Brushless AC Motor Commutation
Contents
1. AN1004 Brushless AC Motor Commutation Sinusoidal AC Brushless Servo Amplifier AC Brushless Motor W Ref optional e e Phase U V Ref DAC 2 e Phase V U Ref DAC 1 e D Phase W Ref O D Case Gnd D D Amp Enabl Wees rnn m nable e H E D HER Amp Fault gt RETUR z Motor Tem as R Gnd D OAR Pes CO z PO O m s IE gt gt Hall Sensors Encoder Hall Tracks optional Encoder signals A B amp Z Uo UO o o UX GE NES IE DCX MC320 H ls 7 28 EE lt lt OLIO H m E x Figure 6 Typical system interconnect diagram Precision MicroControl Corp AN1004 Brushless AC Motor Commutation System Requirements The following components are required to provide sinusoidal commutation for one or more axes PC computer Platform for the user s application program and PMC software tools Motion Control Application Programming Interface MCAPI PMC s motion control software and programming tools for WIndows NT 98 95 Motion Integrator PMC s system integration diagnostics and servo tuning suite of tools DCX AT300 PMC motion control motherboard supports 1 to 6 axes DCX MC320 Sine commutation servo control module 1 per axis DCX BF320 optional Interconnect breakout 1 per axis Sinusoidal Brushless Amplifier 1 per axis A partial listing of suppliers includes e Advanced Motion Control www a m c com Copley Controls w2. resume its rotation Now change the maximum voltage to 0 25V 19Q 0 25 set a low maximum voltage The motor should change direction Verify constant torque and no cogging or sticking Precision MicroControl Corp 16 AN1004 Brushless AC Motor Commutation DCX MC320 Commutation Circuit Block Diagram Encoder Cycle Counter Encoder Repeat Count Register Encoder Clear Pulse Input see Encoder Divider g Encoder Constant Register Counts Encoder Encoder Prescaler Divider Sine Lookup Table Commutation Value 0 4095 Torque Command 0 4095 Phase Shift Register A Phase Shift Adder Register B Commutation Angle 0 65535 Add Phase Shift to Commutation Angle mm gt Clock ial DAC Phase U gt Load 416 bit State Machine 300 KHz Clock Phase V gt Clockeerial DAC Load 16 bit Figure 10 Commutation circuit block diagram Precision MicroControl Corp 17 AN1004 Initialize the commutation and start closed loop motion An incremental encoder is a volatile device if the system is powered down all position data is lost Each time the system is powered up the motor commutation must be initialized The three steps required to initialize the commutation are 1 Bump the motor to a detent 2 Define th
3. are in degrees of the sine commutation table and like the commutation wave forms shown in figures 2 and 8 the parameters of the LA and LB commands must always be 120 degrees apart When parameter n of the LA and LB commands is set to specific angles of the sine table the phase U and V outputs of the MC320 will be set to the sine ratio of the current maximum voltage setting aSQn The phase U and V command outputs from the DCX MC320 can range from 10 volts to 10 volts The resolution of these signals is 16 bit e The Set torQue aSQn command is used to scale the command output voltage range that is applied to the amplifier The default setting for the maximum command voltage is 10 volts aSQ70 For example if LA parameter n 90 1LA90 LB parameter n 30 1LB 30 Maximum voltage is 2 0 volts 1SQ2 0 Enable the amplifier 1MN When running open loop to test the motor and amplifier the voltage outputs to phases U and V will be Output Tqmax sin 0 Offset where Tqmax SQ parameter n maximum voltage 0 0 Offset parameter n of aLAn or aLBn Output U Tqmax sin 0 Offset A E Output U 2 sin 0 90 Output U 2 1 Output U 2 0 volts 90 Output V Tqmax sin 0 Offset B Output V 2 sin 0 30 Output V 2 0 5 Output V 1 0 volts Output Voltage Phase U Figure 8 Example commutation angle output voltage Precision MicroControl Corp 10 AN1004 Brushless AC Motor Co
