Transcript Folie 1 - Electromate Industrial Sales

maxon motion control:
Control loops,
Controller properties
 Control and feedback
 Power, power stages
 Communication
 Features and demonstration of a positioning system
maxon motor control
 What to control: position, speed, current (torque)?
 Which commutation type: DC, EC, block, sensorless,
 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
2, © by maxon motor ag, Jan 05
sinusoidal?
Motion control: servo system
electr. energy
set value
motion
command
controller
amplifier
current
servo amplifier
position
signal
speed
signal
energy
losses
motor
sensor
position,
speed
position,
speed
load
mech. energy
3, © by maxon motor ag, Jan 05
PC,
PLC
What to control ?
 Current control = torque 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"
 Position control
– moving from position to position, stop at and maintain a position
– maxon controllers: EPOS, EPOS P, and MIP
4, © by maxon motor ag, Jan 05
– all maxon controllers can act as speed controllers
Motor type? Commutation?
DC motor
speed controller
EC motor
commutation and
speed controller
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
DC or EC motor
position controller
Position control
 MIP (DC or EC, 50-500 W), block commutation
 EPOS (DC or EC, 20-700 W), sinusoidal commutation
 EPOS P (DC or EC, 120W), Sinusoidal commutation
5, © by maxon motor ag, Jan 05
 DES (250 W, 700W), sinusoidal commutation
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?
 Encoder (resolution, channels, line driver)
6, © by maxon motor ag, Jan 05
 Hall sensors
How to control: open vs. closed loop?
 open loop
set value
– no feedback
– output is not measured
and checked
actuator
set value
– feedback loop
– output value is measured
and the set value is
adjusted , accordingly
– system behaviour is
anticipated
+
output

actuator
-
feedback
sensor
feed
forward
set value +
output

-
measured
value
actuator
7, © by maxon motor ag, Jan 05
 closed loop
 "Feed forward"
output
Open-loop systems: examples
maxon controller:
LSC (Uadj),
DEC (open loop)
AECS (comm. only)
 DC motor operation at fixed voltage
+
nL
nL
-
set value
actuator
output
ML
 another example: stepper motor with amplifier
– set value: signal pulses
– actuator: amplifier and motor
– output: steps/increments
M
8, © by maxon motor ag, Jan 05
U
n
load ML
1Q-controller, 4Q-servocontroller
speed n
quadrant II
braking cw
quadrant I
motor drive cw
n
n
M
M
1-Q
 only motor operation (quadrant I
or quadrant III)
 direction reverse by digital signal
 braking is not controlled
(friction), often slow
M
n
quadrant III
motor drive ccw
4-Q
 controlled motor operation and
M
n
quadrant IV
braking ccw
braking in both rotation
directions
 mandatory for positioning
9, © by maxon motor ag, Jan 05
torque M
DECV 50/5 DEC 70/10 DES
Hall Sens.
Block
HS
2x 1Q
Hall Sens.
Block
HS
2x 2Q
torque ccw
0..5V
500
cw
cw
cw
0..5V
1000
min-1
min-1
+10 V
+10 V 5V
…
…
-10 V
-10 V
DIR
DIR
0..5V
0..5V
ccw
open loop
current mode
specially for
Encoder, HS
Sinusodial
Encoder
4Q
torque cw
cw
Hall Sens.
Block
HS
"4Q" (2x 2Q)
yes
yes
ccw
no
no
EC(-max)16/22
with low R
ccw
0V
ccw
yes with IxR (4Q) no
yes
yes
EC 45, EC 60
with Icont > 2A
see chapt. 4.2
10, © by maxon motor ag, Jan 05
sensors
commutation
n-feedback with
operation ranges
DEC 50/5
Nested current controller
4-Q current controller
e.g. ADS, DES,
DEC 70/10
power
amplifier
DSP
current
command
set value
position
motor
current feedback
path
generator
position
decoder
position feedback
encoder
11, © by maxon motor ag, Jan 05
set value
speed
How to measure the feedback value?
+

system
controller

deviation
+
-
motor
currentfeedback
actual value
IxR
incremental
DC tacho
encoder
DC motor
speed controller
sensor
Hall sensor
DC or EC motor
position controller
resolver
EC motor
speed controller
12, © by maxon motor ag, Jan 05
set
value
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 EC motors: Encoder, Hall-Sensors, sensorless
commutation frequency
 Position control
– feedback devices: Encoder, Hall-Sensor
13, © by maxon motor ag, Jan 05
– feedback devices for DC motors: Encoder, DCTacho, IxR
special DC speed controller: IxR
IxR compensation
motor
Umot  Uind  UR
+
+
Umot

R
motor
voltage





L
Umot 
n
 R mot  Imot
kn
EMF
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)
14, © by maxon motor ag, Jan 05
set

value +
Rmot . K
Imot
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
– no temperature drifts
– parameters set by software, can be recorded and transferred
– bandwidth limited by calculation performance of DSP or microcontroller
15, © by maxon motor ag, Jan 05
– commands from PC, PLC or microprocessors. A/D converted voltages
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)
speed
amplifier (PID)
R
+
E

C
speed
feedback
current
command +
power
amplifier
current

-
motor
currentfeedback
encoder
16, © by maxon motor ag, Jan 05
set value
speed
maxon examples:
LSC, ADS,
(AECS)
Digital control loop
 digital parameters (profile, position, amplification)
 DSP: digital signal processor
 Firmware: software of the controller
power
amplifier
DSP
current
command
motor
current feedback
set value
position
position
decoder
position feedback
speed feedback
encoder
17, © by maxon motor ag, Jan 05
set value
speed
path
generator
maxon examples:
DES, DEC,
PCU, MIP, EPOS
Gain, amplification: PID
amplifier (PID)
set value
+

