Abstract: A brush holder system for an electrical driving device having a brush-holder plate, a central opening for receiving a collector, as well as leaf springs arranged on the brush-holder plate, including respectively a brush, carrying the brush current and pushing the brushes with a preloaded force acting in the direction of the longitudinal axis of the central opening. The brush-holder plate includes guiding means for guiding in a radial direction the brushes or the brush segments including the brushes, the spring leafs.

Abstract: Disclosed is a spindle motor comprising: an integral turntable including: a table on which a rotating body to be installed, and an inner side wall and an outer side wall formed to be recessed upwards at a portion therebetween on a lower surface of the table so that a predetermined hollow is formed, a surface of thereof being formed slant; a ball cover for covering a ball inserted into the hollow and the hollow; a rotation shaft an upper portion of which is inserted into a center of the integral turntable; a bearing supporting a lower portion of the rotation shaft; a coil formed on an outside of the rotation shaft; and a magnet formed on an outside of the coil.

Abstract: Output wires are all led out of Address 1 in slots and vibration-absorbing bent portions are formed on all of the output wires between a leader portion led out from a rear-end coil end group and a tip portion of the output wire.

Abstract: A compact and reliable structure of a multi-rotor synchronous machine which may be employed as a generator/motor for automotive vehicles is provided. The machine includes an outer rotor having permanent magnets, an inner rotor having permanent magnets disposed to be rotatable relative to the outer rotor, a stator core having armature coils interlinking with field magnetic fluxes produced by the outer and inner rotors, and a rotor-to-rotor relative rotation controlling mechanism. A relative angle between the outer and inner rotors is controlled within a given angular range by controlling the phase and quantity of current flowing through the armature coils to rotate the inner rotor relative to the outer rotor through the rotor-to-rotor relative rotation controlling mechanism, thereby changing the magnetic fluxes interlinking with the armature coils as needed.

Abstract: A suspension for an assembly generating, absorbing, and/or transmitting torque in the drive train of a motor vehicle with a combustion engine, with the assembly 10 including materials with a thermal expansion coefficient different from the material of the engine block of the combustion engine 12, and a first non-rotating part 18, 22 of the assembly 10 being connected with the engine block, and a second rotating part 16 of the assembly 10 being connected with an output shaft 14 protruding from the engine block, and with the first and the second part 18, 22; 16 being designed so as to encompass the output shaft 14 at least partially, and with the first non-rotating part 18, 22 of the assembly 10 being connected with the engine block of the combustion engine 12 via a coupling element 40 in a manner so as to be essentially secured against rotation and resilient in the radial direction.

Abstract: An optical disk drive motor includes a rotor and a disk tray. At least one adjusting member is provided between the rotor and the disk tray. The adjusting member is adjustable to adjust a pressing force exerted on one of the rotor and the disk tray, thereby keeping the rotor and the disk tray in a parallel relationship.

Abstract: A motor having a rotor with a plurality of magnetic poles arranged in an arch or circular shape and a stator in which coils are disposed on the magnetic teeth of a stator core having a plurality of the magnetic teeth disposed opposite to the rotor, wherein a magnetic pole part for cancelling a cogging torque is disposed around the rotor.

Abstract: A transmission member for a worm gear having a thrust ring placed over the shaft of a motor. The worm gear is slip-fit over the shaft and has a coupling head with a pair of projections facing away from the motor. A coupling washer is press-fit onto the motor shaft and has a pair of projections as well, each of which is fitted with an O-ring. The coupling washer is mated to the worm gear so both sets of projections intermesh and form a torque-transmitting arrangement, with the O-rings acting as a buffer between the two sets of projections and allowing the motor shaft to turn relative to the worm for a fraction of a revolution to gain inertia and speed helpful to break loose a jammed gear train.