4. prescaler divisor is 4 LE parameter n 64 the resulting value for parameter n of the LD command would be n 16 777 216 ECCC EPRE n 16 777 216 10 000 4 n 1 677 7216 2500 n 6710 8864 n 6711 rounded A prescaler divisor of 1 2 4 and 8 prescale command LE parameter n of 256 128 64 or 32 will yield an acceptable value for the commutation divisor constant LD parameter n Encoder prescale Divisor of 1 LD parameter n 1678 rounded Encoder prescale Divisor of 2 LD parameter n 3355 rounded Encoder prescale Divisor of 4 LD parameter n 6711 rounded Encoder prescale Divisor of 4 LD parameter n 13422 rounded To determine which prescale divisor will yield the most accurate sine commutation table complete the following calculations LD VECCC 16 777 216 _ 16 777 216 PREIS Precision MicroControl Corp 14 AN1004 Brushless AC Motor Commutation where LD commutation divisor parameter n VECC Virtual Encoder Counts per Commutation Cycle ECCC EPRE DTER Divisor Truncation Error Ratio The encoder prescale value that results in the lowest Divisor Truncation Error Ratio DTER will provide the most accurate sine commutation For this example an encoder prescale parameter n of 64 divisor of 4 has the lowest error ratio 0 0000169 95 To define the encoder prescaler and commutation divisor constant issue the following commands 1LE64 Encoder prescaler 64 divide by 4 1LD6711 E
5. Brushless AC Motor Commutation Sinusoidal Commutation with a PC based Motion Controller Application Note AN1004 e gt PM PMC Motion cun Control For Robotics amp Machine Automation Precision mene Corporation N Corte del Nogal Nd CA 92009 1415 USA Tel 760 930 0101 Fax 760 930 0222 Information info pmccorp com Technical Support support pmccorp com AN1004 Brushless AC Motor Commutation Table of Contents aA Agios 3 Sine Commutation e Ee 4 PNIC s Sine COMMUTATION SOIMON si rali oorr opua etre at egene pus s ege 6 System ISOdUIF CHO EE 8 Defining the commutation parameters annanonnannannnnennensnrnnonrrrrrennrerrnrnrrnrrnrnrrrernrnrrnrrnrrrrnrnrrnrrnreerne 13 Initialize the commutation and start closed loop moon 18 E a EE 20 List of Figures Figure 1 Simple Drushless MOTOT E 4 Figure 2 Sine Commutation wa vetormms seen nne nnn nensi sre ssa reis s ar rn asserens 5 Figure 3 DCX AT300 motion Control Motherboard nennen 6 Figure 4 DCX MC320 sine commutation servo control module s sannnnnanannnnnennennnnnnnnnnnnrernnnrnnnne 6 Figure 5 DCX BF320 interconnect Card 6 Figure 6 Typical system interconnect diagram sssesssssssessesseeneenee nennen nnn nnns T Figure 7 WinControl MCCL command user miertace 9 Figure 8 Example commutation angle output voltage eese 10 Figure 9 Linear motor CAG MANN PNE TT 12 Figure 10 Com
6. Control Corp 18 AN1004 r rr s Lc Servo Tuning File Setup Test Help MEN Moto O n Off Trajectory Generator CO Sn Of Test step Plus step Minus Clear fero yj 100 100 Actual 025 50 50 0 05 e HDD 0 D0 Figure 11 Servo Tuning program e Set the trajectory parameters For any move the user must specify the Maximum Velocity Acceleration Deceleration Velocity Profile S curve Parabolic or Trapezoidal For additional information please refer to the DCX AT300 Installation and User s Manual Future DCX AT300 firmware revisions will include auto commutation of the motor during the first move after a power cycle or reset Precision MicroControl Corp 19 AN1004 Index A Auto initialize sine COMMUTATION cccccecececcecececcceceaeeceneaes 19 Axis UO amplifier enable aann0annannnannnnnnannnnnnnnnnnrnnnnnnna 8 amplifier TAM sneen 8 GOGISS DOI IQ s ar aite va bui doe rc cub deris 8 over travel limits enn 8 B Eicher e EEN 6 Brush motor NEA EE 3 Brushless motor SH LEE EEN E alle EE 4 TIRR TES A LEE 4 C Commands issuing NV UA eler tel HE 9 D BCX ATSO SE 6 LI 2 Os A ie ate hea a pee EMEN ION 6 DGKEMG B20 NT 6 Detent CIG IL CG oon tonos uct te P UOCE oe M IPM E DOE 11 E ENCOQOT COS besa ioi a EL EMT de Mis cU 12 F Following error wl e 219 BETTE COCHE
7. E ruri ueri 8 Motion Integrator esses 8 VV GCOMMO lite oes RTT 9 Precision MicroControl Corp T Testing inge emere 9 CIC OGG T RE EE 12 MOO cr 9 Testing COMMUTATION sseeeeeseeessee 15 Torque lelei E 4 Trapezoidal amplifiers 4 Troubleshooting direction of rotation seeeeseseeessssse 12 encoder phasing eese 12 W Wiring example dtes a ocho c Genta ope xR E dap RM ERA T 21
