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IndustryArena Forum > CNC Electronics > Servo Motors / Drives > Understanding AC Servo, Encoder, Servo Amp / Drive
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  1. #1
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    Understanding AC Servo, Encoder, Servo Amp / Drive

    Hi guys,

    I just recently found an old robot arm abandoned in the company. It has Sanyo Denki AC servo motor controlling its joint. There is no servo amp and no controller that come along with it. 2 of the servo has an absolute encoder and 1 has a incremental encoder. Encoder alignment is questionable at best. I also have on my hand a mitsubishi servo amp.

    After some reading up in the past 2 or 3 weeks I get my brain tied up in a knot, and need some help understanding how all these things works together.

    Let me know if I am on the correct understanding...

    1. Theoritically servo motor are just a plain dumb motor, DC brushed servo motor is just normal dc brushed motor with some sort of encoder attached to the shaft. Brushless motor is brushless motor, DC brushless or AC brushless is just about how the servo amp send out the signal to spin the motor.

    2. For brushless motor, the servo amp needs information on how to send out the signal, i.e. commutate the motor. They get this signal either from a resolver, a hall effect sensor (for BLDC), incremental encoder or absolute encoder.

    3. Brushless servo motor need to have their encoder/resolver/hall effect sensor aligned to the stator winding to give best torque characteristic.

    So that's what I think I know from my google-fu, next are my questions, most of them revolve only around brushless AC motor...

    1. Is there any reason why I can't just grab a servo amp that can have the configuration of the encoder/resolver set up in the software and get this servo amp to drive just about any servo motor ?
    2. I seen some specialized equipment and technique required for encoder alignment. Is it correct again, to assume that as long as I set the servo amp to correspond to the correct encoder type installed in the motor, I can do encoder alignment by aligning the zero pulse (for inc enc) or pos 0 (abs enc) to one of the motor natural position and once I get it somewhat correct (i.e. motor start rotating to the correct direction) I can then start to adjust the encoder position slowly and aim for maximum torque ?
    3. Or if the servo amp has configuration data on where is the encoder alignment then we can just adjust this again till we get max torque ?

    Thanks for all the help. Once I gain a little bit of more knowledge, my aim is to start this robot with a mishmash of different servo amp that I can lay my hand on, and try to get it moving.

    Regards,
    Leonard

  2. #2
    Community Moderator Al_The_Man's Avatar
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    One problem with AC and BLDC it is usually harder to find compatible motor/amps etc, many are proprietary such as Fanuc etc.
    With DC it is very easy to find suitable drives, followed by BLDC with quad encoders, the other thing to consider is the nature of your command signal, step/dir, analogue. digital etc.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
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    Hi Al,

    Is there a reason for this ? What makes an ac motor become unique? I.e. why can't a servo amp from e.g. fanuc drive a mitsubishi ac motor ? I can only think that if the motor is a 3 phase brushless design, with a permanent magnet as rotor and 3 phase winding in the stator, then any amp that can drive this type of motor will not know the difference between a fanuc built motor vs sanyo built motor or mitsubishi built motor etc.. again as long as they can be configured with the encoder that is attached to the motor to calculate the correct commutation sequence...

  4. #4
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    Quote Originally Posted by ultrasmurf View Post
    Hi Al,

    Is there a reason for this ? What makes an ac motor become unique? I.e. why can't a servo amp from e.g. fanuc drive a mitsubishi ac motor ? I can only think that if the motor is a 3 phase brushless design, with a permanent magnet as rotor and 3 phase winding in the stator, then any amp that can drive this type of motor will not know the difference between a fanuc built motor vs sanyo built motor or mitsubishi built motor etc.. again as long as they can be configured with the encoder that is attached to the motor to calculate the correct commutation sequence...
    And it would be so cool if they could match up and work like that, but this is not the case, some servo drives can be hacked, but by the time you do get them going, you could of found the right matched Ac servo motor and drive, have fun with your robot
    Mactec54

  5. #5
    Community Moderator Al_The_Man's Avatar
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    Quote Originally Posted by ultrasmurf View Post
    Hi Al,

