Linear Hall Sensor Research Articles

An Embedded Magnetic Encoder-Based Rotor Position Estimation for Switched Reluctance Machine

This paper investigates the possibility of applying embedded magnetic encoder (EME) consisting of three linear Hall sensors (LHS) for rotor position estimation in SRM. The key concept of this scheme is to detect the flux density characteristics (FDC) inside of stator slots. However, the armature field is to be detected in SRM, which is rather different from permanent magnet (PM) machines, where the PM field is detected. In this paper, FDC in stator armature slot openings are firstly analyzed between different winding configurations. Thus, a selection principle of winding configuration is proposed. Secondly, the proper installation location of LHS is investigated, where the sensitivity of FDC to location deviation is discussed. Accordingly, a sensor holder is specifically designed and manufactured to reduce location deviation. Thirdly, based on the detected FDC, a simplified multiple complex-coefficient filter (MCCF) is utilized as a filter to extract the positive sequence of the fundamental component of LHS output signal. As a result, the angular frequency and rotor position can be tracked by the synchronous reference frame-based phase-locked loop (SRF-PLL). Finally, the proposed method is verified by a series of experiments under steady- and transient-state conditions, which confirm the feasibility of EME scheme.

A testing platform for frequency response characteristics of linear Hall sensors

A testing platform for frequency response characteristics of linear Hall sensors

Magnetic Poles Position Detection of Permanent Magnet Linear Synchronous Motor Using Four Linear Hall Effect Sensors

Magnetic pole position detection is the core of the closed-loop control system of the permanent magnet linear synchronous motor (PMLSM), and its position estimation accuracy directly affects control performance and dynamic response speed. In order to solve the problem of the increased estimation error of magnetic pole position caused by magnetic field distortion at the end of PMLSM while also considering the cost of control hardware, the paper uses four linear Hall sensors as magnetic pole position detection components and adopts an optimized estimation algorithm to improve the dynamic performance of the motor. Firstly, a numerical simulation of the magnetic field of poles was conducted using Ansoft Maxwell software, and combined with theoretical analysis, the optimal installation position range of four linear Hall orthogonal placements relative to the motor was obtained. Meanwhile, based on the existing vector tracking position observer, an improved observer detection model is proposed. The Matlab/Simulink software was used to compare the Hall-based detection model with the Hall-based improved observer detection model, verifying the feasibility of the improved detection algorithm. Finally, the rationality of the spatial layout design of linear Hall and the feasibility of improving the estimation algorithm were verified through experiments.

A Robust Forward Compensated Type-2 PLL Without DC Phase Error During Frequency Ramp for Embedded Magnetic Encoder

To achieve high performance vector control of permanent magnet synchronous machine (PMSM), high precision rotor angle is essential. Compared to traditionally used angle feedback device, e.g., encoder and resolver, the embedded magnetic encoder (EME) achieves high precision angle estimation without extra space occupation by installing several linear Hall sensors into PMSM cavity to monitor the flux leakage and rotor angle. The conventional synchronous reference frame (SRF) phase-locked loop (PLL) can extract phase and frequency from three or two Hall signals simultaneously. Although the type-2 SRF-PLL shows good robust performance against parameter variation, phase error emerges when input frequency changes. More specifically, a DC phase error appears in type-2 SRF-PLL during speed ramp stage due to insufficient order. Increase of the loop order removes the DC phase error but leads to instability risk. In this paper, a novel forward compensation (FC) module is attached on type-2 SRF-PLL to achieve phase error-free when frequency changes, where the instability risk is avoided. The effectiveness of proposed FC module is analytically and experimentally proved, where the phase error elimination, noise immunity and dynamic response are evaluated.

Design and Test of A Force Feedback Seedling Pick-Up Gripper for An Automatic Transplanter

Aiming at the problems of seedling injury and planting leakage due to the lack of seeding clamping force detection and real-time control in vegetable transplanting, a force feedback gripper was developed based on the linear Hall element. The mechanical properties of the stem of pepper cavity seedlings were first analyzed to provide a basis for the design of the gripper. A linear Hall sensor, a magnet, an elastic actuator, and an Arduino Uno development board make up the grasping force detecting system. Upon picking up a seedling, the elastic actuator, which is connected to the magnet, bends like a cantilever beam. As a result of the micro-displacement created by the elastic actuator, the Hall sensor’s voltage changes and can be used to determine the clamping force. Detection avoids direct contact between the sensor and the cavity seedlings, reducing the risk of sensor damage. Finite element method (FEM) simulations were used to determine the initial spacing between the magnet and Hall sensor and the effect of the elastic actuator. Control commands are sent to the servo based on the gripping force collected by the Arduino Uno board. Finally, the functions of accurate measurement, display, storage, and control of the clamping force of the cavity tray seedlings are realized, so that the damage rate of the cavity tray seedlings is reduced. In order to explore the influence of the elastic actuators on the clamping force detection system and the performance of the force feedback gripper, a calibration test of the clamping force detection system and a test of the indoor transplantation of pepper seedlings were carried out. Based on the calibration test, the clamping force detection system has a sensitivity of 0.0693 V/N, linearity of 3.21%, an average linear coefficient of determination of 0.986, and a range of 10 N, which fully meet the clamping force detection accuracy requirements during transplantation. Indoor tests showed that the force feedback gripper was stable and adaptable. This study can provide a reference for detecting and controlling clamping forces during transplantation.

Concept and Implementation of Embedded Magnetic Encoder in Flux-Switching Permanent-Magnet Machines

Rotor angle is essential in permanent-magnet (PM) brushless machines. Recently, an embedded magnetic encoder (EME) scheme, consisted of linear Hall sensors installing inside of the PM machines, has been proposed to sense the flux density and consequently provides rotor position. Compared with traditional optical encoder and resolver, the linear Hall sensor prevails over in both space and cost. The aforementioned scheme is employed successfully in rotor-PM machines, where a PM-excited field rotates at the synchronous speed. In this article, the feasibility of EME in stator-PM flux-switching machine is validated, where PMs are located in stator, resulting in a stationary PM field. The stator slots are selected as installation position of linear Hall sensors to avoid changing the existing structure of machines. The variation of linear Hall signal is due to the changing reluctance of rotor rather than rotating PMs. Then, a decoding algorithm is designed based on an add-up operation, a complex coefficient filter, and a synchronous reference frame phase-locked loop. Finally, experiments on a prototype machine are conducted to validate the effectiveness of EME scheme under both speed-varying and load-varying conditions.

Bioinspired, Multifunctional, Active Whisker Sensors for Tactile Sensing of Mobile Robots

Whiskers of some animals, such as rats and cats, can actively sense stimuli from their surrounding environment. Such a capability is attractive for intelligent mobile robots. However, an artificial whisker with similar abilities has not been fully developed so that the robots acquire their surrounding environment information in an active approach such as rats. In this paper, we propose a new bioinspired active whisking tactile sensor (MAWS) capable of sensing the distance, shape, size, and orientation of caves and environmental conditions. Two orthogonally distributed linear Hall sensors are mounted beneath a circular permanent magnet for spatial localization of the whisker. The whisker is then actuated and controlled by an array of nine electromagnetic coils by tuning the excitation current and phase sequence. Conical pendulum and bidirectional sweeping strategies were designed to mimic the simultaneous perception behavior of rats. A reactive obstacle avoidance experiment was also conducted to evaluate the performance of the proposed MAWS installed on a mobile robot.

Analysis and Detection of Rotor Eccentricity in Permanent Magnet Synchronous Machines Based on Linear Hall Sensors

Rotor eccentricity commonly exists in permanent magnet synchronous machines (PMSMs) due to improper assembly, excessive vibration, and continuous operation. Consequently, the unbalanced magnetic pull, introduced by rotor eccentricity, may lead to unfavorable noise, vibration, and even bear damage, which makes the detection of eccentricity meaningful. Although motor current signal analysis is the most popular method to diagnose eccentricity based on the amplitudes of sideband component, it is a big challenge to classify different types of eccentricities and quantify the eccentric ratio due to the spatiotemporal coupling effect. In this article, by installing a set of Hall sensors at stator slots of PMSMs to measure the magnetic flux density in time domain, the static eccentricity and dynamic eccentricity can be easily separated. This article provides a novel complex-analytical model to reveal the single side band modulation effect in air-gap filed due to dynamic eccentricity. Moreover, a diagnosis algorithm based on frequency-adaptive notch filter is designed to identify the eccentricity type and the corresponding degree. The effectiveness of the novel diagnosis method is validated by both simulations and experiments.

Implementation of Embedded Magnetic Encoder for Rotor Position Detection Based on Arbitrary Phase-Shift Phase-Lock Loop

Rotor position is essential in control of permanent magnet synchronous motors (PMSMs). In terms of resolution, structural complexity, occupied volume, anti-interference ability, environmental adaptability, and cost, embedded magnetic encoder based on linear Halls owns strong competitiveness. When linear Hall sensors are selectively installed at stator slot openings in extremely compact scenario, signal phase-shift asymmetry between two or three Hall sensors is inevitable. Conventionally, prefilter synchronous reference frame-phase-locked loops exhibit excellent phase-lock ability at fixed frequency (50/60Hz), but become ill when frequency changes especially at zero frequency. In this article, a novel transformation matrix is derived to map the asymmetric phase-shift signals onto two-phase stationary coordinate system. Then, an arbitrary phase shift-phase-locked loop is formed by replacing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Clark</i> transformation with the proposed transformation matrix, which can accurately extract rotor position and speed information in a simple and effective way, avoiding the utilization of complex notch filter. Simulations in continuous domain based on MATLAB and experiments in discrete domain based on an 18-slot/20-pole prototyped PMSM both confirm the effectiveness of the proposed method.

Position Estimation for Ultra-Low Speed Gimbal Servo System of SGMSCMG Based on Linear Hall Sensors

In the low speed servo system of single gimbal magnetically suspended control moment gyro (SGMSCMG), the accuracy of rotor position is an important factor which influences the speed accuracy. Linear hall sensors with small volume and high precision are usually adopted to the compact equipment and suitable for SGMSCMG. However, the signals detected by hall sensors contain lots of harmonics and noise which influence the accuracy significantly. For this reason, a novel precise position detection method based on 2-step cascaded Kalman filter with phase compensation scheme is proposed to extract the precise position information from `dirty' signals. The proposed method is advantageous since it is very simple and practical, and the phase compensation scheme can primely compensate the phase delay caused by cascaded Kalman filter. Finally, the experiments are carried out in a 50 Nm SGMSCMG, and the results show that the method can effectively estimate the angular position of the ultra-low speed servo motor, and the position accuracy can be improved by 85.7%.

A Three-dimensional Finger Motion Measurement System of a Thumb and an Index Finger Without a Calibration Process.

Various wearable systems have been investigated to measure hand motion, but some challenges remain. Many systems require a calibration process to map sensor signals to actual finger joint angles by the principle of measuring the length change of the finger, or bending sensors. Also, few studies have investigated how to measure thumb motion accurately using the wearable systems. This paper proposes an exoskeleton system with linear Hall sensors to measure three-dimensional hand motion without a calibration process. The calibration process is avoided by measuring finger joint angles through an absolute rotation measurement. A new wearing method with lower parts underneath the hand joints and rubber bands is proposed to fix the structure to the hand and adapt it for various hand sizes. As the thumb has a complex biomechanical feature at carpometacarpal (CMC) joint, a new measuring method of the CMC joint is proposed to directly calculate the orientation of the metacarpal. The prototype of the thumb and index finger was manufactured, and the performance was verified experimentally by using an optical motion capture system.

Research on one-dimensional motion control system and method of a magnetic levitation ball.

Research on the multi-degree-of-freedom and large-displacement motion control of the levitated object makes a contribution to broadening the application field of the Maglev technology. A one-dimensional motion control system and method of the Maglev ball are investigated in this paper. The Maglev ball motion control system is required to have a large operating range. In order to meet this requirement, a novel Maglev system based on double linear hall sensors is designed and implemented. The step-by-step control based on the Proportional-Integral-Derivative (PID) controller is proposed as one method to realize the large step response of the levitated object. The controlled object responds to the successive small step input rather than the large step input. Then, the mathematical model of the system is set up based on the electromagnetic force equation and controller parameters are tuned by following the mathematical model of the Maglev system at different positions. The experimental data show that the position accuracy of the Maglev control system using the PID controller reaches ±0.02 mm. Moreover, step-by-step control can not only safely realize large-displacement motion of the levitated object but also effectively reduce the overshoot of the step response and make the step response process smoother.

A novel inertial sensor exploiting magnetic fluid

Narrow available frequency range and low linearity of traditional magnetic fluid inertial sensors make them unpractical. A novel inertial sensor exploiting magnetic fluid is designed to solve these shortcomings. Through simulation and experiments, characteristics of magnetic fluid such as damping effect and levitation effect are studied. It shows that magnetic fluid has excellent damping effect which can be controlled by magnetic field. In order to improve the frequency response, both levitation and damping effect are used in sensors. Cylindrical permanent magnet is employed as the inertial mass, which can transform acceleration to the change of magnetic field. Linear hall sensor with high sensitivity is the transducer installed on the position where magnetic field gradient of cylindrical permanent magnet is maximal and has best linearity. Verification experiments of the designed sensor are conducted on vibration platform. Experimental results give that application of magnetic fluid for inertial sensor optimizes its performance greatly. Available frequency range of the designed sensor is increased by 256% after using magnetic fluid as damping material. This paper provides a reference for research on magnetic fluid and its application in inertial sensors.

Modelling and analysis on the mechanism of electromagnetic driven weft insertion

In view of the difficulty in improving the weaving efficiency of the projectile weaving machine based on the traditional technology principle, This research presents the electromagnetic-drive gripper weft insertion mechanism, change the existing mechanical pick principle of weft insertion, its goal is to achieve “zero transmission” friction-free high-speed weft insertion, omit complex mechanical transmission mechanism in picking shaft, and breakthrough the bottleneck of the weft insertion rate, wide fabric problem in principle. Based on the theoretical study of electromagnetic projection and electromagnetic levitation, the structural model and motion model of electromagnetic pick and electromagnetic weft are established by comparing the electromagnetic and permanent magnetic model schemes. In order to meet the requirement of electromagnetic levitation, the linear hall sensor is selected and its driving circuit is designed to obtain the real-time height value of the chip shuttle. Through the analysis of the coil response, the advantages and disadvantages of DC-DC regulation and PWM wave regulation are compared, and the high response hardware circuit of DC-DC regulation is designed. MATLAB simulation ensures the feasibility of PID regulation. The feasibility of the scheme was verified by Maxwell electromagnetic picking simulation and electromagnetic filling insertion simulation. The first phase of picking experiment and static filling insertion experiment were carried out. In order to ensure the stability, the double-row soft iron chip shuttle was used, and good experimental results were obtained, which proved the feasibility of electromagnetic suspension weft insertion scheme.

Design and Implementation of a Soft Robotic Arm Driven by SMA Coils

Soft robots may potentially be used for human services and complex environmental locomotion. The bodies of the soft robots are made from soft materials to make them safe for human interactions and to enable them to deform enough to adapt to soft or rough terrains. However, their practical applications are limited because their body stiffness is too low and the deformation is continuous, which make it difficult to control their movements. In this paper, the design and implementation of a soft robotic arm driven by shape memory alloy (SMA) coils are reported. The arm is made from soft silicone, and there are three linear Hall sensors in certain slots on the body wall to measure the changes in height as the arm bends. With a compression compensation algorithm, a proportional-integral differential controller is used to precisely control the bending movement. This soft robotic arm can follow a two-dimensional motion with a relatively high accuracy; indeed, it displays quite a remarkable performance considering its low cost, simple structure, easy control, and small bending error. Since this soft arm can be used as the basic driving unit of a soft robot capable of manipulating and locomoting, it has shed light on the applications of SMA soft robots.

Precision Motion Control of a Linear Permanent Magnet Synchronous Machine Based on Linear Optical-Ruler Sensor and Hall Sensor

The linear optical-ruler sensor with 1 μm precision mounted in the linear permanent magnet synchronous machine (LPMSM) is used for measuring the mover position of LPMSM in order to enhance the precision of a measured mover position. Due to nonlinear friction and uncertainty effects, linear controllers are very hard to achieve good mover positioning of LPMSM. The proposed adaptive amended Elman neural network backstepping (AAENNB) control system is adopted for controlling the LPMSM drive system to bring about the mover positioning precision of LPMSM. Firstly, a backstepping scheme is posed for controlling the tracing motion of the LPMSM drive system. The proposed backstepping control system, which is applied in the mover position of the LPMSM drive system, possesses better dynamic control performance and robustness to uncertainties for the tracing trajectories. Because of the LPMSM with nonlinear and time-varying dynamic characteristics, an adaptive amended Elman neural network uncertainty observer (AAENNUO) is posed to estimate the required lumped uncertainty. According to the Lyapunov stability theorem, on-line parameter training methodology of the amended Elman neural network (AENN) can be derived by use of adaptive law. The error estimated law is proposed to compensate for the observed error induced by the AENN with adaptive law. Furthermore, to help improve convergence and to obtain better learning performance, the mended particle swarm optimization (PSO) algorithm is utilized for adjusting the varied learning rate of the weights in the AENN. At last, these experimental results, which show better performance, are verified by the proposed control system.

Towards a low current Hall effect sensor

Many modern electronic devices utilize linear Hall sensors to measure current and the magnetic field, as well as to perform switching and latching operations. Smartphones, laptops, and e-readers all work with very low (sub-milliampere) currents. To perform a switching function in low-power devices, however, Hall sensors must work in the microampere regime. This paper demonstrates, for the first time, the ability of a standard Hall detector to work linearly in the microampere regime between 0 and 0.7 Tesla. To do so, we developed a current source with RMS noise on the order of 10–100 pA/Hz. An optimized electronic circuit with minimal connections feeds current to the Hall sensor, and the Hall voltage is measured with an industrial nanovoltmeter. After cooling this system down to temperatures as low as 77 K, we found mostly 1/f noise. In this regime the thermal noise was negligible. We demonstrate the capabilities of this system by precisely measuring the slope of the Hall effect with a four-point probe at current intensities of 100, 10, and 1 μA. We expect that our system can work as a microampere Hall sensor using external voltage detectors.

An Improved Displacement Measurement Based on Model Reconstruction for Permanent Magnet Synchronous Motor

Permanent magnet synchronous linear motor (PMSLM) and PM synchronous planar motor are important motion devices in the modern precision industry. Their inherent periodic magnetic fields are highly related to motor position. Correspondingly, the magnetic fields can be utilized to determine their own displacement and replace expensive sensors. However, the measurement result of this strategy seriously depends on magnetic field model (MFM) preciseness. To improve measurement accuracy, a novel MFM with Fourier series is proposed in this paper. First, a high-order theoretical model from theoretical derivation is developed. And the analyses show that even harmonics exist in the magnetic field of motor, which are not included in the theoretical model. This model deviation obviously affects measurement accuracy. Hence, the new MFM is reconstructed based on a high-order theoretical model. Comparative experiments with the three different MFMs are carried out to measure the displacement of the PMSLM. In the experiments, a linear hall sensors array containing eight sensors is self-developed to detect motor magnetic field. The root mean square of displacement measurement errors using a reconstruction model, a high-order theoretical model, and a fundamental model is 4.84, 8.42, and $758~\mu \text{m}$ , respectively. The experimental results validate that the measurement result of the proposed reconstruction MFM is better than the other two MFMs.

Mover Position Detection for PMTLM Based on Linear Hall Sensors through EKF Processing.

Accurate mover position is vital for a permanent magnet tubular linear motor (PMTLM) control system. In this paper, two linear Hall sensors are utilized to detect the mover position. However, Hall sensor signals contain third-order harmonics, creating errors in mover position detection. To filter out the third-order harmonics, a signal processing method based on the extended Kalman filter (EKF) is presented. The limitation of conventional processing method is first analyzed, and then EKF is adopted to detect the mover position. In the EKF model, the amplitude of the fundamental component and the percentage of the harmonic component are taken as state variables, and they can be estimated based solely on the measured sensor signals. Then, the harmonic component can be calculated and eliminated. The proposed method has the advantages of faster convergence, better stability and higher accuracy. Finally, experimental results validate the effectiveness and superiority of the proposed method.

Position Estimation Using Linear Hall Sensors for Permanent Magnet Linear Motor Systems

This paper proposes a new scaleless position estimation method. From the industrial perspective, the Hall sensor has several advantages: tiny size, light weight, extremely low cost, and insensitivity to environmental contamination and external disturbance. Compared to the square wave Hall sensor, the linear Hall sensor provides more detailed information along the position. However, for combining more than two linear Hall sensors, the sensor offset, the difference in scale, and the unwanted phase shift between them and the harmonics would decrease the validity and reliability of sensor measurement. The fast Fourier transform and the fixed point iteration method are applied to compensate for those issues without any low-pass filter or additional signal conditioning. The effectiveness of the proposed scheme is verified through a prototype permanent magnet linear synchronous motor system.