JPH11211543A - Overload prevention device for load cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage of a load cell by the action of excessive loads. SOLUTION: The load cell is provided with a load supporting part 3 arranged on an installation base 2, a load loading part 4 connected to the load supporting part 3 and positioned at some interval from the surface of the installation base and a load detecting part 5 for connecting both parts to be deflected and deformed corresponding to the size of the load acting on the load loading part 4. Then, in the load loading part 4, a stopper pin 8 for blocking the excessive deformation of the load detecting part 5 is disposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cell applied to various weighing devices such as a platform weigher, a weighing tank, a weighing hopper, etc., and more particularly to an overload prevention device for protecting a load detecting portion thereof from an excessive load. It is.

[0002]

2. Description of the Related Art A load cell disclosed by the applicant in JP-A-63-117224, JP-A-8-159858, etc., that is, as shown in FIG. Load supporting part 10 arranged in
2, a load-bearing portion 103 connected to the load-supporting portion 102 and located at some distance from the surface of the installation base 101, and connecting these two portions 102, 103 to each other; The load cell 105 includes a load detecting portion 104 which bends and deforms in accordance with the magnitude of the load acting on the load detecting portion 104. The strain gauge 1 provided in the load detecting portion 104
07 is measured.

[0003]

In the case of such a load cell 105, when an excessive load is applied to the load cell 105, the load detecting portion 104 having the lowest strength is excessively deformed. There is a high possibility that plastic deformation, breakage, and the like of the load detection portion 104 occur, and there is also a possibility that peeling, breakage, and the like may occur in the strain gauge 107 provided in the load detection portion 104.

On the other hand, when an excessive load is applied to the load cell, the lower surface of the load portion 103 is attached to the installation base 1.
It has also been attempted to abut against the surface of No. 01 to thereby prevent the above-mentioned problem from occurring. However, in such a load cell, in most cases, the actual amount of deformation of the load detection portion 104 when the rated load is applied thereto is 0.1 mm or less. When the percentage is set as the allowable limit load, it is necessary to set the distance between the surface of the installation base and the lower surface of the load applying portion with an accuracy of 1/100 mm. In the presence of tolerances in processing and the like, errors in assembling the load cell 105 to the installation base 101, and the like, it is almost impossible to achieve the above-described high interval accuracy.

Accordingly, the present invention provides a load cell which can prevent excessive deformation of a load detecting portion simply, quickly and with high accuracy by on-site construction without depending on the processing accuracy of a load cell and an installation base. To provide an overload prevention device.

[0006]

As described above, the load cell overload prevention device of the present invention includes a load supporting portion which is usually fastened and fixed on an installation base, and a load supporting portion which is, for example, integrated with the load supporting portion. And a load-bearing portion, which is located at some distance above the surface of the installation base, connects these two portions, and bends in accordance with the magnitude of the load acting on the load-bearing portion. In a load cell having a load detecting portion, a base contact member for preventing excessive deformation of the load detecting portion is disposed at an appropriate position of the load applying portion.

According to this, under the actual installation state of the load cell, the distance between the tip of the base contact member and the surface of the installation base is adjusted afterwards by using a screw means, a spacer, a shim or the like. In this way, the maximum deformation amount of the load detection part can be specified simply, quickly and with high accuracy as expected without being affected by the processing accuracy of the load cell and the installation base, their assembly accuracy, etc. be able to.

Here, the base contact member can have its tip protruded downward from the lower surface of the load-applying portion.
In addition, as long as it does not hinder the application of the load to the load-applying portion, it can be attached to a required position of the load-applying portion with an arbitrary structure. A stopper pin protrudes from the load receiving face plate disposed at the portion, penetrates the load applying portion, and projects to the lower surface side thereof.

According to such a configuration, the load is transmitted to the load application portion via the load receiving plate in a sufficiently smooth and reliable manner, and the stopper pin always advances when the load is applied to the load receiving plate. In the limited position,
In addition to substantially eliminating the need for connection and fixing to the load application portion, the structure is simplified, and, for example, interposition of spacers, shims, etc., between the load receiving face plate and the load application portion, and one stop pin It is possible to easily adjust the amount of protrusion of the stopper pin toward the lower surface side of the load applying portion based on the adjustment of the length of the male screw member constituting the part or the whole.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

The load cell 1 shown here has substantially the same configuration as that described in the prior art, and is disposed on an installation base 2 and fixed thereto with bolts or the like. 3, a load-bearing portion 4 connected to the load-bearing portion 3 and located somewhat above the surface of the installation base 2, and interconnecting the two portions 3, 4 and acting on the load-bearing portion 4. And a beam-shaped load detecting portion 5 that bends and deforms in accordance with the magnitude of the load. The load detecting portion 5 has at least one of an extension deformation amount, a compression deformation amount, and a shear deformation amount of the beam-shaped portion. It has a strain gauge (not shown) for detecting one.