    Is there a reason for this ? What makes an ac motor become unique? I.e. why can't a servo amp from e.g. fanuc drive a mitsubishi ac motor ? ...
    The motors themselves are all very similar, the difference is not only in the form of commutation, but the encoder or feedback information. As per the example of Fanuc, the encoder has a proprietary method of producing a sine wave from a 4 bit digital signal, so either the encoder has to be changed or reverse engineering the drive.
    I have replaced the Fanuc encoder with one that has the hall simulated tracks and converted them to BLDC.
    With a off the shelf or surplus BLDC motor that has the standard hall style commutation, I have used A-M-C or Copley Drives etc as they come in order to use these motors, no incompatibility there.
    Incidentally these BLDC drives will also run a DC brushed motor by DIP SW setting.
    And as mentioned, the command signal of a drive can be several methods, incl proprietary.
    Al.
    .
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  6. #6
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    So if I got it right, servo drive/amp is usually pre-programmed/configured at the factory to take in only a specific type of encoder/motor combination, and hence they can only talk to this type of encoder/motor combination. Easiest will be to convert to motor to a BLDC mode with a hall effect sensor, and use AMC or other brand driver that does BLDC + encoder.

    I still couldn't wrap my mind, why can't a servo amp be "programmable". i.e. give it encoder configuration, and encoder to commutation signal phase relation, and drive it. Sounds like a simple work for those programmer to whip up a program to do just that (no unfortunately my brain is not at that level... )

    Found this guy in the net :
    https://harmonicdrive.de/en/products...ukondrive.html

    Is this a universal ac servo amp/driver ?

  7. #7
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    Quote Originally Posted by ultrasmurf View Post
    So if I got it right, servo drive/amp is usually pre-programmed/configured at the factory to take in only a specific type of encoder/motor combination, and hence they can only talk to this type of encoder/motor combination. Easiest will be to convert to motor to a BLDC mode with a hall effect sensor, and use AMC or other brand driver that does BLDC + encoder.

    I still couldn't wrap my mind, why can't a servo amp be "programmable". i.e. give it encoder configuration, and encoder to commutation signal phase relation, and drive it. Sounds like a simple work for those programmer to whip up a program to do just that (no unfortunately my brain is not at that level... )

    Found this guy in the net :
    https://harmonicdrive.de/en/products...ukondrive.html

    Is this a universal ac servo amp/driver ?
    I think you will find it is universal for there product line, most servo drive and servo motor manufacturers do this
    Mactec54

  8. #8
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    Sorry, I get confused again. If I have a mitsubishi amp that was used to drive a brushless motor with an encoder, and if I can get that encoder and place it on a different brand motor, say sanyo denki (similar wattage) and align them according to how it was aligned in the mitsubishi motor, will I then be able to drive the sanyo denki motor ?

  9. #9
    Community Moderator Al_The_Man's Avatar
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    You MIGHT possibly be able to do this, although a pain to do, also the motor pole count would have to be exactly the same.
    Many Mitsubishi combo's use serial data for the control communication.
    Most of the Sanyo-Denki motors I have used worked with a A-M-C or Copley controllers.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  10. #10

    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    Quote Originally Posted by ultrasmurf View Post
    Sorry, I get confused again. If I have a mitsubishi amp that was used to drive a brushless motor with an encoder, and if I can get that encoder and place it on a different brand motor, say sanyo denki (similar wattage) and align them according to how it was aligned in the mitsubishi motor, will I then be able to drive the sanyo denki motor ?
    mitsubishi encoders have a motor id programmed, which is read by amplifier during handshake. then the amp looks thru its internal table of supported motors for this id. each entry in the table has a number of constants unique for each motor which are used in calculations driving the motor. some of those constants are obvious and can be obtained from the motor datasheets, some can be measured. but not all. e.g here's a list of parameters with motor constants for MR-J3

