A magnetless voice coil motor (MLVCM) is generally composed of a closed magnetic circuit stator core (laminated electical steels), two exciting coils on the core and a metal ring mover, without pernament magnets and leading wires connected with the mover. A driving force F is both an electromagnetic force between a mover current J₂ and a gap flux density B_G, which are induced by an exciting current J₁, and a reluctance force due to J₂. The driving force F is proportional to J₁²/g, where g is a gap length, and almost independent of mover position under a constant J₁ and above a lower cutoff angular velocity ω_J1, of an induced current. ω_J1 becomes lower with the lower electric resistance of a mover and the lower reluctance of a magnetic circuit (stator core), and consequently a MLVCM with a closed magnetic circuit generates a higher driving force than that with an open magnetic circuit. The higher permeability and the lower iron loss of a magnetic circuit core increase a mover current J₂ and a gap flux density B_G, and then a driving force becomes greater. A voltage applied to the exciting coil increases proportionally to the distance between an exciting coil and a mover under a constant J₁.

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One of fundamental problems in factory automation or office automation is how to obtain linear motion. Linear motors produce directly the linear motion force without a motion-transform mechanism. Linear d. c. motors (LDM) have excellent performance and controllability. The dynamics of small-sized LDMs is adversely affected by the dead-band due to the friction between brushes and commutators.
This paper considers a positioning system with a linear d. c. motor using neural network. The positioning system consists of a neural servo controller and a fixed gain feedback controller. The neural servo controller requires the reference position signal, the reference speed signal, the reference accelaration signal and tracking error signal, the objective of which is to repress the influence of friction and to improve the tracking performance. The weights of the neural servo controller are adjusted by the back propagation algorithm so that the tracking error is minimized. The effectiveness of the proposed system is demonstrated by experiment.

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The slot harmonics produce a cogging torque and a crawling in a linear induction motor (LIM) with a ladder type rotor. To avoid those defects, we sometimes adopt the V-skewed rotor (or stator) which rise no lateral force. In this paper, we investigate the skew effect by the three-dimensional finite element analysis with A-φ method and specify significant points for adopting skewed slots.
Based on the above approach, we evaluate the skew effect in the LIM, comparing it with the experimental data to confirm the validity of the analysis. The follows are confirmed: (1) the improvement of the cogging torque by introducing V-skewed rotor; (2) the decrease in the thrust force and increase in the sucking force as making the skew angle bigger, and the abnormal temperature rising in V-skewed rotor; (3) the decrease of the abnormal temperature rising by optimizing the shape of rotor; (4) the validity of the skewed stator for short stator machines. And we propose a method that put two stators skewed in the opposite direction to each other for the double-sided LIM.

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The purpose of this work is to clarify the correlation between magnetic reluctance distribution and structural parameters in linear pulse motor (LPM). By clarifying correlation between them, we can control magnetic characteristics of LPM and adapt them to applications. In this paper, we show as follows:
(1) We discuss the correlation between harmonic of gap reluctance and structural parameters in LPM by using multiple regression analysis.
(2) The result of analysis show there is a strong correlation between magnetic reluctance and structural parameters of gap section, gap length, pitch, teeth width and depth of slot.
The magnetic reluctance of air gap is calculated by using a, linear two-dimensional finite element method with scalar potentials. Harmonics of reluctance are obtained through FFT. Multiple correlation coefficients between harmonic and structural parameters are calculated on a linear multiple regression model. We test about regression coefficients at a significance level of 1% and clarify correlation between harmonic and gap length etc.

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It is expected to establish an analytic method and performance equations more suitable for estimation the characteristics and design a reasonable LIM. An approximation for simplified computing the performance of single-sided linear induction motor is presented. The original equations was derived from the two-dimensional electromagnetic analysis and the equivalent circuit quantities, such as magnetizing reactance, secondary resistance and secondary reactance, was expressed in combination with hyperbolic function and trigonometric function of complex number.
In this paper, these functions are approximated by the Maclaurin's expansion and the equivalent circuit quantities are expressed by polynomial approximation. Both computed thrust, primary current, power factor and efficiency-slip curves for the test SLIM for urban transit at Kyushu university calculated by the original equation and the new approximation show a close agreement. Even without the former complicated calculation, we can use the proposed convenient approximation. The magnetizing reactance plays an important role in the LIM performance and the larger, the better. The ratio of air gap length to pole pitch holds the key to goodness of LIM.