8. NER 16 H Hall commutated brushless motor 4 Hall effect sensor cccccccecececececcecececececeueaeanerees 4 Precision MicroControl Corp I Issuing commands NEEN anan 9 L LD encoder divisor constant 13 LE encoder prescale constant 13 Linear motor SIE ele ine 13 LR commutation encoder repeat count 15 M Motion Controller Ee trout ben ih Rive gos vu UE 6 DOGA BF 20 EE 6 DCA MC 320 sistit E 6 O Output voltage setting open Joop 10 Output voltage range eseeeeeeeeseee 10 Tlagili aTo eee UTEM 10 Over travel limits Wl a m 16 P Programming C DIMCCIMGCK Japra diss coque te dave ap 9 jet a 9 S Servo TUNING essi eom poc UE Sca rupi DEED Ru EE 18 oine commutation DIOCK GA GLA N iia 17 Sine Commutation AC EH Ee G 8 amplifiers AMC 8 amplifiers Copley Controls 8 amplifiers Eimo 8 20 AN1004 amplifiers Glentek 8 amplifiers Servo Dynamics 8 auto ID allZG s zs dise bteep oui Ms E a CE bec nas 19 encoder counts per commutation cycle 13 TRY FETA ERR be e 18 rte eR 8 parameter calculation 13 14 required parameters o nnnnnennannannennennennnenennni 13 Sinusoidal Commutation BASICS aon a Ee 4 Waveform EE 4 Software Motion Control APT iiiacc o niet tr R
9. aper and the brushless motor amplifier industry took it to heart Now the servo engineer could reap the benefits of brushless motors without obliterating project budgets What they got with the new breed of DC brushless motors was Higher performance Low rotor inertia results in higher velocity and acceleration High reliability and low maintenance no brushes to wear out Superior heat dissipation coils are mounted in a heat sink stator Reduced EMI emissions No brush to commutator arcing High power to size ratio Precision MicroControl Corp 3 AN1004 Brushless AC Motor Commutation As reliability improved and costs continued to decrease the industry focused its attention on the remaining problems with brushless motors Torque ripple 6 step hall sensor commutation with DC brushless amplifiers also Known as Trapezoidal amplifiers or hall commutated causes significant torque ripple the static torque will vary based on the motor shaft position Hall effect sensors Add to the cost of the motor Alignment tolerances and hysteresis required to reduce signal bounce oscillation reduces commutation efficiency To commutate a motor without Hall effect sensors an encoder with hall tracks must be used which again increases the motor system cost Coupling torque ripple with the deficiencies of Hall effect sensors the performance static and continuous torque of a typical DC brushless motor is reduced by 15 to 20 To address
10. e commutation parameters 3 Offset the angle of U and V by 90 degrees 1 The motor is bumped to a detent using the same command sequence as the Detent and Commutation tests 1SQ0 set maximum output voltage to 0 0v 10M configure axis for Torque mode run open loop no PID 1MN enable motion 1LAO 1LB 120 WA 5 1S01 1WA1 1S00 1MF set output U 0 0V V 0 866V wait 1 second set outputs to 0 0V disable motion You can use values other than LAO and LB 120 The only requirements e are that e LA parameter n is a positive value between 0 and 360 e LB parameter n LA parameter n 120 degrees 2 Define the commutation parameters 1RT l1LE64 1LD6711 1LR2500 reset the axis define the encoder divisor divisor constant and repeat count 3 Offset the angle of U and V by 90 degrees 1LA 90 1LB 210 1MN retard the commutation phasing by 90 degrees enable motion The DCX MC320 is now ready to commutate the motor Prior to executing any Position or Velocity mode moves the user must first e Tune the servo Set the PID Proportional gain Derivative Gain and the Integral gain parameters using PMC s Servo Tuning program This utility is installed as a component of the Motion Integrator suite of tools To download Motion Integrator go to the Support page of PMC s web site www pmccorp com For additional information on servo tuning please refer to the DCX AT300 Installation and User s Manual Precision Micro
11. elp Bro ce gt 1L490 1L6 30 gt ie om LI e Open Command File Look in MO320Commutation Fimma fe ANT1004 dac E Initcamm dcx 3 WRLOOO2 tmp CalLinear1 tat bak LA LE Outputs vs fe AN1004 doc S CommlnitPrac1 tst MC320Commutatic EJ AT 300layout ved CommutationCycle wsd MC320Commutatic BF320layout ved Sie DicxatSbrd2 bmp M25 ye wWinng s File name Open Files of type A Files Cancel ZA Figure 7 WinControl MCCL command user interface The current release of PMC s Motion Control API does yet not provide high level function calls for the commutation parameters The following descriptions use PMC s MCCL Motion Control Command Language commands This two character mnemonic command set provides fields for defining axis numbers and parameter values MCCL commands can be issued directly to the DCX AT300 via the Windows command interface program Win Control or entered into a text file and downloaded to the DCX AT300 controller as a part of the initialization file To issue these parameter settings from a high level program via PMC s Motion Control API use the function pmccmdex This low level function supports issuing any MCCL command via the Motion Control API For additional information please refer to the Motion Control API on line help file Mcapi hlp Precision MicroControl Corp AN1004 Brushless AC Motor Commutation The units for parameter n of the LA and LB commands
