Download machines unit 1

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)
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=ILB
F = Force
B = Magnetic Field
L = Length of Conductor
I = Current in Conductor
•
Torque in Motor:
T = IBA sin θ
A = LW
L = Length of Winding
W = Width of Winding
Ac series motor
Ac series motor Application to mixer
Repulsion motor
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superseded by other types of motors and is now only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.[
Construction
The 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 positions
Idle
Run positions
Position for clockwise
operation
Run positions
Position for counterclockwise operation
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
 1 s 
Pmech  Ph 

 s 
n
Ph  kh  f  Bmax
Th nr
n  1 s 
 kh  f  Bmax 

5252
 s 
nr  ns (1  s )
f r  sf s
Mechanical Power developed
 1 s 
Pmech  Ph 

 s 
n
Ph  kh  f  Bmax
Th nr
n  1 s 
 kh  f  Bmax 

5252
 s 
nr  ns (1  s )
f r  sf s
Mechanical Power Developed (cont)
n
 5252kh f s Bmax

Th  

ns


120  f s
ns 
P
n
5252kh Bmax Independent of frequency and
Th 
speed!
120
P
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
Tmag  sin( mag )
Tmagmax occurs @  mag  90
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
Constant Hysteresis Torque allows the motor to
synchronize any load it can accelerate
“Normal”
Operating
Range
STEPPER MOTOR
J. Belwin Edward
Assistant Professor Senior
School of Electrical Engineering
VIT University
Vellore
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 peripherals
Textile industries
IC fabrications
Robotics
Applications requiring incremental motion
Typewriters
Line printers
Tape drives
Floppy disk drives
Numerically-controlled machine tools
Process control systems
X-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 applications
Automated Test Equipment
Surveillance Systems
Avionics
Defense Contracting
Labeling Machinery
Medical Equipment
Packaging
Semiconductor Manufacturing
Metering and Dispensing
Engraving Machine
Automatic Feeding Machine
3D Image Acquisition System
Label and Die Feeder
Wave Length Meter
Bar Code Printing
Antenna
Fiber optics Switch
Laser Measurement
Press Printing
Color/ Photo Imaging