SU1425482A1 - Resistance strain gauge force cell - Google Patents

Abstract

The invention relates to a load measuring technique and can be used to measure alternating nonstationary forces. The purpose of the invention is to improve the measurement accuracy. In housing 1 there is a force-measuring element 4 connected to the stem 3 with resistance strain gauges 5 glued on its surface. When the measured force acts on the stem 3 of the sensor, the diaphragm 2 deforms. Simultaneously the stem 3 moves the movable damper 6 of the damper on the stem with an axial two-side the gap between the two fixed disks 7. The force of viscous resistance prevents the mixing of the moving disk b and deforms the strain gauges attached to the jumper of the disk. An electrical signal is generated that is proportional to the damping force, which is summed with the electrical signal of the force measuring element 4. 2 Il.

Description

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The invention relates to a force-measuring technique, in particular, for measuring alternating nonstationary forces.

The purpose of the invention is to improve the measurement accuracy.

The dynamic equation of the force sensor, with appropriate assumptions, can be represented as

M X (t) + ci (t) + Kx (t) F (t), (1)

where M, C and K are the parameters characterizing, respectively, the mass, damping and stiffness of the elastic element attached to the sensor rod; x (t) is the deformation of the elastic element, is proportional to the output signal of the sensor; F (t) is the measured force acting on the sensor shaft. It follows from the above relation that the force F t acting on the sensor rod is generally decomposed into three components in the sensor: the inertial Mx (t) damping Cx (t) and the elastic Kx (t. In the overdamped sensor, i.e. In the sensor, in which the degree of damping of oscillations is greater than the critical one (), the inertial component Mx (t) is negligible with any form of effort, and relation (1) in this case is reduced to the form: F (t) Kx ( t) + ci (t), (2)

From which it follows that the input force F (t} is decomposed into only two components and, therefore, if the output signal is a load measuring element (elastic component is) added to the output signal If the signal is proportional to the damping force, then the total signal will reproduce an accurate, without dynamic distortions, large-scale copy of the measured force. In the proposed sensor design, an electrical signal proportional to the 5th component is removed from the strainer resistors, pasted on the load cell, and the signal proportional to the damping force is removed from the strain gauges pasted in a certain way on the power elements of the damper, and then these electrical signals are summed. Fig. 1 shows a strain gauge force sensor; Fig. 2 - section A-A in Fig. 1.

The sensor consists of a housing 1, in which a rod 3 is hung on two centering and sealing membranes 2, supported by a load element 4 with strain gages 5 glued on its surface 5. At the end of the stem a movable disk 6 is fixed, which with an axial clearance is surrounded by two fixed disks 7, rigidly fastened to the sensor housing, closed on both sides of the covers.

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The movable disk of the damper (Fig. 2) is made up of two concentrically arranged rings interconnected by four bridges, on the side surfaces of which are strain gauges 8 that are subject to shear deformation. Other embodiments of the moving disk of the damper are possible, for example with a thin cylindrical neck between the disk and the inner ring, but in any case, strain gages are used that perceive the deformation caused by the damping force on the moving disk of the damper. The strain gauges 8 are combined into a bridge measuring circuit and, through a pressure seal 9, are connected to the electrical circuit of the load cell, for example, according to the parallel circuit circuit of bridge circuits.

The cavity of the damper is filled with polymethylsiloxane damping fluid,

The viscosity of which provides a degree of damping of the sensor oscillations is greater than the critical 4 1 (overdamping) with fixed geometric parameters of the elements of the damper.

5 The sensor works as follows. When the measured force acts on the sensor bar 3, the membranes 2 and the force-measuring element 4 are deformed. The deformation of the force-measuring element is transformed by means of the strain gauges 5 into an electrical signal, which is fed to the connector 10. At the same time, the chopper moves the damping disk 6. In this case, the damping fluid is displaced from the decreasing flat annular gap and is sucked into the increasing gap. In this way, the movement of the movable disk 6 is hampered by the force of viscous resistance, which causes deformation of the bridges connecting the annular active part of the damper to the syringe. Strain gages 8, pasted on the jumpers, form

 an electrical signal proportional to the damping force, which through the pressure inlet 9 enters the connector and is summed with the electrical signal of the load cell.

5 The electric signal in the damper occurs only in transient modes of operation of the sensor, and when measuring static forces, the output signal from the damper is absent and the measured signal fully corresponds to the output signal of the force-measuring element.

Claims (1)

Invention Formula A strain gauge force sensor, comprising a housing in which a ten-strain gauge load cell is connected to the rod, a hydraulic damper made in the form of a movable disk mounted on a shaft with an axial two-sided gap between two fixed disks, a measuring circuit connected to the strain-strain element, characterized in that, in order to increase accuracy of measurements; in it on the movable disk of the damper there are strain gages included in the measuring circuit of the strain-resistive load measuring element. eight FIG. g