SU1516749A1 - Transducer of linear movements - Google Patents

Abstract

This invention relates to a measurement technique. The linear displacement sensor contains a core piezoelectric element 2 fixed on the housing with low-conductive coatings applied on its two side surfaces, one of which is divided into galvanically isolated sections 4.5 and 6. Section 4 is made of ferromagnetic material and is discretely magnetized along the length sections 7, representing elementary permanent magnets. The coating 3 and section 4 are connected to the output of the generator 8 of a DC voltage controlled by the sensor. The frequency of the generator 8 is chosen such that a standing ultrasonic wave is installed in the piezoelectric element 2, the antinodes of which would be located in sections 7. When the indicator moves along the surface of the piezoelectric element 2, bursts of pulses periodically appear at its output, which are recalculated and recorded. In order to correct the temperature error, sections 5 and 6 are connected to the inputs of the differential amplifier 9, the output of which is connected to the control input of the generator 8. At normal temperatures, the voltages on sections 5 and 6, placed at the same distance from one another, as sections 7 will be almost the same, and therefore the signal at the output of amplifier 9 will be equal to zero. When the ambient temperature changes, the wave propagation speed in the piezoelectric element 2 will change, and therefore the voltage on section 5 and 6 will also become different. At the output of the amplifier 9, a correction signal is supplied to the Vits, which is fed to the control input of the generator 8 by changing its frequency until the antinodes of the standing ultrasonic wave are again located in sections 5 and 6. Thus, the temperature error of measurement will be corrected . 4 il.

Description

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from the other, as sections 7, will be almost the same, and therefore the signal at the output of amplifier 9 will be equal to zero. When the ambient temperature changes, the wave propagation velocity in the piezoelectric element 2 changes, and therefore the voltage across sections 5 and 6 will also become different. At the output of the amplifier 9 Vits

The invention relates to a measurement technique and can be used to measure linear movements of objects.

The purpose of the invention is to improve the accuracy due to the digital form of the representation of the output signal and the correction of the temperature error.

Figure 1 presents the functional diagram of the sensor linear displacement; 2 shows the construction of the piezoelement; in FIG. 3, the nature of oscillations of areas of an electrically conductive ferromagnetic coating discretely magnetized in length; in fig. - voltage diagrams at the output of the oscillation indicator.

The linear displacement sensor comprises a housing 1 and a core piezo element 2 fixed on it. On the two side surfaces of the piezo element 2 low-resistance conductive coatings are applied: on one surface coating 3 and on the other a coating divided into three galvanically isolated sections C, 5 and 6, of which Section 4 is made of ferromagnetic material and is discretely magnetized in length in sections 7, spaced one from another at equal distances L. The distance between sections 5 and 6 is also equal to L. By the cover 3 and section k is connected in The exciter of the piezoelectric element 2, made in the form of an alternating current voltage generator 8, controlled in frequency. Sections 5 and 6 are connected to the inputs of the differential amplifier 9, the output of which is connected to the control input of the generator 8. Over the piezoelectric element 2, an oscillation indicator 10 is installed in the form of a magnetically sensitive element connected to block 11

a correction signal, which is fed to the control input of the generator 8, changing its frequency until the antinodes of the standing ultrasound wave

again, they are not placed in sections 5 and 6. Thus, the temperature measurement error will be corrected. 4 il.

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recording the amplitude of oscillation of the piezoelectric element 2.

The linear displacement sensor works as follows.

Under the action of the alternating voltage of the generator 8, elastic transverse oscillations are excited in the piezoelectric element 2 due to the inverse piezoelectric effect. The frequency f of the generator 8 is chosen in such a way that a standing ultrasonic wave is set in the piezoelectric element 2. This is done subject to

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(one)

where c is the velocity of oscillation propagation in piezoceramics; 1 - the length of the piezoelectric element; n is the oscillation mode (the number of half periods of the standing wave). In this case, the wavelength of the established oscillations

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(2)

On the surface of the coating section k, made of a ferromagnetic material (for example, nickel, cobalt, iron, etc.), discrete magnetized portions 7 were previously created, which can be represented as elementary permanent magnets whose linear dimensions are determined by the parameters of the recorder for example, the width of the working gap of the recording magnetic head (usually 1-3 μm).

