|Friday, 13 October 2006|
In the field of electric motors, a variety of configurations have been proposed and are presently in use. An electric motor typically comprises a rotor and a stator, each of the rotor and stator having multiple magnets disposed about the periphery, and a number of phase windings on a yoke. Applying suitable voltages across each of the phase windings causes current to flow through the windings, generating a current flux vector in the air gap between the stator and the rotor. This current flux interacts with the magnetic field of the rotor to cause the rotor to rotate to a point of equilibrium in which the flux vector is aligned with the axis of the rotor magnetic field. The stator and rotor may have various designs and electrical configurations depending upon the type of application, the environment in which they are used, the available power, and other such factors. Electric motors are generally constructed having a cylindrical stator core. The inner circumference of the stator core defines a plurality of radial slots in which electrical windings are maintained. A stator core is generally formed by bending an elongate and straight strip made of thin silicon steel into an annular shape, and by making a lamination with a plurality of the bent strips. In most electric motors, the stator is part of or forms the external housing of the electric motor and the rotor comprises a shaft mounted within the stator for relative rotation therein. A contact support fixed to the stator on the side of the rotor opposite its axially projecting output shaft carries contacts adapted for connection to at least some of the winding ends. Such motors are used with the impeller of a pump or blower mounted directly on the output end of the shaft. The main component parts of electric motors are the rotor, which is usually seated on the motor shaft rotatably mounted in a housing, and the stator, which is fixed in a suitable way in the housing. The rotor may be the actual armature, or else, in particular in wheel-hub motors, the rotor may be the outer exciter part, which surrounds the armature part and is then connected to a rim. A rotor of an electric motor requires high-accuracy balance. If the mass distribution of a member that constitutes the rotor is deflected so that the center of gravity is deviated from the axis of rotation, for example, the rotor shakes as it rotates and applies an undesired load to the rotating shaft member. For motor operation, the electrical components are electrically coupled to an electrical conduit. The housing commonly includes an access aperture which provides access to the electrical components for such purposes. A cover plate closes the access aperture when the motor is in use. The cover plate is a flat metal plate.
In general, an electric motor comprises a rotor having a field system and a stator having n phases armature coils and is adapted to control a rotational speed by controlling a drive current flowing through the armature coils by means of a controller. In an electric motor, electric drive magnets are disposed around a rotatably supported permanent magnet rotor. A rotor is dynamically mounted within the stator and is inductively driven in rotation by an oscillating electric power source applied to coils or windings of the stator. The stator windings are typically disposed within radial slots to create controllable magnetic fields which are forced to rotate by appropriate application of power to the windings during operation. The commutator must switch current to the correct drive magnets in the correct direction at the correct time in order to produce desired rotor movement. The commutator must know the current rotor angle, relative to the stator windings, to provide commutation. For precise motor control, it is generaly desirable to know as much as possible regarding motor operating conditions, including conditions that are parameters which can be measured and assigned a value. Consequently, a wide variety of sensors have been provided that are usefuil for sensing motor operating conditions. Electronic control circuits are used in a wide variety of devices that use electric motors. The control circuit allows a user or system containing the electric motor to adjust various parameters of the power being supplied to the electric motor. A drive unit for driving the motor comprises position sensors, a switch circuit, an acceleration sensor, and a controller. The position sensors detect a rotational angle position of the rotor relative to the stator. The switch circuit switches the exciting phase of the armature coils. The acceleration sensor outputs an acceleration signal having a magnitude corresponding to the opening degree of the accelerator operation member which is detected as a displacement quantity of the accelerator operation member. The controller is used to control the switch circuit so that the armature coils are selectively energized to commutate in accordance with the output of the position sensors which flow through the armature coils to rotate the rotor. The controller comprises a microprocessor to perform a predetermined program, which forms duty factor arithmetical operation means to arithmetically operate a duty factor of the drive current on a value of the acceleration signal, PWM control means to control the switch circuit so as to modulate a waveform of the drive signal into a pulse width modulation waveform (PWM waveform). Current sensors have also been provided that can be coupled to the stator windings so that the current flowing the stator windings may be measured. Many electric motors include governor assemblies which react to changes in the rotational speed of a rotor shaft to open and close an electric switch. Centrifugal governors generally utilize the centrifugal force generated by rotation of the shaft to engage and disengage an electric starting switch. Electric motors often include a fan within the motor housing to direct air through the housing to cool the motor components. Some motor types and configurations include components to modify the motor operating characteristics for particular applications. Examples of such motor types are resistance start, reactor start, capacitor start, permanent split capacitor, and capacitor start-capacitor run motors. These different types of motors are characterized by different speed-torque characteristics and may be designed to provide different theoretical maximum efficiencies. Electric motors often include mechanisms that terminate operation of the motor in response to thermal overload conditions that could result in permanent damage to the motor or associated equipment.
