Design and validation of polarity-changeable magnetizer for encoding patterns on ring-like rotary encoders

Demands for high precision machine tools have been increased as technology advances. Such demands require higher position control to allow the machine tools to produce higher precision end products. To facilitate the position control, magnetic and optical encoders are been widely used in the machine tools. Due to its advantage in withstanding hard environment such as oil, grease and dust over an optical encoder, along with its wide applications in industrial position control, a magnetic encoder has become a desirable choice for machine tools. The objective of this study is to develop a polarity changeable magnetizer for manufacturing coding patterns in a rotary encoder which is used to monitor runout errors for rotating components in machine tools. As opposed to commonly used capacitive pulse magnetizer in which significant amount of energy is required for its electromagnets that potentially causes high energy hazard, in this study, a polarity changeable permanent magnet is proposed and investigated through parameter studies to overcome such issue with the aim placed on producing sufficient magnetization on a thin silicon steel plate to produce desirable coding patterns on the rotary encoders.

This paper investigates the influence of different magnetization patterns on the performances of the surface-mounted permanent magnet synchronous machines (SMPMSMs). Three magnetization patterns are employed, which are radial, parallel, and ideal Halbach magnetizations. These magnetization patterns are applied to 9-slot/10-pole and 15-slot/4-pole permanent magnet (PM) machines. The PM machines are designed and simulated by using Opera 2D finite element. The performances of three PM motors, such as airgap flux density, phase back-EMF, and cogging torque, are evaluated under the influence of different magnetization patterns. The total harmonic distortion of phase back-EMF (THDv) for the motors are investigated. The PM motors with ideal Halbach magnetization provide the lowest cogging torque and the lowest total harmonic distortion of phase back-EMF. Besides that, the optimum setting of the magnet pole-arc can reduce the total harmonic distortion of phase back-EMF and achieve lower cogging torque. The optimum magnet pole-arc produced by radial magnetization in 9-slot/10-pole motor is 24.8° mech., with cogging torque of 0.45 Nm, and THDv of 2.69 %. Meanwhile, the optimum magnet pole-arc produced by parallel magnetization in 9-slot/10-pole motor is 26.0° mech., with cogging torque of 0.41 Nm, and THDv of 2.00 %.

The playback process of magnetic recording is the correlation between the magnetization pattern in the medium and the sensitivity function (the fringing field) of the readback transducer. The correlation is the optimal detection method for signals buried in the noise. Therefore, the obvious way to improve the performance of digital magnetic recording is to realize the potential of the inherently present correlation. Unfortunately, in traditional longitudinal recording systems, the medium magnetization is formed in the trailing zone of a write head field, and the recorded transition bears no resemblance to the whole fringing field of the head. Using perpendicular or isotropic medium, it is possible to imprint encoded 1’s by switching off the current in the winding of a ring head. The imprinted 1’s are then (ideally) copies of a whole fringing field of a ring head and look like ‘‘horse-shoe’’ patterns of magnetization. During readback these patterns correlate almost ideally with the sensitivity function of a ring head. An essential element of the technique is the resumption of the current in the opposite polarity as the imprinted pattern moves downstream. This continues the perpendicular magnetization at the trailing edge of the previously formed ‘‘horse-shoe’’ pattern and fills voids in the magnetization. We present experimental data illustrating this method.

This paper presents an analytical magnetic field calculation for slotted brushless permanent-magnet (PM) machines equipped with surface inset magnets. The analytical expressions can be used to calculate both open-circuit and armature reaction field distributions. Although the expressions can be used for brushless PM machines with any magnetization pattern, the results of the open-circuit magnetic field are presented for three different magnetization patterns: radial, parallel, and Halbach. Different winding structures, such as overlapping, nonoverlapping with all teeth wound and nonoverlapping with alternate teeth wound, can be considered to compute the armature reaction field distribution. The analytical expressions can be used for the surface inset magnet structure with airspace between the magnets and the iron interpoles but they cannot be used in the case of brushless machines with surface mounted magnets. The calculations account for slotting and slot-opening effects via the subdomain technique. The analytical results for a four-pole, six-slot brushless PM machine with three magnetization patterns and nonoverlapping winding are presented and evaluated by comparing them with those obtained from the finite element method.

Variable magnetization pattern machines (VMPMs) capable of dynamic changes in the magnetization pattern and magnitude are discussed in this paper. These machines can behave like brushless DC machines if they have a uniform magnetization pattern. If the magnetization pattern on the permanent magnet is shaped to be sinusoidal through a controlled demagnetizing process, they could behave like brushless AC machines. This paper presents the fundamental principles and the design methods of VMPMs. The design methods including parametric analysis and the overall results are evaluated using finite element analysis (FEA).

