FR2509465A1 - Resistance strain gauge sensor - is formed of parallelepipedal block of alloy with central aperture and symmetrical strain gauges - Google Patents

Abstract

The sensor is constituted by a parallelepipedal block (1) machined or pressure-moulded with a pref. asymmetric central hole (2), trapezoidal in shape with corners rounded into semi-cylindrical grooves (3). The thickness (E) of material between the grooves (3), or between them and the edges (4,5) of the block, may be variable or may differ between the top and base. Four strain gauges (6) are arranged symmetrically on the face (4) of the block corresp. to the longest side (AB) of the trapezoid. After rough machining or moulding the block is either varnished or anodised or simply coated with a thin layer of insulating paint or enamel. Alternatively, the central hole may be a symmetrical arrangement of two intersecting circular cylinders, and the strain gauges consequently arranged asymmetrically.

Description

The present invention relates to improved gauge sensors and their manufacturing process.

Gauge sensors are currently used in scales, in particular, to measure the weight of objects deposited in the pan of said scale.

A gauge sensor is generally constituted by a parallel metallic piece of a certain thickness, hollowed out in the middle to make it elastic, on which one or more gauges are bonded intended to measure the deformation of said piece under the action of the weight d 'an object placed in a tray to which it is connected.

To make this type of sensor more sensitive, more or less deep grooves are made inside the recess which have the effect of increasing the elasticity of the sensor.

Unfortunately, we have realized that the measured value varies when the same weight is placed at different points on the pan, for example in the center or on the side.

To remedy this drawback, sensors have been hollowed out in their central part as before, but they have been provided with a central bar.

These gauge sensors are said to be "at constant time".

Such sensors give an average value, are difficult to machine and, therefore, very expensive.

Indeed, they are generally milled in a metal block taking into account the metal wire to avoid the stresses.

The object of the present invention is to remedy these various drawbacks by producing very economical and reliable gauge sensors.

The subject of the invention is the production of sensors with a parallelepiped shape gauge of the type comprising a central recess which is practically insensitive to the variation in position of the load on the weighing pan.

The sensor according to the invention is obtained by milling
or by die casting, or by injection of a
aluminum alloy, in a mold whose confgura-
tion allows you to get rough foundry the challenge form
final with its central recess.

The central recess of said sensor is characterized in that
that it is asymmetrical or asymmetrical having
preferably the shape of a trapezoid whose vertices
or the angles advantageously have grooves.

In addition, according to the invention, the gauges are arranged
on one side of the parallelepiped, preferably
the one corresponding to the largest side of the recess.

Finally, according to the invention, this shape allows the dis
position of gauges deposited as well as obtaining
very reduced heights.

For example: a 15kg sensor, supporting a pla
40cm x 40cm sheet, was made with
a height of 22mm.

The invention will be better understood on reading the
description which follows and on examining the attached drawings
on which ones
- Figure 7 is a perspective view of a sensor
gauge according to the invention showing its main
characteristics,
FIG. 2 represents a particular embodiment
of a gauge sensor according to the invention.

Bn referring to FIG. 1, it can be seen that the sensor
gauge, according to the invention, consists of a block
of metal parallelepiped 1.

This block 1 has a recess 2 in the middle having
the general shape of a trapezoid, including the four angles
A, B, C, D have grooves 3 having the form
of half circumference.

The thickness E of material remaining between the bases of the
trapezoid AB-CD, or between grooves 3 in half-circumference
and the long sides 4 and 5 of block 1 can
be variable, or different at the top or bottom of the block
1.

Furthermore, tests have shown that the angle of inclination of the two sides AC and BD of the trapezoid which are not parallel depends on its height.

This embodiment makes it possible to arrange the gauges only on one side of the sensor, preferably on that corresponding to the long side of the trapezoid.

In the example shown, there are four gauges 6 on the side 4 of the block 1 corresponding to the long side
AB of the hollowed trapezoid 2.

Block 1, with its recess 2, are obtained, contrary to the manufacturing processes used to date, by simple injection under pressure of aluminum alloy in a conforming mold to obtain the sensor with its raw foundry recess.

This manufacturing process saves material, and does not require any machining.

The sensor, being molded, one then proceeds to deposit the gauge on the side corresponding to the long side of the recess, in an equally original manner. In the methods currently used, the gauge is deposited on the sensor after degreasing, polishing and depositing an insulator.

In the method according to the invention, the raw machining or foundry sensor is varnished, or simply coated with a thin layer of paint, or, optionally of enamel or anodized, on which the gauge is deposited.

This way of operating has proven to be very advantageous and without any drawback as to the reliability of the sensor thus produced.

FIG. 2 represents a particular embodiment of a gauge sensor according to the invention.

In this embodiment, the metal block 21 has the shape of a parallelepiped.

It has in its center a recess 22 in the shape of a trapezium whose sides ABCD consist of two semi-circumference 23 almost tangent in the central part of the block.

The half-circumferences 23, arranged on the long side AB of the recess, include ribs (or webs 28).

This block 21 has on each side, at its lower part and opposite, two fixing lugs 31-32 made rigid by means of ribs 33.

 At its lower part, the tab 32 forms a slight excess thickness 34 so that the assembly, once fixed on a frame, is cantilevered and facilitates a certain elasticity of the assembly.

The gauges 26 are arranged on the side 34 of the block 21
This last embodiment allows a substantial saving of material while ensuring precision and fidelity of the measurements.

The sensors, produced by die-casting of an alloy meeting good elastic characteristics or of any other metal without taking account of the wire of said metal, do not require any machining, hence an appreciable saving.

Such sensors are used in particular for the production of scales.

Claims (3)

- CLAIMS  1. Improved gauge sensor constituted by a metal block of parallelepipedal shape of the type comprising a central recess, characterized in that it is obtained either by machining or by pressure molding of a metal alloy in a mold whose configuration makes it possible to obtain a central recess (2) of asymmetrical shape or comprising asymmetrical grooves (3), the gauges (6) being arranged on only one of the sides of the block, the thickness of material remaining between the recess (2) or the grooves (3) may be different.  Improved gauge sensor according to 1, characterized in that the shape of the central recess (2) is a trapezoid whose four angles include grooves (3) having any shape.  3. Improved gauge sensor according to 1, characterized in that the central recess (22) has the shape of a trapezoid whose angles are formed by two half-circumferences (23) almost tangent in the central part of the sensor, said half-circumferences (23) comprising nerves or sails (28), two other recesses (23) being arranged on either side of the central recess, said sensor further comprising two fixing lugs (31-32 ) one of which (32) forms an additional thickness (34).  4. Perimeter sensor according to 1, characterized in that the gauges (26) are applied to the sensor (21) rough of machining or foundry after varnishing, enameling or with the interposition of a thin. coat of paint.  5. Improved gauge sensor according to 1, characterized in that the gauges (26) can be glued or deposited.