Showing papers on "Magnetic circuit published in 1986"

Cross-Saturation in Smooth-Air-Gap Electrical Machines

Abstract: A detailed analysis of the phenomenon of cross-saturation is presented and it is shown that in a smooth-air-gap quadrature-phase machine this phenomenon is similar to the phenomenon of the demagnetizing effect of cross-magnetizing armature reaction in a d.c. machine. In a quadrature-phase smooth-air-gap machine the resultant air-gap flux density distribution is decreased over one half of the pole-pitch and is increased under the other half of the pole-pitch and due to saturation the decrease is greater than the increase. Thus under saturated conditions, if the resultant m.m.f. distribution is displaced from the magnetic axes of the windings, a change in the quadrature-axis magnetizing current will cause a change of flux linkage in the direct-axis winding and vice versa, a change in the direct-axis magnetizing current will cause a change of flux linkage in the quadrature-axis winding. It is an important result that cross-saturation can also exist if the m.m.f. distributions are assumed to be sinusoidal. A physical derivation of the cross-saturation coupling factor is presented and a test is described which shows the existence of cross-saturation. A theoretical analysis of the experiment gives results which are in good agreement with the experimental results.

Modelling and estimation of leakage phenomena in magnetic circuits

Abstract: A new modelling method for magnetic circuits is presented. The method can be used to model magnetic circuits with any number of windings. The models incorporate adequate information about the correct distribution of leakage energy, the presence of gaps throughout the core, the arrangement of the windings, and the type of core used. Several commonly used arrangements such as toroids with uniformly distributed turns, and bobbin core structures with multiple windings were modelled with the new technique. The measured electric circuit model values always compared favorably with the predicted physical values derived with the new method.

Numerical analysis of transient magnetic field in a capacitor-discharge impulse magnetizer

Abstract: A method for analyzing the magnetic field in a capacitor-discharge impulse magnetizer is established by modifying the finite element method. The effects of charging voltage, capacitance and resistance on the behaviour of the localized fluxes in the Impulse magnetizer are analyzed quantitatively. As the detailed distribution of the flux density can be obtained, the optimum design of the magnetizer which produce desired magnet will be possible using our new method.

Position detecting apparatus using a magnetic sensor and a closed magnetic circuit with non-uniform magnetic flux distribution

Abstract: A position detector having a magnetic sensor for measuring linear or angular displacement, or detecting a position of a body without contact thereto. The detector has a closed circuit including magnets and yokes. The magnetic leakage flux which emanates from the inside surfaces of the yokes is utilized to detect the position of the body. The magnetic sensor is transferred along the inside surfaces of the yokes by a transferring circuit, which senses the magnetic field intensity of the leakage flux distributed thereon. This enables the detector to have a longer measuring range than that of a prior art detectors. An output signal is stable due to the shielding effect of the yokes. The magnetic closed circuit has many magnetic and mechanical configurations. For example, for the magnet, a permanent magnet and an electromagnet can be used. Further, improvements are proposed for enhancing the linearity of the output signal voltage with respect to the transferring distance of the sensing element and for compensating the offset drift of an amplifier or changing the coercive force of permanent magnets.

Electromagnetically-actuated positioning system

Abstract: Apparatus and method for control of actuator anchor plate release time in spring-biased electromagnetically-actuated positioning systems for gas exchange valves in internal combustion engines in which a ferromagnetic actuator anchor plate is moved back and forth between two actuating solenoids. Pursuant to the invention, the poles of the solenoid core and the anchor plate are separated by a member which may be formed of an electrically-nonconductive, paramagnetic or diamagnetic layer, or an air gap. This provides magnetic resistance in the magnetic circuit which reduces generation and propagation of eddy currents in the anchor plate. The magnetic field can decay more rapidly upon cut-off of current to the solenoid coil. The release time of the anchor plate from the actuating solenoid is thereby diminished, and more accurate valve dwell timing is achieved for improved engine performance.

