JPH0326338B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides a strain gauge type load system in which a strain gauge is attached to a columnar flexural body that elastically deforms when a load is applied, and the strain gauge obtains an electrical signal according to the applied load. It concerns a converter.

This type of conventional strain gauge type load transducer is
A load W (load per unit area) applied to the upper surface 2 of a cylindrical strain-generating body 1 as shown in FIGS. The strain gauges 5 and 6 attached to the outer circumferential surface 3 and inner circumferential surface 4 of the cylindrical strain body 1 can detect the total sum of w as an electric signal proportional to the load.

The strain gauges 5 and 6 are attached at multiple locations at equal angular intervals, for example, as shown in FIG. A well-known Wheatstone bridge circuit is formed. still,
7 and 8 are thin plate-like outer and inner covers that protect the strain gauges 5 and 6 from changes in sensitivity due to moisture and damage caused by external forces;
is a hole for wiring.

However, the conventional load converter configured in this manner has the following problems.

That is, FIG. 2 shows a strain distribution diagram on the pressure-receiving surface when a uniformly distributed load is applied perpendicularly to the conventional strain-generating body 1 shown in FIG.
In this example, the same strain output can be detected from the outer and inner strain gauges 5 and 6,
Accurate load measurements can be made based on the output.

However, as shown in FIG. 3A, when a concentrated load applied to the center of the strain body 1 is transmitted to the strain body 1 via the patch plate 10, the patch plate 10 curves downward. As shown in FIG. 3B, the load is concentrated on the inside of the strain body 1, and the strain distribution on the pressure-receiving surface of the strain body 1 is maximum at the inner peripheral edge and decreases as it approaches the outer peripheral edge.

On the contrary, when a load applied to the outside of the strain body 1 is transmitted to the strain body 1 via the patch plate 10 as shown in FIG. 4A, the patch plate 10 curves upward. Therefore, as shown in FIG. 4B, the load is concentrated on the outside of the strain body 1, and the strain distribution on the pressure receiving surface of the strain body 1 is maximum at the outer peripheral edge and decreases as it approaches the inner peripheral edge. In this way, when a non-uniformly distributed load or an uneven load is applied to the pressure receiving surface of the strain body 1, the relationship between the load and the amount of strain in the part to which the strain gauge is attached does not lose linearity, and as a result, the load and the measured value For example, in the case of Figure 3, the relationship with
The measured value tends to appear larger (1.1 to 1.5 times) than the actual load, and in the case of Figure 4 it tends to appear smaller (1.0 to 0.7 times), making it impossible to measure the load accurately in either case. . In other words, the surfaces on which the strain gauges 5 and 6 are pasted are at different distances from the center axis of bending, that is, the neutral line of stress, and therefore the amount of bending strain caused by unevenly distributed loads or uneven loads is different, and as a result, the measurement The value is no longer accurate.

In order to eliminate such drawbacks, a contact structure (not shown) having a considerable height is used to homogenize the transmission of load between the upper surface of the strain-generating body 1 and the load application surface.
The stress distribution within the strain body 1 can be improved by inserting a plate with a large thickness and high rigidity (not shown) and increasing the height of the strain body 1. It has been found that the load reproducibility, that is, the measurement accuracy can be improved.

However, as mentioned above, if the height of the contact structure, pad, and load converter is increased beyond a certain level, buckling phenomenon occurs in the contact structure and the strain-generating body, making it susceptible to tilted loads, making it difficult to detect loads. There is a problem in that the accuracy actually decreases. Furthermore, when a load transducer is inserted into a force transmission system, the height of the strain body cannot be increased.
If it were made larger, not only would the load converter itself become larger and heavier, but it would also be difficult to use the load converter to measure the load on the object being measured (for example, a forging machine, a press machine, etc.). The problem was that the scope of applicability was limited.

Further, as shown in FIG. 1A, the conventional strain body 1 has covers 7 and 8 fixed to the strain body 1 by means such as welding in order to protect the strain gauges 5 and 6. Since the covers 7 and 8 are made of thin plates so as not to affect the sensitivity, they can easily be punctured when hit by other objects or damage the strain gauges 5 and 6. It tended to occur.

