Abstract: A recording disk drive motor is disclosed which is employed in a recording disk drive that retains a removable recording disk that has a diameter of 30 mm or less, as well as a method of manufacturing a stator core used in the same. The core back of the stator core in the motor has an arc shaped inner circumferential surface therein that is offset from the center thereof. The stator core is produced from a laminated body having a stator core, a chuck frame that is integral with and surrounds the stator core, and connector arms that connect the stator core and the chuck frame and integral therewith. After the windings are wound around the stator teeth, the stator core is cut from each connecting arm and the stator core is removed from the chuck frame.

Abstract: A choke 20 is provided for suppressing radio-frequency interference of a brush-type motor. The choke includes a single wire having a portion wound about a coil axis A to define a plurality of coils 24 including two outermost coils 26 and 28. An attaching structure 30 extends from one of the outermost coils and includes a loop structure 42. The loop structure is constructed and arranged to be inserted into a slot 58 in a brush card 48 and moved into hooked relation with a retaining member 60 of the brush card that is associated with the slot so as secure the choke to the brush card. At least a portion of the attaching structure is constructed and arranged to be in electrical connection with a brush 56 of a motor when the choke is secured to the brush card. An elongated end portion 44 of the choke extends directly from the other of the outermost coils.

Abstract: A motor generating cogging torque has one-quarter the cycle of basic cogging torque and an extremely small absolute value. First, in order to reduce the cycle of the cogging torque to one-half the cycle of the basic cogging torque, a basic configuration of the core is determined by setting opening angles of its slots to an appropriate electrical angle ranging from 80° to 95° and from 20° to 35°. Next, to produce the above-mentioned effects, an angular displacement of one-quarter the cycle of the basic cogging torque is provided in the motor. Furthermore, polarizing the core with a skew angle equal to one-half or less the cycle of the basic cogging torque at the same time allows the cogging torque to be reduced effectively while decrease in efficiency is minimized.

Abstract: A motor generating cogging torque has one-quarter the cycle of basic cogging torque and an extremely small absolute value. First, in order to reduce the cycle of the cogging torque to one-half the cycle of the basic cogging torque, a basic configuration of the core is determined by setting opening angles of its slots to an appropriate electrical angle ranging from 80° to 95° and from 20° to 35°. Next, to produce the above-mentioned effects, an angular displacement of one-quarter the cycle of the basic cogging torque is provided in the motor. Furthermore, polarizing the core with a skew angle equal to one-half or less the cycle of the basic cogging torque at the same time allows the cogging torque to be reduced effectively while decrease in efficiency is minimized.

Abstract: The invention relates to a device comprising at least one suppressor (10, 12) for reducing interference, especially in the high-frequency range of an electric machine (18), and also comprising at least one connection element (14, 16) for connection to a pole shoe of the electric machine (18).

Abstract: A centrifugal actuator of an electric motor is modified to reduce noise produced by torque pulses of the motor. The centrifugal actuator comprises a damper sleeve that is mounted in a tight friction fit on the motor shaft. The main body of the centrifugal actuator is mounted on the damper sleeve by a friction fit which permits limited rotational movement of the actuator main body relative to the actuator damper sleeve. In addition, pairs of tabs are provided on both the actuator main body and the actuator damper sleeve and are positioned in circumferentially overlapping relationships whereby engagement of the main body and damper sleeve tabs provides a positive driving connection between the main body and damper sleeve.

Abstract: An ac generator includes a stator having a stator core with a plurality of slots and a stator winding disposed in the slots and a rotor having trapezoidal claw-shaped pole pieces that alternately extend in opposite directions to interleave each other. In such an ac generator, each pole piece has a chamfered surface at the tip. The chamfered surface increases a distance from the inside surface of the stator core as the chamfered surface becomes away from the circumferential center of the pole pieces. The chamfered surface has narrower area at the front half in the rotation direction than the rear half.

Abstract: A housing structure for the heat-dissipation fan comprises a housing, a plurality of axial guide blades and a plurality of radial air inlets. The housing is provided with an air inlet and an air outlet between which receiving a stator and a rotor. The axial guide blades are equi-spaced and radially extended outward from the housing proximate the air inlet. Each of the radial air inlets is formed between any two axial guide blades. When the rotor is rotated, airflow sucked through the radial air inlets is guided parallel to an axis of the housing running from the air inlet to the air outlet so as to increase air inlet amount and reduce air noise.