Spring neutralized magnetic vibration isolator

Abstract: A single degree of freedom suspension element exhibiting substantially zero natural frequency of vibration with electronically controllable response comprising the combination of a mechanical spring and an "electromagnetic spring" which axially supports a mass located on a base. The electromagnetic spring includes two identical and symmetrical permanent magnet circuits having adjacent like-polarity poles joined by a permeable magnetic shunt member. The magnet circuits include an air gap between pairs of pole faces and within which prominences of a magnetically permeable armature extend therein and partially short each of the air gaps. An electromagnetic coil is located inwardly of the magnetic shunt between the magnetic circuits and encircles the armature between the prominences. The mechanical spring is coupled to the armature and acts to center the prominences in the air gap. Motion of the armature induces currents in the coil which are velocity dependent and opposed to the motion, yielding a viscous damping effect. Energization of the coil results in a differential magnetic flux in the air gaps, producing differential forces tending to move the armature in a predetermined axial direction.

Transient Performance of Permanent Magnet AC Motor Drives

Abstract: The transient behavior of permanent magnet ac motor drives is analyzed. A new model is proposed where particular emphasis is placed on the role that armature reaction and saturation effect play on the flux distribution of the machine. Equations for calculation of these fluxes are deduced and verified by experimental tests on the machine. Simulation of motor transients both for constant and variable speed operations are presented and compared with experimental tests.

Brushless D.C. dynamoelectric machine with decreased magnitude of pulsations of air gap flux

Abstract: A dynamoelectric machine which may operate in a motor mode or a generator mode is described wherein substantially the entire magnetic circuit is provided by ferrite material. In one particular embodiment, hard ferrite permanent magnet segments are mounted on a rotor plate while soft ferrite magnet segments with electrical coil windings mounted thereon are provided in a stator spaced apart from the rotor by an air gap. Other embodiments of the concept are described. Provision is made for decreasing mechanical vibration and audible noise by decreasing the magnitude of pulsations of air gap flux.

Wide air gap permanent magnet motors

Abstract: A rotating electric machine with a permanent magnet rotor, provided with a stator composed of a winding and a ferrite structure to provide low power losses and improved efficiency particularly at high rotor revolution rates, is constructed so as to optimize the performance of the permanent magnets on the rotor. In the preferred embodiment of the invention, the ferrite being selected for its low hysteresis and eddy current power losses, generically referred to as core loss and its low loss factor which are frequency dependent, replaces laminated electrical iron. Additionally the permanent magnets selected to exhibit high intrinsic magnetic intensity and low remanent magnetic flux density, are arranged in conjunction with the ferrite to maximize the magnet's energy product as well as the magnetic circuit gap length, which in a combination provides a radical improvement in machine energy density.

Design of Linear Induction Drives by Field Analysis and Finite-Element Techniques

Abstract: Two-dimensional field and finite-element analyses are complementary in evaluating the performance of single-sided linear induction machines, and can be used to develop a machine design for a given drive application. Electromagnetic analysis leads to an equivalent circuit of the machine with speed-and frequency-dependent parameters, in which top cap geometry, core hysteresis and saturation, skin effect, eddy current reaction, and both transverse-edge and longitudinal-end effects can be included. Finite-element analysis provides detailed information on the magnetic field distribution to aid in machine design.

Nuclear magnetic resonance apparatus including permanent magnet configuration

Abstract: An apparatus for nuclear magnetic resonance scanning and imaging which employs a primary magnetic field, an rf field, and a detector for detecting a nuclear magnetic resonance signal, the primary magnetic field being produced by an assembly of relatively low energy flux magnetic material combined with an assembly of relatively high energy flux magnetic material. The magnetic flux of the relatively low energy flux magnetic material is concentrated in a magnetic flux conductor means which is in turn combined with the magnetic flux of the relatively high energy flux magnetic material and is concentrated at a pole piece.

The Measurement of the Magnetization Characteristics of Large Power Transformers and Reactors through D.C. Excitation

Abstract: Transformers and reactors used in the electric power transmission systems show non-linear magnetization characteristics, the exact knowledge of which is essential to the study of system transient operation. This paper describes a measurement method for these characteristics, based on D.C. EXCITATION. During such excitation, only applied voltage and absorbed current are measured and recorded, to be afterwards numerically processed. This measurement requires only a very small power, usually lower than 0.01 p.u. of the tested unit rated power; it is very accurate and makes it possible to obtain magnetization characteristics up to currents higher than the rated current. Theoretical bases on which the measurements are grounded, practical considerations on their performing and a set or relevant results on power high voltage transformers and reactors are afterwards exposed. More, it is possible by a d.c. excitation to measure magnetization characteristics which cannot be otherwise determined.

