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maxon motion control: Control loops, Controller properties. Control and feedback Power, power stages Communication Features and demonstration of a positioning system. What to control: position, speed, current (torque)? Which commutation type: DC, EC, block, sensorless, sinusoidal?

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Maxon motion control control loops controller properties

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, 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

maxon motor control


Motion control servo system
Motion control: servo system

electr. energy

PC,

PLC

motion

command

set value

controller

amplifier

energy

losses

current

servo amplifier

position

signal

speed

signal

motor

position,

speed

sensor

load

position,

speed

mech. energy


What to control
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"

    • 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


Motor type commutation
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, 50-500 W), block commutation

  • EPOS (DC or EC, 20-700 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


Which motor type 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?

      • Hall sensors

      • Encoder (resolution, channels, line driver)


How to control open vs closed loop

actuator

actuator

actuator

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

output

set value

output

+

-

measured

value

feedback

sensor

feed forward

output

set value

+

-


Open loop systems examples
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


1q controller 4q servocontroller
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


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 cw

torque ccw

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


Nested current controller
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


How to measure the feedback value
How to measure the feedback value?

motor

controller

set value

system deviation

+

+

-

-

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


How to measure the feedback value1
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


Special dc speed controller ixr
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)


How to command signal processing
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


Analog encoder speed control loop
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

current

command

E

motor

+

+

-

-

current-

feedback

C

speed

feedback

encoder


Digital control loop
Digital control loop

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


Gain amplification pid
Gain, amplification: PID

amplifier (PID)

set value

E

current

command

  • 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

How the deviation signal E is it amplified to produce a purposeful reaction (current command)?

+

actual value

system reaction

PI

P only

PID

set value

Zeit


How much power amplifier limits
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


Amplifier limits motor selection
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


Power stage linear pulsed chokes

M

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

Umot

UT2

Gnd


Linear power stage

M

controller

Linear power stage

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

R

UT

Umot

Gnd


Pulsed power stage pwm

pulse generator

M

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

Umot

Gnd

ADS,

DEC, AECS, DES,

MIP, PCU, EPOS

Umot, Imot

time

cycle time: 20 - 50 ms


Pulsed power stage current ripple
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%

Umot, Imot

additional motor choke

30% 70%


Special features
Special features

  • 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
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

position controller MIP

speed controller

current controller

speed controller as "link" between fast current controller and a slow position control (PLC)

PWM cycle time

0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 ms

cycle time


Maxon abbreviations for controllers
maxon abbreviations for controllers

others:

LSClinear servo controller

PCUposition control unit

MIP mini position control

EPOSeasy 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


Encoder installation tips
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


Braking energy in 4 q amplifier
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


Braking energy solutions
Braking energy: Solutions

1st choice

reduce acceleration rate (e.g. DES)

power supply

controller

2nd choice

add electrolyte capacitance

C

power supply

controller

3rd choice

add. shunt regulator

C

power supply

controller

R

DSR 70/30 235811

DSR 50/5 309687


Accuracy of speed control
Accuracy of speed control

What can accuracy of speed control mean ...

  • 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


Accuracy of speed control1
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


Measuring motor currents
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


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