The distance between the discrete magnetized regions is equal to and, and at the same time, each of them is located in the antinode of the standing wave established in the piezoelement 2.

Thus, each of the elementary permanent magnets 7 performs

harmonic oscillations in a vertical plane with an amplitude equal to the amplitude of the standing wave in the piezoelectric element 2, which is determined by its size and material, as well as the frequency and voltage of the generator 8.

Moving along the surface of section t, the oscillation indicator 10 periodically (the period is equal to and) hits the alternating magnetic field created by discrete magnetized sections 7 located on the surface of the oscillating piezoelectric element 2. At the same time, the EMF is induced in the oscillation indicator 10 as separate pulse trains (Fig.), the frequency of which is determined by the speed of movement of the indicator 10 oscillations, and the frequency of the pulse in a pack also depends on the frequency of the alternating voltage of the generator eight.

In the registration unit 11, the number of bursts of pulses corresponding to the number of magnetized sections 7 passed by the indicator 10 oscillations is observed when moving along section k of the piezoelectric element 2. Thus, a discrete displacement sensor is realized with a resolution equal to L.

It is known that a change in external factors, in particular temperature, causes a change in speed from the propagation of ultrasonic vibrations in piezoelectric ceramics. Consequently, a change in temperature can cause a violation of the resonance condition (1), the wavelength A changes, and the discrete magnetized portions 7 are no longer located in the antinodes of the standing wave. An imbalance occurs in the circuit, which leads to the appearance of a temperature error.

To improve the measurement accuracy, a differential amplifier 9 is introduced into the sensor, supporting the standing wave mode in the piezoelectric element 2 due to a change in the frequency of the generator 8 proportional to the change in temperature.

For this, two galvanically isolated sections 5 and 6 in the form of narrow strips are separated on the outer surface of the piezoelectric element 2 (Fig. 2). The distance between them is equal to l and both sections under initial conditions (for example, at temperature tj) are located at the antinodes of the standing wave. Due to the direct piezoelectric effect in sections 5 and 6, the voltage of the same magnitude is induced, the frequency of which is equal to the frequency of oscillation of the piezoelectric element 2.

Sections 5 and b are connected to the inputs of the differential amplifier 9, the output voltage of which in the initial state (at t) is close to zero.

Q due to equality of input voltages. With a change in temperature (t), the antinodes of the standing wave are displaced and an inequality of the stresses of sections 5 and 6 arises. This voltage, amplified

5, the amplifier 9 is fed to the control input of the generator 8 and changes its frequency so that a standing wavelength is again set in the piezoelectric element.

0 Thus, the temperature error of the sensor is eliminated, which improves the accuracy of movement measurement.

Claims (1)

5 claims The linear displacement sensor, comprising: a housing, a core piezoelectric element mounted on it, on two 0 side surfaces of which are applied low-resistance electrically conductive coatings, the exciter of the piezoelectric element in the form of an alternating current voltage generator connected to the electrically conductive coatings, and the oscillation indicator in the form of a magneto-sensitive element installed with linear movement along the surface of the piezoelectric element, different The fact that, in order to improve the measurement accuracy, it is equipped with a block for detecting the amplitude of oscillations of a piezoelectric element connected to a magnetosensitive device 5th element and differential the amplifier, the exciter is oscillatory controlled in frequency, and the electrically conductive coating on one of the side surfaces of the piezoelectric element 0 is divided into three galvanically isolated sections, one of which is under the pathogen, made of ferromagnetic material and discretely magnetized in length, and the other two 5 are connected to the corresponding inputs of the differential amplifier, the output of which is connected to the control input of the exciter of the piezoelectric element. five 0 one ch l l l l a l l l l l l l l l l V V VUUA. / V V V V V V V V V V V V V //////////////////////////// g