Abstract: An electric motor having a stator and a rotor, with the rotor having at least one permanent magnet and one rotor shaft and with the stator having at least two coils which produce a rotating magnetic field when alternating currents flow through them, by which the rotor can be driven, and wherein the rotor shaft is mounted radially and axially. The rotor (4) is mounted by at least one elastic thrust ring (1a, 1b), with one thrust ring (1a) being arranged axially on one side of the rotor (4).

Abstract: The present invention is to provide a motor housing including two cover shells each having a hollow cover body and mounts mounted on the outer periphery thereof. The present invention is characterized in that at least one of the two cover shells has at least two ledges, which protrude outwardly from an edge of an opening of the cover body. The mounts are respectively provided on outer sides of the ledges and respectively have a first matching portion at an end of the mount of the first cover shell and a second matching portion at an end of the mount of the second cover shell. The two cover shells are connected with two ends of a stator of the motor by the ends of the mounts of the two cover shells are contacted to each other in pairs and are fastened with each other by screws.

Abstract: In an alternator of this invention, a ratio (t1/t2) between a radial thickness (t1) of a tip and a radial thickness (t2) of a root portion is within a range equal to or greater than 0.10 and equal to or less than 0.25, with a ratio (A/B) between a dimension (A) of overlap between a stator core and disk portions when viewed from a radial direction and an axial dimension (B) of the disk portions being within a range equal to or greater than 0.2 and equal to or less than 1.0, and a ratio (Lp/Lc) between an axial length (Lp) of claw-shaped magnetic poles overlapping the stator core when viewed from a radial direction and an axial length (Lc) of the stator core being within a range equal to or greater than 0.7 and equal to or less than 0.9.

Abstract: An improved shape for a tooth of a rotor assembly in an AC generator is generally trapezoidal in shape and includes a base, a tip, and leading and trailing edges. The leading edge comprises a first portion, and a second portion. The first portion extends from the tip toward the base, and the second portion extends from the first portion toward the base. The second portion slopes at a first rate that would cover about one slot pitch were it allowed to continue all the way up to the tip. However, the first slope continues only to a transition point. The first portion is generally parallel to the trailing edge of an adjacent, magnetically opposing rotor tooth. The modified tooth presents a wider tooth cross-section.

Abstract: A rotor structure of a motor is provided. The rotor structure includes a magnet having a first annular wall, a magnet holder having a base and a second annular wall connected with the first annular wall of the magnet for fixing the magnet, a shaft having one end mounted through the base of the magnet holder, and a stopper mounted in the other end of the shaft.

Abstract: A method and structural means are provided to mechanically modify the electromagnetic structure of a dynamoelectric machine for suppression of the vibration and noise otherwise occurring during machine operation. In doing so, the electrical performance of said modified dynamoelectric machine need not be significantly degraded.

Abstract: A simple, stamped counterweight is formed from a flat sheet of metal. The counterweight is attached to an uppermost portion of the end ring of the motor rotor. In this way, the counterweight requires little axial space, and is a very simple item to produce and assemble.

Abstract: The motor has a motor housing. The motor housing supports therein rotatably an armature having a rotating shaft and a commutator. Brushes are brought into friction contact with the commutator. The brushes have brush holders for holding them respectively. The brush holders are attached to a base plate having a first side and a second side. A plurality of electric parts are mounted on the base plate. These electric parts are allocated to the first side and the second side of the base plate.

Abstract: An electric motor structure includes an electric motor having a housing and an endcap coupled to an end of the housing. The endcap includes a bearing pocket constructed and arranged to cover a bearing structure. The motor structure also includes a heat shield coupled directly to the motor so as to surround and cover the bearing pocket, with a portion of the heat shield being spaced from the bearing pocket.

Abstract: An apparatus and method for suspending a stator core (100) in an electric generator upon a foundation (206), where two natural modes of vibration, including known second and third modes, are excited in the core, each mode having four loops and four nodes displaced 45 degrees between the second and third modes. A non-rigid connection (212) connects a yoke to the foundation, and two connection members connect the yoke to the stator core at opposite sides of the non-rigid connection. The two connection points (210a,b) are located at adjacent loops of one of the second and third vibration modes. By this arrangement, radial deflections of the stator core at the respective connection points are transferred into a rocking movement of the yoke around the non-rigid connection. Thereby, vibrations transferred to the foundation are considerably reduced during operation.

