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This paper investigates the performance of a magnetic lead screw (MLS) equipped with skewed arc magnets. Skewed arc magnets are adopted to approximate the helical ones, because the latter is hard to realize. Although similar method had been proposed in the previous literature, discussion about the parameters of the skewed arc magnets was insufficient and little attention was paid to the gear ratio of the resultant MLS. In this paper, the principle of approximation by skewed arc magnets is proposed and discussed, and the performance of the MLS with skewed arc magnets is evaluated and compared with the ideal MLS in terms of thrust force, torque, and gear ratio. It is highlighted that the gear ratio is the fundamental indicator of the MLS’s performance, besides the thrust force and torque. It is shown that the gear ratio of MLS is mainly affected by the reference angle and the arc angle of skewed arc magnets, and optimal values for the two angles are obtained. In addition, the effects of the magnet magnetization on thrust force and torque are analyzed. Finally, dovetail budge and groove are introduced between the adjacent magnet segments for simpler fabrication. [ABSTRACT FROM AUTHOR]

This paper deals with equivalent 2-D finite-element (FE) models of permanent magnet lead screw (PMLS), to accurately predict the thrust force. Due to the helical-shape permanent magnets (PMs), the magnetic fields of PMLS are typically 3-D and non-symmetric. However, the PMLS is approximately symmetric in some cases and an equivalent 2-D axis-symmetric FE model is developed instead of 3-D models. The problem lies in that no evaluation about the accuracy and applicability of the 2-D axis-symmetric FE model was offered in previous literature. In this paper, the 2-D axis-symmetric FE model is derived based on the concept of equivalent current sheets of PMs. The limitations of the existing 2-D axis-symmetric FE model are clarified, and a novel equivalent 2-D torque FE model is then proposed to predict thrust force with the gear ratio when the 2-D axis-symmetric FE model is not appropriate. It is shown that the choice of equivalent 2-D FE model depends on the lead angle of PMLS, 2-D axis-symmetric FE model is applicable in the range of (0°, 15°), and 2-D torque FE model is preferred in the range of (65°, 90°). [ABSTRACT FROM AUTHOR]

This paper is an investigation in the performance of two types of magnetic screws (MSs). The first is the magnet to magnet and consists of permanent magnet (PM) nut and PM screw and the second is a magnet to reluctance and consists of PM nut and a double-start reluctance screw. It is argued that for cost sensitive and long stoke applications, a magnet-to-reluctance MS may be the preferred option. It is also shown that capacitor discharge magnetization techniques can be employed for imprinting helical magnetization distributions on cylindrical PMs, significantly reducing the complexity and facilitating the practical realization of MS systems. [ABSTRACT FROM AUTHOR]

This paper presents a new type electromagnetic lead screw (EMLS) intended for wave energy application. Similar to the mechanical lead screw, this electromagnetic version can transfer slow linear motion to high-rotational motion, offering gearing effects. Compared with the existing pure magnetic lead screw (MLS) employing permanent magnets only, the new EMLS proposed uses dc current to provide the required helical-shape magnetic field, offering a much simpler, robust structure compared with the MLS. The working principle and the performances of this EMLS are analyzed in this paper. Comparison with PM-type lead screw is given. In addition to this, the theoretical analysis to support the use of a 2-D finite element model to analyze the 3-D magnetic-type lead screw is given, which has not been well covered in the existing literature. [ABSTRACT FROM AUTHOR]

This paper introduces the concept of the trans-rotary magnetic gear (TROMAG). The TROMAG is a magnetic device consisting of a rotor and a translator with an air gap in between, capable of converting linear motion to rotation, and vice versa, and doing the gearing action at the same time. Although its structure suggests that the TROMAG is simply the magnetic dual to the mechanical lead-screw, the authors show that the concept could also be derived from the elementary magnet arrays. The paper tries to establish an analogy between the TROMAG and the ordinary electrical machines with respect to the number of poles and the stack length, thus providing a deeper insight into the device operation. Three-dimensional (3-D) finite element analysis (FEA) is deployed to obtain the torque and force characteristics. Furthermore, it is shown that in addition to the permanent magnet (PM) TROMAG, developing the reluctance and the induction TROMAG is possible as well, but at a lower force density. [ABSTRACT FROM AUTHOR]

This paper introduces a new type of reluctance-based magnetic lead screw (RBMLS) that is attractive for many potential applications. The proposed topology presents the implementation of discretized permanent magnets (PMs) and ferromagnetic semi-rings. The proposed RBMLS has PMs in only one of its movable parts, making it suitable for long-stroke applications. The proposed RBMLS is analyzed through the 2-D and 3-D finite-element method in order to test its topology and obtain the force produced per PM volume. Detailed design features are presented for the realization of a prototype. [ABSTRACT FROM AUTHOR]