Abstract: An external rotor motor is disclosed, which features a stator (11) and a rotor (13) surrounding the stator (11) while leaving an air gap. A damper (16) made of an elastic material is arranged on the outside of the rotor (13) in order to dampen resonant rises in airborne sound, which is emitted by the rotor of the external rotor motor and by an aggregate coupled to it. In the case of a rotor (13) that is designed to be pot-shaped, the damper (16) is preferably embodied as a damping cap (17), which surrounds the pot jacket (132) and at least partially covers the pot base (131) (FIG. 1).

Abstract: The invention concerns an arrangement comprising a plain bearing (36) that contains ferromagnetic material and serves for radial support of a shaft (34) made of ferromagnetic material. The shaft (34) is arranged rotatably and axially displaceably in that plain bearing (36), and has a free end (35). Provided at the latter is a step bearing which has a bearing dome (66) provided at that free end (35), and a contact member (68, 69), coacting with the latter dome, said contact member being made at least partially of ferromagnetic material.

Abstract: A drive assembly in a motorized door opener includes a motor that is mounted on a mounting structure. At least one vibration isolator is provided between the motor and the mounting structure. The vibration isolator includes a first mounting fastener configured to be mounted to a mounting fastener on the motor, a second mounting fastener configured to be mounted to the mounting structure to mount the motor on the mounting structure, and an elastomeric material between the first and second mounting fasteners. The elastomeric material lies between the first and second mounting fasteners so that the isolator's two mounting fasteners are not in physical contact.

Abstract: A rotary electrical machine (10), especially a motor vehicle alternator, having a stator (12) of generally cylindrical annular form, which is arranged in a casing (14) having a rear portion (16) and a front portion (18) in which the outer axial face (24) of the stator (12) and the inner axial face (30) of the casing (14) define an annular radial space (32), and the stator (12) is suspended elastically within the casing (14), wherein at least part of the annular radial space (32) contains thermally conductive resin (50) which is deformable axially and interposed radially between the casing (14) and stator (12), so as to effect radial mechanical decoupling between the stator (12) and casing (14) and so as to dissipate heat energy from the stator (12) to the casing (14).

Abstract: A method of reducing the audible operating noise of an electric power conversion device includes providing a segmented commutator with slots between the segments and smoothing the brush transition between the slots to reduce brush vibration and the associated noise ordinarily created when the motor brush contacts the commutator. The commutator and assemblies for smoothing the commutator surface are disclosed.

Abstract: An electric machine and method for forming the same comprises a rotor, a rotor winding disposed on the rotor and having a body portion and end turn portions, and a non-metallic cylinder arranged around the rotor to restrain both the body portion and the end turn portions of the winding against forces resulting from a rotation of the rotor. No portion of an inner circumference of the cylinder is smaller than an outer circumference of the rotor so that the cylinder may be slid around the rotor without obstruction during construction of the electric machine. The cylinder surrounds a body portion of the rotor and extends axially beyond end faces of the rotor and has a plurality of holes defined therethrough. The rotor includes a plurality of venting passages and at least one opening formed therein to allow a balance plug to be engaged therein.

Abstract: A transmission member for a worm gear having a thrust ring placed over the shaft of a motor. The worm gear is slip-fit over the shaft and has a coupling head with a pair of projections facing away from the motor. A coupling washer is press-fit onto the motor shaft and has a pair of projections as well, each of which is fitted with an O-ring. The coupling washer is mated to the worm gear so both sets of projections intermesh and form a torque-transmitting arrangement, with the O-rings acting as a buffer between the two sets of projections and allowing the motor shaft to turn relative to the worm for a fraction of a revolution to gain inertia and speed helpful to break loose a jammed gear train.

Abstract: An induction apparatus includes a winding arrangement having a winding start and a winding end for inducing a magnetic field in a magnetizable core; and a lossy, magnetizable device through which and/or about which the winding start and the winding end of the winding arrangement is so disposed as to induce a magnetic flux in the magnetizable device. This arrangement prevents an electric breakdown at the star point of winding strands of synchronous motors.

