RU2804254C1 - Strain gauge force sensor - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: invention can be used to create parallelogram and other types of sensors. The elastic element is made in the form of a parallelogram with a monolithic bridge with one open corner in a new topology: strain gauges with even and odd numbers are located one inside the other so that the gratings of one are located inside the grating of the other and are parallel to it. When supply voltage is applied to its input and a force is loaded on the output diagonal, an output signal is generated that is proportional to the measured force.

EFFECT: increase in the measurement accuracy and noise immunity of the sensor.

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Description

The invention relates to measuring technology, and specifically to sensors for measuring forces and weight.

There are known strain gauge force sensors containing an elastic element and bridge circuits consisting of four or more strain gauges [1]. The disadvantage of such sensors is that the bridge circuit consists of discrete strain gauges, which are built into the bridge circuit by soldering. It is known that every soldering inside the bridge circuit is a potential source of instability and reduced measurement reliability.

The closest in technical essence to the proposed invention is a strain gauge force sensor containing an elastic element of a parallelogram type with two rigid supports and a monolithic bridge of strain gauges [2]. Sensors based on topologically closed monolithic bridges have higher reliability and long-term stability, since the number of solder joints in them is reduced to a minimum and is equal to four, and in the case of monolithic bridges with one open corner - five. Moreover, sensors with monolithic bridges have a smaller (5...8 times!) temperature drift of the zero signal, since all four strain gauges are made from a small area of foil and therefore have equal TCRs. And if the strain gauge bridge is made not from constantan, but from nichrome foil, then temperature changes in sensitivity will be reduced by 3...5 times without the use of special compensation means.

However, sensors with monolithic bridges described in [2] also have some disadvantages.

One of them is that all four strain gauges are not topologically located compactly, but are spaced across the area of the elastic element, therefore, the deformations they perceive, although slightly, differ, and the nonlinearity of the transformation increases, which reduces the accuracy of measurements.

Another drawback is due to the fact that the longitudinal axes of the strain gauges are not located along the longitudinal axis of the substrate and, accordingly, after gluing the bridge, their longitudinal axes also do not coincide with the longitudinal axis of the beam, but are located at some distance from it, which reduces the noise immunity of the sensor from parasitic bending and torsion torques at the power input of the sensor.

The purpose of the invention is to improve the accuracy and noise immunity of the sensor. The set goals are achieved by the fact that the monolithic bridge of strain gauges is made in a new topology: strain gauges with even and odd numbers are located one inside the other symmetrically to the longitudinal axis of the substrate so that the lattice of one strain gauge is located inside the grid of the other and parallel to it, while the outermost thread of the second strain gauge is connected by a common bus with the extreme thread of the third strain gauge, the second extreme thread of the third strain gauge is connected by a common bus with the extreme thread of the fourth strain gauge, the second extreme thread of the fourth strain gauge is connected by a common bus with the extreme thread of the first strain gauge, while in the center of the common tires and at the ends of the tires of the extreme threads from the second and The first strain gauges have contact pads and for common busbars they are made in the form of two areas connected by jumpers and located symmetrically relative to the transverse axis of the insulating substrate, and for the second and first strain gauges they are located to the left and right relative to this axis. Another goal is achieved by the fact that thanks to the new topology of the bridge, it becomes possible to use its pairs of even and odd strain gauges discretely, by dividing the bridge into two parts along a line passing through the middle of the jumpers and coinciding with the transverse axis of the substrate, to create sensors with almost any form of elastic elements.

In fig. Figure 1 shows the design of a strain-resistive force sensor with a parallelogram-type elastic element (front view). Here: 1 - two working beams of the elastic element, 2 - its two rigid supports, F - the measured force applied to the elastic element.

In fig. 2 - the same sensor (top view). Here: R2 and R4 are strain gauges located one inside the other, perceiving compression deformation (for a given direction of force), R1 and R3 are strain gauges, also located one inside the other, perceiving tensile deformation. O-O is the longitudinal axis of the monolithic bridge matrix, coinciding with the longitudinal axis of the beam, O-O' is the transverse axis of the monolithic bridge matrix: along it, if necessary, the matrix is cut into two parts. F - measured force.

In fig. Figure 3 shows the topology of the proposed monolithic bridge of strain gauges and the dotted line - its section O-O' into two pairs of strain gauges with even and odd numbers. Here: 3, 4, 5 - common buses, 6, 7 - buses from the second and first strain gauges; the contact pads of the common buses are connected by jumpers 8, the contact pads of the second and first strain gauges 9, 10, respectively.

In fig. 4 - circuit diagram of the sensor, here: R1 R3 and R2 R4 strain gauges located in opposite arms of the bridge; 3-4 power supply diagonal, 5-11 output signal measurement diagonal. The sensor operates as follows: by applying DC electrical voltage to its input diagonal 3-4 and loading the sensor with a force F, an output signal proportional to the measured force is generated on its output diagonal 5-11. The proposed new topology of the monolithic bridge, after it is fixed to the elastic element, makes it possible to increase the accuracy and noise immunity of the sensor due to the special arrangement of strain gauges on the substrate: the longitudinal axes of the strain gauges coincide with the longitudinal axis of the beam and to perceive the same levels of deformation, the strain gauges are arranged in compact pairs, one inside the other.

The proposed monolithic bridge can also be used for any elastic elements discretely, having previously divided it into two parts: (R1, R3) and (R2, R4).

Information sources

1. Design of sensors for measuring mechanical quantities. Edited by E.P. Osadchy, M., Mechanical Engineering, 1979, p. 247-274.

2. Auto. USSR certificate No. 1198398, M. Kl G01L 1/22, 1985, BI No. 46.

Claims (2)

1. A strain gauge force sensor containing a parallelogram elastic element, a monolithic bridge of strain gauges on an insulating substrate, characterized in that the structure of the monolithic bridge is made in a new topology: strain gauges with even and odd numbers are located one inside the other symmetrically to the longitudinal axis of the substrate so that the lattice of one strain gauge located inside the lattice of the other and parallel to it, while the extreme thread of the second strain gauge is connected by a common bus with the extreme thread of the third strain gauge, the second extreme thread of the third strain gauge is connected by a common bus with the extreme thread of the fourth strain gauge, the second extreme thread of the fourth strain gauge is connected by a common bus with the extreme thread of the first strain gauge , while in the center of the common busbars and at the ends of the busbars of the outermost threads from the second and first strain gauges there are contact pads and for the common busbars they are made in the form of two areas connected by jumpers and located symmetrically relative to the transverse axis of the insulating substrate, and for the second and first strain gauges they located to the left and right relative to this axis. 2. The strain gauge force sensor according to claim 1, characterized in that when creating sensors with any form of elastic elements, it is also possible to use a monolithic bridge in a new topology by using separate pairs of even and odd strain gauges due to the possibility of dividing the bridge along a line passing through the middles of the jumpers and coinciding with the transverse axis of the substrate.

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