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The authors have been investigating the applications of a Linear Induction Motor (LIM) to a manufacturing process of sheet glass. It was found that a sheet glass can be sunk into molten metal by supplying electromagnetic force of LIM in the contrary direction to the gravity force.
This paper describes the study on the glass sheet elevation control with LIM in molten metal. The points discussed are followings:
(1) A mathematical model of the sinking length of sheet glass in molten metal is derived on the principle of the glass sheet elevation control with a LIM.
(2) Experiments verified that the LIM can elevate a sheet glass in molten metal and that the locus of the glass movement has a mysterious hysteresis loop, which is due to the end effect of the LIM.
(3) It is shown that the calculated positions of a sheet glass in molten metal are depth in 12% errors with the measured ones.
(4) It is clarified that the sinking length by the friction force of molten metal flow is no more than 3% compared to the gravity force and the electromagnetic force is dominant to control the elevation of sheet glass.

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A novel Maglev train system can be constructed by using a long-stator controlled-PM LSM which has functions of propulsion and attractive-mode levitation with a minimum loss. To realize this system, it is extremely important to simplify manufacture of the long-stator guideway. In the long-stator on the ground, semi-closed large slots are adapted and designed to install easily one-turn coils of a wave form. The large slots cause the PM LSM detent forces which give strong influences on dynamic operations of the running vehicle. A two-dimensional FEM is used for the dynamics simulations, which is capable of precisely analyzing the detent forces produced between the stator teeth and the PM's.
This paper presents FEM dynamics simulations and experiments in mass-reduced-control mode of 1/2 scale model Maglev vehicle which is supported by small rubber rollers. A simulation model is also developed which includes the performance of vehicle speed and position sensors and the drag force due to frictions between rubber roller and rail. The detent force problem in propulsion motion is successfully solved by adapting the feedback control of the vehicle propulsion based on the I₁₀-controlled method. The trajectory control is thus accomplished for the vehicle to follow the speed and position patterns. The dynamics simulations are verified from the experiments. The simulation program proposed here enables us to investigate the Maglev train system including the LSM design and the vehicle dynamic operations.

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The Linear DC Motor (LDM) are used for CD players and other many equipments, but these are MC-type LDMs as these movers are light. MM-type LDM has advantages at long stroke machines because its mover's feeding wires for driving is not necessary. But control system needs detectors for mover's position and velocity, so detectors are provided along whole stroke length. So that MM-type LDM is not so used because of its large structure for its driving element and detectors.
The trial motor is MM-type LDM without wires, and its simple detector detects both position and velocity at every position along stroke length. As no-wire system, infrared rays transmits the detective signal to the controller. Using this signal, mover is cotrolled at constant velocity by Phase-Lock-Loop (PLL).
On this system, an error by slip of detector is very small. This LDM drived without wires has good character as there is a little effect of this infrared rays transmitter at the velocity control.

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The urban transit with single-sided linear induction motor (SLIM) propulsion and wheel on rail support and guidance have been in the stage for practical application.
This paper presents a method of optimizing the design parameters of the SLIM using nonlinear optimization technique. In the formulation of the optimization problem, the performance characteristics are estimated using space harmonic analysis taking into account the end effect, skin effect and air gap leakage. The transformation method and the simplex method are applied to solve the problem. As the transformation methods, the exterior point transformation are used. Seven parameters are chosen as the independent variables, such as the number of poles, the pole pitch, the stack height, the secondary aluminium sheet thickness, the overhang length, the slot width/slot pitch and the rated slip. The output KW/input KVA, the maximum flux density in teeth, the temperature rise, the primary length, the stack height, overhang length, the maximum thrust and the vertical force are selected as the constraint function.
The SLIM design is analyzed under four objective functions; the primary weight, the input KVA, the cost of secondary materials and energy consumption. Furthermore, the design is regarded as the multi-objective programing problem and the computed design example is shown.

