special mechanies
DESCRIPTION
SPECIAL MECHANIES. Motor Basics. What is a motor Converts electrical energy into kinetic energy Where did it come from Identification of rotating magnetic field principle by Nicola Tesla in 1882 Introduction of Electric Motor by Nicola Tesla in December 1889 (U.S. Patent 0416194). - PowerPoint PPT PresentationTRANSCRIPT
SPECIAL MECHANIES
Motor Basics
What is a motorConverts electrical energy into kinetic energy
Where did it come fromIdentification of rotating magnetic field principle
by Nicola Tesla in 1882Introduction of Electric Motor by Nicola Tesla in
December 1889 (U.S. Patent 0416194)
How It Works
• When electric current passes through a coil in a magnetic field, the magnetic force produces a torque which turns the motor.
• Force in Motor:F=ILBF = Force B = Magnetic FieldL = Length of ConductorI = Current in Conductor
• Torque in Motor:T = IBA sin θA = LWL = Length of WindingW = Width of Winding
Ac series motor
Ac series motor Application to mixer
A repulsion motor is a type of electric motor for use on alternating current (AC). It was formerly used as a traction motor for electric trains but has been superseded by other types of motors and is now only of historical interest. Repulsion motors are classified under single phase motors. In repulsion motors the stator windings are connected directly to the AC power supply and the rotor is connected to a commutator and brush assembly, similar to that of a direct current (DC) motor.[
Repulsion motor
ConstructionThe motor has a stator and a rotor but there is no electrical connection between the two and the rotor current is generated by induction. The rotor winding is connected to a commutator which is in contact with a pair of short-circuited brushes which can be moved to change their angular position relative to an imaginary line drawn through the axis of the stator. The motor can be started, stopped and reversed, and the speed can be varied, simply by changing the angular position of the brushes.
Stop positionsIdle Run positions
Position for counter-clockwise operation
Position for clockwise operation
Run positions
RELUCTANCE MOTOR
CROSS SECDTIONAL VIEW OF RELUCTANCE MOTOR
Cross-section of reluctance machine with 6 stator and 4 rotor poles. Notice the concentrated windings on the stator poles.
• A reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. Torque is generated through the phenomenon of magnetic reluctance. There are various types of reluctance motor:•Synchronous reluctance motor•Variable reluctance motor•Switched reluctance motor•Variable reluctance stepping motor
Hysteresis Motors
• Stator– same as for induction
motor• Rotor
Smooth cylinder
Principle of Operation
Stator Flux establishes these magnetic poles
Rotor poles “induced” by Stator Flux
Spin the stator poles with the rotor blocked
Stator poles moving CCW
Rotor poles follow the rotating flux, but lag behind by angle δh
Spin the stator poles with the rotor blocked
If the rotor is released, it will accelerate to synchronous speed
Mechanical Power developed
max
max
1
15252
(1 )
mech h
nh h
nh rh
r s
r s
sP Ps
P k f B
T n sk f Bs
n n sf sf
Mechanical Power developed
max
max
1
15252
(1 )
mech h
nh h
nh rh
r s
r s
sP Ps
P k f B
T n sk f Bs
n n sf sf
Mechanical Power Developed (cont)
max
max
5252
120
5252120
nh s
hs
ss
nh
h
k f BT
n
fnPk BT
P
Independent of frequency and speed!
Hysteresis Motor at Synchronous Speed
No load and negligible rotational losses
Induced rotor magnets remain locked with the rotating poles produced by the stator
Hysteresis Motor at Synchronous Speed
Apply a step increase in shaft load.
The rotor slows down and the induced rotor magnets lag the rotating poles of the stator by an angle δmag .
The rotor returns to synchronous speed at the new torque angle.
Hysteresis Motor at Synchronous Speed
max
sin( )
@ 90mag mag
mag mag
T
T occurs
max
sin( )
@ 90mag mag
mag mag
T
T occurs
If shaft load causes δmag>90°, the rotor pulls out if synchronism, the magnet torque drops to zero, and the machine develops hysteresis torque. This torque is not sufficient to carry the load.