Abstract: A reciprocating compressor provided with a plurality of gas compression means having a cylinder and a piston. The piston of each gas compression means is cooperated with the compressor by converting a rotating motion of a crankshaft provides on an electric drive source to a reciprocating motion by a scotch yoke mechanism. A cylindrical attachment portion of a flywheel has an outer diameter corresponding to an inner diameter of a rotor shaft hole of the electric drive source, and the cylindrical attachment portion of the flywheel is inserted into the rotor shaft hole to contact with a lower end surface of the crankshaft. The fly wheel may be fastened to the crankshaft via a fastening bolt.

Abstract: An automatic balancing apparatus may be mounted in a rotator body such as a spindle motor having a rotary shaft defining an axis of rotation. The automatic balancing apparatus has a plurality of balancing members rotatable about the axis of rotation in a non-contact manner. Each of the balancing members has a balance action section spaced a distance in a radial direction from the axis of rotation and a connection section that rotatably couples the balance action section to the axis of rotation. The balance action section has a mass that effects a balance correction action to cancel a rotational unbalance of the rotator body when the rotator body rotates at a rotational speed that exceeds a resonant rotational speed CR thereof. The connection section has a mass that substantially does not affect the balance correction action compared to the balance action section.

Abstract: A rotor for a flywheel magneto generator comprising a flywheel having a reluctor of projection provided on an outer face of a peripheral wall portion of the flywheel and a hole provided in a bottom wall portion of the flywheel at a position close to the reluctor for correcting static unbalance of the flywheel caused by a presence of the reluctor, the flywheel further comprising at least one recess provided in the peripheral wall portion of the flywheel on an end face thereof on the opening side of said peripheral wall portion for getting dynamic balance of the flywheel.

Abstract: A motor has plural through-holes punched in a top surface of its frame. A cap made of magnetic material is placed at a location on a stator which corresponds to the through-holes, and the cap is spaced axially from the through holes. An attracting magnet is placed outside the cap. This structure allows a bearing to hold its oil, and generates attracting force in an axial direction without adversely affecting driving-magnetic-circuits. As a result, an apparatus using this motor can be low in profile and run at a high speed.

Abstract: It is disclosed a device for axial stopping of a rotor, in particular an armature of an electric motor, for balancing machines, the device comprising a thrust unit having an abutment surface (8) adjacent to an end face (4b) of the support shaft (4) of the rotor (5) and adapted to exert on the end face (4b), a repulsive force which is able to keep an interstice (1a) between the abutment surface (8) and the end face (4b), the thrust unit comprising fluid-emitting means (9) suitable to form a layer of fluid between the abutment surface (8) and the end face (4b).

Abstract: It is an object of the present invention to provide magnetic bearing controller which is able to levitate the controlled object stably by using controlled magnetic forces. In the magnetic bearing controller which supplies a controlled current to an electromagnet for levitating a rotating body at a predetermined position, the controller is provided with an eliminator unit for eliminating frequency components of frequency area which is used by the status detector unit. The eliminator unit is inserted between signal amplifier unit and power amplifier unit for generating controlled current.

Abstract: A wiper motor has brushes slidable in contact with a commutator, choke coils connected in series with the brushes, and a circuit breaker for preventing burn-out caused by excessively high current. The circuit breaker is disposed in the vicinity of the choke coils and operates based on heat generated by the choke coils.

Abstract: Brushless motor is provided which includes an outer stator and an inner rotor having a plurality of permanent magnets. One or inner surface of the outer stator, opposed to the inner rotor, is covered with a cover formed of a magnetic material and in the shape of a cylinder of a small wall thickness. The magnetic cover has a plurality of slits inclined with respect to the rotational axis of the inner rotor. Magnetic portions formed or left between the slits of the cover are also inclined with respect to the rotational axis of the inner rotor. With such magnetic portions, boundaries between magnetic poles are virtually inclined with respect to the rotational axis of the inner rotor, so that undesired cogging torque of the motor can be minimized.

Abstract: A balancing plate comprises an axial hole for engagement with a stator and at least two induction edges symmetrically arranged with respect to the axial hole. Each induction edge includes an arc length that is not greater than a length of one of plural poles of an annular permanent magnet of a rotor. When the motor rests, the induction edges of the balancing plate face at least two of the poles of the annular permanent magnet having the same polarity, forming a mating therebetween to thereby allow easy restarting of the motor.