Abstract: The present invention has been made for the purpose of obtaining a permanent magnet type dynamo electric machine, and a permanent magnet type synchronous generator for wind power generation, each of which is capable of reducing an eddy current loss of a rotor while having a construction of an integral one-piece rotor yoke.

Abstract: A motor for reducing torque ripple includes a shaft having a shaft axis, a rotor positioned about the shaft, a first magnet ring positioned on the rotor, the first magnet ring having magnets each occupying a magnet angle &egr; on the rotor, and a second magnet ring positioned on the rotor, the second magnet ring having magnets each occupying a magnet angle &egr; on the rotor, wherein the second magnet ring is shifted a non-zero number of degrees relative to the first magnet ring and wherein ends of each magnet within the second magnet ring are located at different angular positions than ends of each magnet within the first magnet ring relative to the shaft axis of the shaft. The magnet angle &egr; is preferably an optimal magnet angle for minimizing cogging torque and line to line back emf harmonics.

Abstract: In a brushless DC motor constructed by a rotor 2 to which a permanent magnet 3 is attached; and a stator 1 having a plurality of slots, when an effective opening angle of magnetic pole of the rotor 2 that was set to a predetermined opening angle whose base is the rotation axis of the rotor 2 is &thgr;2 and a salient area opening angle of magnetic pole formed within the effective opening angle &thgr;2 of magnetic pole is &thgr;3, the opening angles &thgr;2 and &thgr;3 are set so that cogging torque generated by the effective opening angle &thgr;2 of magnetic pole and cogging torque generated by the salient area opening angle &thgr;3 of magnetic pole are mutually in antiphase. Accordingly, a brushless DC motor capable of reducing cogging torque is realized.

Abstract: A rotor assembly includes a stack of laminations that are bonded together by a dielectric bonding agent. The laminations and the dielectric bonding agent have matching coefficients of thermal expansion.

Abstract: In a rotary electric machine with a stator elastic support structure, conductor segments of a stator winding, each which is formed into an approximate U-shape, are inserted into slots of a stator core in such a manner that leg parts of each conductor segment penetrate through the slots from one end of the stator core to the other end thereof and are connected at top ends. Further, the conductor segments are arranged to have a predetermined clearance between adjacent two thereof at both coil ends of the stator winding, and a cooling fan is disposed so that air is blown toward the clearances of the conductor segments. Accordingly, when the stator core is supported in a frame through an elastic member, a magnetic noise can be reduced while it can effectively prevent heat deterioration of the elastic member due to heat radiated from the stator core and the stator winding, in low cost.

Abstract: A damper for a stator assembly, the stator assembly comprising a stator segment and a seal mounted to the stator segment. The damper locates between the stator segment and the seal, and comprises: a medial section; and opposed arms extending from the medial section. The medial section engages one of the stator segment and the seal and the opposed arms engage the other of the stator segment and the seal. A method of making the damper, comprising the steps of: providing a sheet of material having a medial section and opposed arms extending from the medial section; forming a bend at the medial section so that the medial section can engage one of the stator segment and the seal; and forming a bend at each of the arms so that the arms can engage the other of the stator segment and the seal.

Abstract: A small-size motor has a case cover 11 formed with three voids, and electric elements such as chip capacitors are contained in the three voids. A first electric element is mechanically fixed between a pair of brush units in a first void and is electrically connected. The remaining two second and third electric elements are located on both sides of the first electric element and are pressed on a brush base in a motor shaft direction by a body earth terminal 14 in second and third voids, so that the body earth terminal 14 is fixed to the case cover 11 and the two electric elements are mechanically fixed and electrically connected. A sufficient space is secured in the motor case cover made of synthetic resin, so that three electric elements such as chip capacitors can be incorporated together with their wiring and support arrangement.

Abstract: A method for facilitating damping torsional or ring vibrations of a dynamoelectric machine including a rotor assembly with a first amortisseur bar and a second amortisseur bar extending therefrom and terminating at an endring is provided. The method includes providing a damping assembly, and positioning the damping between the first amortisseur bar and the second amortisseur bar such that the damping assembly contacts the first and second amortisseur bars, and is substantially proximate the endring or alternatively the damping assembly is positioned only over one amortisseur bar.