12. ides the OEM machine builder with a powerful and flexible control system for brushless AC servo applications This system combines a RISC processor based motion control motherboard DCX AT300 zeo LIS soe 7 Figure 3 DCX AT300 motion control motherboard with one or more 40 MHz TI 32054 DSP Dual DAC DCX MC320 motion control modules Figure 4 DCX MC320 sine commutation servo control module Each DCX MC320 Sine Commutation module provides both U and V phase outputs for controlling the motion of one brushless AC servo As many as six DCX MC320 s can be installed on a single DCX AT300 motion control motherboard allowing the user to simultaneously control six axes The DCX MC320 uses a high density FPGA to implement a high speed hardware sine lookup table A hardware sine commutation table results in the phase U and V DAC outputs being updated at a frequency of 300KHz This is a significant improvement over traditional software based sine commutation which is limited to the frequency of the servo loop typically 2KHz to 20 KHz To simply system wiring an optional DIN rail mounted interconnect card DCX BF320 is available J1 DCX BF320 REV A EV PMC CORP Figure 5 DCX BF320 interconnect card A typical single axis system interconnect diagram is shown on the next page Precision MicroControl Corp 6
13. mmutation Setting the MC320 phase U and V outputs to non zero values with the aLAn and aLBn commands should cause the amplifier to apply current to the motor windings causing the motor to move a detent position A detent is one of the many locations where a motor magnet and the C motor coils are aligned For this example the maximum voltage output was set to 2 0 volts For some motor amplifier combinations this may be more than enough for others the maximum command voltage may need to be as high as 10 volts Start with a SQ setting of 1 volt a8Q1 if the motor moves and then resists attempts at manual repositioning before the Wait two seconds command times out then there is no need to apply a higher voltage to the coils If when manual force is applied the motor does not return to its position the maximum output voltage SQ parameter n should be increased Don t get in a hurry and set the maximum voltage too high Besides possibly ripping your fingers off applying high current to the coils for an extended period of time may cause damage to the motor After the motor moves set the outputs to 0 0 volts by issuing the Set torQue command with parameter n O 1500 If the motor doesn t move the possible reasons include Amplifier not enabled Amplifier Fault under voltage over voltage over temperature over current etc Improper connections Detent Test The can be used to verify proper connections and operation of
14. mutation circuit block diagram cc cece eccs eee eeeceeceeeseeceeeceeceeeseeeeeeseeeseeseeeseeeeeeaeeeaes 17 Figure 11 Servo TUNING Progra ee ttt et enn ie aetna en ee eh 19 Precision MicroControl Corp 2 AN1004 Brushless AC Motor Commutation Brushless AC Motor Commutation Sinusoidal Commutation with a PC based Motion Controller First a little history For years the brush type permanent magnet motor has been successfully used in a wide range of motion control applications Relatively low cost and easy to manufacture brush type motors still account for the majority of servo motor sales worldwide But the brush motor does have it limitations High inertia to torque ratio reduces maximum velocity and acceleration High maintenance Limited ability to dissipate heat causes bearing failure resulting in motor failure Arcing of brushes causes electrical and audible noise Fueled by technology advancements in the aerospace and defense industries in the 70 s and 80 s two milestone events paved the way for acceptance of brushless motors for industrial applications The development of high energy rare earth magnets which reduced motor size weight and significantly increased motor velocities Power MOSFET s and later IGBT s allowed brushless motor amplifiers to overcome switching latency and heat buildup to reliably drive motors using a wide range of supply voltages In the early to mid 1990 s the mantra was smaller faster che