Abstract: A power generation system (10) including an apparatus for attaching a generator stator core (20) to a frame support (30) and associated methods are provided. The system (10) preferably includes a stator core frame support member (30) and a generator stator core (20) including a plurality of keybars (22) positioned spaced-apart and extending along outer peripheral portions of the generator stator core (20). The generator stator core (20) is positioned to overlie the stator core frame support member (30). The system (10) further includes a core supporter (40) connected to the stator core frame support member (30) and positioned to contact the generator stator core (20). The core supporter (40) includes first (43) and second (44) core connectors (42) for stabilizing the power generation system and relieving vibration and eliminating lateral movement of the generator stator core (20) during operation.

Abstract: A method and an apparatus which removes vibration of a pickup. The apparatus adaptively controls a multi-speed of a disc drive to remove vertical vibration of the pickup, which occurs due to various wobble masses of a disc in the disc drive. The method includes detecting a mass of a wobble of a disc inserted into the disc drive using a focus driving signal generated in response to a driving of the disc drive, determining an allowable high multi-speed with respect to the disc according to the detected mass of the wobble of the disc, and driving the disc drive within a range that does not exceed the determined allowable high multi-speed. Accordingly, it is possible to prevent the vertical vibration of the disc in the disc drive regardless of the mass of the wobble of the disc.

Abstract: A rotor for an automotive alternator comprises a cylindrical bobbin fitted over the base portions of a pair of field cores having a cylindrical portion and a pair of first and second annular flange portions projecting perpendicularly from both ends of the cylindrical portion, and a field winding wound a predetermined number of turns into multiple layers on the cylindrical portion of the bobbin, wherein the field winding has a flat shape in which a pair of opposite flat surfaces are parallel, the field winding being wound onto the cylindrical portion of the bobbin such that the pair of opposite flat surfaces face the inner circumferential side and the outer circumferential side, respectively, relative to the radial direction.

Abstract: The invention relates to a motion absorber comprising a housing (1), a connecting member (2) that is mounted to be movable with respect to the housing and that is linked with a movable part whose motion should be absorbed, and an absorber element that absorbs the motion of the connecting member (2) in the housing (1). Conventional motion absorbers are disadvantageous in that their operability is limited at wide temperature variations. The aim of the invention is therefor to provide a motion absorber whose absorbing effect is as independent of the ambient temperature as possible. To this end, the absorber element is a two-part structure and comprises a permanent magnet (3) and an opposite pole (4). One part is arranged on the housing (1) and the other part is arranged on the connecting member. The magnetic force acting between the permanent magnet (3) and the antipole (4) absorbs the motion of the connecting member (2) in the housing (1).

Abstract: A motor assembly 10 includes a DC motor 12 having a motor housing 14 defining a stator, a rotor assembly 18 supported for rotational movement with respect to the stator, and a shaft 22 coupled to the rotor assembly for rotation about an axis of rotation A. The assembly 10 includes a supporting structure 30 carrying the motor and decoupling structure 32. The decoupling structure 32 mounts the motor housing 14 to the supporting structure 30 in a manner to provide a certain natural frequency of the motor in torsion around the axis of rotation A of the shaft 22 while providing natural frequencies higher than the certain natural frequency for degrees of freedom of the motor other than torsion. The assembly 10 also includes pivot structure 44 and 46, associated with the supporting structure and the motor defining a pivot between the motor and the supporting structure with a center of the pivot being aligned with the axis of rotation.

Abstract: An apparatus for stabilizing the spin axis of a rotating system, the rotating system having a rotor and motor means to cause rotation of the rotor about the spin axis and a magnet, windings, a source of drive current and an actuator combined with the motor means and forming a source of actuator current energizing the windings to generate a radial force which stabilizes the position of the spin axis and dampens other than rotational movements of the rotor.

Abstract: An angle measuring system that includes a stator and a rotor for measuring an angular position between a stationary first object and a second object, which is rotatable about an axis of rotation. A coupling couples the stator to the stationary first object so that the stator is fixed against relative twisting, but is also radially and/or axially resilient. A mounting element that clamps a face of the stationary first object by expanding in a radial direction with respect to the axis of rotation. An expansion element that interacts with the mounting element so as to cause the expanding in a radial direction and a screw that actuates the expansion element, wherein the screw is screwed into the stationary first object.