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Linear elevators using cylindrical linear induction motor (CLIM) increases the assemblies gradually in Japan. It, however, was published few scientific paper concerning the linear elevator analysis. This paper deals with CLIM as the actuator for vertical motion and linear induction motor-driven elevator, that is Linear elevator, our investigation revealed as follows; (1) The constitution of the linear elevator using CLIM is comparatively simple, the good motion characteristics was obtained by means of vector control. (2) The developed CLIM has the thrust/input of 43.2N/kVA, the simulated characteristics of starting thrust by the equivalent circuit constants agreed with the measured values. (3) Thrust of the CLIM has thrust ripples in twice frequency, 32Hz, of the driving frequency, natural frequency in the transmission mechanism was 15.4Hz.
The linear elevator developed by the authors was almost satisfied the target specifications of the conventional elevator.

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By use of pole position sensor, it becomes possible to drive a linear pulse motor as a servo motor and to reduce the risk of step-out exceedingly.
However a linear pulse motor remains the vibrational characteristics itself. Therefore, there is the problem of how to suppress the over shoot and transient vibration of response for step type position reference. In addition, this problem stands out remarkably in heavy load operation.
In this paper, we propose a novel method of adjusting the parameters of two degrees of freedom controller which is positively able to take into consideration the suppression of vibrational characteristics of a linear pulse motor. By comparison with conventional PID controller, the improvement of performance of a linear pulse servo motor control system using two degrees of freedom controller are discussed.
With the experimental and simulation results, it was made clear that the introduction of two degrees of freedom controller designed by the proposed method not only improves the over shoot and transient vibration of response for step type position reference, but also removes the undesirable characteristic variation by altering the value of load mass in the linear pulse servo motor control system.

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Magnetically-levitated (MAGLEV) railway has been studied intensively in many countries for the purpose of its large scaled realization and in fact some plans have already also started in Japan.
In case of large scaled realization, a problem of how to reduce energy consumption must be discussed. To solve this problem a light weight vehicle is also used for a MAGLEV vehicle as well as convensional ones. Such a vehicle is flexible, which sometimes induces deterioration of ride-quality. Therefore to obtain high ridequality, active suspensions are applied to the vehicle. In this paper, we apply an H∞ control method to a system-model of the light weight vehicle including oscillation modes by adopting a suitable weighting function to be effective for a special frequency band at which high ride-quality is required.
In adition we pursue robust stability for both mass-variation by passengers' in and out and a modeling error by the neglect of the 3rd order oscillation mode and over.
At last the effect of our method proposed here is comfirmed by PSD (power spectral density) of the vehicle's acceration.

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Recently, many kinds of magnetic levitation systems have been proposed and developed for a utilization in factory automation systems. This progress of the development is depending on the appearance of new types of permanent magnets and new control theories. On the other hand, some systems have simple structures in which couples roles are given for both levitation and conveyance. As for these systems, however, we need many trials to establish the system configurations and the control theory. The authors have developed a new magnetically levitated carrying system driven by LIM. The system can be completely detached from guide way both in mechanical and electrical meanings. In this paper, the experimental results, especially the driving characteristics of a vehicle without any contacts to the LIM guide way are discussed.

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This paper demonstrates that phase-locked loop techniques can be applied to stabilize an active magnetic suspension system with displacement sensors of frequency type. Feeding back the difference of frequency in addition to PLL control is proposed to speed up the process of phase-locking. It is also pointed out that the self-sensing magnetic suspension is realized with a hysteresis amplifier, which is a switching power amplifier whose switching frequency varies with the position of the suspended object. In the experiments, a PLL control feeding back the switching signal of a hysteresis amplifier is successfully implemented in a magnetic suspension system with a conventional PD controller. The measured responses to step and sinusoidal disturbances show that an integral feedback arises automatically in the magnetic suspension system because the control input is produced from the difference in phase between the reference and feedback signals in the PLLs.

