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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 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 L choke ) 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