Simulation of flaw detection by eddy-current testing requires the calculation of the eddy-current signal due to the presence of the flaw. In this paper, the surface integral method (SIM) is applied for the calculation of the crack signal in the workpieces composed of a conducting plate with a borehole. The adopted approach makes use of Green’s operator that takes into account the effect of the borehole, and thus, the integral formalism is restricted to the crack surface only. The truncated region eigenfunction expansion method is followed for the construction of Green’s operator. Comparisons of the computed crack signal with numerical simulations carried out using a hybrid volume integral method-SIM approach and experimental results show excellent agreement. [ABSTRACT FROM AUTHOR]

Force-controllable actuators are essential for guaranteeing safety in human–robot interactions. Magnetic lead screws (MLSs) transfer force without requiring contact between parts. These devices can drive the parts with high efficiency and no frictional contact, and they are force limited when overloaded. We have developed a novel MLS that does not include spiral permanent magnets and an MLS-driven linear actuator (MLSDLA) that uses this device. This simple structure reduces the overall size of the device and improves productivity because it is constructed by a commonly used machined screw as a screw. The actuator can drive back against an external force and it moves flexibly based on the magnetic spring effect. In this paper, we propose a force estimation method for the MLSDLA that does not require separate sensors. The magnetic phase difference, as measured from the angular and linear displacements of the actuator, is used for this calculation. The estimated force is then compared against measurements recorded with a load sensor in order to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In the automobile industry, the simple inspection method of detecting the slack of the high-tension bolt in the engine section is desired. Since the permeability of the compression direction inside the steel is decreased when the steel material is compressed, the permeability of the compressed domain in the bolt is decreased when the fastened force of the bolt is increased. Therefore, the evaluation of the slack of the bolt is possible by detecting the difference of the magnetic characteristics near the compressed position in the bolt. However, the detection signal is also influenced by the change of distance (lift-off) between the bolt and an electromagnetic sensor. In this paper, the inspection method for measuring the slack of the bolt taking account of the lift-off is proposed using the 3-D edge-based hexahedral nonlinear finite element method and the experimental verification. [ABSTRACT FROM AUTHOR]

The high-temperature superconductor (HTS) machines are more attractive due to the advantages of high power density and efficiency. This paper introduces a new HTS electromagnetic screw (HTS-EMS) that is developed for artificial heart. Two helical-shaped slots are introduced to the translator; the key to the HTS-EMS is that the HTS coils carrying dc currents are placed in the helical-shaped slots. The permanent-magnet array is placed in the rotor. Due to the high current density of the HTS coil, the power density of the HTS-EMS can be improved effectively. The electromagnetic performance of the HTS-EMS is analyzed, including the flux, thrust force, as well as torque. The proposed HTS-EMS is evaluated compared with the existing magnetic screw using time-stepping finite-element method, verifying the advantages of the proposed structure. [ABSTRACT FROM AUTHOR]

This paper presents structure thermal mechanics analysis of spindle disk assembly used in spinning magnetic data storage hard disk drives (HDDs). With the view toward understanding the underlying physics and to minimize the corresponding repeatable run-out (RRO) of track following position error signal (PES) in high track per inch (TPI) magnetic disk drives, analytical representation of thermal expansion mismatch between disk and spindle hub structure formulated in form of operators and finite element analyses (FEA) are employed in this paper. Parameter studies with analyses taken at different operational temperatures suggest that RRO can be minimized significantly when location of spindle notch, which is can be the internal feature used to position bearings to the hub structure, is properly located. RRO harmonics resulted from the thermal expansion mismatch and structure misalignments having ramping characteristics from disk outer diameter to inner diameter are studied and concluded with simple algebraic expression related to number of fasteners used in disk-spindle assembly. [ABSTRACT FROM AUTHOR]

This paper introduces a high-force-density linear actuator for an artificial heart, which is based on the concept of a magnetic screw–nut. The novelty of the proposed magnetic screw is adaptation of Halbach permanent-magnet (PM) array disposed helically. PMs are placed on both the screw and the nut. The configuration of the newly designed magnetic screws is presented, and its electromagnetic performances are analyzed. The proposed Halbach magnetized magnetic screw is evaluated as compared with a radially magnetized magnetic screw using the time-stepping finite-element method, verifying the advantages of the proposed structure. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel capsule-type magnetic microrobot (CMM) that can navigate along a tubular environment and selectively release drugs in different target points actuated by a magnetic navigation system. The proposed CMM is a capsule-type structure with two cylindrical drug chambers that contain different drugs. It can navigate through a tubular environment by a magnetic gradient and release drugs at different positions by using uniform rotating magnetic fields. The proposed CMM was prototyped using 3-D printing technology. The operating conditions of a drug-releasing motion were determined by investigating the magnetic and friction torques within the body. Finally, we performed various experiments in a tubular environment to verify the validity of the proposed CMM. [ABSTRACT FROM AUTHOR]

