1. maxon motion control: Control loops, Controller properties
Control and feedback
Power, power stages
Communication
Features and demonstration of a positioning system

2. maxon motor control
What to control: position, speed, current (torque)?
Which commutation type: DC, EC, block, sensorless, sinusoidal?
How to control: open – closed loop, 1Q – 4Q
How to measure the feedback value?
What kind of Signals: digital - analog?
How much power: current and voltage, voltage drops?
Controller power stage: linear, pulsed, chokes?
Special features: time scales, braking, measuring motor currents

3. Motion control: servo system
electr. energy
PC,
PLC
set value
motion
command
controller
amplifier
energy
losses
servo amplifier
current
position
signal
speed
signal
motor
position,
speed
sensor
load
position,
speed
mech. energy

4. What to control ? Current control = torque control Speed control
maintaining current (torque) constant
mostly included in controller (but not always accessible)
for fast motor reaction
no special feedback device needed
Speed control
maintaining speed constant
"speed = 0" does not mean "position is held"
all maxon controllers can act as speed controllers
Position control
moving from position to position, stop at and maintain a position
maxon controllers: EPOS, EPOS P, and MIP

5. Motor type? Commutation?
4-Q DC servoamplifier
LSC (50 W), ADS (250 W, 500W)
1/4-Q-EC amplifier
AECS (sensorless, 100 W)
DEC (24 W-700 W, Hall sensor), block commutation
4-Q-EC servoamplifier
DES (250 W, 700W), sinusoidal commutation
Position control
MIP (DC or EC, W), block commutation
EPOS (DC or EC, W), sinusoidal commutation
EPOS P (DC or EC, 120W), Sinusoidal commutation
DC motor
speed controller
EC motor
commutation and
speed controller
DC or EC motor
position controller

6. Which motor type, commutation?
For which motor types is the controller made: DC, EC, Stepper
With EC motors:
What commutations system is foreseen?
Block with Hall sensors, sensorless
Sinusoidal commutation
What kind of position sensors are needed for commutation?
Hall sensors
Encoder (resolution, channels, line driver)

7. How to control: open vs. closed loop?
open loop
no feedback
output is not measured and checked
closed loop
feedback loop
output value is measured and the set value is adjusted , accordingly
"Feed forward"
system behaviour is anticipated
set value
actuator
output
set value
actuator
output  + -
measured
value
feedback
sensor
feed forward
actuator
output 
set value + -

8. Open-loop systems: examples
maxon controller:
LSC (Uadj),
DEC (open loop)
AECS (comm. only)
DC motor operation at fixed voltage
load ML n + nL U nL -
set value
actuator
output ML M
another example: stepper motor with amplifier
set value: signal pulses
actuator: amplifier and motor
output: steps/increments

9. 1Q-controller, 4Q-servocontroller
speed n
1-Q
only motor operation (quadrant I or quadrant III)
direction reverse by digital signal
braking is not controlled (friction), often slow
4-Q
controlled motor operation and braking in both rotation directions
mandatory for positioning
quadrant II
braking cw
quadrant I
motor drive cw n n M M
torque M M M n n
quadrant III
motor drive ccw
quadrant IV
braking ccw

10. DEC 50/5 DECV 50/5 DEC 70/10 DES
sensors Hall Sens. Hall Sens. Hall Sens. Encoder, HS
commutation Block Block Block Sinusodial
n-feedback with HS HS HS Encoder
operation ranges 2x 1Q 2x 2Q "4Q" (2x 2Q) 4Q cw cw cw cw
0..5V
0..5V
+10 V …
-10 V
+10 V 5V …
-10 V 0V
1000 min-1
500 min-1
torque ccw
torque cw
DIR
DIR
0..5V
0..5V
ccw
ccw
ccw
ccw
open loop yes no yes with IxR (4Q) no
current mode yes no yes yes
specially for EC(-max)16/22 EC 45, EC 60
with low R with Icont > 2A
see chapt. 4.2

