LV11766B - Measuring force transducer - Google Patents

Abstract

This invention refers to metering devices, especially to power metering sensors, whose mechanical loading changes to an electrical signal and which can be used in the manufacturing of electronic weighing-machines. The offered sensor has a flexible element like massive beam with protuberance on both ends and with symmetrically positioned fortification holes in both sides, which have fortification components to connect with upper and lower foundations. At the central part of the beam in the longitudinal way, a semicircular hollow cut is made; on its upper and lower surfaces are located tenzoresistors by the pair, marked as R1, R2, R3 and R4. Tenzoresistors are connected to the bridges scheme in such a way as when half-bridges are connected themselves with inverse polarities. When loading changes, tenzoresistors distort, change their resistance, so from metric diagonalis is taken off the bridges voltage difference δU, which is proportional to the given loading P and which is measurable with a special control device. So, when half-bridges are connected themselves with inverse polarities, then the voltage difference δU of the half-bridge signals is not conditional by the torsion moment and choosing the place for adding load, but only from bending moment, it indicates the added load.<IMAGE>

Description

DOWER FOR MEASUREMENT OF LUBRICANTS

The invention relates to a measuring technique, in particular to sensors for measuring force, which convert mechanical load into an electrical signal and which can be used in the manufacture of electronic scales.

There is a known gauge for measuring force, for example, after the USSR aut. app no No. 1566235, SKI 5 G01L 1/22, 1990, containing a resilient member formed in the form of a console on which tensor resistors are located. Two of the tensor resistors are active, but two are compensation resistors. The tensor resistors in pairs are switched on the bridge circuit adjacent the shoulders, the circuit further comprising three differential amplifiers. As the load changes, the tensor resistors are deformed, their resistance changes and hence the voltage drop measured by the control device. The disadvantage of the known converter is that the tensor resistors are attached to the outer surface of the device and are not protected against mechanical damage. Such a sensor also has a large measurement error.

Also known is a force transducer (prototype) manufactured by CARDINAL, which contains a cantilever-type elastic member having a hollow hole in the torque sensitive area. Tensor resistors are glued to the surface of this hole. The disadvantage of these sensors is that due to their small and unipolar deformations, their accuracy is not high enough because the electrical signal varies with the point of application of the load.

The object of the invention is to increase the accuracy of the transducer by providing a force measurement independently of the moment of tangling and eliminating the impression of the application of the load.

The object of the invention is achieved by providing to the transducer a force measuring device comprising a resilient member having a hollow longitudinal cutout on which the surface is bonded with tensor resistors engaged on a bridge circuit adjacent the shoulders and two fastening means for centrally securing half-circuits in the circuit are connected with opposite polarities. To prevent torque by placing the load in the corners of the platform at maximum distance from the transducer on opposite surfaces of the elastic member

-2-tensor resistor deployment areas have segmented cutouts.

The essence of the invention is explained in the accompanying drawings, in which:

FIG. 1 shows a proposed transducer, FIG. 2 is a schematic diagram of the electrical connection of tensor resistors, FIG. Figure 3 shows a proposed transducer with segmental cutout.

The force transducer comprises a resilient element in the form of a continuous beam 1 (fig. 1) with protrusions 2 at each end thereof and symmetrically disposed on both sides fastening holes 3 which are provided with fastening units 4 and which in turn are intended for connection to the upper and lower base. 5. In the central part of the beam 1, a semi-hollow recess 6 is formed in the longitudinal direction, on which upper and lower surfaces in pairs A and B are arranged in tension resistors 7, designated R1, R2 and R3, R4, respectively. The tensor resistors R1, R2, R3, R4 are connected in accordance with the circuit diagram of the electrical connection bridge shown in Fig. 2, in such a way that R3 and R4 right half-bridges are interconnected with opposite polarities to provide half-bracket signal subtraction. The supply voltage in the circuit is denoted by U and the voltage difference by AU, applied force by P, distances to tensor resistors by X _A and X b respectively.

The action of the transducer in the force measurement process is as follows.

The upper base 5 is loaded with a certain load. As the load changes, the tensor resistors R1, R2, R3 and R4 are deformed, their resistance changes, and thus the bridge voltage difference AU, which is proportional to the applied load P and measured with the corresponding control device, is removed from the measuring diagonal. Since the left half bridge with tensor resistors R1, R2 and the right half bridge with tensor resistors R3, R4 are connected with opposite polarities, the voltage difference at the output of AU bridge is proportional to the difference of bending moments applied to the planes A and B:

where U is the supply voltage,

-3S - Tensile Sensitivity,

Sl - of material

- the location of the material in the deformation of the tensor resistor R1, the location of the deformation in the tensor resistor R2,

- the location of the tensile resistor R3 in the deformation of the material,

- deformation of the material at the location of the tensor resistor R4,

M _a - bending moment relative to plane A,

Me - bending moment relative to the plane B of the cut,

X _A is the distance from the point of application of force P to the midpoint of the location of the tensor resistors in the plane A,

Xe is the distance from the point of application of force P to the midpoint of the displacement of the tensor resistors in the plane B,

E - modulus of elasticity of the material,

W - moment of resistance of the beam plane, k = WE / US - constant value of the bridge, which depends on the properties of the beam and is determined during calibration.

In this way, the bridge unbalance voltage AU is proportional only to the load P and does not depend on the bending moment, i.e., in fact, the magnitude of the tanging torque caused by the difference between the pure bending moment and the perpendicularity, for moments. It is able to produce platform scales using only one sensor whose output signal is proportional to the load, regardless of the load location.

In order to eliminate the torque effect acting on the transducer by positioning the load at the corners of the platform which is the maximum distance for this structure, the modified transducer design (Fig.3) on the beam 1 opposite sides of planes A and B R4 is a circular or segmental cut 8.

The proposed solution can also be implemented in other types of force measuring devices, such as dynamometers (not shown).

The proposed force measuring transducer is industrially manufactured and can be widely used in electronic weighing scales up to 600 kg with a single transducer in the center of the platform.

Claims (2)

INVENTION FORMULA 1. A force transducer comprising a resilient member having a hollow longitudinal recess having surface-tensor resistors applied to a bridge circuit shoulder and attachment assemblies for centering the resilient member between two bases, wherein for providing a half-bridge signal to subtract and to exclude the effect of the tangential moment on the measurement results, the tensor resistors in the circuit are interconnected with opposite polarities. A force transducer according to claim 1, characterized in that segmental cut-outs are formed on opposite sides of the resilient element in the corners of the platform at maximum distance from the transducer.