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Magnetic suspension systems with linear actuators and permanent magnets have been developed. The bearing forces are controlled by adjusting the air between permanent magnets and levitated objects. The feature is using permanent magnets. Therefor the systems are effective for reducing energy consumption and heat generation of coils. This paper describes a 3 degrees of freedom disk suspension system. First, the principle of this suspension mechanism is explained on a simple model. Secondly, we introduce the disk suspension system which can suspend a circle plate by 3 permanent magnets and its drive mechanisms. This system is analyzed theoretically from kinematics and linear control theory. Two control methods are proposed. One is a decentralized feedback control system and the other is a centralized one. Feedback gain matrices are calculated on each control system. The performances of two systems are compared by means of numerical simulations and experimental examinations.

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The yoke of a Linear DC motor (LDM) was made of a carbon steel (annealed S15C) in high speed hydraulic valve using a LDM, which was developed the authors. The paper deals with a consideration of seven magnetic materials for the LDM, which may be used in the future, the conclusion as follows: (1) In the case of flux density, B, of 1.0 tesla, annealed carbon steel, S10C, has the field strength, H, of 100%, the relative permeability, μ_r, of 95% and the hysteresis loss, W_h, of 120% compare with annealed carbon steel, S15C, as the standard, among four carbon steels. (2) Annealed spheroidal graphite, FCD450, has H of 200%, μ_r of 41%, and W_h of 59% compare with S15C, among two iron castings. The value of W_h was the minimum among seven materials. (3) In the case of free-cutting pure iron has H of 88%, μ_r of 102%, and W_h of 78% of S15C. The values of H and μ_r exceeded S15C, and it was the best material in the seven.

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A linear motor is controlled by feedback control. The characteristic of the linear motoris determined by the characteristic of the motor itself, a position detector and a controlsystem. So the position detector is needed fine positioning and fast response.
This paper states new type position detector which is able to built in the moving magnet type (MM-type) linear DC motor (LDM). As the MM-type LDM has merit that it needs no wire fordrive to move, this position detector is developed for making the best use of this merit. This position detector uses the capacitance between the mover and electrode which is installed on the stator. The capacitance changes in proportion to the displacement of themover. It is important to convert accurately the change of capacitance depending on displacement of the mover into direct voltage. After several electric circuits are examined, as the result, the best circuit is chosen, and then the simple, non-contact, cheap and accu-rate differential type position detector is developed.

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In the semiconductor manufacturing industries, the demand for semiconductor wafer processes in an ultra-high vacuum chamber is increasing in connection with development of more highly integrated circuits. This may impose severer restrictions on wafer transfer robot with regard to contamination of the vacuum environment. In the severest case, a robot mechanism without use of lubricant, generation of dust particle and release of gases will be necessary. One of advantage methods for realizing such mechanism is to drive robot arm directly without mechanical contact by means of magnetic suspention techniques. For example, it is considered to employ a linear motor and magnetic bearings which are hermetically enclosed in a box-like casing.
In this paper, a magnetically suspended linear pulse motor (LPM) is proposed as contactless direct drive mechanism of vacuum chamber robot. Here the major problem is a marked lowering of thrust caused by a broad air gap which must be arranged between stator teeth and mover ones in consideration of the wall thickness of the motor casing. So the LPM is designed to be composed of a pair of flat-type stators and a ladder-like robot arm corresponding to the floating mover so that it can be compensated for the resultant decrease of the ratio of thrust to mover mass. The validity of this approach is examined by the static thrust measurements for a tested LPM, and confirmed through the experiments on the robot arm transfer with a magnetic suspention system.

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A new type of actuator with both magnetic levitation and linear drive is proposed. The actuator is called “magnet wheel”, which has rotating magnetic field obtained by revolving permanent magnets with high coercivity mechanically. The induction repulsive type magnetic lift force with self-stabilization can be obtained by linking the rotating flux to a conducting plate . The induced simultaneously drug torque which causes power loss is made good use to get the thrust by the two proposed ways which are called “tilt type” and “partial overlap type”, respectively. In the “tilt type” the magnet wheel is tilted against the surface of conducting plate. In the “partial overlap type” the magnet wheel operates near over the edge of conducting plate.
In this paper, first, the fundamentals of the structure of proposed magnet wheels are described. The basic characteristics at parallel to the conductor are shown by using a numerical three-dimensional electromagnetic analysis and measured results. The generation of both lift force and thrust in “tilt type” and “partial overlap type” magnet wheel are proved by experiments respectively.

