a signal line terminal case.

The sealed load cell configured in this way is used by mounting it at a desired position using the mounting portion 37. Load platform 41
When a load is placed on the load cell body 20, the strain-flexing portion 34 of the load cell body 20 is distorted according to the magnitude of the load, and the strain gauge detects this. At this time, if the load acts on the load platform 41 in a biased manner as shown in FIG. 5, a twisting force as indicated by an arrow in the figure acts on the beam 22. The torsional force based on this load is transmitted from the beam 22 to the load cell main body 20 via the support 38, but the load cell main body 20 and the beam 22 are formed in advance to have large torsional rigidity against such a torsional force. , Almost never twist. Therefore, the load cell main body 20 bends at the strain-flexing portion 34 according to the magnitude of the load within a predetermined vertical plane, and the load applying side 31 is slightly displaced downward while maintaining the vertical posture. Therefore, according to this small displacement, the beam
22 only slightly moves downward. The bellows 23, one end of which is coupled to the beam 22, is reasonably deformed according to the minute displacement of the beam 22. That is, the bellows 23 receives a force in the direction of bending a shaft that is easily deformed, but does not receive a force that is twisted around the shaft that is difficult to deform. As a result, the reaction force from the bellows 23 is extremely small and does not affect the load detection of the load cell body 20.

FIG. 6 shows the characteristics after adjusting the four corners of the above-mentioned embodiment, and the same load is applied to the position deviated from the center of the mounting table and the maximum value deviated from the indicated value when the load is applied to the center of the mounting table. The error between the indicated value and the indicated value in% is shown together with the bias direction. The size of the platform 41 is 300 mm × 200 mm.

The general direction of adjustment of the four corners of the balance using the load cell body 20 is to finely adjust the dimensions of the strain-flexing portion as described above. This operation needs to be performed with the load cell main body 20 installed in the housing 21, and for this purpose, for example, as shown in FIG. An operation hole 51 that can be closed by using is provided.

[Effect of device]

According to this invention, the torsional rigidity of the beam provided between the load cell main body and the load cell main body and the load mounting table is increased, and the bellows is provided at this beam portion.
Even if a biased load is applied to the load platform, the bellows are made less susceptible to torsional forces.Therefore, the load cell and platform are fixedly connected instead of the hanging type, but the biased load is accurate. It is possible to provide a hermetically sealed load cell that can be detected without fail and that can reliably protect the load cell body and the strain gauge portion with a housing against a harmful atmosphere.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a plan view, FIG. 2 is a front view, and FIG. 3 is a partially longitudinal front view. FIG. 4 is a front view of a modified example of the same embodiment in which an operation hole is provided with a lid removed, and FIG. 5 is a schematic right side view for explaining the action of the bias load of the embodiment, Sixth
The drawing is a schematic plan view showing the indicated value characteristic of the embodiment.
FIG. 7 is a front view of a conventional concrete load cell, FIG. 8 is a front view showing an example of a scale using the load cell of FIG. 7, and FIG. 9 is another scale using the load cell of FIG. Fig. 10 is a front view showing an example of Fig. 1 and Fig. 10 shows a scale 1 using a conventional closed type load cell.
It is a fragmentary front view showing an example. 20 …… load cell body, 21 …… case, 22 …… beam, 23
…… Bellows, 30 …… Fixed side, 31 …… Load application side, 34…
… Straining part (thin wall part), 40 …… hole, 41 …… load platform.

Claims (1)

(57) [Scope of utility model registration request] 1. A load cell main body provided with a Roberval structure having a large size and formed of an elastic body so that a sufficient torsional rigidity can be obtained against an unbalanced load, and a load cell main body accommodating the load cell main body and a fixed side of the load cell main body. The fixed casing and the load applying side of the load cell main body are allowed to pass through the holes formed in the casing protruding outward at a right angle to the flexible direction due to the load of the Roberval structure. One beam having a large torsional rigidity with a load platform fixed to its end and a portion of the beam outside the housing is provided so as to surround one end of the beam and the other end of the beam. A sealed type load cell comprising: a bellows connected to an outer end or the load mounting table so as to partition the inside of the housing from the outside.