RU214164U1 - Measuring element for magnetostrictive linear encoder - Google Patents

Abstract

The utility model relates to measuring technology and can be used in magnetostrictive sensors for measuring and controlling linear displacements and the position of various mechanisms.

The measuring element for a magnetostrictive linear displacement transducer is made in the form of an excitation coil wound on a dielectric tube, along which a magnetic positioner (one or more) can move freely, having the possibility of mechanical connection with the controlled object. Inside the dielectric tube there is a waveguide made of a material with a pronounced magnetostrictive effect, which appears when the waveguide is magnetized by the magnetic field of the excitation coil. At one end of the waveguide, a concentrating pad and a piezoelectric element are fixed, forming an electroacoustic transducer that converts the ultrasonic signal caused by the longitudinal vibration of the waveguide into an electrical signal for further processing.

The essence of the utility model is to use as a waveguide material a metal rod made of ferritic steel grade 12X17 according to GOST 5632-2014, which significantly improves the magnetostrictive properties of the waveguide compared to the prototype, by increasing the efficiency of the system response and reducing the ratio of the amplitude of the signal generated by the residual magnetization, to the amplitude of the useful signal generated by the magnet.

The technical result of the utility model consists in a significant increase in the accuracy of measurements in magnetostrictive linear displacement sensors operating on the basis of the principle of longitudinal vibrations, using the inventive measuring element, by selecting an alloy for the waveguide based on ferritic chromium steel grade 12X17 according to GOST 5632-2014. When using this alloy as a waveguide of the measuring element, the measurement error of linear displacements is reduced compared to the prototype, which makes it possible to create magnetostrictive linear displacement sensors based on the claimed utility model of the measuring element with a measurement accuracy of ±0.1 mm, that is, 10 times more accurate than existing devices based on patented technologies.

Description

Technical field

The utility model relates to measuring technology and can be used in magnetostrictive sensors for measuring and controlling linear displacements and the position of various mechanisms.

State of the art

Known analogues for measuring displacements based on the magnetostrictive effect.

Known measuring element for a magnetostrictive linear displacement sensor, described in the patent [1], containing a waveguide made of magnetostrictive material with dampers at the ends, interrogating and output windings placed on the waveguide, a permanent magnet associated with the object of movement.

The disadvantage of the device [1] is the absence of the specified material of the sound guide, as well as its impact on the measurement accuracy.

A known measuring element for a magnetostrictive sensor [2], containing a sound guide made of a magnetostrictive material, which is a wire with a significant magnetoelastic effect - low-carbon steel 10 or 20. There is no justification for the choice of material for the sound guide and an assessment of its effect on measurement accuracy.

Measuring elements for magnetostrictive angular displacement sensors are known, described in patents [3] and [4], which contain a sound guide in the form of a wire with a cross section of 1.0 mm, made of precision ferromagnetic alloys 44NKhTYu, 42NKhTYu or the like, the use of which in known devices guarantees given measurement accuracy in a known temperature range.

Known magnetostrictive sensor of angular displacements [5], which justified the use of a sound guide made of inexpensive elinvar ferroalloys, the use of which guarantees a given measurement accuracy in a wider temperature range, compared with ferroalloys 44NKhTYu, 42NKhTYu.

At the same time, in the devices [3], [4], [5] there is also no study of the influence of the waveguide material on the measurement accuracy.

The closest analogue, taken as a prototype, is a measuring element for a magnetostrictive linear displacement transducer [8], made in the form of an excitation coil wound on a dielectric tube, along which a magnetic positioner (one or more) can freely move, which can be connected to a controlled object , a sound duct made of a material with a pronounced magnetostrictive effect is placed inside the dielectric tube, and a piezoelectric element made in the form of an electroacoustic transducer is fixed at one of the ends of the sound duct. Low-carbon steel 10 is used as the material of the sound guide in the prototype.

The disadvantage of the prototype, as well as devices [1], [2], [3], [4] and [5] is the lack of substantiation of the choice of the material of the sound guide (waveguide) and evaluation of its impact on the measurement accuracy. The waveguide alloys used in these devices have significant drawbacks associated with the magnetostrictive effect, which limit the increase in the accuracy characteristics of magnetostrictive displacement transducers.

In the well-known works [6] and [7], the properties of magnetostrictive displacement transducers, which are determined by the waveguide (sound guide), as the main transforming element associated with the measurement of the physical parameters of motion, are studied. The operational and metrological properties of magnetostrictive displacement transducers directly depend on the physical-mechanical, electrical and magnetic characteristics of waveguide materials, which, in turn, are sensitive to the chemical composition of the material, the presence of impurities and manufacturing technology.

The well-known works [6] and [7] allow us to consider the problem of increasing the accuracy of measurements of linear displacements, taking into account the influence of the magnetoelastic properties of the waveguide material.

