JPH0127072Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load cell, and particularly to a load cell suitable for use in scales to detect small loads.

Generally, as a load cell for a scale, a Roberval type load cell is used, as shown in FIG. 1, which shows a conventional load cell in order to eliminate errors in the eccentricity of the load on the pan. This Roberval type load cell has two elastic beams 1 that are parallel to each other and has two flexible portions 1a in the longitudinal direction.
are connected by two parallel rigid beams 2 perpendicular to each other to form a roberval mechanism in which flexible parts 1a are arranged at positions forming the four vertices of a parallelogram, and one of the rigid beams 2 is The elastic deformation of the Roberval mechanism, which is fixed to a base or the like and occurs when a load W is applied to the other side, is detected by a resistance wire strain gauge 3, and the load W is converted into an electrical signal. When a scale is manufactured using such a conventional Roberval type load cell, the smaller the load of the scale, the smaller the thickness t of the flexible portion 1a of the Roberval mechanism must be made to increase the sensitivity. As a result, it is difficult to process, easily damaged, and must be handled with care. Moreover, since the resistance wire strain gauge is attached to a thin flexible part, the elastic force of the strain gauge, adhesive, and moisture-proof coating material becomes too large to ignore compared to the elasticity of the flexible part, and the load cell The disadvantage is that it affects the accuracy of Furthermore, if the width b of the roberval mechanism is narrowed to increase the sensitivity, a problem arises in that the strength against uneven loads is reduced. Furthermore, in order to completely eliminate eccentric loads, each flexible portion 1a of the Roberval mechanism must be placed at a position that forms the apex of a perfect parallelogram, but due to machining errors, , as shown in FIG. 2, which is a cross-section taken from FIG. This means that the thickness t of the flexible portion 1a becomes thinner as the load cell is used for smaller loads, and the strength against the torsional moment of the elastic beam portion 1 due to unbalanced loads decreases.
Damage may occur during repair work. Considering the above-mentioned torsional moment, it would be advantageous to modify the flexible portion 1a by cutting the center portion in the width direction, but this is not possible in terms of workability and performance.

The present invention was devised in view of the above, and is easy to manufacture, can respond to smaller loads than conventional ones, and is easy to work with when correcting eccentricity errors.
The purpose of the present invention is to provide a load cell for small loads that is advantageous in terms of strength against torsional moments.

Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 3 is an external perspective view of an embodiment of the present invention.

Two mutually parallel elastic beams 11 each having two flexible portions 11a in the longitudinal direction are connected at both ends with two mutually parallel rigid beams 12 and 12' orthogonal to the elastic beams 11. A Roberval mechanism is formed in which flexible portions 11a are arranged at positions that are connected to form four vertices of a parallelogram, and one rigid beam portion 12 of the Roberval mechanism is provided with a resistance by a fixing member 13. One end of a strain-generating body 15 having linear strain gauges 14 . . . 14 attached to its upper and lower surfaces is fixed. An elastic band 17 is fixed to the other end of the strain body 15 by a band attachment member 16.
The other end is fixed to the other rigid beam 12' of the Roberval mechanism. Each elastic beam part 11
A total of four holes 11b are bored in each flexible portion 11a on the longitudinal center line of the
1b, the cross-sectional area thereof is reduced. The diameter of the hole 11b is determined depending on the required sensitivity, and it can be made into a long hole if necessary.

Next, FIGS. 4a and 4a show a front view and a side view of the above-described embodiment of the present invention incorporated into a scale, respectively.
It is shown in Fig. b and its action will be explained.

One rigid beam part 12 of the Roberval mechanism is
The other rigid beam part 12' is fixed to the base 21 of the scale and is connected to a tray holder 23 via a spring wire 22, and above the tray holder 23 is provided a tray 24 on which a load is placed. Therefore, plate 2
When a load is placed on 4, the rigid beam 12' is pressed downward via the plate support 23 and the spring wire 22 to deform the Roberval mechanism, and this deformation also causes the elastic band 17 to move downward. A load is applied to the tensile strain body 15, and the resistance wire strain gauge 14 outputs a signal corresponding to the load. Since each flexible portion 11a of the Roberval mechanism has a small cross-sectional area due to the hole 11b, it responds well to small loads. Further, in order to correct the eccentric load of the load cell of the present invention, as shown in FIG. 5, which is a cross-sectional view of the flexible portion 11a, the vicinity of the hole 11b (black portion in the figure) may be cut.

FIG. 6 is an external perspective view showing another embodiment of the present invention. In this embodiment, the Roberval mechanism is divided into left and right parts along the center line in the longitudinal direction of the elastic beam, and each of the divided Roberval mechanisms 31, 3
A spacer 3 is placed between each rigid beam part 32, 32' of 1'.
Each Roberval mechanism 31, 3 via 3, 33'
1' are connected. By doing so, an opening 35 is substantially formed in the elastic beam 34.

As explained above, according to the present invention, the thickness of the flexible part is t compared to the conventional Roberval type load cell.
The sensitivity of the load cell can be improved without making it thinner, it is easier to process, and it can respond to smaller loads. Furthermore, the workability is improved when correcting the eccentricity error, and since the inner portion of the flexible portion can be shaved, its strength against torsional moments is improved. Furthermore, like the conventional Roberval type load cell,
Since the strain gauge is not attached directly but is assembled by attaching it to the strain body, the work of attaching the strain gauge is simplified, and a high-precision load cell with a small load suitable for mass production is obtained. be able to.

[Brief explanation of the drawing]

Fig. 1 is an external perspective view of a conventional Roberval type load cell, Fig. 2 is an explanatory diagram of eccentricity error correction shown in its cross section, Fig. 3 is an external perspective view of an embodiment of the present invention, and Fig. 4 is an external perspective view of a conventional Roberval type load cell. A front view (a) and a side view (b) of a scale using the embodiment of the present invention, FIG. FIG. 2 is an external perspective view of the embodiment. 1a... Flexible part, 3... Resistance wire strain gauge, 11... Elastic beam part, 11a... Flexible part, 11b... Hole, 12,
12'...Rigid beam part, 14...Resistance wire strain gauge, 1
5... Flexible body, 17... Elastic band, 24... Plate, 3
1, 31'...Divided Roberval mechanism, 33,
33'...Spacer, 35...Opening.

Claims (1)

[Claims for Utility Model Registration] (1) Two parallel elastic beams having two flexible parts in the longitudinal direction, and a mutually parallel elastic beam connecting these elastic beams at both ends of the elastic beams. and a Roberbal mechanism comprising two rigid beams perpendicular to the elastic beam, and each of the flexible portions being arranged at a position forming each vertex of a parallelogram; a strain-generating body having one end fixed to one of the rigid beams and strain gauges affixed to the upper and lower surfaces; the other end of the strain-generating body being connected to the other rigid beam of the Roberval mechanism; an elastic band; and by providing an opening in the elastic beam portion extending from the inside to the outside of the Roberval mechanism, the cross-sectional area of each of the flexible portions is reduced. A load cell for small loads characterized by a configuration that increases sensitivity. (2) The load cell for small loads according to claim 1, wherein the openings are four holes bored in each flexible portion on the longitudinal center line of the elastic beam. . (3) The opening is formed by dividing the Roberval mechanism into left and right parts along the longitudinal direction of the elastic beam, and connecting them via a spacer at the inner rigid beam of the divided plane. A load cell for small loads according to claim 1 of the utility model registration claim, characterized in that: