Magnetostrictive Torque Sensor Research Articles

Nonlinearity of Magnetostrictive Torque Sensor under Varying External Magnetic Field Strength

Abstract Correctly torquing bone screws is an important factor in achieving positive patient outcomes during orthopaedic surgery. A torque-limiting smart screwdriver concept has been proposed, and ongoing work is being undertaken to model the screwing process and allow the concept to work. These models require experimental validation, so a test rig was developed. The magnetostrictive torque sensor in this test rig was affected by magnetic parts of the test rig, which offset the zero-torque point; this raised concerns over the effects on linearity, which were tested here. The torque sensor was tested against a non-magnetostrictive reference under varying external magnetic conditions. While the magnetic field offset the torque, there was no notable change in linearity under the conditions tested, and the linearity was always within the datasheet specifications. Hence, we conclude that in the context of this test rig, there were no negative effects on linearity, although under higher loading or stronger magnetic conditions, this may not hold.

Electrodeposited Fe–Ga Alloy Films for Directly Coupled Noncontact Torque Sensing

Torque measurements are used in a number of controls applications, but indirect coupling, size, and the quality of commercially available sensor materials can limit their utility. Here, a compact magnetostrictive torque sensor is made by electrodeposition of Fe1–xGax (0.1<x<0.4, aka Galfenol), onto Cu shafts using rotating cylinder electrodes (RCEs). The alloy composition is controlled by tuning the RCE rotation rate between 500 and 2000 RPM, while the electrode potential is varied from 1.15 to 1.20 V. Direct coupling of Fe1–xGax to the shaft with the electrodeposition process enables magnetic anisotropy to be induced via shaft surface texturing, as seen by a 260% increase in susceptibility along a 400 grit texturing direction versus perpendicular to the texture and compared with the isotropic behavior of films deposited on polished shafts. Inverse magnetostriction-based torque sensing is demonstrated by measuring stray fields from Fe1–xGax films as torque loads of 0–16.9 Nm were applied to the shaft. Films electrodeposited on circumferentially textured shafts had torque responses almost 1.5 times greater than films electrodeposited on longitudinally textured shafts and five times greater than films on polished shafts.

Design of an isokinetic knee dynamometer for evaluation of functional electrical stimulation strategies

BackgroundThe limitations of functional electrical stimulation (FES) cycling directly affect the health benefits acquired from this technology and prevents its’ full potential to be realised. Experiments should be done on a test bed which can isolate and focus only on one muscle group, namely the quadriceps. The aim of this work was to design and develop an isokinetic robotic leg extension/flexion dynamometer which can mimic knee joint motion during actual cycling to be used for evaluation of novel functional electrical stimulation strategies. Although the main motivation for development of the dynamometer was for application in FES studies, it has the potential to be used for various different muscle physiology studies. MethodsA feedback control system with integrated electrical stimulation for isokinetic knee joint torque measurement has been developed and tested for safety and functionality. The leg extension/flexion device was modified and equipped with a DC motor drive system to imitate isokinetic knee joint motion during cycling when the hip joint remains fixed. Real-time bi-directional effective torque on the lever arm was measured by a magnetostrictive torque sensor and a load cell. Closed-loop motor control system was also designed to mimic the cyclical motion at desired angular velocity. ResultsA functional model of the robotic dynamometer was developed and evaluated. The dynamometer is capable of simulating the knee angle during cycling at a cadence of up to 70 rpm with range of motion of 72∘. The magnetostrictive torque sensor can measure torque values up to 75 Nm. The lever arm can be adjusted and the target knee angle was controlled with RMSE tracking error of less than 2.1∘ in tests with and without a test person, and with and without muscle stimulation. ConclusionsThe isokinetic knee joint torque measurement system was designed and validated in this work, and subsequently used to develop and evaluate novel muscle activation strategies. This is important for fundamental research on effective stimulation patterns and novel activation strategies. This will, in turn, enhance the efficiency of FES cycling exercise and has the potential to improve the health-beneficial effects.

Proposal of Pre-load-type Magnetostrictive Torque Sensor for EPS

Proposal of Pre-load-type Magnetostrictive Torque Sensor for EPS

Modelling of a Magnetostrictive Torque Sensor

Existing magnetostrictive torque sensor designs typically measure the rotation of the saturation magnetization under an applied torque and their theoretical treatment revolves around the minimization of the free energy equation adapted according to the assumptions considered valid in each design. In the torque measurement design discussed in this paper, Ni-rich NiFe films have been electrodeposited on cylindrical austenitic steel rods. Contrary to existing designs, the excitation field is applied along the axial direction and is low enough to ensure that the resulting magnetization along the same direction remains in the linear region of the M(H) characteristic. Assuming homogeneous magnetization, positive magnetostriction constant λ, negligible hysteresis and demagnetizing fields, torque T may be expressed in terms of an effective uniaxial anisotropy constant Ku around 45° to the axial direction. It is shown, that for the proposed arrangement, the resulting M is the linear superposition of the effect of a torque-induced effective field and the excitation field, the applied field accounts for the vertical offset of the magnetization response and the applied torque increases the slope of the M(H) characteristic.

Design and Characterization of a Magnetostrictive Torque Sensor

Design and Characterization of a Magnetostrictive Torque Sensor

J0404-8-1 自動車ステアバイワイヤー用磁歪合金リング式トルクセンサ感度に及ぼす機械材料学的影響因子([J0404-8]知的材料・構造システム(8):各種センシング)

J0404-8-1 自動車ステアバイワイヤー用磁歪合金リング式トルクセンサ感度に及ぼす機械材料学的影響因子([J0404-8]知的材料・構造システム(8):各種センシング)

A Figure-of-Eight Flexible Pickup Coil for a Magnetostrictive Torque Sensor

A new structure of the pickup coil made on a double-layered flexible printed circuit board (PCB) is proposed for a magnetostrictive torque sensor. The pickup coil employs a pair of figure-of-eight coils in which one coil is 90deg angle rotated from the other. Each of figure-of-eight coils has 14 turn windings made of 18-mum-thick copper conductor with 100-mum/100-mum line and space. The shape of the coil is a square, and its side length is 15 mm. A torque sensor is constructed by using a shaft with a magnetostrictive sleeve made of a martensitic stainless steel. The pickup coil system was coupled to it with an airgap of 0.3 mm. The performance of the torque sensor is reported

The effect of shot peening process on improvement of a magnetostrictive torque sensor with helical knurls

The sensitivity and hysteresis of a magnetostrictive torque sensor using helical knurls are much improved by applying shot peening after roll-forming helical knurls on the surface of the shaft. In this paper, the effect of shot peening is investigated experimentally using several shafts of various Ni contents (4.3–18%).

トルクセンサを用いた介助型パワーアシスト車椅子の開発

This paper describes a power-assisted attendant-propelled wheelchair employing a model reference control algorithm based on velocity feedback control. The model equation encompasses two parameters, mass and viscous damping factor. The input of the control system is operator's force. Choosing the model mass less than the real value enables the operator to move the wheelchair with less effort. The goal is to realize functionality where the operator would always feel as though he/ she were propelling a lighter wheelchair on level ground.In order to measure the operator' s force we developed a propelling force sensing mechanism utilizing magnetostrictive torque sensors. The control circuit uses a16-bit single chip microcomputer and DC motor driver boards. The model parameters were chosen through experiments on surfaces indoors. Test drives with dummy weight(65kg)on surfaces indoors and slopes to buildings, and so on were conducted. Both young adults and elderly people took part in the tests. The results shown by the subjects indicate that they started the wheelchair with less than half of the force required when they operated a normal wheelchair. Adaptations of the parameters to the operator' s characteristics and to situations such as quick start or slow stop are to be solved.

Analysis of characteristics of a magnetostrictive torque sensor with helical knurls

A torque sensor based on a pair of symmetrical helical knurls is described. Operation is based on the distinctive anisotropy and separation of principal stresses attributable to knurl shape and helix angle. This is made clear by finite-element method analysis. Maximum sensitivity is found for knurls having /spl plusmn/45/spl deg/ helix angles. A model for the output signal as a function of applied torque is developed based on the uniaxial anisotropy associated with the knurl shape and the stress anisotropy arising with the torque.

Development of a Torque Sensor using Giant Magnetostrictive Material for Electric Power-Assisted Bicycles

We developed a new light-weight power-assisted bicycle using a giant magnetostrictive torque sensor, which is a new mechatronics product for individual use. The key components for power-assisted bicycles are sensors, which are vital for detecting the extremely large forces (maximum crank axle torque: about 160Nm) of power exerted on the pedals by the riders. In this paper we propose a torque detection method that uses a giant magnetostrictive material with a high force detection sensitivity, where the capacity to resist stress is extremely large.Improving the hysteresis has become an issue for raising the precision of force sensors that use giant magnetostrictive elements. As a method to improve the hysteresis, we focus on the point of integrating these force sensors into microcomputer-equipped digital control systems, and construct a detection circuit such that the magnetostrictive elements are expanded instantaneously by the application of a pulse magnetic field during the sampling of discrete sensor data. this paper also examines this hysteresis reduction method and reports the contents of an actual construction method for force sensors.

Magnetic domain behaviour in magnetostrictive torque sensors

In this paper magnetic domains are observed dynamically for the first time in-situ on Fe 81B 13.5Si 3.5C 2 amorphous ribbon chevron design torque sensors. The domains are observed using the Kerr magneto-optic bench whilst the sensor is in operation on a specially constructed torque rig. The effect of torque, applied field, bending stresses and attachment technique on the magnetic domains is illustrated by means of domain images. Investigations into how these effects influence the output characteristics and repeatability of the sensor are presented. This leads to a simplified design with improved hysteresis and sensitivity in the 10 Nm range.

Development of a Magnetostrictive Torque Sensor for Milling Process Monitoring

This paper deals with a sensor system based on the magnetostrictive effect which is installed in a tool holder for sensing cutting torque in order to monitor the milling process. Changes in the magnetic permeability of ferromagnetic alloy layers formed onto a rotating shaft due to torque are detected by coils as changes in impedance without contacting the rotating shaft. By mounting the magnetostrictive sensor on a tool holder, it has become possible to detect cutting torque as close to the cutting point as possible. The accuracy of the proposed sensor system is confirmed through static and dynamic evaluation tests. In order to investigate the relationship between tool failure and cutting torque, cutting tests were performed. As the results, the possibility of estimating flank wear and tool fracture from cutting torque detected by the proposed sensor system is recognized.

Metal-bonded Co-ferrite composites for magnetostrictive torque sensor applications

A new class of magnetomechanical sensor materials, Co-ferrite (CoO/spl middot/Fe/sub 2/O/sub 3/) and metal-bonded (Ag, Ni, Co) Co-ferrite composites, has been investigated. These materials exhibited magnetostriction in excess of 200 ppm and high d/sub 33/ (/spl part//spl lambda///spl part/H)/sub /spl sigma// coefficient, 1.3/spl times/10/sup -9/ A/sup -1/ m, at low applied field (<100 kA/m). Selected compositions were formed into test samples in the form of rings brazed to stainless steel through-shafts. Changes of surface axial magnetic field in response to applied torque as high as 64 AN/sup -1/ m/sup -2/ were observed for a demonstration sample of dimensions 25 mm OD, 12.5 mm ID, and 8 mm high. A hysteresis of /spl plusmn/0.5 N/spl middot/m was observed. These materials appear to be promising candidates for torque sensors, and other magnetostrictive sensor and actuator applications.