There're various types of motors, such as an induction motor, a DC motor with a brush, a stepping motor, a torque motor, a permanent magnet motor, and a brushless motor. A common type of electrical motor is the induction motor used throughout industry and in many varied applications. Induction motors typically employ a stator including a core in which a plurality of windings are installed. Single phase induction motors (SPMs) constitute the majority of motors used in home appliances today. SPIMs include permanent split capacitor (PSC) motors, split phase motors, capacitor start motors, capacitor run motors, permanent magnet synchronous motors, and shaded pole motors. A stepper motor is a type of electric motor that "steps" or rotates in an increment in response to an energizing of the stepper motor's windings. A stepper motor is controlled by a translator or sequencer circuit, which determines the sequence by which the windings of the stepper motor are energized for a particular desired motion. A driver circuit further buffers the control signals from the translator circuit and switches current to the windings of the stepper motor. To rotate a stepper motor, the windings of the stepper motor are activated or energized in a sequence. Stepper motors can generate a "holding torque" to maintain a particular position. These features make stepper motors quite useful in many automated control applications. A typical one-dimensional linear electric motor has a magnet track with pairs of opposing magnets facing each other. Within spaces between the pairs of opposing magnets, an armature moves. The armature has windings of a conductor which are supplied with an electrical current. In a multiphase motor, the armature has various windings grouped into phases. The phase groups are selectively pulsed with electric current to create a more efficient motor. A linear electric motor generally has a one-dimensional magnet assembly and a one-dimensional coil assembly positioned along the magnet assembly. In a linear motor, there is provided a stationary shell, in which is mounted a linearly movable member, such as a shaft or a piston. One of the shell and movable member has a magnet or a set of magnets mounted to it, and the other has a coil that receives operating electric current. Supply of operating electric current to the coil produces a magnetic field that interacts with the magnet to produce linear movement of the movable member. A planar electric motor generally has a two-dimensional magnet assembly and a two-dimensional coil assembly positioned near the magnet assembly. Linear and planar electric motors are used to precisely position a semiconductor wafer during photolithography and other semiconductor processing. A switched reluctance motor (SR motor) includes a rotor from which a plurality of equally-pitched pole portions are outwardly extended in the radial direction and a stator from which a plurality of equally-pitched pole portions are inwardly extended in the radial direction.
A direct current (DC) motor driven by a DC power source includes a stator of a permanent magnet, fixably mounted on an outer side of a main body, a rotor rotated by attraction and repulsion with the stator, and a brush for supplying current to a coil in contact with the rotor. The rotor includes an iron core fixably mounted on a rotary shaft to be rotated, a coil wound in the iron core to provide the iron core with an electromagnetic property by means of current applied to the iron core, and a commutator for supplying current to the coil. In basic DC motors, an electric current is supplied to the coil through brushes in contact with the commutator piece on the rotor shaft while switching the polarities of the electric current, the rotation of the rotor shaft being thus continued. A brushless DC motor makes use of control circuitry to operate switches that replace the combination of brushes and electrical contacts on the commutator. While the control circuitry can add to the expense of the brushless DC motor, the elimination of the brushes and commutator reduces maintenance, as there is no wear on an associated brush, and prevents arcing in the motor that can occur as the commutator moves past the brushes. In a brushed DC motor, the brushes make mechanical contact with a set of electrical contacts provided on a commutator secured to an armature, forming an electrical circuit between the DC electrical source and coil windings on the armature. In a permanent magnet direct current (DC) brush motor, a typical speed control system includes a controller that interfaces with an external speed-sensing element such as an incremental/rotary encoders or a system including magnets and hall effect sensors for sensing the rotational speed of the motor. A DC brushless motor is a synchronous motor and it has a stator winding, a permanent magnet rotor assembly, and internal or external devices to sense rotor position. The rotor assembly may be internal or external to the stator in the brushless motors. A major advantage of brushless DC motors over many other types of motors is that the motor's speed can be accurately variably controlled over a wide range of speeds and load conditions, throughout which the motor can produce full, or nearly full rated torque. Brushless motors are typically more efficient and quieter than induction motors because brushless motor designs avoid losses related to the induction process. A brushless direct current (BLDC) motor is made by removing a brush and a commutator from a direct current motor and by installing an electric rectifying device not to generate mechanical and electrical noise. A DC brushless motor typically includes a movable rotor portion having permanent magnet structures disposed about a circumference thereof and a stationary stator portion having a plurality of coils wound thereon in fixed relation to one another. By properly driving the coils on the stator, the rotor portion is set in motion to revolve about an axis of rotation in a desired manner. The combination of an inner permanent magnet rotor and outer windings in a offers the advantages of lower rotor inertia and more efficient heat dissipation with respect other type of electric motors A DC brushless motor has been increasingly applied to electronic equipment in recent years because of its simple construction and superior maintainability, being easy to construct in small size, and being easily driven by three phase AC power source controlled by power electronics. Many modern devices make use of direct current (DC) brushless motors to provide rotational movement within the device. For example, hard disk drives commonly use DC brushless motors as spindle motors to rotate a disk carrying hub about an axis of rotation.
Alternating current (AC) motors provide much of the motive force for industry. AC motors come in a variety of styles and horsepower ratings, from fractional horsepower ratings to multiple thousands of horsepower. AC motors may be classed as low, medium and high voltage. AC motors are typically categorized into three-phase AC induction motors, three-phase AC synchronous motors, two-phase AC servo motors, single-phase AC induction motors, and single-phase AC synchronous motors. Alternating current motors are generally known to be more rugged than an equivalent size direct current motor. A typical AC motor consists of an outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field. There are two fundamental types of AC motor, depending on the type of rotor used, including the synchronous motor which rotates exactly at the supply frequency or a submultiple of the supply frequency, and the induction motor which turns slightly slower, and typically (though not necessarily always) takes the form of the squirrel cage motor. Induction motors commonly include a rotor and a stator, the rotor positioned within a cylindrical stator frame and including a plurality of rotor windings equi-spaced about an external wall. An internal surface of the stator frame forms longitudinally running winding slots which receive stator windings. The shaft of an AC induction motor is often supported by bearing assemblies maintained in position by the machine housing. In order to control a multiphase AC motor such as an asynchronous motor, a frequency converter is used which controls the motor at variable frequency and voltage from the AC network. Alternating-current (AC) induction motors are heavily employed in industrial and manufacturing facilities. AC induction motors are used to provide mechanical inputs for machinery in manufacturing facilities.