In such a load cell 1, here, a through hole 6 extending vertically is provided at the center of the load applying portion 4, and is projected downward from a load receiving face plate 7 arranged on the load applying portion 4. The stopper pin 8 provided is inserted through the through hole 6, and the tip of the stopper pin 8 is protruded toward the lower surface side of the load portion 4, so that the distance 8 between the tip of the stopper pin 8 and the installation base surface is reduced. The load detection portion 5 is made to conform to the critical deformation amount.

If the absolute length of the stopper pin 8 is too long, for example, the load load portion 4 and the load receiving face plate 7
By interposing a shim 9 having a required thickness in a range of about 0.01 to 0.02 mm between the above and the above, the interval 8 can be accurately adjusted to a desired one.

The load receiving face plate 7 shown in the figure is composed of upper and lower plate members 7a and 7b, and both plate members 7a and 7b.
And a plate-like elastic member 7c bonded by, for example, vulcanization or the like. This elastic member 7c applies a vertical load acting on the upper plate 7a under its own small compressive deformation, While functioning to smoothly and reliably transmit the load to the load applying portion 4, the plate 7a largely shears for a load in the horizontal direction, and a plate member 7a for a load acting from a direction inclined with respect to the vertical direction. , 7b are deformed so as to allow the relative tilt displacement thereof, and function to prevent an undesired force on the load detecting portion 5 from acting on the measurement accuracy.

Here, the elastic member 7c can also be constituted by a laminated structure of an elastic plate and a rigid plate, and in this case, the spring constant in the compression direction can be increased with an increase in the number of layers. it can.

As shown by the imaginary line in FIG. 7, such a load receiving face plate is composed of upper and lower plate members and a rigid sphere disposed between them and directly or indirectly in contact with both plate members. When the rigid sphere is constituted by an elastic body which surrounds the rigid sphere and connects the two plate members, the vertical load can be directly transmitted to the load load portion without loss under the action of the rigid sphere.

The load cell 1 provided with the overload prevention device as described above can be used alone, and, of course, a plurality of load cells 1 arranged on the installation base 2 can be used.
By disposing a rigid plate common to those load cells on the load receiving face plate 7 of the above-mentioned type, it can be used.

As shown in FIG. 2A, the planar structure of the load cell 1 has four beam-shaped load detecting portions 5 at the inner central portion of a rectangular frame-shaped load supporting portion 3. In addition to a structure in which the load-carrying portions 4 each having a rectangular outline are connected and supported, as shown in FIG. 2B, a frame shape having an approximately rectangular outer outline and an arc-like inner outline is provided. The load supporting portion 4 having a circular contour can be connected and supported by eight beam-like load detecting portions 5 extending substantially radially at the inner central portion of the load supporting portion.

A stopper pin 8 is set on such a load cell as shown in FIG. 1, and the distance δ between the tip and the surface of the installation base 2 is set to, for example, 0.01 to 0.0.
When the required number of shims having a thickness of about 2 mm is used to match the limit deformation amount allowed for the load detection portion 5, the load acting directly or indirectly on the load receiving face plate 7 is the allowable limit load. When the load is less than the predetermined value, each load detecting portion 5 is deformed according to the magnitude of the load to accurately detect the magnitude of the mounting load. On the other hand, the mounting load has a magnitude equal to or larger than the allowable limit load. As a result, when the amount of deformation of the load detecting portion 5 reaches the limit amount of deformation, the stopper pins 8 2, the load detecting portion 5 is supported by a load exceeding the allowable limit load, so that the load detecting portion 5 is not deformed beyond its limit deformation amount. It is possible to sufficiently protect each of the strain gauges disposed therein and to effectively prevent damage to the strain gauges.

FIG. 3 is a sectional view showing another embodiment of the stopper pin 8 using a male screw member.
As shown in (b), the lower end portion of the stopper pin 8 is formed by a male screw member 8a, and the interval δ can be adjusted by the amount of screwing of the male screw member 8a into the stopper pin body 8b. Here, the mode shown in FIG. 3A is for tightening the lock nut 9 in the through hole 6, and the mode shown in FIG.
The lock nut 9 is tightened on the outside of the mounting base 1, and a nut accommodating recess 10 is provided on the installation base 1 side. Therefore, according to the latter, the distance δ is specified between the bottom wall of the nut receiving recess 10 and the tip of the male screw member 8a.

FIG. 3 (c) shows that the stopper pin 8 is entirely composed of a male screw member, and the interval δ is adjusted by the amount of screwing of the male screw member into the lower plate 7b. The lock nut 9 is screwed into the upper end portion of the male screw member in the central recess 7d of the load receiving face plate 7.

According to each stopper pin 8 having such a configuration, by finely adjusting the amount of tightening of the male screw member, the interval δ can be reduced without having to prepare a plurality of types of shims having a specific thickness.
It can be installed simply, quickly and accurately as required.

FIG. 4 is a front view and a plan view showing another embodiment of the present invention. In particular, the load cell is of a cantilever type.