This paper presents the design of a low-cost rare-earth free external rotor permanent magnet assisted synchronous reluctance motor (EFa-SynRM) for traction motor applications. In recent design innovations, rare-earth free permanent magnet (PM) motors have been proposed as an alternative to the rare-earth based PM motors. However, rare-earth free PM motors exhibit lower power density, lower torque, lower efficiency, and higher prone to demagnetization issues. With proper design of flux barrier and PM shapes, the Fe PM based electric motor design can be optimized to overcome the above mentioned drawbacks. In this study, an optimal five-phase ferrite PM based EFa-SynRM is developed to achieve high power density and no demagnetization effect. Extensive finite element simulations are carried out to depict the higher average torque developed, lower torque pulsations, and higher efficiency. The proposed EFa-SynRM design has shown no demagnetization effect at three times of rated input current. A 3.7kW design prototype is fabricated and experimentally tested under no load conditions. Results are compared with a same size five-phase internal rotor 3kW Fa-SynRM.

Permanent magnets (PMs) are widely used in a variety of industrial equipment and devices. In magnet design, the shape of a PM plays an important role and minimization of the leakage flux improves the performance of the device. The shape optimization of PM devices using gradient based inverse problem methodology (GIPM) is presented. The paper describes for the first time the use of analytical sensitivities for shape optimization of PM devices. Furthermore, the adjoint method of the direct differentiation approach is used for the computation of the sensitivities of the object function. Two case studies are presented. The first involves a magnetic circuit with an air gap and PM excitation, the second is that of a PM pole face. In both cases, design optimization is employed to obtain a desired flux density profile in the air gap with a minimum leakage flux and minimum size of the PM material.

Partial encased composite (PEC) members with thin steel plates and three types of constructional detailing are studied. Six pieces of PEC column specimens were tested under constant vertical load and cyclic horizontal loads. A numerical FE model is established. In the model, the in-filled concrete is decomposed as transverse and longitudinal springs, considering the functions and the properties of the concrete in two directions. This model simplifies the numerical computation with high efficiency, and acquires a satisfied agreement with test results in both capacity and deformability of the PEC member. The parametrical study by the FE model is performed. By tests and numerical analysis, it is found that though local buckling of thin plate of H steel is a crucial factor, when the compressively axial load does not surpass the encased steel capacity, the PEC could behave quite well under cyclic horizontal loads. No distinguished difference in three kind details was observed, so that PEC member could be built in a simple way.

In order to solve the problem of the impact of the magnetic plate design on the yield of the OLED evaporation machine, a theoretical calculation method for the Z‐direction magnetic field of the magnetic strip is constructed, and an analytical expression for calculating the Z‐direction magnetic field Bz of the magnetic plate is obtained. Using VB programming, the calculation of the magnetic plate Bz is computerized, achieving the goal of quickly iterating the design scheme to select the optimal magnetic plate design.By comparing the theoretical calculation results with the measured data, the correctness of the theoretical calculation is verified. By analyzing the distribution pattern of Bz corresponding to different magnetic strips and arrangement designs, the results show that a narrow and dense arrangement of magnetic strips on the magnetic plate is beneficial to the effective magnetic field area and magnetic field uniformity, but it sacrifices the maximum Gaussian intensity. At a height of 13t and a target Gaussian of 250‐450Gs, the ideal pitch range of the magnetic strip is 9‐15mm, with a gap of 1‐5mm.

This paper presents an innovative design for magnetic poles used in active magnetic bearings (AMBs). The proposed hybrid sandwiched magnetic pole design not only practically reduces the bearing size, but also dramatically diminishes its cost. The magnetic force to counterbalance the gravity of the rotor is provided by the embedded permanent magnets (PMs), while the electromagnetic bearing is merely used to regulate the position deviation of the rotor. Therefore, the required electricity consumption to activate the coil wound on the poles is fairly limited. This implies that the required ampere-turns and size of the AMB can both be reduced efficiently. The numbers of associated amplifiers, sensing circuits, and magnetic poles are thus reduced as well. The coupling effect of magnetic forces is taken into account such that either poles for electromagnets (EMs) or the embedded PMs are located 90° apart. The merits of this type of design by orthogonal pole allocation include: simpler control synthesis and decoupled sensing signals for rotor position deviation. Since the variation of coil current is a function of flux density change between PMs and the silicon steel strips attached on the rotor, the PMs can also be used to provide necessary magnetic flux source for sensing rotor position deviation. More importantly, two perpendicular PMs can prevent the rotor from getting extremely close to either PM, such that the magnetic attraction force becomes too strong to be counterbalanced. On the other hand, the concave-like pole profile design enhances the average flux density by 11% and the required ampere-turns are further reduced by 18%, compared with the traditional rectangular pole design. One of the induced benefits of reduced size for AMB is to diversify applications where the operating space is limited. The proposed design has been assessed using intensive computer simulations and experiments.

