Electric

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• Electric
• Motor
• Selection

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Servosystem Selection

• Servo generally is used as a synonymous of
  brushless.
• Brushless motors are generally defined in terms
  of torque, not power, since the torque is
  available from zero to nominal speed, while P C
  w

Velocity
Torque
servo
servo
Induction vector controlled
Induction vector controlled
induction V/F cost.
induction V/F cost.
time
velocity
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Motion Transmission

• 1) Gearboxes
• Moment of inertia
• to the motor shaft
• J1 (n1/n2)2 J2
• Jtot Jmot J1

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Motion Transmission (contd)

• 2) Belt
• J m r2 m (v/w) 2
• 3) Screw
• J m (s/(2p))2

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Motors poles number

• Brushless can technically be built with any pole
  pair number.
• A high pole pair number generally
• gives high torques.
• The limit given by permanent
• magnets distance on the rotor and
• from the diameter of the motor.

AHR190J8 rotor with NdFeBo magnets
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Motors Basic Equations
Speed rad/s

• Electrical Equations
• e fcem Kt w V
• C Kt I Nm
• Mechanical Equations
• P dE/dt C w w dE/dq Nm/s W
• C J dw/dt Nm

Current A
Energy JNmWs
Angle rad
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Field-weakening (Deflussaggio)

• Increasing velocity the DC bus limit is reached
• (e fcem Kt w).
• For increasing furthermore the speed it is
  necessary to lower the statoric flux with 1/w
• (and doing so also Kt will be lowered and so also
  C Kt Iq).
• (The effect can be obtained changing the phase of
  is beyond p/2 with respect to the rotor position
  the current thus staying maximum and thus
  avoiding quantization effects due to small
  digital vectors).
• We thus have P C w cost.

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Field Weakening (contd)
Torque
fcem e
velocity w
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Torque characteristics of the different motor
types
DC brush motor
Torque
Torque
Peak torque
Universal Motors (motori serie)
Nominal torque
Nominal Work area
Velocity
Field weakening
Velocity
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Torque characteristics of the different motor
types (contd)
Stepper motor
Torque
pull-out torque
Max speed possible to put as set point at speed
zero
Resonance zone
Nominal Work area
Load inertia
Velocity (steps frequency)
pull-in rate
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Torque characteristics of the different motor
types (contd)
Pull-out torque
AC induction motor
Torque
Torque
Unstable zone
brake
const. power with Is max
Torque follows pull-out torque
const. torque
Nominal Work area
w
1/w
s 1
s 0
1/ w2
generator
w
B prop. to V/f cost.
V cost.
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Torque characteristics of the different motor
types (contd)
AC brushless motor
Torque
Peak torque
Nominal torque
Nominal Work area
Field weakening
Velocity
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Formulas Summary

• Rotational Case
• E C Da P Dt NmWsAm2T
• P dE/dt C w w dE/dq Nm/s
• C F leverage J dw/dt Nm
• F I L B l B F/ A N T
• F LI MMF/R MMFNI wb A

Linear Case E F Ds P Dt JNm P dE/dt
F v N m/s F m a NKgm/s2
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Rewinding (Riavvolgimento cave statoriche)

• For increasing Kt with the same motor is
  sufficient to rewind stator slots with smaller
  section cable so to make more windings
• Kt F Srot N / A will be thus increased.
• With the same motor, I will thus have more torque
  C Kt I with the same current I,
• But with a smaller max. speed since e Kt w

prop. to N I a little bigger due to Better slot
filling
It increases proportionally to number of windings
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Shannon Sampling Theorem
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Servo digital control loop

• sampling time (tempo di campionamento) to avoid
  z-transform analysis (that would mean to work at
  the control system limits) it is necessary to
  sample 5-10 times faster than Shannon theorem
  says.
• Generally we have
• Load Response Bandwidth 10-50Hz
• SampleUpdate Rate gt 1KHz

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Servo digital control loop (contd)

• lag error, following error
• (Errore di inseguimento) each control block
  introduces a delay (integral action plays an
  important role in this respect) that leads to a
  lag error naturally different from zero. To
  minimize it the feed-forward could be useful it
  bypasses closed loops regulating blocks (and thus
  it does not load the integral actions). The
  feed-forward action it is dependent from
  velocity, inertia, acceleration, viscous
  friction, that thus have to be known with good
  accuracy.

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DC Motors (motori in continua o motori a
spazzole o motori a collettore)

• Simple drive electronics
• Cheap
• Possible problems with commutator and brushes

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Ironless Motors(DC motor)
(With integrated gear)
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Ironless Motors(brushless)
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AC induction motors (a induzione o in alternata
o a gabbia di scoiattolo)

• Frequency-controlled asynchronous (induction)
  motors are mostly used for simple drive
  functions, without feed-back. For example to
  regulate the speed. The motor is a squirrel-cage
  asynchronous motor, and the control unit a
  frequency converter.
• The squirrel-cage asynchronous motor is the
  absolutely most commonly used AC induction motor
• it is CHEAP,
• it is VERY RELIABLE,
• it is a STANDARD PRODUCT within the IEC std.

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AC induction motors (contd)
230VAC
230VAC
Squirrel Cage (gabbia di scoiattolo)
D-Connection (Connessione a triangolo)
Y-Connection (Connessione a stella)
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AC induction motors (contd)

• The synchronous speed is the rotation speed of
  the magnetic field, generated in the field
  windings when supplied with a three-phase AC
  voltage
• The actual, true, speed of the rotor is
  determined also by how great a load the motor is
  driving. This speed is called the asynchronous
  speed, and the difference between the two is
  termed slip (scorrimento).

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AC induction motors (contd)

• Note that the AC induction motor (asynchronous)
  has always a physiological slip (in speed), while
  the AC brushless motor (synchronous) has always a
  physiological lag error (in position).
• From a construction point of view the stator of
  an AC induction motor and the one of an AC
  brushless are quite similar (both has a winding
  lay-out so to obtain a single sinusoidal rotating
  field from 3 sinusoidal pulsating fields).
• Often an AC brushless drive can also control
  (with Vector Control techniquies) an induction
  motor.

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Steppers(motori passo o passo-passo)

• 2 phases,
• 4 poles
• 6 rotor teeth

• Small loads
• No feed-back
• Cheap

2 phases, 8 poles 50 rotor teeth
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Steppers

• Half Stepping
• 4 poles 6 teeth 24 steps

1-phase-ON (FullStep) 4 poles 6 teeth / 2 12
steps
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Distribuzione del campo magnetico al traferro di
un motore passo-passo
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Steppers Motor Types

• Variable Reluctance (iron teeth)
• Permanent Magnets (PM teeth)
• Hybrid (rotor iron teeth misaligned axially,
• PM inside the rotor with N-S axially spaced)
• Direct Drive Variable Reluctance (ring-like
  rotor, double face stator)
• Multi-Stack (rotor divided axially in 3 parts
  with teeth misalingned of 1/3 stator also
  divided in 3 parts each energized in sequence
  only 1/3 of Fe used at the same time)

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