Efficient calculation of force in electromagnetic devices

Abstract: The calculation of electromagnetic force in electromechanical devices usually requires accurate values of field quantities. This can be expensive in terms of computational effort and manpower. By using a complementary finite-element approach it is possible to significantly reduce the effort needed, and provide an error estimation on the solutions obtained. The technique is applied to practical problems to demonstrate its efficiency.

Step-up type magnetic head

Abstract: A magnetic head integrally assembled with a step-up transformer. The magnetic head portion is formed on a lower substrate by a thin film technology and the number of turns of the signal winding is 1 or a value near 1. The transformer portion mainly comprises a transformer magnetic circuit which is formed by the lower substrate and upper substrate. A one-turn primary coil of a thin film formed over the lower substrate and a secondary coil by a bulk wire are arranged so as to couple inductively with each other through the transformer magnetic circuit. The signal winding and the primary coil winding are formed by the same thin film process. The head portion and the transformer portion thus are arranged very closely and hence coupled with very little transfer loss of signal.

Self-biased modular magnetostrictive driver and transducer

Abstract: The drive modules of a magnetostrictive transducer are fabricated from interleaved permanent magnet disks (samarium cobalt) and high-strain, low-permeability magnetostrictive lanthanide alloy (Terfenol-D) disks to form a stack of such interleaved materials of substantially uniform magnetic field distribution in the stack. Two such stacks in side-by-side relationship provide a series-aiding magnetic circuit completed through high-permeability flux return pole pieces at their ends thereby providing a substantially uniform magnetic field distribution in the stack. Each stack has longitudinally-extending and electrically-insulated planar cuts and each flux return pole piece is a laminate of thin sheets of high-permeability electrically-insulated steel to reduce eddy current losses resulting from the AC field. The steel sheets are constrained by a nonmagnetic end-block into which the steel sheets are inserted and bonded.

Permanent magnet synchronous machine with transverse flux paths

Abstract: Embodiments of an armature and magnet arrangement are specified with the aim of implementing large winding cross-sections with a small pole pitch in order thus to produce more favourable dimensioning and more favourable properties of electrical machines. In consequence, relatively large forces can be achieved per unit of the active pole surfaces (force densities) with lower losses in the armature winding, and thus lower utilisation of material with a high efficiency. A common feature of the proposals is that configurations of the magnetic circuits are specified whose parts enclose the armature winding on a plurality of sides transversely with respect to the movement direction, for example Figure 6. The magnetic flux is thus guided transversely, at least in subregions. Coils are provided which (related to their cross-sectional centre) have a greater extent than the pole pitch in the movement direction. They extend, for example, over more than two pole pitches before being closed in the transverse direction and running back. An approximately wave-shaped coil arrangement leads to additional material savings in the magnetic circuits and permits a reduction in the stray fluxes. As a result of their limited extent in the lateral direction, the arrangements are more suitable than conventional armature shapes (with projecting winding ends) for the design of double-acting disc machines. In consequence, very high powers can be achieved per rotor disc, as well as short structural lengths with a limited machine diameter.

Shaping of cylindrically symmetric magnetic fields with permanent magnets

Abstract: With the increasing sophistication of electron-beam devices, there has arisen a need for more complex magnetic field profiles. Some novel permanent-magnet configurations are described which can provide cross-sectionally uniform magnetic field profiles with arbitrary field variation and almost no flux leakage to the environment. This is accomplished by an arrangement of axially and radially oriented magnets that achieve axial field modulation by variation of their geometrical dimensions, in one case, and of their magnetic properties, in another.

