RU2472122C1 - Induction force transducer - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: proposed transducer comprises transformer of mechanical strain 1 arranged in symmetry and perpendicular to force application axis and has two pairs of parallel crossing side surfaces whereon secured are two pairs of inductors 2, 3 and 4, 5 shaped to flat rectangular meander Said pairs of inductors are arranged on parallel dielectric substrates. Inductors of every pair are arranged with clearance between them. One of said pairs is connected to variable-voltage source while outputs of other two 3, 5 of every pairs make force transducer output.

EFFECT: higher accuracy of measurements, minimised errors.

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Description

The claimed technical solution relates to measuring equipment and can be used for accurate and long-term measurement of mechanical forces or deformations of structures in various fields of technology.

It is known "Device for measuring loads" according to the copyright certificate of the USSR: SU 213385 from 03/12/1966, class. 42k, 7/02 - [1], containing an elastic element - a transformer of mechanical deformation (TMD) in the form of an I-beam, to the shelves of which are attached strain gauge wires.

A disadvantage of the known device [1] is that the readings of the strain gauges used in it are highly dependent on temperature, which significantly reduces the accuracy of the measurements. In addition, the materials of the strain elements are subject to "aging", that is, they stretch over time, and have a limited number of measurement cycles.

It is known "Device for measuring forces" according to the author's certificate of the USSR: SU 514212 dated 15.15.1976, IPC G01L 1/16 - [2], containing TMD in the form of a U-shaped plate with a slot in the crossbar, forming two parallel jumpers, on which On the one hand, PCEs in the form of piezoelectric quartz resonators are installed.

A disadvantage of the known device [2] is that the internal angles of the U-shaped plate are stress concentrators. Therefore, due to the fragility of the plate of piezoelectric material, this sensor can only be loaded with relatively small compressive or tensile forces, as a result of which its field of use is limited, due to small deformations of the U-shaped plate. In addition, mounting piezoelectric quartz resonators on metal TMD is difficult, because of which such sensors have low reliability.

Known "Device for measuring the compression force" according to the patent of the Russian Federation: RU 2320968 dated 03/27/2008, IPC G01L 1/16 - [3], comprising a housing, TMD in the form of a cup spring with an axial pusher and an L-shaped console, fixed part of which has internal slots on the inner and outer surfaces that allow the console to bend along the length of the slots, in which the PCEs are installed in the form of piezoelectric quartz resonators.

The disadvantages of the analogue [3] are as follows:

- a metal (steel) L-shaped plate is used as TMD, which makes it difficult to reliably install two PCEs on it, one of which will work in compression and the other in tension, especially working in tension. The installation of PCEs on metal is possible, mainly, only by the glue method, and this requires additional costs and manual labor, and also leads to a decrease in accuracy due to damping of bending forces by an adhesive layer;

- a large difference in the coefficients of linear expansion of the steel plate and PCE (quartz material), which determines the use of the device in narrow temperature ranges, reduces its functionality and increases measurement errors. With significant changes in temperature conditions in the high or low side, the strength of the glued structure increases up to its destruction;

- two PCEs installed on a steel L-shaped plate, due to the asymmetry of the latter, will work differently and introduce distortions into the operation of the sensor’s sensitive element;

- the device only works on compression, which narrows its scope.

The well-known “Induction converter of linear displacements” according to the USSR author's certificate: SU 1516751 of 10.23.1989, IPC G01B 7/00 - [4], containing movable and stationary parts of a dielectric material in the form of coaxial tubes with longitudinal sections and coated on them printed zigzag rectangular windings whose active conductors are mutually parallel and arranged with the same pitch.

Known "Position Sensor" according to US patent: US 2942212 from 06/21/1960, Cl. 336-30 - [5], containing movable and stationary parts of dielectric material with printed zigzag rectangular windings, the active conductors of which are mutually parallel and are arranged at the same pitch.

A common disadvantage of the known position sensors [4] and [5] is that they, in their present form, cannot be used to measure mechanical forces. In addition, the readings of the sensors [4] and [5] strongly depend on the gap between their windings, which requires the precision manufacturing of sensors, which complicates their design and greatly increases its cost.