The proposed utility model provides a solution to the technical problem of significantly increasing the accuracy of measuring linear displacements with a magnetostrictive transducer, by choosing a waveguide alloy that combines optimal mechanical, electrical and magnetic characteristics.

Disclosure of the essence of the utility model

The measuring element for a magnetostrictive linear displacement sensor is made in the form of an excitation coil wound on a dielectric tube, along which a magnetic positioner (one or more) can freely move, having the possibility of mechanical connection with the controlled object. Inside the dielectric tube there is a waveguide made of a material with a pronounced magnetostrictive effect, which appears when the waveguide is magnetized by the magnetic field of the excitation coil. At one end of the waveguide, a concentrating pad and a piezoelectric element are fixed, forming an electroacoustic transducer that converts the ultrasonic signal caused by the longitudinal vibration of the waveguide into an electrical signal for further processing.

General view of the measuring element for a magnetostrictive linear displacement sensor is shown in Fig.1.

Based on the studies of various alloys carried out by the authors, as well as taking into account the analysis of the available literature data, an alloy was chosen that significantly improves the magnetostrictive properties of the waveguide compared to the prototype, by increasing the efficiency of the system response and reducing the ratio of the amplitude of the signal formed by the residual magnetization to the amplitude of the useful signal generated by the magnet. The essence of the utility model lies in the use of a metal rod made of ferritic steel grade 12X17 according to GOST 5632-2014 as a waveguide material, which provides a significant reduction in the measurement error of linear displacements compared to the prototype.

Brief description of the drawings

In FIG. 1 shows a general view of the utility model - a measuring element for a magnetostrictive linear displacement sensor, where the positions are indicated:

1 - waveguide,

2 - piezoelectric element,

3 - concentrating pad,

4 - excitation coil,

5 - polyethylene tube,

6 - permanent ring magnet.

In FIG. 2 shows a diagram of a test setup for testing samples of waveguides made of various materials, where positions are indicated:

7 - constant pulse generator (G5-63),

8 - oscilloscope (Rohde & Schwarz RTC1002),

9 - operational amplifier with signal amplification 40:1.

In FIG. Figure 3 shows an oscillogram for calculating the ratio of the amplitude of the signal generated by the residual magnetization to the amplitude of the useful signal generated by the magnet.

In FIG. 4 shows oscillograms of the output signal pulse taken from the prototype and from the claimed utility model.

Implementation of the utility model

The utility model contains an excitation coil 4 wound on a dielectric tube 5, along which a permanent magnet 6 (one or more) can move freely. Inside the dielectric tube 5 there is a waveguide 1 made of steel grade 12X17 according to GOST 5632-2014. At one end of the waveguide 1, a concentrating pad 3 and a piezoelectric element 2 are fixed, forming an electroacoustic transducer.

The authors of this technical solution of the utility model have studied a large number of alloys that are suitable in terms of magnetic and operational characteristics for use as a waveguide for a measuring element in a magnetostrictive linear displacement sensor based on the principle of longitudinal vibrations, and also analyzed the available literature data to select the chemical composition of the alloy , which significantly improves the magnetostrictive properties of the waveguide, by increasing the efficiency of the system response (K _EOS ) and reducing the ratio of the amplitude of the signal generated by the residual magnetization to the amplitude of the useful signal generated by the magnet (K _N/PS ).

When selecting the waveguide material, in addition to electromagnetic characteristics, the following additional factors were taken into account: the availability of the material of the required assortment (and its quality) on the Russian market; material properties related to the performance of devices (corrosion resistance, strength, etc.).

To select the waveguide material, tests were carried out on samples differing in chemical composition. A test setup was set up to test the samples. The setup diagram is shown in Fig. 2. A waveguide (1) with a diameter of 1 mm and a length of 1000 mm with a piezoelectric element (2) installed on it was placed in a polyethylene tube (3) with an inductor coil (4) wound around it, turn to turn. A permanent ring magnet was installed on the coil and moved several times along the entire length of the waveguide (from the edge of the cut of the waveguide to the point of attachment of the piezoelectric element) to remove the magnetization, which may be in the material supply state, after which the ring magnet is installed approximately in the middle of the measuring element. A short electrical pulse of a given amplitude and duration is applied to the coil from the generator (7), and the amplitude of the electrical signal generated by the piezoelectric element as a result of the conversion of the acoustic elastic pulse generated at the point of impact on the waveguide (1) of the permanent ring magnet is recorded on the oscilloscope (8). (6). To be able to fully capture the pulse generated by the piezoelectric element, it is amplified with a factor of 40:1 by an operational amplifier (9).