Flux cancelling yoke type magnetic transducer head

Abstract: A yoke type magnetic transducer head utilizing a magnetoresistance effect in which a magnetoresistance effect sensing portion is provided so as to magnetically couple a cut-away portion in a magnetic circuit including an operation gap and a magnetic yoke having in its one portion the cut-away portion and in which a first bias magnetic field is applied to the magnetoresistance effect sensing portion by a first magnetic flux that is generated when a current is flowed through the magnetoresistance effect sensing portion, or when a current is flowed through both the magnetoresistance effect sensing portion and a bias conductor, which includes a hard magnetic layer for generating a second magnetic flux by which a second bias magnetic field is applied to the magnetoresistance effect sensing portion and for passing through the magnetic yoke a magnetic flux which cancels at least a part of the first magnetic flux which passes through the magnetic yoke.

Remanence varying in a leakage free permanent magnet field source

Abstract: A magnetic circuit with a remanence varying cylindrical magnet having a b and a remanence varying cladding magnet circumscribing the cylindrical magnet creating a longitudinally increasing axial magnetic field within the bore. The cladding magnet has a radial magnetization transverse to the axial magnetization of the cylindrical magnet resulting in a constant magnetic potential along the outer exterior surface of the magnetic circuit.

Position responsive control signal generator having relatively movable sensor and magnetic flux concentrators

Abstract: Control signals are provided by means of a magnet, a sensor sensitive to magnets, and elements influencing the magnetic field and having a relative movement. A magnetoresistive circuit is placed between one stationary and at least two simultaneously linear or circular movable magnetic flux concentrators having an U- or V-shaped arrangement and being alternately effective in the magnetic circuit. The magnetoresistive circuit is operated in its saturation range, if at least one of the magnetic flux concentrators is effective.

Magnetic tachometer or accelerometer having highly permeable eddy current flux circuit

Abstract: A tachometer or accelerometer features a nonmagnetic, electrically-conductive, moving member whose velocity or rate of change of velocity is to be measured. A magnetic field is generated in a direction generally perpendicular to the direction of motion, creating eddy currents in the moving member which, in turn, create an eddy current magnetic field. The flux density of the eddy current field is measured by a Hall effect sensor to produce a signal representative of velocity or, alternatively, the rate of change of flux density of the eddy current field is measured by a coil producing a signal representative of the rate of change of velocity. A separate magnetic circuit for the Hall effect sensor or coil sensor, as the case may be, is provided so as to maximize the strength of the eddy current field by concentrating the sensed eddy current flux and thereby maximizing the device's sensitivity and accuracy while minimizing its susceptibility to error through interference.

Floating carrier type transporting system

Abstract: A floating carrier type transporting system comprises guide rails whose bottom section is formed by a ferromagnetic material, a carrier free to run along the guide rails, a magnetic supporting device for floating the carrier, a linear induction motor for drining the carrier that is floated by the magnetic supporting device to run along the guide rails, a sensor unit for detecting the changes in magnetic reluctance and/or magnetomotive force in the magnetic circuit that is mounted on the carrier, a control device for controlling the excitation current that is to be flowed in the electromagnet based on the output from the sensor unit, and a roll damping device for damping the rolling that is generated in the carrier in the state of running under the action of the magnetic supporting device and the linear induction motor.

Dot matrix printer

Abstract: A dot matrix printer has a vertical array of wires for printing on paper, pivotal armatures having plungers, coils wound around cores, main and auxiliary yokes the latter of which has drawn inner and outer peripheries, and posts at positions of the auxiliary yoke corresponding to the shortest paths of magnetic fluxes generated by the coils Displacement of the auxiliary yoke upon pivotal movement of armatures is minimized to keep a constant gap between the cores and the plungers and to reduce noise The reluctance of the magnetic circuit is small to improve magnetic efficiency

Very low frequency magnetic hysteresis measurements with well-defined time dependence of the flux density

Abstract: For the investigation of magnetic properties at frequencies between 5 mHz and 400 Hz we present an electronic device for measurements at well defined time dependence of the magnetic field strength or the flux density. Any function which is monotonous between two peak values can be produced. The measuring device may be used in connection with all conventional magnetizing systems according to the transformer principle, especially with the Epstein frame. The set-up comprises an arbitrary waveform generator, a power amplifier delivering the magnetizing current, and two ADC channels to sample and digitize the magnetic field strength and the induced voltage. The flux control is accomplished by software feedback using a personal computer which also handles the control of the experiment and the documentation. To demonstrate the capabilities of the apparatus we present a hysteresis family measured at .1 Hz with sinusoidal flux density, and the frequency dependence of the complex spectral components of the magnetic field strength measured at peak inductions of 1.0 T and 1.5 T, resp., in the range from 5 mHz to 70 Hz.