The prototype of the proposed technical solution is the "Inductive displacement sensor" according to the patent of the Russian Federation: RU 2367902 from 09.20.2009, IPC G01B 7/00 - [6], containing TMD with mutually moving surfaces on which two inductances are fixed respectively (a pair of inductances ), the conductors of each of them are made in the form of a flat rectangular meander and are located on the inner surfaces of parallel dielectric substrates displaced in the initial position relative to each other by a quarter of the meander period, ciency on the one hand are connected by flexible conductors, and on the other side - with the capacitor plates to form an oscillating circuit consisting of an alternating voltage generator whose frequency generation depends on the resonant frequency of the oscillatory circuit, and the outputs are the inputs of the recording unit.

The disadvantages of the prototype [6] the following:

- the dependence of the resonant frequency of the self-oscillating circuit on temperature, which narrows the range of measurements by temperature and reduces their accuracy;

- a strong dependence of the readings on the size of the gap between the planar inductances moving relative to each other.

The disadvantages of the prototype set the task of increasing the accuracy of measuring elastic strains and minimizing the temperature errors of the inductive sensor.

This problem is solved by the fact that in the "Inductive force sensor" containing TMD with mutually moving surfaces, on which a pair of inductors in the form of a flat rectangular meander are respectively mounted on parallel dielectric substrates, the TMD is made symmetrical perpendicular to the axis of application of force and contains two pairs of parallel mutually alternating side surfaces on which two pairs of inductances are respectively fixed, the inductances of each pair are installed with a gap relative to each other One of each pair of inductors is connected to an alternating voltage source, and the other two outputs of each pair of inductors are output force sensor.

In addition, it is known the implementation of the "Scheme with linearly adjustable differential transformer LVDT as a displacement sensor or a force sensor and the method of using such a circuit" according to the German patent: DE 10313021 B3 from 02.09.2004, IPC G01B 7/02 - [7], one primary winding and two secondary windings, the outputs of which through respectively two integrators are connected to the adder, the output of which is connected to the connector of an external electrical device.

However, in the known analogue [7] and in the claimed technical solution, there are significant differences. So, in the analogue [7], from the master oscillator to the primary winding are fed “triangular” signals (pulses) with adjustable leading and trailing edges, and in the claimed technical solution from the master oscillator, sinusoidal signals are fed to the primary winding, and there is no core between the coils, which allows you to increase the operating frequency and the corresponding sensitivity of the induction sensor.

Introduction to the formula of the invention the feature: “a transformer of mechanical deformations is symmetrical perpendicular to the axis of application of force and contains two pairs of parallel mutually alternating side surfaces on which two pairs of inductances are fixed respectively, the inductances of each pair are installed with a gap relative to each other”, allows you to compensate for the effect of changes in the gap between inductances. So, when in one pair of inductances the gap increases by a certain amount, then exactly the same amount the gap in the other pair of inductances decreases, and the total signal remains unchanged.

An introduction to the formula of the invention for the feature: “one of each pair of inductances is connected to a source of alternating voltage, and the outputs of the other two of each pair of inductances are the output of the force sensor” is necessary for the implementation of the power supply system of the inductive force sensor and taking readings from it.

Figure 1 presents a diagram of an induction force sensor. Figure 2 is an equivalent circuit of an induction force sensor with two pairs of inductances. Figure 3 - circuit design to ensure the health of the sensor of figure 2. Figure 4 presents the front view (photograph) of the induction force sensor. Figure 5 is a view (photograph) of the induction force sensor at the rear. Figure 6 is a view (photograph) of an induction force sensor from above. 7 is a photograph of one of the four inductances, in the form of a flat rectangular meander on a dielectric substrate.

The induction force sensor contains TMD 1, made symmetrical perpendicular to the axis of application of force, and has two pairs of parallel mutually alternating side surfaces on which two pairs of inductors 2, 3 and 4, 5 in the form of a rectangular rectangular meander are respectively fixed. Pairs of inductors 2, 3 and 4, 5 are placed on parallel dielectric substrates. The inductances of each pair are set with a gap relative to each other. One of each pair of inductors 2 and 4 is connected to an AC voltage source, and the outputs of the other two from each pair of inductors 3 and 5 are the output of the force sensor.