Abstract: A mount is provided for an electric motor of the type having a stationary shaft. The mount comprises a yoke with two opposed bushings and a clamp for holding the stationary shaft, wherein the clamp is mounted to the bushings within the yoke. Thus, the mounting block damps vibrations of the motor in all directions while maintaining torsion stability.

Abstract: The invention relates to an apparatus for vibration-insulated mounting of an electric motor (20), in particular a blower motor, having a first housing part (10), which encloses at least one pole ring (22) and magnets (24) of the electric motor (20) and has at least one opening (14, 16), through which the shaft (18) of the motor (20) reaches, and having a second housing part (54), which is embodied as a motor flange for securing the electric motor (20) to a carrier element, for instance a motor vehicle heating and/or air conditioning system, and at least partly embraces the first housing part (10) in the axial direction of the motor shaft (18).

Abstract: A stator for a dynamoelectric machine includes an annular stator core in which a large number of slots extending in an axial direction are disposed in a circumferential direction so as to open radially inward; a stator winding having a plurality of winding phase portions installed in the stator core, lead wires of the plurality of winding phase portions being led axially outward within a predetermined circumferential range from an axial end of a first coil end group formed at a first axial end of the stator core; and a first mass adjusting portion disposed at a first end of the stator core, the first mass adjusting portion adjusting a circumferential mass imbalance relative to a central axis of the stator core resulting from a circumferential bias in positions from which the lead wires are led out.

Abstract: A vacuum line (10) comprising a vacuum-tight flexible tube section (22) and a vibration damper (16) axially parallel to the flexible tube section (22) serves to connect two vacuum devices (12,14). The vibration damper (16) is an actively regulated axial magnetic bearing. Thereby, a vibration damper with good dampening properties is realized. By changing the regulation parameters, the vibration damper is adaptable and not subjected to any mechanical wear. The transmission of structure-borne noise is avoided by the contactless vibration dampening.

Abstract: A motorized device including a first element, a second element, a third element, a fourth element, and a fifth element, wherein in this device the fifth element is constructed around an elongated piece perforated by an axial channel, which elongated piece is referred to as a sixth element, an axial channel of the sixth element is of an inner diameter greater than an outer diameter of the first element such that an entire longitudinal axis of the sixth element is able to be engaged along the first element, at least one of the first element and the sixth element is equipped with a seventh element, the function of the seventh element is to ensure a coupling in rotation of the first and the sixth elements.

Abstract: An electrical tool includes a housing having inlet (7) and outlet (8) openings, a brushless electric motor (2) and an inverted rectifier (3) both arranged in the housing (9) between inlet (7) and outlet (8) openings in an air stream (5) of an air volume (6), and a link condensator (10) located in the housing (9) in the air stream (5), with the inverted rectifier (3) being arranged, in the air flow direction, downstream of the link condensator (10) and upstream of the electric motor (2).

Abstract: The present invention relates to a stator for a rotary electric machine, the stator comprising a stator body made up of a stack of stator laminations and first and second nested concentric disposed with clearance about the stator body. First resilient damping elements are placed between the two parts. These resilient damping elements are disposed circumferentially around the inner one of said two parts between the outer surface of said inner part and the facing inner surface of the outer part. Relative movement between the two parts is limited both axially and circumferentially by second damping elements.

Abstract: A spindle motor for a disk drive is disclosed having a carrier assembly supported on a mounting structure by an elastomeric damper for damping and isolating mechanical vibration and noise generated by the spindle motor. The carrier assembly includes a carrier on which is supported the remaining components of the spindle motor such as the hub, bearings, rotor and stator.