The present invention was made in order to eliminate the drawbacks of the conventional strain gauge type load transducer described above.The purpose of the present invention is to make it small and lightweight, and to be able to change load application conditions without causing buckling. To provide a strain gauge type load transducer that can obtain a constant rated output without sensitivity change even when the load is applied, can effectively protect a strain gauge by eliminating the need for a conventional protective cover, and can greatly improve measurement accuracy. There is a particular thing.

In order to achieve the above-mentioned object, the present invention provides a load formed by attaching a strain gauge to a columnar flexural body having a circular columnar shape, a hollow circular columnar shape, a square columnar shape, or a hollow prismatic columnar shape that elastically deforms when a load is applied. In the converter, a hole or a through hole of a predetermined depth is formed in the columnar flexure body from one end surface side of the columnar flexure body toward the other end surface side with the axis centering on the neutral line of stress of the columnar flexure body. A plurality of holes are formed at equal angular intervals with respect to the central axis of the distorted body, and are opposed to each other in a side circumferential surface of each hole or each through hole that is symmetrical with respect to the axial center of each hole or each through hole. At least two strain gauges are attached to each of the strain gauges, the strain gauges form a Wheatstone bridge circuit, and an electric signal corresponding to the applied load is obtained from the Wheatstone bridge circuit. be.

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 5A and 5B are a front center cross-sectional view and a cross-sectional view taken in the direction of the line arrow in FIG. 5, showing the configuration of an embodiment of the present invention.

In the figure, the cylindrical strain body 11 has a stress neutral line 12 extending from one end surface (lower end surface in this case) to the other end surface (upper end surface in this case). A plurality of holes 13, 13, . It is perforated. In each hole 13, strain gauges 14 and 15 are installed at symmetrical positions on the inner and outer sides of the center axis.
is attached by adhesive or other means. Here, the stress neutral line 12 of the flexure body 11 is a line that is similar to the outer contour line (outer contour line) of the flexure body 11 in the cross section of the flexure body 11; A line that divides the cross-sectional area into two parts: inner and outer.

The operation of the above-described embodiment configured in this manner will be explained with reference to FIGS. 6A to 6C.

When a compressive load is applied to the cylindrical strain body 11 along its central axis direction, the strain body 11 generates compressive strain in the direction along the central axis direction, and the compressive strain detection strain gauge 14A ( (not particularly shown) decreases, and tensile strain occurs in the direction perpendicular to the central axis of the tensile strain detection strain gauge 14.
The resistance value of D (not specifically shown) increases. Although not shown, these strain gauges form a single or double Wheatstone bridge circuit as is well known, so that the output terminal of the Wheatstone bridge circuit receives a signal corresponding to the applied load. The electrical signal can be extracted.

That is, when a uniformly distributed load is applied perpendicularly to the pressure-receiving surface of the strain body 11 as shown in FIG. The strains on the inner peripheral surfaces of hole 17 and hole 13 are equal. Therefore, in this case it is clear that the Wheatstone bridge circuit formed by the strain gauges 14, 15 provides an electrical signal (detection output) that exactly corresponds to the applied load.

As shown in FIG. 6B, when a load is concentrated and applied to the inside of the strain body 11, the strain distribution on the pressure-receiving surface becomes maximum at the inner peripheral edge of the strain body 11 and approaches the outer peripheral edge. However, since the hole 13 is a stress-neutral point, the strain gauge 14 attached to the inner circumferential wall of the hole 13,
There is no difference in the strain gauge detected by 15, and even when an unbalanced load is applied, the hole 13 drilled at the neutral point
Both sides (circumferential sides facing each other at 180°) are symmetrical, and the absolute values of the strain gauges attached thereto are the same, so by forming a Wheatstone bridge, the difference due to unbalanced loads can be completely canceled. be done. Therefore, in this case as well, an electrical signal corresponding to the applied load can be obtained from the Wheatstone bridge circuit formed by the strain gauges 14 and 15.

Furthermore, even when a load is applied in a concentrated manner to the outside of the strain-generating body 11 as shown in FIG. An electrical signal corresponding to the applied load can be obtained.