In figure 1 and figure 2: IPN - source of alternating voltage, preferably 1 ÷ 10 MHz, UPS - signal conversion device. Figure 3: BU - buffer amplifier, designed to coordinate the output of the inductive force sensor with the input of the UPS; PD - peak detector, designed to convert an alternating signal into an alternating voltage signal; U is a large-scale amplifier designed to coordinate the amplitude of the output signal with the scale of the analog-to-digital converter (ADC), from the output of which the signal is transmitted to an indication or to an indication or to a microprocessor. To implement this scheme, UPS (figure 3) can be used traditional circuit solutions. In particular, when using an ADC with a conversion frequency greater than the frequency of an IDI (1 ÷ 2 MHz or more), the signal from the output of the inductive force sensor can be immediately fed to the input of a large-scale amplifier U.

It is real for operating frequencies of the order of 2 MHz in the overall dimensions of the pairs of inductances (2, 3 and 4, 5) 84 × 22 mm, the pitch of the conductors of all inductances equal to 0.8 mm, with the width of the conductors 0.4 mm and the air gap between the movable and fixed part of 0.1 mm the working area for the mutual movement of pairs of inductances is 0.2 mm, with a load on the TMD up to 900 kg. Moreover, the range of the output signal is ± 2 V with a conversion error of no worse than ± 0.5%.

Structural and technological characteristics (width and pitch of conductors, choice of materials, sensor dimensions, etc.) can be changed to specific technical requirements. Modern technology of printed circuit boards allows the manufacture of printed coils with a high degree of accuracy, in this regard, if it is necessary to obtain a higher conversion accuracy, the requirements for the pitch and width of the conductors, as well as the air gap between the coils, can be more rigid.

The inductive force sensor operates as follows. When a force (load) is applied to TMD 1, the latter is compressed within elastic deformations, which leads to the same displacement of inductors 2 and 4 (radiating) relative to inductors 3 and 5 (receiving) in each pair of inductances. This also leads to a change (increase) in the amplitude of the total output signal of the inductive force sensor, proportional to the applied load to the TMD 1. Moreover, with possible lateral displacements of the TMD 1, the gaps in the pairs of inductors 2, 3 and 4, 5 will change inversely. When one gap decreases, the other increases, which compensates for the effect of changing the gap between the inductances, since the total signal of the induction force sensor remains unchanged. The induction force sensor will also behave in case of possible temperature deformation changes.

As can be seen from the foregoing, it is most advisable to use such an induction force sensor in the control systems of the deformation forces of various objects. The claimed technical solution will significantly increase the accuracy of strain measurements, minimize the dependence of the sensor readings on temperature and increase the duration of its operation.

We believe that the proposed induction force sensor has all the criteria of the invention, since the combination of restrictive and distinctive features of the claims is new to the designs of induction force sensors and, therefore, meets the criterion of "novelty."

The set of features of the claims of the proposed device is not known at this level of technology and does not follow well-known rules for the development and construction of induction force sensors, which proves compliance with the criterion of "inventive step".

The development, construction and implementation of the proposed induction force sensor does not present any structural, technical and technological difficulties, from which the criterion "industrial applicability" follows.

Literature

1. USSR author's certificate: SU 213385 dated 03/12/1966, cl. 42k, 7/02, "Device for measuring loads."

2. USSR author's certificate: SU 514212 dated 15.15.1976, IPC G01L 1/16, “Device for measuring forces”.

3. Patent of the Russian Federation: RU 2320968 dated 03/27/2008, IPC G01L 1/16, “Device for measuring the compression force”.

4. USSR author's certificate: SU 1516751 of 10.23.1989, IPC G01B 7/00, "Induction converter of linear displacements."

5. US patent: US 2942212 from 06.21.1960, Cl. 336-30, "Position Sensor".

6. Patent of the Russian Federation: RU 2367902 dated 09/20/2009, IPC G01B 7/00, “Inductive displacement sensor” - prototype.

7. German patent: DE 10313021 B3 dated 02.09.2004, IPC G01B 7/02, “A circuit with a linearly adjustable differential transformer LVDT as a displacement or force transducer and a method for using such a circuit”.

Claims (1)

An induction force sensor containing a mechanical strain transformer with mutually moving surfaces, on which a pair of inductors in the form of a flat rectangular meander, respectively mounted on parallel dielectric substrates, characterized in that the mechanical strain transformer is symmetrical perpendicular to the axis of application of force and contains two pairs of parallel mutually moving lateral surfaces on which two pairs of inductances, inductances Doi pair are arranged with a gap relative to each other, one of each pair of inductors is connected to an alternating voltage source, and the other two outputs of each pair of inductors are output force sensor.

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