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Special Purpose Motors and Control DevicesPermanent Magnet MotorsPermanent Magnet MotorsA brushless electric motor is an electric motor driven by an electrical input, which lacks any form of commutator or slip ring. Depending on their design they can be either AC or DC driven.Generally the term 'brushless motor' will refer to a permanent-magnet synchronous motor (PMSM) or permanent-magnet motor (PMM), a synchronous motor which uses permanent magnets rather than windings in the rotor. PMSMs are either axial flux, radial flux, transverse flux, or flux switching depending on the arrangement of components, with each topology having different tradeoffs among efficiency, size, weight, and operating speed.Alternative designs may use reluctance rather than magnets. Asynchronous induction motors are also brushless motors.The brushless DC motor is a brushless AC motor with integrated inverter and rectifier, sensor, and inverter control electronics. The AC inverter/controller electronics are a modern age invention, only available since roughly 1984 and were developed by inventor Miro Zoric.- Wikipedia, the free encyclopediaClassification and CharacteristicsClassificationcharacteristicsConventional PM MotorSimilar to wound rotor DC motorCoreless PM MotorHas no iron or steel in the rotorTorque PM motorRuns for a long time at the stalled or low speed condition

The characteristic of permanent magnet motor depend on the material of the magnet. The material control the flux density and coercivity.Coercivity - is a measure of a ferromagnetic or ferroelectric material to withstand an external magnetic or electric field.

Coercivity ung H para maging zero ung Flux Density .. Magnetizing force (H)4Materials used in MagnetsAlcinoHas high flux density and low coercivityCeramic or ferriteHas low flux density and high coercivityRare EarthHas high flux density and high coercivity

Conventional PM MotorsAlso known as wound rotor PM motor, is like a shunt wound-rotor DC motor.Its rotor is assembled with laminated core, windings are coiled in the rotor slots, a commutator, and brushes. The difference is that the magnetic field is set by permanent magnets in the PM Motor as opposed to electromagnets in the DC motor.Permanent magnetized along their length or width.Magnetization along lengthMagnetization along width

Conventional PM Motors have applications in electrical equipment that require high efficiency, high power and minimal size.Motorized forkliftsWheel chairsScooters

ApplicationsCoreless PM MotorThe coreless PM motor, also known as the ironless-rotor and the moving coil motor, has no iron or steel in the rotor, as its name suggests. This lack of iron provides the following benefits:It has lower inertia and thus respond quickly to changes in speed.It has less armature inductance and thus respond quickly to changes in input voltage.It has no eddy current and hysteresis losses and thus produces high efficiency.It has no tendency to remain in any particular location relative to the structure, which eliminates the cogging effect. The cogging effect occurs when the rotor slips into a rotational position and stalls there until the torque makes it advance.

Two types of Coreless PM Motor structuresShell structureThe shell structure, also called the cup structure or the can structure, is a thin hollow cylinder with one attached to the shaft next to the commutator and the other fitted between the permanent magnets. The cylinder typically made of fiber glass with copper wires bonded on both interior and exterior surfaces; wire segments on the end of the cylinder connect the surface wires.

Disk structureThe disk structure for a coreless PM motor consist of thin, donut shaped fiberglass board with copper conductors on both sides, and six permanent magnets thar are attached to the end plates.

Torque PM MotorsTorque PM motors, sometimes called torquers, are designed to operate at a low speed or at a stalled condition for long time. Not all DC motors are designed for this type of operation. Torque PM motors can dissipate heat from the large amount of current flow. Torque PM motors have three main industrial application:Spooling, where the torque PM motor runs at a stalled condition, exerting tension or pressure for machine operation.Opening and closing valves, where the torque PM motors turn only a few revolutions at a low speed.Driving tape transports, where the torque PM motor must run continually at a low speed.Brushless DC MotorBrushless DC MotorThe brushless DC motor is an electronically commutated DC motor with a position sensor whose output is used in the control of commutation. The sensor system signals the controller on rotor position, and the controller sequences the electronic commutator, which in turn drives the stator windings.

Electronic CommutatorControllerStatorRotorSensor System

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Sensor SystemTwo popular sensor system is Hall effect sensor system (electrical) and Optical sensor system (mechanical).

Hall EffectWhen a magnet was placed perpendicular to one side of a current carrying conductor, a voltage appeared on the opposite side of the conductor. This voltage is usually in millivolt range.

Optical sensorThe optical sensor is a device that combines a disc mounted on the shaft of the motor, with light emitting diode and light detectors mounted mounted around shaft.

Power Control SystemsVoltage Control SystemVary the voltage to the commutator switches, which in effect for a series regulator, thus controlling the voltage that is switched to the stator windings.Current Control SystemAllow the commutator switches to vary the current to motor, which means either operating the switches in a constant current mode, or use a pulse width modulation scheme that adjust the on-time and off time of the switches.

Brushless DC Motor ApplicationsBecause the Brushless DC Motor has high reliability and low maintenance and runs at a high speed, it is well suited for the aerospace and biomedical industries.Aerospace industryGyroscopes; tape drives for rugged, high reliability video recorders; tape transport systemBiomedical industryArtificial heart pumps, cryogenic coolers

Stepper MotorsStepper MotorsA stepper motor converts electronic digital pulses into mechanical rotational steps. When the motor receives a digital pulse that energize the stator winding, the shaft of stepper motor turns(steps) a specific angular distance, then remains at that position until next incoming digital pulse. The shaft can be driven clockwise or counterclockwise at various pulse.

Stepping rate The maximum number of steps the motor can make in one second.Step angleThe number of degrees the motor moves per stepHolding torqueThe maximum load originating torque that the motor can stand without moving from its position with the stator energized.Detent torqueThe maximum load originating torque that the motor can stand without moving from its position with the stator de-energized. Its value is typically 10 percent of the holding torque.

Permanent Magnet Stepper Motors

Variable Reluctance Stepper MotorsThe variable reluctance stepper motor consist of electromagnetic stator winding and non magnetized toothed rotor. The motor shaft rotates to a position that minimizes the magnetic reluctance of the flux path.Variable reluctance motor have much less holding torque and effectively zero detent torque compare to PM motors because the rotor is non magnetic.

Operation and excitation modesRest ModeThe stator windings are de-energized, the rotor is not turning, resisting movement until load originating torque exceeds detent torque.Stall ModeThe stator windings are energized, the rotor is not turning, resisting movement until load originating torque exceeds holding torque.Bidirectional ModeThe rotor turns continually, then stops. It can continue in the same direction or the reverse direction.Unidirectional ModeThe rotor is accelerated(ramped up) beyond directional rate and cannot be reversed instantaneously. Also called Slew Mode.Speed-torque curves for operational modes.

The excitation modes of the stepper motor can be categorized as follows:

Two-phase and two phase modified modeHalf-stepping and microstepping modesThree phase and three-phase modified modes.Two-phase and two phase modified mode

Two phase modified mode

Half step mode for stepper motor

Three phase and three-phase modified modes: Rotor rotation

ApplicationsComputer peripheralsPrintersPlottersDisk drives.Business machinesLens positioningPaper feedProcess controlParts positioning in assembly linesX-Y positioning in laser trimming operations.Machine toolAxis positioning for robotsMilling machines and lathesEnd