E
current
command
actual value
 P: Proportional (a multiplication = "amplification")
system reaction
– Problem: very small deviation lead to small corrections
only. The set value cannot be reached.
– Remedy: Combination of P and I
PI
 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
P only
PID
set value
Zeit
18, © by maxon motor ag, Jan 05
How the deviation signal E is it
amplified to produce a purposeful
reaction (current command)?
How much power? Amplifier limits
Vcc,max
thermal limit of the
amplifier or the
motor (adjustable)
Umot,max
Vcc,min
max current:
different
possibilities
reserve
~20%
continuous
operation
short term
operation
Icont
Imax
current
19, © by maxon motor ag, Jan 05
voltage
voltage drop over
the power stage:
• 5 -10%
• LSC: 5V
Amplifier limits - motor selection
reserve: ~20%
n0,max
Vcc,max
• variations of the
supply voltage
• load variations
• varying friction
• tolerances of the
components
• varying ambient
conditions
thermal limit of
the amplifier or
motor
continuous
operation
max. current
Umot,max
short term
operation
Mcont
Icont
Mmax
Imax
torque
current
20, © by maxon motor ag, Jan 05
speed
Power stage: linear, pulsed? Chokes?
 4-Q power stage:
4 power MOSFETs
Vcc
motor
UT1
Umot
Gnd
M
UT2
– MOSFETs acting as valves, driven by analog voltages
 Pulsed
– MOSFETs acting as switches
21, © by maxon motor ag, Jan 05
 Linear
Linear power stage
LSC
Umot, Imot
Vcc
time
advantages
controller
R
UT
– simple, low priced controller
– low electromagnetic noise level
– no minimum inductance needed
M
Gnd
Umot
– 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
22, © by maxon motor ag, Jan 05
disadvantages
Pulsed power stage (PWM)
– low power losses
Vcc
– high efficiency
pulse
generator
– for higher nominal power
disadvantages
– electromagnetic noise in
the radio frequency
range
Gnd
Umot, Imot
Umot
power
stage
ADS,
DEC, AECS, DES,
MIP, PCU, EPOS
– high power losses in the
motor at standstill
– minimum inductance
necessary
M
time
cycle time: 20 - 50 ms
23, © by maxon motor ag, Jan 05
advantages
Pulsed power stage: current ripple
2  fS  (Lmot  Lchoke )
50% 50%
low motor inductance
additional motor choke
Umot, Imot
30% 70%
24, © by maxon motor ag, Jan 05
Imax 
Vcc
general measures:
 reduce motor voltage
 enhance total inductance
- motor choke in controller
- additional motor choke
 enhance PWM frequency
Special features
25, © by maxon motor ag, Jan 05
 time scales in drive control
 names of maxon controllers
 encoder installation tips
 braking
 accuracy of speed control
 measuring motor currents
Time scales in control loops
frequency kHz
50
20
10
5
2
1
0.5
0.2
0.1
0.05
mechanical time constants
"slow" position controller
speed controller
speed controller as "link" between
fast current controller and a slow
position control (PLC)
current
controller
PWM cycle time
0.02
0.05
0.1
0.2
0.5
1
2
5
10
20 ms
cycle time
26, © by maxon motor ag, Jan 05
position controller MIP
maxon abbreviations for controllers
others:
signal processing
A analog
D digital
amplifier type
C
S
1Q – controller (2x 2Q)
4Q - servocontroller
max. supply voltage
in V
LSC
linear servo controller
PCU
MIP
EPOS
position control unit
mini position control
easy to use positioning
system
EPOS P easy to use positioning
system Programmable
max. continuous current
in A
motor type
D DC motor
E EC motor
commutation type
S sensorless
V improved
27, © by maxon motor ag, Jan 05
AECS 35 / 3
Encoder installation tips
 use line driver
– to enhance signal quality
– with long encoder lines
– mandatory for position control
– A with /A
– B with /B
– I with /I
 separate encoder and motor lines
– particularly with PWM amplifiers
 look up details in FAQ
28, © by maxon motor ag, Jan 05
 use shielded cables
 use twisted encoder cables
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
I1
C
Udc
D1
I2
L
D2
S2
E
R
U0
S3
C "full":
 supply voltage increases
 damage to controller
D3
S4
D4
29, © by maxon motor ag, Jan 05
S1
Braking energy: Solutions
1st choice
reduce acceleration
rate (e.g. DES)
power supply
power supply
C
2nd choice
add electrolyte
capacitance
controller
controller
power supply
C
R
add. shunt
regulator
DSR 70/30 235811
DSR 50/5 309687
controller
30, © by maxon motor ag, Jan 05
3rd choice
Accuracy of speed control
– absolute accuracy: speed corresponds exactly to the set value, e.g.
1000 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
31, © by maxon motor ag, Jan 05
What can accuracy of speed control mean ...
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
– 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
32, © by maxon motor ag, Jan 05
example
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
PWM
controller
do not
measure here
PWM
controller
A
EC motor
A
DC motor
DC: measure here with
a true RMS Amp-meter
EC: with an oscilloscope
(blocked shaft at max.
phase current)
use current monitor
33, © by maxon motor ag, Jan 05
A
power
supply