Ｔｉ合金またはＳＵＳ３０４ステンレス鋼シャフトとＮｉ‐Ｆｅスパッタ膜で構成した磁歪式トルクセンサ出力の温度ドリフト補償法

Ｔｉ合金またはＳＵＳ３０４ステンレス鋼シャフトとＮｉ‐Ｆｅスパッタ膜で構成した磁歪式トルクセンサ出力の温度ドリフト補償法

Ｔｉ合金シャフトとＮｉ‐Ｆｅスパッタ膜で構成した磁歪式トルクセンサの出力値に及ぼす要因

Ｔｉ合金シャフトとＮｉ‐Ｆｅスパッタ膜で構成した磁歪式トルクセンサの出力値に及ぼす要因

Evaluation of steel shafts for magnetostrictive torque sensors (abstract)

Based on the magnetostrictive effect in steel, a robust, noncontacting shaft torque sensor can be obtained. A fundamental problem in this scheme is compatibility between mechanical strength required for a shaft and a magnetic one needed for a torque sensor. In order to find shaft material accommodating these two requirements, we investigated basic characteristics, such as hysteresis, linearity, and zero-level fluctuation associated with shaft rotation, of the magnetostrictive torque sensor for various nickel chromium molybdenum steel shafts (SNCM in Japanese Industrial Standard) subjected to case hardening. We prepared three kinds of shafts of 25 mm in diameter: SNCM 420 (Ni=1.69%, C=0.2%), SNCM 616 (Ni=2.91%, C=0.15%), and SNCM 447 (Ni=1.67%, C=0.49%). Shafts of the first two materials were carburized, whereas those of the last one were quenched. We used a magnetic head-type torque sensor consisting of a pair of cross-coupled figure-eight coils (14 turn), which has been already proposed by us.1 The hysteresis in the input–output relationship was measured for the excitation current from 0.1 to 1.0 A at the excitation frequency of 60 kHz. The hysteresis of the SNCM 420 shaft changes sign from negative to positive with the increase in excitation current and that of the SNCM 616 shaft decreases monotonically but never reaches zero, whereas that of the SNCM 447 shaft exhibits minimum. The smallest values obtained are nearly zero for the SNCM 420 shaft at 0.3 A, 1.5%/(full scale (FS)=400 Nm) for the SNCM 616 shaft at 1.0 A and 0.7%/FS for the SNCM 447 shaft at 0.8 A, respectively. The linearity measured for the SNCM 420 shaft, which has the smallest hysteresis of the three, at 0.3 A and 60 kHz was virtually straight for the applied torque range −400–400 Nm and 0.8% of nonlinearity error for the range −1000–1000 Nm. The zero-level fluctuation was measured for the SNCM 420 shaft by rotating the shaft without applying torque. The level of the fluctuation was as small as ±1.8%/FS (FS=1000 Nm). It is interesting to consider the effect of carburization on the performance of the shaft seen from the torque sensor. The sensitivity of the as-ground SNCM 420 shaft is approximately ten times larger than that of carburized shafts, however, the input–output relationship measured for the as-ground shaft was saturated completely at the applied torque of 400 Nm. The zero-level fluctuation for the as-ground shaft was about the same in terms of %/FS as that of carburized shaft. Considering that the reduction of the sensitivity by carburization is a factor of 10, magnetic inhomogeneities at the surface are well improved by the carburizing process. We measured the two-dimensional pattern of magnetic anisotropy distribution by scanning the shaft surface using a 6.5 mm square eddy current probe that is sensitive to magnetic anisotropy.2 We found that the as-ground shaft has a peculiar magnetic anisotropy pattern, which is probably induced during manufacturing steel bars. The pattern was erased by the heat treatment at 920 °C for 4 h, which is a main course of carburization treatment.

Imaging of Magnetic Nonuniformity on the Surface of Steel Shafts Used for Magnetostrictive Torque Sensors

Imaging of Magnetic Nonuniformity on the Surface of Steel Shafts Used for Magnetostrictive Torque Sensors

Eddy current probe for nondestructive testing using cross-coupled figure-eight coils

It is shown that the pickup head consisting of cross-coupled figure-eight coils originally developed for the magnetostrictive torque sensor is well suited for the eddy current probe detecting small defects in a nonmagnetic conductive material. The probe is easily extended to a one dimensional array form, which substantially reduces the number of times of scanning the targeted materials. The response of a single unit of the probe to a trough hole defect in an aluminum plate are presented. A halfway hole at the back of an aluminum plate of 1.2 mm in thickness was successfully detected from the front using this probe. A five-channel array was developed in which the excitation coil is shared by all the channel. A small through hole defect in an aluminum plate was detected clearly by a single scan with the array probe.