RU2354941C1 - Device to measure rotary shaft axial force and rpm - Google Patents

Abstract

FIELD: physics, measurements.

SUBSTANCE: invention relates to instrumentation and can be used for measurement of axial loads and RPM of rotary shafts. The proposed device comprises a transducer arranged with a gap relative to the shaft, phase shifter, AC voltage source with its output connected to the transducer excitation winding and to the phase shifter, adder with its one input connected with the transducer output and the other one connected with phase shifter output. Note that the adder output is connected, via bandpass filter and rectifier connected in series, to the first low-pass filter input. There are also the second and third low-pass filters with their outputs connected with the instruments. Note here that a reference sensitive element fitted on the shaft surface is used as a transducer and is made from a homogeneous high magneto-elastic sensitivity material. Note that, additionally, the proposed device incorporates a contactless key with its first input connected to the first low-pass filter output and its output connected to the second low-pass filter input, comparator with its input connected to the high-pass filter output and its output connected to the second input of aforesaid contactless key, a clock element with input connected to the comparator output and its output connected to the third low-pass filter input.

EFFECT: higher reliability, noise immunity, accuracy of measurement and ease of operation.

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Description

The invention relates to measuring technique and can be used to measure the axial force and speed in the rotating shafts of various power plants used on ships, in metallurgy and other fields of technology.

Known devices for measuring axial force in rotating shafts:

1) Copyright certificate No. 142445. Bulletin No. 21 of 1961. A device for measuring axial pressure in rotating shafts. Solodovnikov A.I., Mikhailov B.C.

2) Copyright certificate No. 421579. Bulletin No. 12 of March 30, 74. Non-contact propeller stop meter. Mikhailov B.C., Stepanov S.V.,

action, which is based on the use of changes in the magnetic properties of the shaft material under the influence of elastic deformations.

However, such devices have a number of disadvantages, in the first case due to technological difficulties in manufacturing and installing an annular magnetoelastic axial force sensor, and in the second case due to low noise immunity caused by the harmful effect of magnetic inhomogeneity of the shaft material. In addition, in both cases, due to the fact that the magnetic properties of the shaft material are not always known, difficulties arise associated with the calibration of the readings of these devices.

The aim of the invention is to increase the reliability, noise immunity, measurement accuracy and ease of operation.

This is achieved by the fact that to measure the axial force and speed in the rotating shafts it is proposed to use a transformer magnetoelastic transducer (TMUP) of the axial force of the attached type with a reference sensing element (ECE) made of a uniform material with a high magnetoelastic sensitivity.

Figure 1 presents the structural diagram of the proposed device; figure 2 - installation of the reference sensor and sensor on the propeller shaft; figure 3 - plot of electrical voltages at the outputs of the blocks of the device.

The device contains a cross-mounted magnetoelastic sensor 1 and a phase shifter 2, the outputs of which are connected to the inputs of the adder 3. The output of the latter through a series-connected bandpass filter 4 and a rectifier 5 is connected to the input of the first low-pass filter 6 (low-pass filter). The output of the first low-pass filter is connected through a contactless key 7 to the input of the second low-pass filter 8. The output of the first low-pass filter is also connected to the input of the high-pass filter 9 (HPF), the output of which is connected through a series-connected comparator 10 and a time element 11 to the input of the third low pass filter 12. The output of the comparator is connected to the second input of the first key. The field winding of the magnetoelastic sensor and the input of the phase shifter are connected to the output of the alternating voltage source 15. Measuring instruments are not shown in the drawing.

The device also contains a reference sensing element (ECE) 16, which is mounted on the shaft 17. The measuring poles of the sensor 18 and the excitation poles 19 are installed around the circumference of the shaft in accordance with figure 2.

The device operates as follows.

Cross magnetoelastic sensor 1 is installed in close proximity to the propeller shaft with some initial clearance between the poles of the magnetic circuit and the measured surface of the shaft. From source 15, an alternating voltage is applied to the field winding of the sensor 1 and to the input of the phase shifter 2, which varies with frequency ω.

In the absence of a load on the shaft due to the initial magnetic anisotropy of the shaft surface and the electromagnetic asymmetry of the sensor 1, a zero signal acts at the output of the sensor (one input of the adder 3). At the other input of the adder from the output of the phase shifter, an electrical compensation voltage is supplied. The compensation voltage is selected when setting up the device equal in value and phase opposite to the first harmonic component of the zero signal so that at the output of the adder 3 the zero signal takes a minimum value. The axial force applied to the shaft causes the appearance of mechanical stresses on its surface, which determine the additional magnetic anisotropy of the shaft and the reference sensor 16 mounted on its surface. When the shaft 17 is rotated at certain time intervals, the reference sensing element is located under the poles 18 and 19 of the sensor; at other time intervals, the shaft surface passes under the poles with a different gap. The magnetic anisotropy induced by the applied axial force and the alternation of the passage of either the sensor element or the shaft surface under the measuring poles 18 cause amplitude modulation of the magnetic flux and the output signal of sensor 1, the carrier frequency of which is equal to the excitation frequency ω. The modulation depth is proportional to the axial force, and the frequency of the modulating signal is proportional to the shaft rotation frequency Ω. The band-pass filter 4 selects the first harmonic component of the carrier frequency, without further passing into the subharmonic measurement path. From the output of the bandpass filter, the voltage of the useful signal is supplied to the rectifier 5, from where the rectified voltage is fed to the input of the first low-pass filter 6, which at its output emits a useful modulation signal (envelope of the carrier frequency). The selected modulating signal V ₁ is an electric voltage having the form of a continuous sequence of unipolar rectangular pulses following with a shaft rotation frequency Ω. One measurement period T _{Ω of} voltage V ₁ contains two pulses. These pulses have different values and durations, depending on the time interval in which they are formed, or when the reference sensor 16 is located under the poles of the sensor and the gap between the measurement poles and the reference sensor has a value of δeche (V _1eche , t _eche ), or when the shaft 17 is located under the measuring poles and the gap between the measuring poles and the shaft surface has a value of δв (V _1B , t _в ). The value of the voltage V ₁ eche depends on the gap δ _eche and the magnetoelastic properties of the reference sensing element, and the voltage V _1c depends on the gap δc and the magnetoelastic properties of the shaft surface. Since δ _eche <δ _{in the} reference sensitive element is made of a ferromagnetic material with a magnetic permeability far exceeding the magnetic permeability of the shaft material, the voltage V _{1 eche} is much greater than the voltage V ₁ v. This determines the pulse nature of the voltage change V ₁ . To isolate the voltage V of the _op-amp , proportional to the axial force P and independent of the magnetic inhomogeneity of the material of the shaft, the voltage V ₁ from the output of the first low-pass filter 6 is fed to the input of the second low-pass filter 8 through a contactless key 7. The latter is controlled by the output voltage of the comparator 10, which opens it to time interval teche and closes for a time interval tv. Key 7 passes to the input of the low-pass filter 8 voltage V ₁ eche. The voltage at the output of the low-pass filter 8:

where α is the length along the arc of the measuring element;

    P is the axial force applied to the shaft.

The voltage V of the _{op-amp is} applied to the measuring (recording) device of the axial force P. To generate an electric voltage V _Ω proportional to the shaft rotation frequency Ω, voltage V ₁ from the output of the low-pass filter 6 is fed to the input of the high-pass filter 9. At the output of the high-pass filter 9, an alternating pulse voltage is obtained without constant component. This voltage is fed to the input of the comparator 10, the output of which is a pulse voltage of strictly rectangular shape. The pulse repetition rate at the output of the comparator is equal to the shaft speed, and the amplitude does not depend on the axial force. Pulses having a teche duration open the key 7. From the output of the comparator 10, the pulse voltage is supplied to the input of the time element 11, the output of which is unipolar pulses. The duration of these pulses to is constant and does not depend on the time interval teche, the amplitude A ₀ does not depend on the axial force, and the repetition rate is equal to the shaft rotation frequency Ω. From the output of the time element 11, the voltage is supplied to the input of the low-pass filter 12. At the output of the low-pass filter 12, a constant voltage V _Ω = A ₀ · t ₀ · Ω = n is applied, which is fed to the measuring (recording) device of the speed.

Often, the magnetoelastic effect in the material of the shaft itself is used to measure the characteristics. However, the use of the measuring element in the proposed device has the following advantages. Significantly improved accuracy and easier calibration of the device. Improving the accuracy is achieved by the fact that the measuring element is made of a homogeneous and with a high magnetoelastic sensitivity of the material. The propeller shaft has a low magnetoelastic sensitivity and a pronounced magnetic heterogeneity both around the circumference and along the length, which leads to strong noise and large measurement errors. In addition, the measuring element in the proposed device is removable. This allows graduation to be carried out simply and with great accuracy at the laboratory or factory stands. You can also make a sufficient number of the same measuring elements from a material with the same properties. The indirect calibration method of the known device used without a measuring element is characterized by low accuracy.

In order that the magnetic heterogeneity of the propeller shaft does not affect the accuracy of the proposed device, it is necessary that the variable magnetic flux of the excitation of the sensor 1 does not penetrate the surface layer of the shaft. In practice, this means that the magnetic induction in the surface layer of the shaft should be much less than the value of magnetic induction in the measuring element. This condition is satisfied if the thickness of the measuring element is not less than twice the depth of penetration of an alternating magnetic flux into it. At a fixed frequency of the excitation voltage, the conditions are achieved by choosing the thickness of the measuring element, and at a given thickness of the element, the frequency of the excitation voltage is changed (increased).

The measuring element can be made, for example, in the form of a rectangular plate. The width of the plate is chosen equal to the overall size of the sensor 1. If the shaft has significant axial displacements, then the width of the plate is equal to the sum of the size of the sensor and twice the axial displacement of the shaft. The length of the plate is chosen two or three times its width so that during the passage of the plate under the poles of the sensor a clear rectangular pulse is formed, allowing its further processing. In the device, the sensor 1 is installed so that the projection of the poles of the magnetic circuit on the surface of the shaft correspond to figure 2.

Literature.

1. Zhadobin N.E. “Magnetoelastic sensors in marine automation.” L .: Shipbuilding, 1985, 36 p.

2. Zhadobin N.E., Krylov A.P., Malyshev V.A. "Elements and functional devices of ship automation". St. Petersburg: 1998, 440 p.

Claims (1)

A device for measuring axial force and speed in rotating shafts, comprising a magnetoelastic sensor mounted with a clearance relative to the shaft, a phase shifter, an AC voltage source, the output of which is connected to the sensor excitation winding and the input of the phase shifter, an adder, to one input of which a sensor output is connected, to the other input is the output of the phase shifter, and the output of the adder through a series-connected bandpass filter and rectifier is connected to the input of the first low-pass filter, the second and third filters are frequencies, to the outputs of which measuring devices are connected, characterized in that for measuring the axial force and shaft speed, a reference sensor is used mounted on the surface of the shaft and made of a homogeneous and with high magnetoelastic sensitivity material, as well as the introduction of a contactless key into the device, the first input of which is connected to the output of the first low-pass filter, and the output is connected to the input of the second low-pass filter, the high-pass filter, the input of which is connected to the output ode to the first low-pass filter, a comparator whose input is connected to the output of the high-pass filter, and the output is connected to the second input of the contactless key, a time element whose input is connected to the output of the comparator, and the output is connected to the input of the third low-pass filter.

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