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Characteristics of “tilt type” and “partial overlap type” magnet wheels with revolving permanent magnets, which were proposed by authors, are analyzed respectively at standstill condition for linear running. First, eddy current distribution, three directional components of generated forces and variation of instantaneous forces are shown respectively by three-dimensional numerical analysis. The analysis is proved by comparison between computed results and measured results. It is found that the lateral force of magnet wheels operates to move away from conducting plate, but the force in the “tilt type” is very small. It becomes clear that the lift force and lateral force of the “partial overlap type” have, respectively, relative large cyclical change with number of poles in a rotation. Second, the simplified two-dimensional analysis is described. The equivalent magnetomotive force of permanent magnet is corrected according to the flux density on the magnet surface in order to consider the effect of circular arrangement of magnets and the edge effect of eddy current. It is confirmed that the forces in the “tilt type” are estimated by using the model of horizontal revolving magnet wheel with various air gaps, the forces in the “partial overlap type” are estimated by considering only the overlap region between the area of revolving magnets and conducting plate.

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Permeability in down draft sintering process in steelmaking processes is well known not to be good because load of sinter cake oppress permeability in the lower layer of sintering bed. If the sinter cake as paramagnetic material could be suspended by magnetic force, it is expected that permeability will be improved. This paper presents theoretical and experimental characteristics of three magnets, i.e. electromagnet using permanent magnets, electromagnet using a high Tc superconductor as a permanent magnet and superconducting magnet in order to develop electromagnets for magnetic suspension of the sinter cake. The following results were obtained.
(1) It was verified that the sinter cake as paramagnetic material having relative permeability of 1.2 _??_1.8 could be suspended by the magnetic force,
(2) Calculated values to the magnetic flux density and the electromagnetic force were agreed with measured values within the error of ±10%.
(3) As a result of comparison to above three electromagnets, it was clarified that performance of supercondcting magnet is better than those of other electromagnets considering form saving energy and magnetic force.

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A general solution of levitation control to PM synchronous type and induction type rotating motor is presented. It is intended that the rotor has the levitation force which is controlled by the stator magnetic flux. The rotor of the permanent magnet motor is assumed to have the sinusoidally distributed magnetic poles along the axial surface, while the rotor of the induction motor is assumed to have the uniform magnetic property. The inner wall of the stator is also assumed to have a current sheet, which can produce an arbitrary current distribution. The same number of magnetic pole gives the rotating torque to the rotor, while the plus minus two magnetic pole of the motoring control produces a pure drag force to the rotor. By controlling the magnitude and phase of the plus minus two pole current distribution relative to the motoring magnetic pole, the drag force can be controlled in the radial coordinate. This general solution is experimentally confirmed by using a simple experimental setup and the load test is conducted and reported.

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For power supply on-borad of Maglev vehicle using EDS (electrodynamic suspension) Maglev system and super-conducting magnets (SCM), an inductive power collection method is proposed, which gets electric power from induced voltage of the on-board power collection coils using magnetic field harmonics of ground coils. As for EDS, adoption of null-flux levitation and guidance is proposed because of less ground coil current being obtained than in the case of normal-flux levitation. In this case, a smaller magnetic field harmonics of ground coils and eddy currents of the outer vessel of the SCM result in a smaller electromotive force per one turn so that we need current collection coils with more turns, which means high source impedance. A normal full-wave rectifier can not give the needed electric power. So a PWM converter with a unity power factor control, which can cancel the power supply side impedance, is proposed. We have developed a PWM converter, which functions just like the active capacitor, using IGBT and instantaneous current control. We achieved a power factor × efficiency value of 0.97 in a stationary experiment of the system. Here are described the working principle, the simulation and the result of the stationary experiment.

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