This paper reports the development of self-deployed magnetic polygons at the centimeter scale. These permanent-magnet (NdFeB) devices can be folded into a constraining catheter for delivery, before spontaneously unfolding into a polygon upon extrusion. The devices use a combination of dipolar and quadrapolar magnetic components along their sides, which facilitate self-deployment. Four-, six-, and eight-sided devices are reported and the effects of varying the geometry, the number of sides, and the duty cycle of the quadrapolar sides are examined in simulation and through experimental testing. As well as self-deployment, two N-sided devices (N\in\4,6,8\) are capable of face-to-face magnetic mating of opposing north and south poles with a minimum of difficulty. This capability is justified by modeling of the system's magnetic potential energy, and by experimental validation. Optimized design parameters are proposed. Magnetic mating of two N-sided devices facilitates applications where access to an adjoining orifice is desirable with a minimally sized access port (e.g., in the case of minimally invasive surgical technology). Current and future applications are considered. [ABSTRACT FROM AUTHOR]

Eddy-current testing (ECT) is widely used in inspection of multilayer aircraft skin structures for the detection of cracks under fasteners (CUF). Detection of deep hidden CUF poses a major challenge in traditional ECT techniques largely because the weak eddy-current signal due to a subsurface crack is dominated by the strong signal from the aluminum or steel fastener. Giant magnetoresistive (GMR) sensors are finding increasing applications in directly measuring weak magnetic fields associated with induced eddy currents. The measured flux image at a fastener site is in general symmetric and an asymmetry is introduced by the presence of a subsurface crack, which is used for defect detection. This paper presents novel methods that employ the resident phase information, for improving detection probability of GMR signal analysis. Using computational model, the effectiveness of the proposed methods for enhancing detection of CUF is investigated. Results demonstrating the potential of these techniques for detection of second layer CUF are presented. [ABSTRACT FROM AUTHOR]

This paper describes a high force density linear electromagnetic actuator based on the concept of magnetic screw-nut, in which helically disposed, radially magnetised permanent magnets are placed on both the screw and the nut. Magnetic force and torque can be developed between the two parts without direct mechanical contact. Analytical and numerical analysis has been carried to predict the performance of the magnetic screw-nut assembly. It has been shown that a thrust force density in excess of 10 MN/m^3 can be achieved for airgap lengths varying from 0.4 mm to 0.8 mm and a lead \lambda greater than 7 mm. When combined with a naturally cooled permanent magnet brushless machine having a torque density of \sim 15\ kNm/m^3, the resulting thrust force density of the combined system, i.e. electrical machine and magnetic screw-nut assembly, is an order of magnitude higher than that of a liquid-cooled tubular permanent magnet brushless machine. [ABSTRACT FROM AUTHOR]

The inspection of the slack of the steel high-tension bolt is important in the maintenance of various mechanical parts and buildings, etc. There occurs the difference of the magnetic property of the bolt head when the axis force of the fastened bolt is increased. Therefore, the evaluation of the slack of the bolt is possible by detecting the difference of the magnetic characteristics. In this paper, the electromagnetic method for measuring the slack of the steel high-tension bolt using an alternating magnetic field is proposed. The stress and flux density in the bolt head are estimated by 3-D stress analysis using the finite-element method and nonlinear electromagnetic finite element analysis taking account of the electromagnetic property under various compressive stresses. In addition, the experimental verification is also carried out. [ABSTRACT FROM AUTHOR]

Cracks in conductors are detected through changes in the impedance of a coil that induces current in the material. In order to gain insight into the physics of the inspection, we have developed a theoretical and computational model that predicts the signals due to cracks in circular cylindrical holes using a boundary element calculation. In formulating the problem, the electromagnetic field is decomposed into transverse electric and transverse magnetic scalar modes. The effect of a planar crack in an electromagnetic field is represented by an electric current dipole layer orientated normal to the crack surface. The dipole density is determined by the integral equation whose dyadic kernel ensures that the tangential electric and magnetic fields are continuous at the surface of the hole. Instead of solving this equation, a numerical approximation is found in the form of a discrete system of linear algebraic equations formed using either boundary and volume elements depending respectively, on whether the crack opening is negligible or not. Because the kernel embodies the interface conditions at the surface of the hole, a discrete approximation of the field is only necessary in the flaw domain which means that relatively few unknowns are needed. The probe impedance variation has been computed for both ideal cracks, defined as having negligible opening but impenetrable to current, and open cracks/slots. Open crack model predictions of coil impedance variations with position relative to a semi-elliptical axial crack are in good agreement with measurements. [ABSTRACT FROM PUBLISHER]

We present results from studies of the effectiveness of an overlap technique for forming a magnetic seal across a gap at the boundary between a cylindrical magnetic shield and an end-cap. In this technique a thin foil of magnetic material overlaps the two surfaces, thereby spanning the gap across the cylinder and the end-cap, with the magnetic seal then formed by clamping the thin magnetic foil to the surfaces of the cylindrical shield and the end-cap on both sides of the gap. In studies with a prototype 31-cm diameter, 91-cm long, 0.16-cm thick cylindrical magnetic shield and flared end-cap, the magnetic shielding performance of our overlap technique is comparable to that obtained with the conventional method in which the end-cap is placed in direct lapped contact with the cylindrical shield via through bolts or screws. [ABSTRACT FROM AUTHOR]