The load cell 1 has a substantially prismatic shape as a whole.
1 and a concentric recess 12 which is circular from both the front side and the rear side of the protruding portion from the load supporting portion 3.
Is formed, and a load detecting portion 5 which is made thin is provided, and a distal end side of the load detecting portion 5 is a load applying portion 4 which is located at a distance from the surface of the installation base 2. Here, as shown in FIG. 1, a stopper pin 8 protruding from a load receiving face plate 7 is inserted into a through hole 6 provided to penetrate the load applying portion 4 vertically, and a tip of the stopper pin 8 is formed. In particular, the load detection portion 5 can be sufficiently protected from the action of an excessive load by setting the required distance δ between the mounting base and the surface of the installation base. Here,
The configuration of the stopper pin 8 may be any of the configurations shown in FIG.

[0025]

1 has a structure shown in FIG. 1 and FIG.
Using a planar load cell 1 having a rated load of 1 t, a stopper pin 8 projecting from a load receiving surface plate 7 having a structure as shown in FIG. 5 was inserted into a through hole 6 provided at the center of the load applying portion 4. .

Here, in order to increase the permissible limit load of the load receiving face plate 7, a rigid projection 13 projecting from the center of the lower plate 7b is brought into contact with the upper plate 7a. The two plate members 7a and 7b are connected by an elastic member 7c, thereby increasing the allowable limit load to 5t. According to such a load receiving face plate 7, the vertical load acting on the upper plate 7a is directly transmitted to the load load portion 4 without going through the elastic member 7c, as in the case shown in FIG. become.

In this case, the stopper pin 8 has a diameter of 20 mm.
mm hardened steel, the length of which is 28.85 m
m. That is, in this load cell 1, as shown in FIG. 6, the height from the lower surface of the load supporting portion 3 to the upper surface of the load applying portion 4 is 29.00 mm, and the rated load is applied to the load applying portion 4 of the load cell 1. When the load is applied, the amount of downward displacement of the portion, in other words, the amount of shear deformation of the load detecting portion 5 is 0.10 mm. Therefore, when the allowable limit load of the load cell 1 is set to 150% of the rated load, the load is determined by the limit load. , The amount of reduction in the height of the upper surface of the load applied portion is 0.15
mm. Therefore, here, an allowable limit load is applied to the load cell 1 so that the upper surface of the load applying portion 4 is 0.15 mm.
At the time of drop, the tip of the stopper pin 8 is
To prevent the load detecting portion 5 from being further deformed, the length of the stopper pin 8 is set to (29.00).
−0.15 =) 28.85 mm.

In order to test the performance of the apparatus constructed as described above, the load cell 1 was tightened and fixed to the installation base 2 made of a hardened steel plate,
When the load t is applied vertically three times, a load exceeding the allowable limit load of the load can be reliably supported by the stopper pin 8, and as a result, the load detection portion 5 and the load detection portion 5 are disposed there. In addition to being able to prevent the occurrence of damage to the strain gauge, it was also possible to sufficiently prevent a decrease in measurement accuracy.

On the other hand, when a similar load test was performed using a load cell without an overload prevention device, a load exceeding the allowable limit load of the load cell was naturally applied to the load cell, and the load detection portion was plastically deformed. Occurred, and the strain gauge bonded thereto was broken, and the load cell could not be output, that is, was broken.

[0030]

As is apparent from the above description, according to the present invention, when an unexpectedly large load acts on the load cell, the load exceeding the allowable limit load is supported by the stopper pin. , The load cell, especially the load detecting portion, can be sufficiently prevented from being damaged, and always excellent load measurement accuracy can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a planar structure of a load cell.

FIG. 3 is a cross-sectional view showing another configuration of the stopper pin.

FIG. 4 is a diagram showing another embodiment of the present invention.

FIG. 5 is a view showing a load receiving face plate and a stopper pin of the embodiment.

FIG. 6 is a sectional view of a main part showing a performance test state.

FIG. 7 is a longitudinal sectional view showing a conventional load cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Load cell 2 Installation base 3 Load supporting part 4 Load applying part 5 Load detecting part 6 Through hole 7 Load receiving face plate 7a, 7b Plate material 7c Elastic member 7d Central recess 8 Stopper pin 8a Male screw member 8b Stopper pin main part 9 Lock nut 10 Nut accommodation Depression 11 Spacer 12 Depression 13 Rigid protrusion δ spacing

Claims (2)

[Claims] 1. A load-bearing portion disposed on an installation base, a load-bearing portion connected to the load-bearing portion and located at some distance from a surface of the installation base, and connecting both of these portions. A load detecting portion that bends and deforms in accordance with the magnitude of the load acting on the load applying portion, wherein the load applying portion is provided with a base contact member that prevents excessive deformation of the load detecting portion. A load cell overload prevention device. 2. The device according to claim 1, wherein the base contact member is formed by a stopper pin projecting from the load receiving face plate disposed at the load applying portion, penetrating the load applying portion, and projecting to the lower surface side thereof. 3. The load cell overload prevention device according to claim 1.