15. ncoder divisor constant 6711 Define the encoder repeat count The Load commutation encoder Repeat count aLRn command is used to define the number of encoder counts after prescaling per commutation cycle At the end of each commutation cycle the commutation position register is reset to zero This prevents the accumulation of error that may be caused by the truncation of the encoder divisor constant aLDn The linear motor example has 10 000 encoder counts per commutation cycle Parameter n of the encoder repeat count is calculated by ERC ECCC EPRE where ERC Encoder Repeat Count ECCC Encoder Counts per Commutation Cycle EPRE Encoder Prescaler ERC 10 000 4 ERC 2 500 1LR2500 Define the encoder repeat count Testing the commutation After defining the commutation parameters aLEn aLDn aLRn your can verify that the MC320 is properly commutating the motor The first step is to move the motor to the detent position in the Detent Test 1SQ0 set maximum output voltage to 0 0V 10M configure axis for Torque mode run open loop no PID 1MN enable motion 1LAO 1LB 120 WA 5 1S01 1WA1 1SQ00 1MF Set output U 0 0V V 0 866V wait 1 second set outputs to 0 0V disable motion The next step is to define the commutation parameters 1RT l1LE64 1LD6711 1LR2500 reset the axis define the encoder divisor divisor constant and repeat count Precision MicroControl Corp 15 AN1004 Brushless AC Mo
16. r commutation cycle is the number of encoder counts per rotation divided by three For a rotary motor with 6 000 counts per rotation the number of counts per commutation cycle is encoder counts per rotation 3 counts per commutation cycle 6 000 3 2 000 The MCCL commands Load commutation Encoder prescale constant aLEn and Load commutation encoder Divisor constant aLDn can now be calculated for the axis These commands define two of the three commutation sine table parameters Parameter n of the Load commutation encoder Divisor constant aLDn command is calculated as n 16 777 216 ECCC EPRE Precision MicroControl Corp 13 AN1004 Brushless AC Motor Commutation where ECCC Encoder Counts per Commutation Cycle EPRE Encoder Prescaler The allowable range for this value is an integer between 0 and 16 000 Using the linear motor example with 10 000 encoder counts per commutation cycle if the encoder prescale divisor is set to one the resulting commutation divisor constant aLDn parameter n would be 16 777 216 ECCC EPRE 16 777 216 10 000 1 16 777 216 10 000 1 677 7216 1 677 rounded 3 332335 H Hn gu wg ou This resulting value is within the allowable range 0 to 16 000 for the LD command The encoder prescaler command LE is used to scale parameter n of the LD command The following table lists the available prescaler values for parameter n of the LE command Parameter n Divisor If the
17. re is no reference made to the voltage level of phases U V and W The velocity of a brushless AC motor is controlled by the amplitude peak to peak voltage level of the sine output The greater the amplitude of the sine waves the more current flows through the coils the greater the torque velocity of the motor The phase relationship of the sine signals does not change with velocity In the past intelligent digital drives were required to provide the sine commutation These digital drives coupled sophisticated digital electronics for sine commutation and feedback loops with high power PWM amplifier circuitry The resulting system performance was impressive but for many OEM applications the cost per axis was prohibitive Over the last few years as Digital Signal Processors DSP have revolutionized the architecture and capabilities of PC based motion control cards a cost effective solution for sine commutation of brushless motors has emerged This solution has three main benefits e The PC provides the platform for developing sophisticated user interfaces e Low cost Sinusoidal three phase current mode amplifiers provide the PWM drive current e Powerful PC based motion control cards tightly integrate trajectory planning feedback loops and sine commutation control signals Precision MicroControl Corp 5 AN1004 Brushless AC Motor Commutation PMC s Sine Commutation Solution PMC s DCX AT300 Modular Motion Control System prov