11. Nested current controller
4-Q current controller
e.g. ADS, DES,
DEC 70/10
power
amplifier
set value
speed
DSP
current command
motor
set value
position
current feedback
path generator
encoder
position
decoder
position feedback

12. How to measure the feedback value?
motor
set value
system deviation
controller   + + - -
current-
feedback
sensor
actual value
incremental
encoder
IxR
DC tacho
Hall sensor
resolver
DC motor
speed controller
DC or EC motor
position controller
EC motor
speed controller

13. How to measure the feedback value?
Open loop
no feedback system
DEC, AECS for commutation only
Current control
no special feedback
Speed control
feedback devices for DC motors: Encoder, DCTacho, IxR
feedback devices for EC motors: Encoder, Hall-Sensors, sensorless commutation frequency
Position control
feedback devices: Encoder, Hall-Sensor

14. special DC speed controller: IxR
Imot
IxR compensation
Rmot . K
motor L +
set value
Umot R   + + -
EMF
motor voltage K
Umot
maxon examples:
LSC, ADS
without speed sensor, low price, few cables
feedback value: motor voltage
set value: compensation for the voltage drop over Rmot
compensation factor adjusted on controller (ideal = Rmot)
not very dynamic, not very stable (Rmot depends on temperature)

15. How to command? Signal processing?
analog signal processing
for speed and current controllers
set values from external voltages, internal or external potentiometers
very high bandwidth
problem of temperature drifts
digital commands and signal processing
more sophisticated digital speed and position controllers
commands from PC, PLC or microprocessors. A/D converted voltages
no temperature drifts
parameters set by software, can be recorded and transferred
bandwidth limited by calculation performance of DSP or microcontroller

16. Analog encoder speed control loop
speed control loop with encoder feedback
amplification (gain) depends on parameters PID
applies also to Hall Sensor feedback with EC motors (6 IMP)
current control loop
subordinate control loop, enhances system dynamics
power amplifier (MOSFET)
maxon examples:
LSC, ADS,
(AECS)
speed
amplifier (PID)
power
amplifier R
set value speed
current
command
current E  
motor + + - -
current-
feedback C
speed
feedback
encoder

17. Digital control loop motor DSP encoder maxon examples: DES, DEC,
PCU, MIP, EPOS
digital parameters (profile, position, amplification)
DSP: digital signal processor
Firmware: software of the controller
power
amplifier
set value
speed
DSP
current command
motor
current feedback
set value
position
path generator
position
decoder
position feedback
encoder
speed feedback

18. Gain, amplification: PID
amplifier (PID)
set value E
current
command
How the deviation signal E is it amplified to produce a purposeful reaction (current command)?  +
actual value
P: Proportional (a multiplication = "amplification")
Problem: very small deviation lead to small corrections only. The set value cannot be reached.
Remedy: Combination of P and I
I: Integration
A persisting deviation is summed up (integrated) and eventually corrected.
D: Differentiation
a sudden increasing deviation (e.g. a set value jump), produces a strong reaction
for dynamic reaction
overshoot, instability
system reaction PI
P only
PID
set value
Zeit

19. How much power? Amplifier limits
voltage drop over
the power stage:
5 -10%
LSC: 5V
thermal limit of the amplifier or the motor (adjustable)
max current:
different possibilities
voltage
Vcc,max
Umot,max
reserve ~20%
continuous operation
short term operation
Vcc,min
Icont
Imax
current

20. Amplifier limits - motor selection
reserve: ~20%
variations of the supply voltage
load variations
varying friction
tolerances of the components
varying ambient conditions
speed
thermal limit of the amplifier or motor
n0,max
Vcc,max
continuous operation
max. current
Umot,max
short term operation
Mcont
Icont
Mmax
Imax
torque
current

21. Power stage: linear, pulsed? Chokes?
4-Q power stage:
Linear
MOSFETs acting as valves, driven by analog voltages
Pulsed
MOSFETs acting as switches
4 power MOSFETs
motor
Vcc
UT1 M
Umot
UT2
Gnd