In this case, the neutral line of stress is similar to the outer contour line (outer contour line) of the strain body 11 in the cross section of the strain body 11, and its cross-sectional area is divided into two directions inwardly and outwardly. It has been experimentally confirmed that the line divides into equal parts. On this neutral line, even if the load application conditions change, the strain that occurs there is the nominal strain (also called the theoretical strain), that is, the cross-sectional area of the strain body,
The strain is close to that calculated from Young's modulus and load, and the same rated output can be obtained even under uneven load. Therefore, as in the embodiment described above, by drilling a hole on the neutral line of stress and attaching strain gauges 14 and 15 at symmetrical positions on the inner surface, the absolute values of the generated strain will be the same. The difference due to unbalanced load is canceled by the Wheatstone bridge circuit, and a constant rated output can be obtained.

In addition, as in the above embodiment, the strain gauge 14,
15 is the inside of the strain body 11, that is, the strain body 11
Since it is attached to the inner circumferential surface of the hole 13 drilled from the lower end, the strain gauge is completely protected even if it is hit by an object from the outside, as the sturdy strain element 11 itself functions as a protective cover. be done. At the same time, this eliminates the need for a conventionally necessary cover, and as a result, the shape of the strain-generating body 11 is not only simple, compact, and lightweight, but also when considering only the shape of the strain-generating body 11 in stress calculations. This has the advantage of simplifying calculations and facilitating safe design.

Furthermore, since accurate load detection can be performed even if the height of the strain-generating body 11 is reduced, there is no risk of buckling, and since it can be made thinner, the range of application can be greatly expanded. can.

Note that the present invention is not limited to what has been described above and shown in the examples, and various modifications can be made without departing from the gist of the present invention.

For example, in the embodiment, the columnar strain-generating body 11 is cylindrical, in other words, a hollow circular column. It is also applicable to columnar flexure bodies exhibiting

In addition, holes 1 to which strain gauges 14 and 15 are attached
3 is suitably 4 to 8, but it is of course possible to increase or decrease the number as appropriate depending on the capacity, shape, etc.
The direction in which the strain gauges 14 and 15 are attached is as follows.
Center line of strain body 11 (may be center line of hole 13)
Although it may be attached only in the direction along this, it is advantageous to attach it also in the direction perpendicular to this, that is, in the circumferential direction of the hole 13, since the sensitivity will be increased.

Furthermore, in the case of the above embodiment, each hole 13 is
Although shown as having a predetermined depth from the lower end surface of the strain generating body 11, it may also be a through hole reaching the upper end surface of the strain generating body 11. In that case, each hole 13 or the opening end of the hole is desirably sealed by a sealing means to prevent deterioration of the strain gauges 14 and 15 due to moisture absorption.

As detailed above, according to the present invention, it is small and lightweight, there is no risk of buckling, and even if the load application conditions change, a constant rated output can be obtained without any change in sensitivity. It is possible to provide a strain gauge type load transducer that can effectively protect the strain gauge by eliminating the need for a cover for protecting the strain gauge, and can significantly improve the measurement accuracy of applied loads.

[Brief explanation of drawings]

1A and 1B are front center cross-sectional views of the cylindrical strain body of a conventional strain gauge type load transducer, and sectional views taken in the direction of the line arrows in the same figure; 4A and 4B are diagrams for explaining the operation of the first illustrated embodiment, and FIGS. 5A and B are respectively diagrams for explaining the operation of the first illustrated embodiment.
are a front center cross-sectional view and a cross-sectional view taken in the direction of the arrow in the same figure, respectively, showing the configuration of an embodiment of the present invention;
6A, B, and C are diagrams for explaining the operation of the embodiment shown in FIG. 5. FIG. 11... Cylindrical strain body, 12... Neutral line of stress, 13... Hole, 14, 15... Strain gauge,
16...Outer peripheral surface, 17...Inner peripheral surface.

Claims (1)

[Claims] 1. A circular column that deforms elastically when a load is applied.
In a load transducer in which a strain gauge is attached to a columnar flexural body having a hollow circular column shape, a prismatic column shape, or a hollow prismatic column shape, the columnar flexure body A plurality of holes or through holes having a predetermined depth centered on the neutral line of stress of the strain body are bored at equal angular intervals with respect to the central axis of the columnar strain body, and each of the holes or through holes is At least two strain gauges are attached oppositely to each other on the side circumferential surface of each hole or at a symmetrical portion with respect to the axial center of the through hole, and the strain gauges form a Wheatstone bridge circuit;
A strain gauge type load transducer characterized in that the Wheatstone bridge circuit is configured to obtain an electrical signal according to an applied load.