18. st the user finds that the motor moves to the left and the encoder is incrementing the user must 1 Swap the A and B A and B amp A and B signals from the encoder to the DCX MC320 and 2 Swap the U and V outputs signals from the MC320 to the amplifier Defining the commutation parameters To configure the DCX MC320 for sine commutation the following parameters must be defined Encoder counts per commutation cycle The encoder repeat count Please refer to Figure 10 for a block diagram of the DCX MC320 sine commutation logic Defining the encoder counts per commutation cycle The first step in setting the commutation parameters is to identify the number of encoder counts per commutation cycle This information should be available from the manufacturer It may be specified as the combination of two different values Distance of a commutation cycle inches centimeters etc Quadrature encoder counts lines 4 per unit inches centimeters etc For example a linear motor has one commutation cycle every 0 5 inches The encoder resolution is 20 000 quadrature counts per inch The system will have 10 000 encoder counts per commutation cycle units per commutation cycle encoder counts per unit counts per commutation cycle 0 5 20 000 10 000 For a rotary motor the resolution of an encoder is typically specified as the number of encoder counts per rotation For a three phase brushless AC motor the number of encoder counts pe
19. test than at the beginning Looking at macro 100 of the Detent Test after the first move the position of the encoder is reported 1TP An updated encoder position will be is reported after every step voltage detent search change If the motor moves but the reported encoder position does not change there is a problem with either the encoder or the encoder decode circuitry of the MC320 module Use an oscilloscope to verify proper operation of the outputs from the encoder If both the A and B or A A B and B outputs change state while the motor encoder is rotated refer to the DCX MC320 schematics in the DCX AT300 User s Manual or contact PMC Tech Support for help with the encoder decode circuit If the motor moves but the reported encoder position decrements the system is not properly phased To change the phasing of the system either 1 Swap the A and B A and B amp A and B signals from the encoder to the DCX MC320 2 Swap the U and V outputs signals from the MC320 to the amplifier Many times the user will require the motor to move a certain direction when commanding a positive move For example a linear motor is oriented such that a move to the right must be commanded as a positive move positive move Stage coil assembly o ES Magnet track SS Figure 9 Linear motor diagram Precision MicroControl Corp 12 AN1004 Brushless AC Motor Commutation If upon running the Detent Te
20. the amplifier and motor 1SQO set maximum voltage to 0 0 volts TOM configure axis for Torque Mode ALO AR100 aLAn register AL 120 AR101 aLBn register AL15 AR102 detent increment register AL1 AR103 maximum voltage aSQn register AL23 AR104 Set macro 100 repeat count ALO AR105 clear Detent Test loop counter WA1 wait one second MD100 1MN 1LA 100 1LB 101 15Q0 103 WA 5 1TP MJ101 set phase U and V outputs Precision MicroControl Corp 11 AN1004 Brushless AC Motor Commutation MD101 AL 100 AA 102 AR100 AL 101 AA 102 AR101 1SQ0 MJ102 increase LA and LB by 15 degrees MD102 AL 105 AA1 AR105 IG 104 BK NO MJ100 increment Detent Test loop counter Issuing the command Macro Call 100 MC100 will start the motor rotating through one commutation cycle 1 3 of a rotation of a rotary motor To cause a rotary motor to complete one full revolution increase the repeat count in stored in register 104 to 72 AL72 AR104 If the motor does not move increase the maximum voltage torque that is set by the sequence AL1 AR103 If the motor does not move after the maximum voltage has been increased to 5 volts contact PMC Tech Support This Detent Test is similar to a DC voltage step response that is typically o used to tune setup a DC brushless or brush amplifier Encoder operation during Detent Test During the Detent Test as the motor moves the encoder should increment In other words the reported position should be larger at the end of the
