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Maxon motion control: Control loops, Controller properties  Control and feedback  Power, power stages  Communication  Features and demonstration of.

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Presentation on theme: "Maxon motion control: Control loops, Controller properties  Control and feedback  Power, power stages  Communication  Features and demonstration of."— Presentation transcript:

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

2 2, © by maxon motor ag, Jan 05 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 3, © by maxon motor ag, Jan 05 Motion control: servo system PC, PLC controller amplifier motor sensor electr. energy mech. energy energy losses current position, speed signal motion command set value load position signal servo amplifier position, speed

4 4, © by maxon motor ag, Jan 05 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

5 5, © by maxon motor ag, Jan 05 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 or EC motor position controller DC motor speed controller EC motor commutation and speed controller

6 6, © by maxon motor ag, Jan 05 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 7, © by maxon motor ag, Jan 05 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 actuator set valueoutput sensor actuator  + - set valueoutput measured value feedback actuator  + - set value output feed forward

8 8, © by maxon motor ag, Jan 05 Open-loop systems: examples  DC motor operation at fixed voltage + - U load M L nLnL actuatorset valueoutput M n MLML nLnL  another example: stepper motor with amplifier –set value: signal pulses –actuator: amplifier and motor –output: steps/increments maxon controller: LSC (U adj ), DEC (open loop) AECS (comm. only)

9 9, © by maxon motor ag, Jan 05 1Q-controller, 4Q-servocontroller quadrant I motor drive cw speed n n M quadrant III motor drive ccw quadrant II braking cw quadrant IV braking ccw torque M n M n M n M 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

10 10, © by maxon motor ag, Jan 05 DEC 50/5DECV 50/5DEC 70/10DES sensorsHall Sens.Hall Sens.Hall Sens.Encoder, HS commutationBlockBlockBlockSinusodial n-feedback withHSHSHSEncoder operation ranges2x 1Q2x 2Q"4Q" (2x 2Q)4Q torque cw torque ccw open loopyesnoyes with IxR (4Q)no current modeyesnoyesyes specially forEC(-max)16/22EC 45, EC 60 with low R with I cont > 2A see chapt. 4.2 cw ccw DIR 500 min -1 cw ccw cw ccw cw ccw DIR 1000 min V +10 V … -10 V +10 V5V … -10 V0V

11 11, © by maxon motor ag, Jan 05 Nested current controller power amplifier motor encoder position feedback current command set value speed current feedback position decoder DSP set value position path generator 4-Q current controller e.g. ADS, DES, DEC 70/10

12 12, © by maxon motor ag, Jan 05 How to measure the feedback value? DC or EC motor position controller DC motor speed controller EC motor speed controller resolver incremental encoder DC tachoIxRHall sensor actual value set value   current- feedback controller motor sensor system deviation

13 13, © by maxon motor ag, Jan 05 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 14, © by maxon motor ag, Jan 05 special DC speed controller: IxR  without speed sensor, low price, few cables  feedback value: motor voltage  set value: compensation for the voltage drop over R mot  compensation factor adjusted on controller (ideal = R mot )  not very dynamic, not very stable (R mot depends on temperature) motor voltage set value  + - K R mot. K  + + IxR compensation I mot U mot L R EMF motor maxon examples: LSC, ADS

15 15, © by maxon motor ag, Jan 05 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 16, © by maxon motor ag, Jan 05 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) power amplifier motor encoder current speed feedback current command set value speed   current- feedback speed amplifier (PID) R E C maxon examples: LSC, ADS, (AECS)

17 17, © by maxon motor ag, Jan 05 Digital control loop  digital parameters (profile, position, amplification)  DSP: digital signal processor  Firmware: software of the controller power amplifier motor encoder position feedback current command set value speed current feedback position decoder maxon examples: DES, DEC, PCU, MIP, EPOS DSP set value position speed feedback path generator

18 18, © by maxon motor ag, Jan 05 Gain, amplification: PID  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 actual value current command set value  amplifier (PID) + E How the deviation signal E is it amplified to produce a purposeful reaction (current command)? set value Zeit system reaction PI PID P only

19 19, © by maxon motor ag, Jan 05 How much power? Amplifier limits current voltage V cc,max V cc,min U mot,max I cont I max continuous operation short term operation reserve ~20% voltage drop over the power stage: 5 -10% LSC: 5V thermal limit of the amplifier or the motor (adjustable) max current: different possibilities

20 20, © by maxon motor ag, Jan 05 Amplifier limits - motor selection torque current speed V cc,max M cont I cont M max I max reserve: ~20% variations of the supply voltage load variations varying friction tolerances of the components varying ambient conditions U mot,max n 0,max continuous operation short term operation max. current thermal limit of the amplifier or motor

21 21, © by maxon motor ag, Jan 05 Power stage: linear, pulsed? Chokes?  4-Q power stage:  Linear –MOSFETs acting as valves, driven by analog voltages  Pulsed –MOSFETs acting as switches Gnd 4 power MOSFETsmotor M U T1 U T2 U mot V cc

22 22, © by maxon motor ag, Jan 05 Linear power stage 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 (P V = R I 2 ) –for small nominal power up to 100 W M R controller UTUT V cc Gnd LSC U mot time U mot, I mot

23 23, © by maxon motor ag, Jan 05 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 M power stage U mot V cc Gnd pulse generator ADS, DEC, AECS, DES, MIP, PCU, EPOS time cycle time:  s U mot, I mot

24 24, © by maxon motor ag, Jan 05 Pulsed power stage: current ripple general measures:  reduce motor voltage  enhance total inductance - motor choke in controller - additional motor choke  enhance PWM frequency 50% 30% 70% low motor inductance additional motor choke U mot, I mot

25 25, © by maxon motor ag, Jan 05 Special features  time scales in drive control  names of maxon controllers  encoder installation tips  braking  accuracy of speed control  measuring motor currents

26 26, © by maxon motor ag, Jan 05 Time scales in control loops ms PWM cycle time "slow" position controller position controller MIP current controller mechanical time constants speed controller speed controller as "link" between fast current controller and a slow position control (PLC) frequency kHz cycle time

27 27, © by maxon motor ag, Jan 05 maxon abbreviations for controllers max. supply voltage in V signal processing Aanalog Ddigital motor type DDC motor EEC motor 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 commutation type Ssensorless Vimproved amplifier type C1Q – controller (2x 2Q) S4Q - servocontroller AECS353/ max. continuous current in A

28 28, © by maxon motor ag, Jan 05 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 29, © by maxon motor ag, Jan 05 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 30, © by maxon motor ag, Jan 05 Braking energy: Solutions power supply C R 1 st choice 2 nd choice 3 rd choice C reduce acceleration rate (e.g. DES) add electrolyte capacitance add. shunt regulator controller DSR 70/ DSR 50/

31 31, © by maxon motor ag, Jan 05 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 32, © by maxon motor ag, Jan 05 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 33, © by maxon motor ag, Jan 05 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 I mot higher than supply current power supply do not measure here DC: measure here with a true RMS Amp-meter PWM controller DC motor AA PWM controller EC: with an oscilloscope (blocked shaft at max. phase current) use current monitor EC motor A


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