This paper proposes a topology optimization formulation for the three-dimensional (3-D) design of segmented permanent magnet (PM) arrays. Specifically, the proposed formulation aims to find an optimal 3-D structural topology of PM segments and their discrete magnetization directions. To achieve this, a design variable is defined in the vector form of a Cartesian coordinate system. The magnitude of the design variable vector determines a PM density, and the directional cosines of the vector determine PM magnetization directions. To acquire a segmented PM design with discrete magnetization directions, a PM strength penalization scheme is proposed. In this scheme, a PM strength is controlled using a minimum distance function between a magnetization direction and target discrete directions. Here, the minimum distance function is approximated using the p-norm for sensitivity calculation. To validate the effectiveness of the proposed formulation, three design examples are provided. In the first example, a two-dimensional (2-D) dipole Halbach cylinder is designed to confirm that the proposed formulation can be applied for a 2-D design problem. The second example aims to design 3-D dipole PM arrays with a cuboid cavity. In the third example, a 3-D PM arrays are designed for maximizing the magnetic force acting on a soft ferromagnetic material.

For thin steel plates, which are used in many industrial products including those of the automobile industry, we have proposed a magnetic levitation control system and confirmed its realization by means of a digital control experiment. However, the use of a limited number of electromagnets cannot suppress static deflection and high-order-mode elastic vibration, which are characteristics of a flexible magnetic material. To solve this problem, we have proposed a hybrid levitation control system for the thin steel plate using the magnetic force generated by permanent magnets, which have no operational costs, in the areas where the attractive force of the electromagnets is negligible. In this study, we attempt to determine the optimal placement of permanent magnets to reduce the deflection and elastic vibration of a thin steel plate under the generated magnetic field. To verify the usefulness of optimal placement of the permanent magnets, experiments concerning elastic vibration were performed on a magnetically levitated thin steel plate. As a result, it was confirmed that the control performance was improved by the optimal placement of the permanent magnets.

A new computational program is developed for solving the inverse magnetic problem for determining the magnetic design necessary to produce a desired field pattern. The conception of an innovative source-modeling algorithm allows the program to be universally applied, unlike currently particularized methods. This new method termed Variable Field Generation (VFG) facilitates the synthesis of arbitrary magnetic designs and inversely defines new and unique magnetic systems for difficult three-dimensional magnetic field patterns. Such complex field patterns are necessary for proposed applications based on current advances in high-temperature superconductors. This paper reports the evaluation of VFG as a universal solution to the design challenges of magnet applications, including analysis of test cases for different magnetic applications using various solvers.

Molten metal flow and magnetic field of the permanent magnet stirring (PMS) were investigated by experimental study and numerical simulation, respectively. A laboratory experiment was first performed to study the effects of PMS on the flow velocity of the Sn-20%Pb hypereutectic alloy during solidification. The results showed that the center magnetic flux density and stirring frequency were the two key factors affecting the electromagnetically-driven convection of the molten alloy. The electromagnetic field analysis software Opera-3D was used to develop a materials-saving and highly effective final permanent magnet stirring (FPMS) apparatus comprising a reasonable magnetic field design. Based on the scalar potential formulation, the stationary magnetic fields of the PMS were calculated and the number, arrangement and size of the permanent magnets were optimized. Thereafter, a pair of arc NdFeB permanent magnets with optimally designed geometrical dimensions was developed for industrial use in the FPMS apparatus. Consequently, with the industrial application of the new equipment in continuous casting, an improvement of the macrosegregation and other macro-defects of the rectangular billet were obtained.

This work presents results from a numerical investigation on the influence of fluid-structure interaction (FSI) on the dynamic response of thin steel plates subjected to blast loading. The loading was generated by a shock tube test facility designed to expose structures to blast-like loading conditions. The steel plates had an exposed area of 0.3 m × 0.3 m and experienced large deformations during the tests. Numerical simulations were performed using the finite element code EUROPLEXUS. An uncoupled FSI approach was compared to a coupled FSI approach in an attempt to investigate FSI effects. Reduced deformation was observed in the plates due to the occurrence of FSI during the dynamic response. The general trend was an increased FSI effect with increasing blast intensity. The numerical results were finally compared to the experimental data to validate their reliability in terms of deflections and velocities in the steel plates. A good agreement with the experimental data was found, and the numerical simulations were able to predict both the dynamic response of the plate and the pressure distribution in front of the plate with good accuracy. Hence, the numerical framework presented herein could be used to obtain more insight regarding the underlying physics observed in the experiments. The clear conclusion from this study is that FSI can be utilized to mitigate the blast load acting on a flexible, ductile plated structure, resulting in reduced deformations.