22. Linear power stage advantages R disadvantages M Umot, Imot LSC Vcc
time
advantages
simple, low priced controller
low electromagnetic noise level
no minimum inductance needed
disadvantages
high power losses at the final stage at high currents or low motor voltages (PV = R I2)
for small nominal power up to 100 W
controller R UT M
Umot
Gnd

23. Pulsed power stage (PWM)
advantages
low power losses
high efficiency
for higher nominal power
disadvantages
electromagnetic noise in the radio frequency range
high power losses in the motor at standstill
minimum inductance necessary
Vcc
power
stage
pulse generator M
Umot
Gnd
ADS,
DEC, AECS, DES,
MIP, PCU, EPOS
Umot, Imot
time
cycle time: ms

24. Pulsed power stage: current ripple
general measures:
reduce motor voltage
enhance total inductance
motor choke in controller
additional motor choke
enhance PWM frequency
low motor inductance
50% 50%
additional motor choke
Umot, Imot
30% 70%

25. Special features time scales in drive control
names of maxon controllers
encoder installation tips
braking
accuracy of speed control
measuring motor currents

26. Time scales in control loops
frequency kHz
mechanical time constants
"slow" position controller
position controller MIP
speed controller
current controller
speed controller as "link" between fast current controller and a slow position control (PLC)
PWM cycle time ms
cycle time

27. maxon abbreviations for controllers
others:
LSC linear servo controller
PCU position control unit
MIP mini position control
EPOS easy to use positioning
system
EPOS P easy to use positioning system Programmable
signal processing
A analog
D digital
amplifier type
C 1Q – controller (2x 2Q)
S 4Q - servocontroller
max. supply voltage
in V
AECS 35 / 3
max. continuous current
in A
motor type
D DC motor
E EC motor
commutation type
S sensorless
V improved

28. Encoder installation tips
use line driver
to enhance signal quality
with long encoder lines
mandatory for position control
use shielded cables
use twisted encoder cables
A with /A
B with /B
I with /I
separate encoder and motor lines
particularly with PWM amplifiers
look up details in FAQ

29. Braking energy in 4-Q amplifier
during braking energy flows back from motor
part of this energy can be absorbed in the amplifier, or it is fed back to the power supply: capacitance C
C "full":
supply voltage increases
damage to controller

30. Braking energy: Solutions
1st choice
reduce acceleration rate (e.g. DES)
power supply
controller
2nd choice C
add electrolyte capacitance
power supply
controller
3rd choice
add. shunt regulator C
power supply
controller R
DSR 70/
DSR 50/

31. Accuracy of speed control
What can accuracy of speed control mean ...
absolute accuracy: speed corresponds exactly to the set value, e.g rpm
repeatability: speed deviation at identical set values
linearity: 1 V set value = 1'000 rpm
10 V set value = 10'000 rpm
-1 V set value = -1'000 rpm
long time stability: today 1'000 rpm, and in a year?
drift stability: speed deviation because of temperature drifts (warm up)
short time stability: e.g. within one motor revolution (torque ripple, speed ripple)
dynamic accuracy: speed deviation after
a perturbation (load change)
changing the set values

32. Accuracy of speed control
… and most of the time, this is what the customer thinks of
static accuracy due to load changes:
static/constant speed deviation after a certain time following a load change
given as % of the whole control (speed) range
example
1% accuracy at maximum speed of 5000 rpm
at 5000 rpm: speed deviation of 50 rpm (4950 rpm; 1%) at load change from 0 to nominal torque
at 100 rpm: speed deviation of 50 rpm (50 rpm; 50%) at load change from 0 to nominal torque

33. Measuring motor currents
PWM controller acts as an electronic transformer:
input power (from power supply) = output power (to motor)
motor voltage lower than supply voltage
motor current Imot higher than supply current
power
supply A
PWM
controller A
DC motor
do not measure here
DC: measure here with a true RMS Amp-meter
EC: with an oscilloscope (blocked shaft at max. phase current)
use current monitor A
PWM
controller
EC motor