Torque-Speed Characteristic
“Normal” Operating
Range
Constant Hysteresis Torque allows the motor to synchronize any load it can accelerate
STEPPER MOTORJ. Belwin Edward
Assistant Professor SeniorSchool of Electrical Engineering
VIT UniversityVellore
Stepper motor characteristics•Stepper motors are constant power devices.•As motor speed increases, torque decreases. Most motors exhibit maximum torque when stationary, however the torque of a motor when stationary (holding torque) defines the ability of the motor to maintain a desired position while under external load. The torque curve may be extended by using current limiting drivers and increasing the driving voltage (sometimes referred to as a 'chopper' circuit; there are several off the shelf driver chips capable of doing this in a simple manner).
•Steppers exhibit more vibration than other motor types, as the discrete step tends to snap the rotor from one position to another (called a detent). The vibration makes stepper motors noisier than DC motors. This vibration can become very bad at some speeds and can cause the motor to lose torque or lose direction. This is because the rotor is being held in a magnetic field which behaves like a spring. On each step the rotor overshoots and bounces back and forth, "ringing" at its resonant frequency. If the stepping frequency matches the resonant frequency then the ringing increases and the motor loses synchronism, resulting in positional error or a change in direction. At worst there is a total loss of control and holding torque so the motor is easily overcome by the load and spins almost freely. The effect can be mitigated by accelerating quickly through the problem speeds range, physically damping (frictional damping) the system, or using a micro-stepping driver. Motors with a greater number of phases also exhibit smoother operation than those with fewer phases (this can also be achieved through the use of a micro-stepping driver).Stepper motors with higher inductance coils provide greater torque at low speeds and lower torque at high speeds compared to stepper motors with lower inductance coils.
Switched reluctance motor
Stepper motor
Stepper motor
Applications
Computer peripheralsTextile industriesIC fabricationsRoboticsApplications requiring incremental motion
TypewritersLine printersTape drivesFloppy disk drivesNumerically-controlled machine toolsProcess control systemsX-Y plotters
Applications contd….
•Commercial, military and medical applications•Mixing, cutting, striking, metering, blending•Application in manufacture of packed food stuffs•Application in manufacturing of commercial end products•Production of science fiction movies.
Step Angle - β
• As small as 0.78o to 90o
• Most commonly used – 1.8o, 2.5o, 7.5o, 15o
β = (Ns-Nr) x 360o = 360o
Ns.Nr mNr
Ns – No. of Stator poles (teeth)Nr – No. of Rotor poles (teeth)m - No. of stator phases
Types
• Variable Reluctance - VR• Permanent Magnet - PM• Hybrid
VR, PM and Hybrid types
Variable Reluctance ( VR) stepper motor
• Wound Stator poles– Single Stack – Multiple Stack – smaller step angle
• Rotor poles – ferromagnetic material• Direction – stator current polarity• Reluctance of the magnetic circuit formed by
rotor and stator teeth varies with angular position of the rotor
Variable Reluctance stepper motor
Single Stack
VR – Multi stack
VR-Operation
Modes of operation –VR type
• 1-phase ON – full step operation
• 2-phase ON• Half-step – alternate 1-phase & 2-phase mode
• Micro stepping
Permanent Magnet (PM) Stepper Motor
Permanent Magnet stepper motor
• Wound Stator poles – Single Stack – Multiple Stack – smaller step angle
• Rotor poles – permanent magnet• Rotor Shape - Cylindrical• Direction – stator current polarity
PM - operation
PM - operation
Modes of Operation – PM type
• 1-phase ON mode• 2-phase ON mode• Half step mode
Modes of Operation – PM type
Hybrid Stepper Motor
Hybrid stepper motor
• Combination of VR and PM• Wound Stator poles – (similar to VR)
– Single Stack – Multiple Stack – smaller step angle
• Rotor poles – permanent magnet• Rotor shape – not Cylindrical• Direction – stator current polarity
Stepper motor applicationsAutomated Test EquipmentSurveillance SystemsAvionicsDefense ContractingLabeling MachineryMedical EquipmentPackagingSemiconductor ManufacturingMetering and DispensingEngraving MachineAutomatic Feeding Machine3D Image Acquisition SystemLabel and Die FeederWave Length MeterBar Code PrintingAntennaFiber optics SwitchLaser MeasurementPress PrintingColor/ Photo Imaging