    PG01 **POLE Number of motor poles pole 0-24
    PG02 **INA Motor inertia G_MAG*kg*m^2 0-32767
    PG03 **STQ Rated motor torque G_MAG*N*m 0-32767
    PG04 **MTQ Maximum motor torque (Nominal value) % 0-1000
    PG05 **AMR Rate motor current G_MAG*Arms 0-32767
    PG06 **MAMR Maximum motor current (Internal limit value) % 0-1000
    PG07 **LDQ dq axis inductance mH 0.00-655.35
    PG08 **RDQ dq axis armature resistance m-ohm 0-65535
    PG09 **VDQ dq axis induced voltage constant mV*s/rad 0-65535
    PG10 **BAS Rated motor speed r/min 0-20000
    PG11 **TOP Maximum motor speed r/min 0-20000
    PG12 **MAG Rate crnt/inrt mom/rate torq 0-4
    PG13 **OLN Overload level 0-5
    PG14 **OCL Overcurrent level % 0-200
    PG15 **TDG S/W Td compensation gain rad/s 0-9999
    PG16 **IQGN Q axis gain V/A -9999-9999
    PG17 **IDGN D axis gain V/A -9999-9999
    PG18 **IQIC Q axis integral compensation V/A*S -9999-9999
    PG19 **IDIC D axis integral compensation V/A*S -9999-9999
    PG20 **MTSP Speed at max. torque output (not supported) r/min 0-65535
    PG21 **MSPT Output torque at max. speed (not supported) % 0-65535
    PG22 **FBA Average speed feedback count 0-16
    PG23 **TWPK Axis torsional resonance frequency Hz 0-65535
    PG24 **KTC1 Cogging torq correct coefficient 1 (not supported) 0-65535
    PG25 **KTC2 Cogging torq correct coefficient 2 (not supported) 0-65535
    PG26 **KTC3 Cogging torq correct coefficient 3 (not supported) 0-65535
    PG27 **KTC4 Cogging torq correct coefficient 4 (not supported) 0-65535
    PG28 **KTC5 Cogging torq correct coefficient 5 (not supported) 0-65535
    PG29 **KTC6 Cogging torq correct coefficient 6 (not supported) 0-65535
    PG30 **VLF Control mode flag 1 0000-FFFFh
    PG31 **VLA Torq max. control dq axis volt comm limit coeff a % -100-100
    PG32 **VLB1 Torq max. control dq axis volt comm limit coeff b1 deg -90-90
    PG33 **RTC Torq max. control dq axis volt comm limit coeff b2 % -500-500
    PG34 **VDQG Torq max. control dq ax volt satur avoid q ax gain % -100-100
    PG35 **VDDG Torq max. control dq ax volt satur avoid d ax gain % -100-100
    PG36 **MRO Servo motor capacity 10W 0-65535
    PG37 **AMO Servo amplifier capacity 0000-FFFFh
    PG38 **CARR carrier frequencies 0000-FFFFh
    PG39 **ORT Regenerative time constant 0-32767
    PG40 **ORL Regenerative level 0-32767
    PG41 **OLT1 Overload time constant 1 0-32767
    PG42 **OLL1 Overload level 1 0-32767
    PG43 **OLT2 Overload time constant 2 0-32767
    PG44 **OLL2 Overload level 2 0-32767
    PG45 **OLT3 Overload time constant 3 0-32767
    PG46 **OLL3 Overload level 3 0-32767
    PG47 **OLT4 Overload time constant 4 0-32767
    PG48 **OLL4 Overload level 4 0-32767
    PG49 **PITCH Linear motor pole pitch 0.01mm 0-32767
    PG50 For manufacturer setting 0000-FFFFh

  11. #11
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    Re: Understanding AC Servo, Encoder, Servo Amp / Drive

    ultrasmurf, your description up top is really well written and I think it's pretty much accurate. The comments above are right, however... each motor may be a bit different and the driver for one may not work with another. There are all sort of differences, including the type of winding (the maximum current, correct voltage, etc...) and also the encoder or hall effect sensor will put out different signals, etc... However: It would be really cool if there was some sort of database or general knowledge about which motors and drivers ARE the same or close enough to work. If you search for your motor, or for the original driver, you might find someone who has gotten away with what you are trying before. If you can find the specs or technical details of the originals system... although that probably isn't shared by the mfgr... Or you could just throw caution to the wind and try something close. Either way, let us know.
    James hosts the single best wiki page about steppers for CNC hobbyists on the net:
    http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)

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