Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as...
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![Page 1: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/1.jpg)
Mechatronics
Electric Motor
Selection
![Page 2: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/2.jpg)
Mechatronics
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 *
Velocity
time
servo
Induction vector controlled
inductionV/F cost.
Torque
velocity
servoInduction vector controlled induction
V/F cost.
![Page 3: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/3.jpg)
Mechatronics
Motion Transmission
1) Gearboxes:Gearboxes:
Moment of inertiato the motor shaft:
J1 = (n1/n2)2 J2
Jtot = Jmot + J1
Motor n1 teeth
n2 teeth
![Page 4: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/4.jpg)
Mechatronics
Motion Transmission (cont’d)
2) Belt:Belt:
J = m r2 = m (v/) 2
3) Screw:Screw:
J = m (s/(2))2
mv
r
m
s
![Page 5: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/5.jpg)
Mechatronics
Motor’s 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 rotorwith NdFeBo magnets
![Page 6: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/6.jpg)
Mechatronics
Motors Basic Equations
Electrical Equations:e = fcem = Kt [V]
C = Kt I [Nm]
Mechanical Equations:P = dE/dt= C = dE/d[Nm/s =
W]
C = J d/dt [Nm]
Speed [rad/s]
Current [A]
Angle [rad]Energy [J=Nm=Ws]
![Page 7: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/7.jpg)
Mechatronics
Field-weakening (Deflussaggio)Increasing velocity the DC bus limit is
reached (e = fcem = Kt ).
For increasing furthermore the speed it is necessary to lower the statoric flux with 1/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 /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 = cost.
![Page 8: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/8.jpg)
Mechatronics
Field Weakening (cont’d)
Torquefcem “e”
velocity
![Page 9: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/9.jpg)
Mechatronics
Torque characteristics of the different motor types
DC brush motorDC brush motorTorque
Velocity
Peak torque
Nominal torque
Field weakeningNominal
Work area
Universal MotorsUniversal Motors((motori seriemotori serie))
Torque
Velocity
![Page 10: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/10.jpg)
Mechatronics
Torque characteristics of the different motor types (cont’d)
Stepper motorStepper motorTorque
Velocity(steps frequency)
NominalWork area
Resonance zone
pull-out torqueMax speed
possible to put as set point
at speed zero
pull
-in
rate
Load
inertia
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Mechatronics
AC induction motorAC induction motorTorque
const. torque const. powerwith Is max
B prop. to V/f = cost.
V cost.
Pull-out torque
Torque follows pull-out torque
Torque characteristics of the different motor types (cont’d)
Torque
Unstable zone
NominalWork area
brake
generator
s = 0s = 11/1/ 2
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Mechatronics
AC brushless motorAC brushless motorTorque
Velocity
Peak torque
Nominal torque
Field weakeningNominal
Work area
Torque characteristics of the different motor types (cont’d)
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Mechatronics
Formulas Summary
Rotational Case
E = C = P t [Nm=Ws=Am2T]
P = dE/dt= C = dE/d[Nm/s]
C = F leverage= J d/dt [Nm]
F = I B l ; B= / A [N] [T]
= LI = MMF/R ;MMF=NI [wb] [A]
Linear Case
E = F s= P t [J=Nm]
P = dE/dt= F v[N m/s]
F = m a [N=Kgm/s2]
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Mechatronics
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 = 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
prop. to N I: a little bigger due toBetter slot filling
It increases proportionally to number of windings
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Mechatronics
Shannon Sampling Theorem
signalsample ff 2
-1.5
-1
-0.5
0
0.5
1
1.5
0 0.005 0.01 0.015 0.02 0.025
45Hz < signal bw
55Hz > signal bw 50Hz
fsample = 100Hz = 2fsignal
fsample = 110Hz > 2fsignal
fsample = 90Hz < 2fsignal
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Mechatronics
Servo digital control loop• sampling time (sampling time (tempo di tempo di campionamentocampionamento):): 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
Sample&Update Rate > 1KHz
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Mechatronics
•lag error, following error lag error, following error ((Errore di inseguimentoErrore 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.
Servo digital control loop (cont’d)
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Mechatronics
DC Motors DC Motors (motori in continua o motori a spazzole
o motori a collettore)
•Simple drive electronics
•Cheap
•Possible problems with commutator and brushes
![Page 19: Mechatronics Electric Motor Selection. Mechatronics Servosystem Selection Servo generally is used as a synonymous ofbrushless. Brushless motors are generally.](https://reader035.fdocuments.in/reader035/viewer/2022062219/551a25f5550346a4248b513e/html5/thumbnails/19.jpg)
Mechatronics
Ironless Motors
(DC motor)
(With integrated gear)B
iF1
i F2
B
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Mechatronics
Ironless Motors
(brushless)
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Mechatronics
AC induction motorsAC 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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Mechatronics
AC induction motors (cont’d)
D-Connection(Connessione
a triangolo)
Y-Connection(Connessione
a stella)
Squirrel Cage(gabbia di scoiattolo)
230VAC
230VAC
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Mechatronics
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 slipslip ((scorrimentoscorrimento).).
AC induction motors (cont’d)
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Mechatronics
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.
AC induction motors (cont’d)
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Mechatronics
SteppersSteppers(motori passo o passo-passo)2 phases,
4 poles6 rotor teeth
2 phases, 8 poles50 rotor teeth
• Small loads• No feed-back• Cheap
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Mechatronics
Steppers
Half Stepping:4 poles * 6 teeth = 24 steps
1-phase-ON (FullStep):4 poles * 6 teeth / 2 = 12 steps
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Mechatronics
Distribuzione del campo magnetico al traferro di un motore passo-passo
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Mechatronics
Steppers Motor Types:
1. Variable Reluctance (iron teeth)
2. Permanent Magnets (PM teeth)
3. Hybrid (rotor iron teeth misaligned axially, PM inside the rotor with N-S axially spaced)
4. Direct Drive Variable Reluctance (ring-like rotor, double face stator)
5. 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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Mechatronics