Eddy Current Displacement Sensor Research Articles

An optimum structural design method for a torque sensor measuring the control moment of the micro flapping-wing robot

Abstract This paper presents an optimum structural design method for a sensor capable of measuring the control torque of the micro flapping-wing robot. Torque measurement in flapping-wing robots has special demands on the sensor bandwidth. The method in this paper focuses on the development of a multi-objective optimization method based on the surrogate model to solve the sensor indicator design issues, for example, increasing sensitivity while meeting bandwidth requirements. Initially, Latin hypercube sampling was applied to the choice of the characteristic parameters of the sensor. Based on finite element techniques, the surrogate models describing displacement and eigenfrequency were established to characterize the sensor indicators, and a multi-objective optimization was conducted. According to the optimization results, the sensor structure was manufactured, and a torque measurement platform was set up. Calibration experiments and frequency response experiments demonstrated a high level of consistency between the surrogate model and the experimental data. With the assistance of the eddy current displacement sensor, the actual displacement sensitivity coefficient of the torque sensor is determined to be 0.4325 mm mNm−1, consistent with the calculation of the surrogate model. The characteristic frequency is 488.5 Hz, with a relative error of 7.47% compared to the surrogate model. This indicates that the optimum structural design method can be utilized for the rapid design of torque sensors for special requirements, thus laying the foundation for the control torque measurement of micro flapping-wing robots.

Novel Direct Digital Interface of Frequency-Modulated Eddy-Current Displacement Sensor (ECDS) for Real-Time Control of AMB

Novel Direct Digital Interface of Frequency-Modulated Eddy-Current Displacement Sensor (ECDS) for Real-Time Control of AMB

Simultaneous measurement and analysis of gas needle lift and injected rate for HPDI fuel injector

Achieving a sufficient understanding of the transient fuel injection process is key to improving the efficiency of direct injection engines and reducing emissions. In this research, the momentum method and pressure–volume method are applied to measure the gas injected rate, the eddy current displacement sensor is installed underneath the open-type gas needle to measure the needle lift. The dynamic characteristic of the dual-fuel injector is studied by measuring the gas injected rate and the needle lift simultaneously. To simulate to the actual high-pressure environment of the engine, the influence of back pressure on the dynamic behavior of the injector is paid more attention in the experiment. In addition, the experiment of the main-after injection strategy is investigated to analyze the influence of the interval time on the after-injection. The experimental results are as follows: Firstly, the increase of back pressure will significantly promote the needle rising stage. That is, the maximum position that the needle can reach increases under the short energizing time, while the needle reaches the maximum limit faster under the long energizing time. When the injected pressure is 30 MPa while the energizing time is 0.7 ms, the gas injected mass increases by 33.92 mg (an increase of 86.8 % compared with the gas injected mass under atmospheric pressure), and the gas injected mass increased by 20.3 mg (an increase of 11.9 % compared to atmospheric pressure). Secondly, the reflected compression wave generated by the diesel supply system will inhibit the needle rising stage, resulting in the speed change of the needle lifting process. With the increase of back pressure, the affected proportion of the needle rising stage is sharply decreased even no longer influenced by the reflected compression wave. Finally, the gas injection rate develops from fusion to separation with the interval time increasing, resulting in two different trends during injected mass growth. The increase in back pressure leads to the delay of the main injection ending and the advance of the after injection starting, which facilitates the injection fusion.

Eddy Current Position Measurement in Harsh Environments: A Temperature Compensation and Calibration Approach.

Eddy current displacement sensors (ECDSs) are widely used for the noncontact position measurement of small displacements (lift-offs). Challenges arise with larger displacements as the sensitivity of the ECDSs decreases. This leads to a more pronounced impact of temperature variations on the inductance and, consequently, an increased position error. Design solutions often rely on multiple coils, suitable coil carrier materials, and compensation measures to address the challenges. This study presents a single-coil ECDS for large displacement ranges in environments with high temperatures and temperature variations. The analysis is based on a sensor model derived from an equivalent circuit model (ECM). We propose design measures for both the sensing coil and the target, focusing on material selection to handle the impact of temperature variations. A key part of improving performance under varying temperatures includes model-based temperature compensation for the inductance of the sensing coil. We introduce a method to calibrate the sensor for large displacements, using a modified coupling coefficient based on field simulation data. Our analysis shows that this single-coil ECDS design maintains a position error of less than 0.2% full-scale for a temperature variation of 100 K for the sensing coil and 110 K for the target.

Design and analysis of an eddy current displacement sensor with extended linear range

Eddy current displacement sensor (ECDS) is a non-contact sensing device. This paper proposes an ECDS by using the colpitts circuit with the characteristics of longer measurement range and better linearity. The parameter Rp is separated from an improved colpitts circuit. By measuring Rp and optimizing probe sensitivity, the measurement range of the sensor is increased, which extends to 56% of probe diameter, the maximum measurement distance reaches 72% of probe diameter. A linear-fitting method based on MCU is proposed, which improves the linearity, consistency, and response speed of the sensor. The principle and design are explained in detail, and verified through field circuit coupling simulation. Finally, the ECDS is tested by using a precision electronically controlled displacement platform, the experiment results show that the sensor performance has a high consistency, and linearity can be reduced to within ± 0.4%, sensitivity is 0.28 V/mm, resolution is 6 µm. The ECDS is identified to be practical, the method proposed in this article effectively improves the measurement range and linearity, therefore, the ECDS is widely used in displacement measurement, which need long distance, high precision and fast response.

Experimental Investigation of the Dynamic Response of a Flat Blade with Dual Dry Friction Dampers

One test rig comprising two blades and dual under-platform dampers (UPDs) was built to enhance the understanding of the dynamic response behavior of blades with dual UPDs. A turnbuckle was applied to enable the smooth and uninterrupted linear adjustment of the normal load on the dual UPDs. Non-contact vibration-response measurements were achieved through eddy-current displacement sensors. Contact excitation was employed using an electromagnetic exciter to determine the magnitude of the excitation load, which was measured using a force sensor mounted on the excitation rod. A feedback system was established to maintain a constant magnitude of the excitation force throughout the excitation process. The chosen experimental variables include the normal load, the amplitude of the excitation force, the effective contact area, and the position of the damper action. The frequency response function of the blade under various experimental parameters was obtained through frequency sweeping under sinusoidal excitation. The influence of each parameter on the dynamic characteristics of blades was studied. The results demonstrate that the double-layer damping system offers distinct advantages over its single-layer counterpart. The upper damping has a wider frequency-adjustment range and a lower resonance amplitude and takes a larger share of the damping efficiency.

A magnetic head-based eddy current displacement sensing method

Eddy current displacement sensors are popular for sensing changes in displacement in industrial fields with many advantages. The eddy current induced by a conventional coil is distributed over a large range and the energy is not concentrated. The size of the minimum measured surface is 1.5 to 3 times the diameter of the coil. A magnetic head-based eddy current displacement sensor is proposed in this paper. Theoretical analysis confirms that the coil generates a highly concentrated magnetic field at the magnetic core gap. The simulations based on the finite element method are performed. The simulation results demonstrate that the proposed method can induce the eddy current field which has a small distribution range and high degree of concentration of energy on the surface of the specimen. Finally, experiments are conducted for different sized ring-shaped surfaces. The high similarity between the experimental results indicates that the magnetic head-based eddy current displacement sensor can induce a highly focused eddy current field with a distribution range of 3 mm. The sensitivity of the sensor is 5 V mm−1 and the spatial resolution of the sensor is 3 mm.

A Novel Eddy Current Sensor for Displacement Measurement With High Accuracy and Long Range

To enlarge the measurement range of traditional eddy current displacement sensors, a novel eddy current linear sensor for displacement measurement with high accuracy and long range is proposed in this paper. The sensor consists of a stationary component with metal reflection conductors and a movable component with spiral coils. The metal reflection conductors below the movable component will generate an eddy current and radiate an eddy current magnetic field after the high-frequency alternating excitation signal is applied to field spiral coils. The inductive electromotive forces (EMFs) will be generated in inductive spiral coils. The measurement of displacement relies on the inductive EMFs variation of inductive spiral coils caused by the change of coupling areas between the spiral coils and the metal reflection conductors. The absolute positioning is realized by the combination of a coarse measurement channel and a fine measurement channel. The structure and measurement principle are described in detail. A sensor prototype is fabricated by PCB technology, and the experiments are carried out. Based on the experimental results, some error sources are analyzed and the sensor is optimized. The experimental results show that the sensor can achieve absolute positioning, and the worst-case error is 6.75 μm within the measurement range of 500 mm.

A real-time shaft alignment monitoring method adapting to ship hull deformation for marine propulsion system

Shaft alignment states are strictly stipulated in the marine propulsion system. However, there are relatively limited studies on shaft alignment monitoring and control considering the effects of ship hull deformation (SHD). SHD can be caused by wave load, loading, depth, speed, etc., and leads to various relative displacements at different shaft supporting points between the ship foundation and the support bearings of the propulsion system. It leads to shaft misalignment, increases shaft vibration and noise, and even endangers the safety of shaft system during the operation stages. To overcome this problem, a real-time shaft alignment monitoring method based on laser displacement sensors (SAMM/LDS) is proposed. Firstly, the defects of a present shaft alignment monitoring method based on eddy current displacement sensors (SAMM/ECDS) are analyzed when considering the effects of SHD. The structure and working principle of a shaft alignment monitoring system adapted to SHD (SAMS/SHD) are proposed. It consists of three sub-systems: the shaft alignment monitoring sub-system adapting to SHD (SAMSS/SHD), the present shaft alignment monitoring sub-system (SAMSS/P), and the shaft alignment correcting sub-system (SACSS). Based on SHD data-driven, SAMS/SHD can not only take advantage of SAMSS/P for long-time operations but also reflect SHD by exploiting the advantages of SAMSS/SHD. Secondly, SAMM/LDS is deduced. Two laser displacement sensors (LDS) are placed on the driving shaft and the driven shaft to reflect the spatial relative displacement and attitude information affected by SHD. Therefore, two reference coordinate systems are fixed at the center of LDS, and the coordinate expressions of their imaging points are derived using a 4 × 4 homogeneous coordinate transformation matrix. For reducing computing complexity in engineering applications, a simplified monitoring model is proposed for very small rigid-body rotational angularities. Finally, the effectiveness and testing accuracy of the SAMM/LDS is verified on a five-DOF platform which can simulate the effects of SHD. The SAMM/LDS can be used to realize real-time and high-precision shaft alignment monitoring for marine propulsion system which can adapt to the effects of SHD and so on. Based on the foundation of this research, compensation control algorithms to solve the misalignment effects deduced by SHD will be studied for marine propulsion system with resilient mounts in the next few years.

Sensitivity Improvement to Eddy Current Displacement Sensor in Full Maglev LVAD

Eddy current displacement sensors in full-maglev left ventricular assist devices (LVADs) suffer from low sensitivity resulting from the use of a stator titanium alloy frame. The aim of this study was to develop a methodology to improve the sensitivity of eddy current displacement sensors and formulate a mathematical model of coil impendence to illustrate the impact of the addition of a titanium alloy frame between the sensor coils and the measured conductor. An equivalent mutual inductance model in the circuit was established for LVADs with and without a titanium alloy frame stator wall. Comparing the differences in excitation frequency and measured metal conductivity considering the relation of inductance with displacement enabled the development of methods to improve the sensitivity of the sensor when a titanium frame is added to the stator. An experiment was conducted to collect and analyze data to ascertain the relation between impedance and rotor displacement considering different excitation frequencies, stators with and without a titanium alloy frame, and the copper ring. Relatively high sensitivity was acquired when titanium frames of 0.25-mm thickness were applied to both the stator and rotor with an additional copper ring attached to the rotor frame at an excitation frequency of 475 kHz.

Spiral Spring-Supported Force Plate with an External Eddy Current Displacement Sensor

This study proposes a force plate with a planar spring and an eddy current displacement sensor to measure the ground reaction force (GRF) of a small insect and reveal its motion characteristics. The proposed force plate comprises a circular aluminum plate, four aluminum springs symmetrically connected to the plate, and an eddy current displacement sensor under the plate. The diameter and thickness of the fabricated plate were 8 and 0.1 mm, respectively. The spring width was 0.4 mm. When a force is applied to the plate, the plate moves vertically downward. Then, an eddy current displacement sensor detects the plate displacement without contact. The applied force can be measured using Hooke’s law. The proposed force plate has the advantages of ease of fabrication and cost-effectiveness. The central displacement variation and resonant frequency of the designed springs were evaluated by simulation. Then, we calibrated the fabricated force plate to obtain the sensitivity variation and resonant frequency. The experimental results suggest that the proposed force plate can effectively measure the GRF of a small insect.

Design and Analysis of Small Size Eddy Current Displacement Sensor.

A systematic method is employed for the design and analysis of a small size eddy current (EC) displacement sensor. Simulations are first performed to determine the optimal winding structure and dimensions of the sensor. A linear-fitting approach is then developed for converting the AC displacement signal of the sensor to a DC signal. Finally, a compensation method is proposed for mitigating the temperature drift of the EC sensor under different working temperatures. The experimental results show that the proposed sensor has a sensitivity of approximately 3 μm, a working temperature range of 25–55 °C, and a linearity of ±1.025%.

Wide-Range Displacement Sensor for Vibration Measurement of Magnetically Suspended Air-Blower

The displacement measurement is critical to the stable suspension and position control of magnetically suspended air-blower, and the eddy current sensor is a typical sensor to measure the dynamic displacements between the rotor shaft and the stator part. The displacement coordinate of magnetically suspended air-blower on multi degrees of freedom is firstly developed, and then the detection principle of eddy current displacement sensor is researched. Furthermore, the design processes of displacement sensor including dimensional parameters and quality factor are presented, and then the simulation had been conducted. Finally, the measurement experiments of magnetically suspended air-blower using the displacement sensor system are conducted, the results indicate that the linear range of displacement measurement approaches to 7.5 mm, the relative error is smaller than 2%, and the temperature stability is 0.022%/°C. Therefore, the displacement measurement and vibration analysis of magnetically suspended air-blower could be realized by the designed displacement sensor system.

Temperature Compensation of an Eddy-Current Displacement Sensor Using an Improved Sparrow Search Algorithm Method

Eddy-current displacement sensor (ECS) has been applied widely to the production of modern industry by reason of its characteristics of high sensitivity, good reliability, powerful anti-interference capacity, and noncontact measurement. However, it cannot be used when severe temperature drift occurs at high temperature. Some traditional compensation methods are difficult to achieve good performance with neglecting the nonlinearity. Hence, it is essential to propose a better method for temperature compensation. A novel temperature compensation approach for ECS problem using an improved sparrow search algorithm (ISSA) and radial basis function neural network (RBFNN) is proposed in this article. In the ISSA, a chaos strategy is introduced in the algorithm for avoiding local optimal point, and an elite opposition-based learning strategy is integrated to promote global search ability of ISSA with high efficiency. RBFNN is elected to model the temperature drift, and its parameters are determined by the proposed ISSA. The proposed method compensates the significant deterministic errors caused by temperature variation within a wide temperature range. The experimental schemes were designed to the effectiveness of the proposed method according to data fusion technology. The various test results obtained confirm the potential and effectiveness of the proposed approach compared to some other traditional temperature compensation methods presented in the literatures.

Simultaneous Temperature Drift Compensation for Eddy Current Displacement Sensors Used in Magnetically Levitated Rotor

The eddy current displacement (ECD) sensors used for displacement measurement are the core component of the magnetically levitated rotor (MLR) system. The temperature compensation of the ECD sensor is an important condition to ensure the stable operation of the MLR system in a wide temperature range. This paper proposes a simultaneous compensation solution based on an improved signal extraction circuit to the issue of temperature drift for the ECD sensor. Firstly, according to the operating principle of the ECD sensor, the generating mechanism and effect of the temperature drift is analyzed. Then, the principle of the simultaneous compensation method based on auxiliary temperature sensor is expounded, which has simple structure and strong universality. Furthermore, in order to determine the resistance ratio parameters, the procedure of designing temperature self compensation circuit are given in detail. Finally, the experimental results on an ultra-high speed magnetically levitated centrifugal compressor validate the effectiveness of the proposed method.

A High Resolution Synchronous Demodulation Method Based on Gated Integrator for Precision Sensors

This article proposes a synchronous demodulation method based on gated integrator for precision sensors, which shows significant improvement in signal-to-noise ratio (SNR) and resolution. Several traditional demodulation methods are introduced, especially the lock-in amplifier in detail for comparison. Through a comprehensive analysis of the gated integrator, it is proven that the proposed method shows a larger useful signal output with similar noise suppression capability compared with the lock-in amplifier so a better SNR could be obtained. Circuits of the two demodulation methods are manufactured and tested, and the results show that the output characteristic of the proposed method is consistent with the theoretical analysis. A precision eddy current displacement sensor prototype with the two demodulation methods is designed and tested as an example. It is found that the resolution of the sensor is improved with the proposed method by about 0.4 bits. Furthermore, this method is expected to function efficiently for any precision sensor requiring synchronous demodulation.

A synchronous demodulation technology based on sample-and-hold for eddy current sensors

This paper proposes a synchronous demodulation technology based on sample-and-hold which shows significant advantages in the application of precision sensors. The traditional synchronous demodulation methods are discussed, and then the working principle of the proposed method is theoretically analyzed in detail. It is found that the proposed method can not only effectively suppress the harmonic components caused by the signal source but is also beneficial to improving the dynamic range of precision sensors. The eddy current sensor is adopted as an example of precision sensors, and a high-precision eddy current displacement sensor prototype was designed and tested. The results show that with the proposed method, the harmonics in the output signal are suppressed more effectively, and the demodulation circuit is relatively simplified. This synchronous demodulation method has an extensive application prospect in precision sensors.

Analytical design and experiment of radial inductive displacement sensor with full-bridge structure for magnetic bearings

In magnetic bearing systems, the air gap between the stator and the rotor is generally measured with an eddy current displacement sensor. However, the inductive displacement sensor (IDS) is a preferred choice due to its structural consistency with magnetic bearings, which contributes to a compact system design. While most of the reported IDS research studies are based on three-dimensional finite element method (3D FEM) simulation and the IDS of such studies is designed with a half-bridge structure, in this paper, a higher sensitivity IDS with a full-bridge structure is proposed. To optimize the response of the sensor, an accurate theoretical analysis method is presented for the sensor based on the Schwarz-Christoffel transformation, which is used for compensating fringe effects of sensor inductance. Compared to traditional 3D FEM simulation, fast sensor design and optimization can be achieved with the proposed method. Experimental results agree well with theoretical predictions. The sensitivity of the proposed sensor is nearly 15.5 mV/μm, and the displacement resolution is better than 1 µm.

Three-Axis Inductive Displacement Sensor Using Phase-Sensitive Digital Signal Processing for Industrial Magnetic Bearing Applications

Non-contact rotor position sensors are an essential part of control systems in magnetically suspended high-speed drives. In typical active magnetic bearing (AMB) levitated high-speed machine applications, the displacement of the rotor in the mechanical air gap is measured with commercially available eddy current-based displacement sensors. The aim of this paper is to propose a robust and compact three-dimensional position sensor that can measure the rotor displacement of an AMB system in both the radial and axial directions. The paper presents a sensor design utilizing only a single unified sensor stator and a single shared rotor mounted target piece surface to achieve the measurement of all three measurement axes. The sensor uses an inductive measuring principle to sense the air gap between the sensor stator and rotor piece, which makes it robust to surface variations of the sensing target. Combined with the sensor design, a state of the art fully digital signal processing chain utilizing synchronous in-phase and quadrature demodulation is presented. The feasibility of the proposed sensor design is verified in a closed-loop control application utilizing a 350-kW, 15,000-r/min high-speed industrial induction machine with magnetic bearing suspension. The inductive sensor provides an alternative solution to commercial eddy current displacement sensors. It meets the application requirements and has a robust construction utilizing conventional electrical steel lamination stacks and copper winding.

Study on High Lift-Off of Eddy Current Type Rail Displacement Sensor by High Quality Factor

As the conventional eddy current type rail displacement sensor has a small distance (liftoff) from the railhead top surface to a sensor, there is the possibility that a sensor wakes up trouble and malfunction for a collision with the snow and the gravel. As the conventional triangle coil has low Q level, a change of the impedance to depend on rail displacement for when I raise a liftoff is not provided enough. Therefore, the problem that the detection precision of the rail displacement falls to occurs. In this article, I improved a Q level by becoming examination, the high frequency of the drive circuit of the coil structure and enabled measuring it at 50mm that was conventional double size by a liftoff.