21. these issues another form of motor commutation was required The answer was Sinusoidal Commutation Sine Commutation basics The following diagram demonstrates the principals of very simple brushless motors Rotor motor shaft y9 Coil Coil E phase W phase V Magnet Figure 1 Simple brushless motor Three coils are mounted 120 degrees apart When current is applied to a coil it will attract the nearest rotor magnet If current is applied to the phase U coil the rotor will turn clockwise until magnet A is aligned with the coil at a detent This simple brushless motor is similar to a how a stepper motor operates turning on one coil will cause the shaft to rotate by one magnet pole When using sinusoidal commutation to drive a three phase brushless AC motor different current levels are applied to each of the three coils The current levels are phase shifted by 120 degrees as are the motor coils The diagram below shows the outputs of a sine commutation motion controller for one commutation cycle For the example brushless motor in figure 1 it would take three commutation Precision MicroControl Corp 4 AN1004 Brushless AC Motor Commutation cycles to complete one rotation of the motor shaft Rotor Angle 0 30 60 90 120 in degrees Commutation Angle 0 90 180 270 360 in degrees Phase U RETRO NES Phase V Phase W Figure 2 Sine commutation waveforms You may notice that in figure 2 the
22. tor Commutation Offset the commutation angle by 90 degrees 1LA 90 1LB 210 1MN retard the commutation phasing by 90 degrees enable motion Brushless AC motors produce optimum torque when the magnetic vector of the stator is at a 90 degree angle to the magnetic vector of the rotor By retarding the phasing of U and V by 90 degrees the voltage outputs can be calculated Output Tqmax sin 0 Offset where Tqmax SQ parameter n maximum voltage 0 Initial angle detent Offset 90 degrees Output U Tqmax sin 0 Offset Output U 10 sin O 90 Output U 10 1 Output U 10 0 volts Output V Tqmax sin 0 Offset Output V 10 sin 120 30 Output V 10 0 5 Output V 5 0 volts Start the motor moving by setting the maximum voltage to a non zero value 19Q 0 25 set a low maximum voltage In this mode of operation Torque Mode aQM the motor will move until command by the user to stop The DCX controller will not monitor limit switches or following error To stop the motor either e Set the maximum voltage to 0 a8QO0 e Reset the computer which will disable the DCX controller The motor should start moving smoothly in the positive direction If you now grab and hold the shaft you should feel constant torque being applied by the motor Manually rotate the motor in the negative direction You should feel constant resistance no cogging or sticking Let the motor go and it should
23. ww copleycontrols com Elmo Motion Control www elmomc com Glentek www glentek com Servo Dynamics www servodynamics com Motor Three phase AC brushless motor with incremental encoder or Linear AC motor with incremental encoder Hall effect sensors or encoder hall track recommended required for pending auto commutation initialization feature Axis UO optional Travel Limit inputs opto isolated 12V to 24V Coarse Home input opto isolated 12V to 24V Amplifier Fault input opto isolated 12V to 24V Amplifier Enable output open collector 5V to 24V Precision MicroControl Corp 8 AN1004 Brushless AC Motor Commutation Open loop motion and encoder tests Verify basic amplifier and motor operation Prior to configuring closed loop sine commutation servo control the DCX controller can be used to move the motor in an open loop manner This will allow the user to verify the operation of the amplifier motor and MC320 dual DAC outputs Referring to the typical system wiring diagram Figure 6 and documentation provided by the motor and amplifier manufacturer wire the motor amplifier and DCX motion control system To set the output voltages of phases U and V use the Load commutation phase shift A aLAn and the Load commutation phase shift B aLAn commands Issue these commands to the DCX AT300 using the Windows MCCL command interface WinControl a MCAPI component Ww inControl3 File Edit H
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