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: In one aspect of the present invention discloses a dual-stiffness damping system for an evacuated energy storage system, the damping system comprising one or more flexible dampers and a plurality of more rigid bumpers, and a method of damping an evacuated energy storage system using dual-stiffness damping. Indeed, under normal operating conditions, a flexible damper, having a stiffness of about 500 lb/in to about 4000 lb/in, minimizes the rigid body critical speed of the rotor assembly of the energy storage system, allowing relative displacement between the stator assembly and rotor assembly but preventing the assemblies from physically contacting each other. Under more extreme external loading conditions, e.g., during an earthquake, the plurality of more rigid bumpers, having a stiffness of about 50,000 to 250,000 lb/in, engages the outer race of the bearing assembly to arrest further relative displacement substantially.

Abstract: An electric motor, in particular an external rotor motor, comprising a stator which is attached by means of latching elements to a motor carrier using a plug-in joining operation. The elastic elements for isolating vibration are arranged in the connecting region between the stator and the motor carrier in a way that the stator is indirectly connected to the motor carrier by means of the elastic elements.

Abstract: A rotor assembly for an electric motor comprises rotor elements formed integrally as a pressing from strip steel, whereof adjacent rotor elements (8) comprise pole portions (12) which are mutually offset, particularly with respect to a central plane B-B of the body portion (10) of the rotor element. In particular each rotor element is produced by the use of a die assembly to punch the rotor element from strip material, part at least of the pole portion of the rotor element being produced by a first die member, and part at least of the body portion being produced by a second die member, in which relative movement is effected between the first and second die members between successive punching operations.

Abstract: The motor apparatus includes a motor and an insulating device. The motor such as a spindle motor is driven with pulse width modulation. Then, the insulating device insulates an object to be protected, which should be protected from a noise current generated from the motor, from the motor.

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 electric motor with a stator structure having a high thermal conductivity from coils to a stator core, and capable of suppressing vibration of coils and adjusting an output torque and a cogging amount of the motor. A stator core is provided at its inner periphery with main teeth extending radially and spaced at regular intervals from one another. Auxiliary teeth are provided in slots formed between adjacent main teeth. Coils are arranged such that, when wound around the main teeth, their outer peripheral faces are in close contact with the auxiliary teeth. Since the coils are in contact at their central portions with the main teeth and in close contact at their outer peripheral portions with the auxiliary teeth, heat generated from the coils energized is efficiently conducted to the stator core, and removed by cooling devices provided at outer peripheral portions of the stator, thereby cooling the motor. Since the coils are fixedly held between the main and auxiliary teeth, vibration can be prevented.

Abstract: For a method of operating of a synchronous compensator including a rotating electric machine including a rotor and a stator with at least one winding with a solid insulation enclosing the electric field, relevant parameters for temperature conditions in the rotor are determined, and during over-excited operation, to temporarily enlarge the field of operation of the synchronous compensator, cooling of the rotor is forced depending on a rotor temperature value determined from the parameters. The synchronous compensator measures parameters relevant for the temperature conditions of the rotor. A mechanism is also provided to force the cooling of the rotor depending on rotor temperature values determined from the parameters during over-excited operation of the electric machine.

Abstract: A rotary electromechanical device includes a first motor including a first stator and a first rotor, a second motor including a second stator and a second rotor, and variable power supplies for driving the respective motors independently of each other, The motors are arranged in series along the axial direction of a rotary shaft. Magnetic poles of the same polarity of the rotors are located at uniform angular positions around the rotary shaft while magnetic poles of the stator of the motor and magnetic poles of the stator of the second motor are displaced from each other in the circumferential direction of the rotary shaft.

Abstract: An apparatus and method for damping vibration of a vehicle part, such as a steering wheel or an electric motor. According to one embodiment, an apparatus (26) for damping vibration of a vehicle part (12) includes at least one container (50) having a chamber (56) defined by at least one interior wall (58). The container (50) is associated with the vehicle part (12). A plurality of particles (52) is disposed in the chamber (56). The particles (52), when at rest, occupy a first portion (82) of the chamber (56) and define an unoccupied second portion (84) of the chamber. The particles (52) move back and forth between the first and second portions (82 and 84) of the chamber (56) in response to vibration of the vehicle part (12) and collide with each other and with the interior wall (58) defining the chamber to damp the vibration of the vehicle part.