The measuring element works as follows: an excitation pulse with an amplitude of 10 V is applied to the coil (4), which causes a magnetostrictive effect in the waveguide (1). At the moment a pulse is applied to the coil, an external control circuit starts a timer, which starts the countdown. At the point of interaction between the permanent ring magnet (6) and the waveguide (1), an acoustic pulse occurs, which travels along the waveguide and, reaching the electroacoustic transducer (2), is converted into an electrical signal, after which the timer is turned off, and the measured time is used to calculate the distance from the constant ring magnet (6) to electroacoustic transducer (2). In this test setup, time (T) is measured with an oscilloscope (8) and manually converted to units of length (L) using the formula:

(1)

(one)

where V _SV is the propagation velocity of ultrasonic vibrations in the waveguide.

In the prototype, a metal rod with a diameter of 1 mm made of steel 10 according to GOST 1050 without heat treatment (as delivered) was used as a waveguide.

By applying a signal with amplitude Uin = 10 V to the coil, we obtained the amplitude of the output signal on the piezoelectric element (enhanced) Uout = 2 V.

The value of the system response efficiency factor (K _EOS ) for the prototype, while:

(2)

(2)

To calculate the ratio of the amplitude of the signal generated by the remanence to the amplitude of the useful signal generated by the magnet (K _N/PS ), on the oscillogram, the measured level of the useful signal (U _PS ) was correlated with the measured level of residual magnetization (U _H ) (figure 3).

With the obtained output signal Uout = 2 V, the measured amplitude of the magnetization level for the prototype is U _N = 0.3 V. The ratio of the amplitude of the signal generated by the residual magnetization to the amplitude of the useful signal generated by the magnet is:

(3)

(3)

The objective of the claimed utility model is to increase the accuracy of measurements in magnetostrictive linear displacement sensors, in which the principle of longitudinal oscillations is implemented, due to a significant improvement in the magnetic properties of the measuring element waveguide compared to the prototype.

The technical result is achieved by selecting an alloy having a minimum value of K _N/PS , with a maximum value of K _EOS .

At the first stage of the study, testing of measuring elements with waveguides made of materials with special magnetic properties, widely used in magnetostrictive devices, was carried out. The characteristics of the tested steels are shown in Table 1.

Table 1 - Characteristics of steels with special magnetic properties

Alloy grade Coercive force,
Ns (A/m) residual magnetization,
Sun (T) 65K 100 2.20 NP2 80 1.60 44NKhTYu 0.28 47.75 42NKhTYu 0.18 47.75

The results of tests and calculations according to formulas (2) and (3) for steels from table 1 are shown in table 2. For convenience of analysis, data of steel 10 used in the prototype are also listed in table 2.

Table 2 - Results of testing and calculation of K _EOS and K _{N / PS} for steels with special magnetic properties

Alloy grade Input signal amplitude, Uin, V Output signal amplitude, Uout, V The amplitude of the signal generated by the residual magnetism,
Ush, V System response efficiency coefficient, K _EOS The ratio of the amplitude of the signal formed by residual magnetization to the amplitude of the output signal, K _{N / PS} 10 (prototype) ten 2.0 0.3 0.20 0.15 65K ten 3.2 0.5 0.32 0.16 NP2 ten 5.0 3.0 0.50 0.60 44NKhTYu ten 4.4 2.1 0.44 0.48 42NKhTYu ten 4.8 2.0 0.48 0.43

The obtained data on the coefficients K _EOS and K _{N / PS} for special alloys do not allow choosing one of them as the material of the waveguide, since despite the higher coefficient K _EOS , the coefficient K _{N / PS} is also increased, compared with the data on the prototype, which will not significantly improve the output signal. According to the key indicator K _{N / PS} , the material of the prototype turned out to be significantly better than special steel grades intended for magnetostrictive devices.

At the second stage of the study, structural steel grades available on the Russian market with the lowest value of residual magnetization according to [6] were selected and tested. Selected steel grades and their characteristics are shown in Table 3.

Table 3 - Magnetic characteristics of structural steels

Steel Coercive force,
Ns (A/m) residual magnetization,
Sun (T) 10 (prototype) 240 0.8 twenty 320 1.17 08Х17Т 400 0.41 12X17 230 0.3 20X13 1110 0.58

In accordance with table 3, steel grade 12X17 has the lowest residual magnetization. Table 4 shows the test data, as well as the calculated values of K _EOS and K _N/PS .