Abstract: A rotary electrical actuator for mounting to a support surface in industrial applications having integral electronics that are isolated by vibration isolators from vibrations. The rotary actuator comprises a stator housing supporting a lamination stack and coils. The actuator housing has a mounting structure for mounting to the support surface (such as the mounting surface of an engine or a turbine for example) for support thereby. A rotor is carried for rotation in the stator housing. The actuator further comprises an electronics housing containing the electronics that control output of the electrical actuator. Vibration isolators supported by the stator housing in turn support the electronics housing, whereby vibrations received at mounting structure and traveling through the stator housing are dampened prior to traveling to the electronics housing. A number of embodiments are disclosed utilizing a tie rod assembly concept for the vibration isolators.

Abstract: A method for making an armature assembly is provided that reduces the level of acoustic noise during initial engagement of the armature, during slippage, and during disengagement. The armature assembly includes an armature disc, an annulus of sound damping material, and a hub assembly having a flexible spider with a web portion. The armature assembly is made by first forming the annulus of sound damping material with a plurality of angularly spaced molding tabs. The annulus is affixed to the web portion of the hub assembly using the molding tabs and is then compressed by securing the armature disc to the web portion such that one side of the annulus is disposed against the web portion and a second side of the annulus is disposed against the armature disc.

Abstract: A drive system, in particular for a vehicle, includes an electric machine, by means of which a shaft can be driven to rotate and/or electrical energy can be obtained when the shaft rotates. The electric machine includes a stator arrangement with a stator interaction region and a rotor arrangement with a rotor interaction region. The rotor interaction region is coupled or can be coupled to the shaft for common rotation by means of a carrier arrangement. A torsional-vibration damper arrangement includes which is formed at least in part by said carrier arrangement, a primary side and a secondary side which can rotate, counter to the action of a damper element arrangement, about an axis of rotation (A) with respect to the primary side.

Abstract: A balance correcting method, a dynamic pressure bearing, and an optical scanning apparatus. For balance correction a method of attaching weight to the rotatable body and another method of partly removing the rotatable body are jointly used. At the time of a first balance correcting process step, a balance correction is performed by applying adhesive agent to a recess portion formed on a circular circumference of a polygon mirror or a recess portion constructed with a rotor flange. At the time of a second balance correcting process step, the polygon mirror is partly removed or the rotor flange is partly removed. The method can be applied to a dynamic pressure bearing capable of stabilizing a rotation balance and an optical scanning apparatus having a structure capable of not changing the direction of the reflection surface of the rotatable polygon mirror. The rotating shaft is supported in the radial direction by sucking air existing between the fixing shaft and the rotating shaft.

Abstract: The present invention relates to an assembly for preventing rotation of a damper in a stator system. The rotation preventing assembly comprises a slot in the damper and a block for engaging the slot to prevent rotation of the damper. The block is positioned within a groove located at a mid span portion of an inner air seal.

Abstract: An improved DC electrical starting motor and method for starting internal combustion engines that reduces starter motor noise in the period after the engine starts by damping the vibrations caused by motor cogging as it coasts to a halt, is done by reducing cogging torque and or rigidifying the starter motor housing. In addition several new structures foe reducing cogging torque are disclosed.

Abstract: The invention relates to a fitting arrangement for an antivibration mounting of an electromotor (1) on a load-bearing component by means of several interelements (6) arranged distributed around the perimeter and consisting of an elastic material. To always achieve an optimum vibration isolation independently of the motor's fitting position, it is provided that the interelements (6) are designed as oblong, radially aligned web elements (8) and are arranged axially, clamped under elastic prestress, between a mounting surface (12) on the motor side.

Abstract: A motor housing assembly houses a motor having a casing defining an axial length and an output shaft extending from the casing. The assembly includes a housing defining a cavity with an open end for receiving the motor and a partially closed end opposite the open end. The housing has a length larger than the axial length of the casing such that the entire casing of the motor can be received within the cavity. The assembly further includes an end cap configured to substantially close the open end of the housing and retain the motor in the housing, a first isolator member configured to be sandwiched between the casing and the end cap to substantially isolate the motor from both the housing and the end cap, and a second isolator member configured to be sandwiched between the casing and the housing to substantially isolate the motor from the housing.