Variable force linear actuator

Abstract: A linear electromechanical actuator having a variable drive force. The actuator includes a moving coil which moves along a stroke path in response to an input current. A magnetic circuit provides a magnetic flux through which the coil is driven. The flux density along the stroke path is non-uniform, with a higher flux density being present only in that region of the stroke path where a higher actuator drive force is required. Thus, less expensive magnetic material can be used. Since the overall flux density in the magnetic circuit is reduced, the dimensions of the soft iron elements of the magnetic circuit can be reduced without magnetic saturation so as to further reduce construction costs.

Ignition arrangement for an internal combustion engine of a handheld portable tool

Abstract: The invention is directed to an ignition arrangement for an internal combustion engine of a handheld portable tool such as a chain saw or the like. The engine has a crankshaft and a fan wheel is seated on the crankshaft for rotation therewith. The ignition arrangement includes a permanent magnet. The magnet has two pole shoes and an exciter coil is mounted on the permanent magnet. The permanent magnet equipped in this way is fixedly mounted on the tool to save weight. A relatively light self-supporting annular member with projections is mounted in the fan wheel. The projections of the annular member and the permanent magnet with its pole shoes conjointly define a magnetic circuit. As the projections pass the pole shoes at a minimal spacing therefrom during operation of the engine, the projections alternately open and close the magnetic circuit thereby causing changes in the flux of this circuit. The flux changes cause a voltage to be inducted in the exciter coil which serves to generate the igniting spark via an appropriate electronic circuit.

Circuit breaker with trip delay magnetic circuit

Abstract: A circuit breaker with a magnetic circuit for delaying the trip function and characterized by a dual variable magnetic circuit air gap which allows a time delay at low level overcurrents, such that motor starting transient currents do not prematurely trip the circuit breaker.

Nonlinear Vector Potential Formulation and Experimental Verification of Newton-Raphson Solution of Three Dimensional Magnetostatic Fields in Electrical Devices

Abstract: An iterative technique, based on magnetic vector potential formulation and the Newton-Raphson method, for the determination of the three dimensional magnetostatic field distributions in electrical devices is given. The proper degrees of magnetic saturation in the various materials within a given volume under consideration are obtained by repeated evaluation of the reluctivities in that volume, using a cubic spline representation of the B-H magnetization characteristics of composite materials (laminations). The formulation has been applied to a practical example of determining the field in and around a shell type 1.5 kva single phase transformer. The convergence and implementation characteristics of the developed method are given in this paper which show a saving of about 34% in CPU solution time in comparison with previously published methods. Experimental verification is given in terms of a comparison between computed and experimentally obtained values of flux densities surrounding the transformer core and winding, under heavily saturated conditions. Excellent agreement between test and calculated flux densities was achieved. This method is thus quite applicable to the solution of a wide class of three dimensional magnetostatic field problems associated with electrical apparatus.

Apparatus for detecting position of piston rod of hydraulic cylinder

Abstract: PURPOSE:To enhance detection accuracy by increasing the change width of a secondary output voltage level, by detecting the change in the quantity of the eddy current at the conductor part provided to the peripheral surface of a piston rod generated with the movement of the piston rod. CONSTITUTION:Magnetic fluxes by primary coils 1A-1D having different phases are passed through magnetic cases 4, 5 and a piston rod 6. An eddy current is flowed to the conductor parts 6b and the change in magnetic resistance due to the loss of said eddy current is generated in a magnetic circuit. An Ac signal corresponding to this magnetic resistance is induced to each secondary coils 2A-2D having different phases.

Rolling magnetic friction electricity generator

Abstract: In accordance with the invention the magnetic friction force is overcome by a rolling motion whereby there is physical contact between the field magnets and the core As experiments show, reversal of magnetic flux polarity on and in a ferromagnetic object was 14 times less difficult to realize by such rolling motion Because full contact is realized between field magnets and winding cores, a greater flux density is produced by the magnetic circuit The above concept introduces a whole new breed of distinctly different rolling motion electricity generators