Table 4 - Results of testing and calculation of K _EOS and K _{N / PS} for steels

Alloy grade Input signal amplitude, Uin, V Output signal amplitude, Uout, V The amplitude of the signal generated by the residual magnetization,
Ush, V System response efficiency coefficient, K _EOS The ratio of the amplitude of the signal formed by residual magnetization to the amplitude of the output signal, K _{N / PS} ten ten 2.0 0.30 0.20 0.15 65K ten 3.2 0.50 0.32 0.16 NP2 ten 5.0 3.00 0.50 0.60 44NKhTYu ten 4.4 2.1 0.44 0.48 42NKhTYu ten 4.8 2.0 0.48 0.43 12X17 ten 3.0 0.15 0.3 0.05

In accordance with the test results, the waveguide made of ferritic steel grade 12X17 according to GOST 5632-2014 has a system response efficiency coefficient (K _EOS ) higher than that of the prototype, and the ratio of the amplitude of the signal generated by the residual magnetization to the amplitude of the useful signal generated by the magnet ( K _N/PS ), which is significantly lower, which will make it possible to consider steel with a content of 16-18% chromium, the rest of iron, with a minimum content of other impurities in the composition, the best waveguide material (from those studied) for a measuring element as part of a magnetostrictive linear displacement sensor, in which implements the principle of longitudinal oscillations, with increased measurement accuracy.

In FIG. Figure 4 shows the oscillogram of the output signal for the tested measuring element with a waveguide in the form of a rod made of steel grade 12X17 according to GOST 5632-2014 (Fig. 4b) and an oscillogram of the prototype (Fig. 4a).

The result of the use of a new waveguide material, reflected on the oscillograms, is a decrease in the influence of residual magnetization on the formation of a useful signal, which occurs in the process of interference (addition) of two types of acoustic waves generated in the waveguide during the measurement cycle. In this case, one type of waves occurs simultaneously along the entire length of the waveguide as a result of the residual magnetization of the latter, and the other type occurs at the point of interaction of the waveguide with a permanent ring magnet and is a useful signal. The phenomenon of interference that occurs when these types of waves interact causes distortion of the fronts of the useful signal, which are used as reference points for measuring time (and, as a result, linear distance). As a result of the inhomogeneity of the pulses caused by the residual magnetization, both in amplitude and in the time of occurrence, it is practically impossible to compensate for the error by the calibration method and the introduction of correction factors. Thus, the error is reduced by reducing the ratio of the amplitude of the signal generated by the residual magnetization to the amplitude of the useful signal generated by the magnet (K _N/PS ), which is practically achieved by choosing the waveguide material with the lowest residual magnetization, at the highest value of the system response efficiency coefficient (To _EOS ).

When evaluating the effect of the coefficient K _{N / PS} on the accuracy of measuring linear displacements, it was found that in the case of using alloys from Table 1, the measurement error is from ± 0.5 to ± 1.0 mm, which is confirmed by the lack of linear displacement sensors on the market operating on based on the principle of longitudinal vibrations, with an error in measuring linear displacements less than ±1 mm. In the case of using steel 12X17 according to GOST 5632-2014, the error is reduced to ±0.1 mm.

The technical result of the utility model consists in a significant increase in the accuracy of measurements in magnetostrictive linear displacement sensors operating on the basis of the principle of longitudinal vibrations, using the inventive measuring element, by selecting an alloy for the waveguide based on chromium steel. When using this alloy as a waveguide of the measuring element, the measurement error of linear displacements is reduced compared to the prototype, which makes it possible to create magnetostrictive linear displacement sensors based on the claimed utility model of the measuring element with a measurement accuracy of ±0.1 mm, that is, 10 times more accurate than existing devices based on patented technologies. At the same time, a rod made of steel 12X17 according to GOST 5632-2014 used as a waveguide combines optimal mechanical, electrical, magnetic and operational characteristics.

Sources of information

1. Patent RU 2 121 658 C1, class. G 01 B 17/00, 1998.

2. Patent RU 2 222 786 C1, class. G 01 F 23/28, 2004.

3. Patent RU 2 343 645 C2, class. H 04 R 15/00, G 01 B 17/00, 2009.

4. Patent RU 2 452 918 C2, class. G 01 B 17/00, 2012.

5. Patent RU 2 032 179 C1, class. G 01 P 3/481, 1995.

6. Materials for sensitive elements of magnetostrictive transducers of motion parameters / E.A. Artemiev, V.N. Proshkin // Proceedings of the International Symposium "Reliability and Quality". - Penza: 2012 - Vol. 2 - S. 258.

7. Artemiev E.A. Materials for sound ducts of waveguide paths of magnetostrictive displacement transducers. // Uch. settlement - Astrakhan: AGTU, 1997. - 93 p.

8. Patent RU 134 631 U1, class. G 01 B 17/00, 2013 - prototype.

Claims (1)

Measuring element for a magnetostrictive linear displacement sensor, made in the form of an excitation coil wound on a dielectric tube, inside which a waveguide is placed, made of chromium steels with a chromium content of 15 to 19%, the rest is iron, with a minimum content of other impurities in the composition, while at one end of the waveguide, a concentrating pad and a piezoelectric element are fixed, forming an electroacoustic transducer.

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