Abstract: Provided is a durable spindle motor with a precise rotation but free from a shaft vibration, a decrease of rotation accuracy or a contact due to a swing during rotation. A shaft (11) is inclined relative to a sleeve (12) by an external biasing force, generating and then utilizing a hydrodynamic pressure generated during the rotation. The sleeve (12) has a central cylindrical section (C) extending parallel to the axis and two tapered sections (A), (B) each connect(d with the cylindrical section (C) at its opposite ends and enlarged outwardly, so that a dynamic force is generated between the tapered sections (A), (B) and the shaft (11). Preferably, an inclination of the tapered sections (A), (B) is identical to that of the shaft (11), and lengths of the tapered sections (A), (B) is one fourth of that of the sleeve (12).

Abstract: A support structure for a drive source such as a motor of the blower is disclosed in which the generation of noise caused by the vibration of the motor is suppressed. The flange of a support member has a low-stiffness portion having a thickness smaller than a high-stiffness portion of the same flange. The low-stiffness portion is thus vibrated more easily than the high-stiffness portion. When the motor vibrates, therefore, the vibration rate of the low-stiffness portion increases beyond that of the high-stiffness portion, so that the low-stiffness portion vibrates considerably. The motor vibration is thus absorbed by the flange (support member) and the transmission of the motor vibration to a casing can be suppressed. As a result, the area of the sound source of the blower is decreased as a whole, thereby making it possible to suppress the generation of noise caused by the vibration of the motor.

Abstract: The present invention, as the construction of an image reading apparatus used for a motor to scan an original for image reading, provides first damper means mounted on the drive shaft of the motor to reduce vibration caused during acceleration for raising up to a target speed at the start of the load driving of the motor, and second damper means mounted on the drive shaft of the motor to reduce vibration caused during the constant speed driving of the motor to thereby reduce vibration caused during the driving of the motor.

Abstract: A rotor for a flywheel magneto generator comprising a flywheel having a reluctor of projection provided on an outer face of a peripheral wall portion of the flywheel and a hole provided in a bottom wall portion of the flywheel at a position close to the reluctor for correcting static unbalance of the flywheel caused by a presence of the reluctor, the flywheel further comprising at least one recess provided in the peripheral wall portion of the flywheel on an end face thereof on the opening side of said peripheral wall portion for getting dynamic balance of the flywheel.

Abstract: Vibrator attaching structure is provided in which the working efficiency at the assembly time and the disassembly time is good, the required arrangement space is made small, and a device can be miniaturized. A vibrator-attaching base (20) has at its lower portion a shield case (22) that is a box-shaped base member functioning also as a shield member on a print circuit board (10). At the upper portion of this shield case (22), a holder (26) that is a holding member is integrally formed.

Abstract: A disc drive spindle motor for reducing the idle noise of a disc drive includes a stator having a first cylindrical surface for contacting a motor mount of the spindle motor. The motor mount includes a second cylindrical surface for contacting only a portion of the first cylindrical surface of the stator to reduce the transmission of vibrations from the stator to a base plate of the disc drive. The motor mount may be attached to a base plate of the disc drive when the spindle motor is formed separately from the disc drive. Alternatively, the motor mount may be formed integrally with the base plate of the disc drive.

Abstract: A motor including a washer assembly that facilitates reducing or eliminating end bump noise generated as a result of a rotor contacting a bearing assembly during motor operation is described. The rotor assembly includes a shaft rotatably supported within the housing with a pair of bearing assemblies. Each washer assembly includes a snap ring and a damping washer. The damping washer includes three layers, wherein the first and third layers are fabricated from a wear resistant material and the second layer is between the first and third layers, and is fabricated from an energy absorbing material.

Abstract: The present invention provides a method and system for stabilizing a rotor about its geometric center in a magnetic bearing system at a constant rotor speed. In the method, the controller for controlling the magnetic bearing uses an adaptive control algorithm which simultaneously identifies and compensates for synchronous sensor runout and rotor mass unbalance while determining a control action that drives the rotor rotating at a constant speed to its geometric center. The identification of sensor runout and mass unbalance is by varying the magnetic stiffness which is achieved by perturbation of the bias currents in opposing electromagnet coils in a manner that does not alter the equilibrium of the rotor while it is rotating at a constant speed.