Abstract: The invention relates to a device in a deck for playing information discs (2), which preferably have been provided or can be provided with digital information, the information disc (2) being rotated, in the operating condition, about its center by a drive motor (5) and magnetically cooperating material parts (8, 9) being present, which are offset radially with respect to the axis of rotation (3) and in the direction thereof parallel with respect to one another and of which one part (8) is disposed on the base plate (4) which carries the motor (3) and of which the other part (9) is disposed on the disc support (1) which is moved by the motor shaft (6), one of the material parts (8, 9) being a ring-shaped permanent magnet, at least one of the two magnetically cooperating material parts (8, 9) being arranged eccentrically with respect to the axis of rotation (3) and both material parts (8, 9) are ring-shaped, the directions of the lines of field not being changed during rotation.

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: Disclosed is a brushless DC motor used for driving a fan or the like, wherein the brushless DC motor comprises: a stator core; motor coils wound around the stator core; a rotor core supported rotatably with respect to the stator core; a rotor magnet attached to the rotor core, which is magnetized into a multi-pole so that the waveform of a counter electromotive force generated on the motor coils is resulted in a sine wave-like shape, and has an uneven space being faced to the stator core so that the waveform of a cogging torque is resulted in a cosine wave-like shape having a twice rotation cycle with respect to the sine wave of the waveform of the counter electromotive force; a magnetic pole position detector that detects magnetic pole positions of the rotor magnet, and is disposed at a position where the waveform of an output signal is resulted in a sine wave-like shape; and a drive unit that amplifies the output signal of the magnetic pole position detector so that the maximum value of an exciting torque i

Abstract: Embodiments of the present invention are directed to gear transmission apparatus that are configured to largely eliminate the cogging effects and to reduce the backlash effects. In one embodiment, a transmission apparatus comprises a follower gear, a first drive gear set coupled with the follower gear to drive the follower gear, and a second drive gear set coupled with the follower gear to drive the follower gear. The first drive gear set includes at least one gear, and the second drive gear set includes at least one gear. A first motor is coupled with the first drive gear set. The first motor includes a first rotor having a plurality of poles which are movably disposed relative to a plurality of magnets. A second motor is coupled with the second drive gear set. The second motor includes a second rotor having a plurality of poles which are movably disposed relative to a plurality of magnets.

Abstract: An electromagnetic machine includes a rotor having a plurality of poles and a stator also having a plurality of poles. The poles for the rotor are divided into a first and second set of radially opposed pairs. The first set has uniform faced poles. The second set has a notched face. The stator includes radially opposed pairs of poles having uniform faced poles. The rotor and stator are disposed for movement relative to each other such that the first and second sets of poles for the rotor are movable in relation to the radially opposed pairs of the stator. The electrical interaction between uniform faced poles of the rotor with uniform faced poles of the stator produces a first normal force profile. The electrical interaction between notched faced poles of the rotor with uniform faced poles of the stator produces a second normal force profile. The first and second normal forces act dynamically in time or position on the stator as the rotor moves in relation to the stator.

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: A vibration testing device includes a computer system having: a measurement processing block for inputting an output of the monitoring sensor and processing the output; a model substituting block for modeling characteristics of the test piece, calculating a response quantity corresponding to a drive condition of an actuator, and inputting the calculation result to a numerical simulation block and the parameter changing block; the parameter changing block for comparing the calculation result of the model substituting block with the processing result of the measurement processing block, and changing the parameter; the numerical simulation block for calculating a vibration response in accordance with a previously input structure numerical model; and a waveform generating block for calculating a time function of a deformation to be applied to the test piece, and outputting the time block to the actuator controlling device.

Abstract: An image reading apparatus used for a motor to scan an original for image reading, includes a first damper 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 a second damper 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.