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Optical Encoder diagnostic

Discussion in 'Troubleshooting and Repair' started by adel2014, Oct 1, 2014.

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  1. adel2014

    adel2014

    22
    1
    Dec 1, 2013
    Hello every one , greetings from Egypt , I have a servo motor controlled the x-axis motion of a wide format solvent printer , yesterday , it stops suddenly and it was free to move , i replaced it by a new one and the printer worked fine , Now i want to get it working again ;) , the encoder consists of 1- IC: AM26LS31C
    2- Encoder Sensor : Avago H9731
    3- three SMD cap + 2 SMD res
    the motor is 36V DC - 3000 RPM & Encoder : 1000P/R
    the question is , how could i diagnosis the error part to replace it and get the motor run correctly again ? any suggestions could be help :)
     
    Last edited: Oct 1, 2014
  2. davenn

    davenn Moderator

    13,669
    1,891
    Sep 5, 2009
    hi there :)

    do you have any overall info for the system full schematics etc ?
    can you do some sharp and well lit pics of the controller board, both side

    cheers
    Dave
     
    adel2014 likes this.
  3. adel2014

    adel2014

    22
    1
    Dec 1, 2013
    thanks for replay ,Dave , here are the pics DC_motor_for_printer_JHF_vista.JPG DSC08521.JPG DSC08517.JPG DSC08522.JPG DSC08525.JPG
     
    Last edited: Oct 1, 2014
  4. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    adel2014,

    Are you familiar with servo motors in general? Most modern servo motors are built using 3-phase motors with an external driver and the encoder functions both as rotor position sensor and commutation sensor, though there are plenty of 3-phase servos with independent rotor position sensors and commutation sensors as well as motors with drivers built into the motor itself, and then there are synchronous 3 phase motors and BLDC motors that do not require a dedicated commutation sensor. In addition to the various 3 phase servo motors there are AC and DC servo motors and even two-phase stepper motors configured as servos.....All this being said, from what I can see on the tag, it appears to be a 36V brushed DC motor....and there are two common reasons a DC motor stops functioning: 1) the insulation on the windings fail 2) the brushes/armature wear out. In a servo, depending on the driver circuit, it is also possible the driver could "fault" if the encoder fails to send the proper signal, so it is possible that the problem is in the encoder.....You need to verify that the motor is in-fact a brushed DC motor...assuming it is, it should have two primary power leads (likely the heavier Red & Black leads visible in the first picture)...connect these to a 12V - 36Vdc supply and ascertain if the motor runs or not. If the motor runs, then the problem is likely in the encoder, if it does not then the problem is likely the brushes or possibly the windings themselves.

    Brushes should be available either from the motor MFG or Online once you know the dimensions and should be very easy to fix....

    If the problem is the windings then you need to decide how much effort this motor is worth....it can be professionally re-wound, typically reserved for much more expensive motors, or you can DIY the re-wind. I have re-wound many, many DC motors over the years...most of the motors I have done have only taken a few hours to do, but the higher the pole count the more important it is to proceed slowly and meticulously document how the motor was wound....a 3 to 5 pole motor doesn't require much effort, but higher pole count motors can get pretty tricky. You will need to source wire of the proper size, don't "unwind" the motor until you have the new wire in hand. Clean the rotors thoroughly so you can write on them with a sharpie, or if you can't get them clean enough to write on, get some tape that you can write on that will adhere to the rotors and put a piece on each rotor.....First count the rotors. Find the place on the armature where the windings "end" and carefully pry-up the copper "clamp". In some cases these will be soldered and you will need to heat it in order to pry it up....if you break one of these you are pretty much finished and can throw the motor in the recycle bin. Once the "end wire" is loose, un-wind it one wrap and then label the Armature AND the rotor that it was wound around "N" (where N = >> if there are 3 rotors N=3, if there are 5 rotors N=5 ..... if there are 11 rotors N = 11...etc) ALSO note on the rotor the direction of the winding by drawing arrows.....this may seem silly, but once all the wire is off the rotor you will be very glad you did this....Continue unwrapping the winding, BE SURE TO Carefully keep count of how many "wraps" was on the rotor....in some cases motors will be wound with 2, 3 or 4 wires in "parallel", this is typically referred to as "N turns X strands in Hand" (ie, 62 turns 4 strands in hand). Once the "Last" rotor ("N")is fully un-wound write down the number of turns....I have never seen a motor that had a different number of turns on one rotor than another, but I still always count the turns on each rotor....follow the wire to the next "clamp" on the armature and mark the armature with N-1....then again carefully pry up the "clamp" and follow the wire to the next rotor and then number it N-1 (where N =>> if there are three rotors then N-1 = 2, if there are 5 rotors then N-1 = 4 etc....) and again mark the rotor with arrows indicating the direction of rotation.....continue until the rotor is devoid of windings....while I have only seen one motor that had "dual windings", it is something to be aware of....instead of having "N turns 2 in Hand", this motor had two distinct sets of windings and three armatures (and three-leads).....it was a "two speed" variant of a style motor I had re-wound a bunch of, and in the application (an electric fishing reel) no one ever used/wanted the "low speed", so I simply re-wound it as if it were a single speed motor....I would NOT expect a servo motor to have multiple windings (though it may well have multiple strands wound in parallel). Once you have all the windings off the motor (typically a single "long" piece of wire with the insulation removed where the clamps go....) you need to strip the insulation off the end of the wire where and replace it under the clamp marked "1" and re-secure the clamp.....Carefully wind the wire around the rotor slot marked "1" in the directions of your arrows the number of appropriate number of turns....then carefully remove the insulation from the wire where it will connect to the clamp on the armature marked "2"....continue until finished...

    If the armature is "bad" (not common) then add the motor to the recycle bin.

    Once you have determined if the motor is "bad" or the "encoder" is bad you can post back if you need more help...

    Good Luck!

    Fish
     
  5. adel2014

    adel2014

    22
    1
    Dec 1, 2013
    I appreciate your effort and thanks for a good replay , i tested the motor and it ran correctly , it seems to be the encoder is malfunctioning , so as i explained , the encoder have only one ic : AM26LS31C , and Encoder Sensor : Avago H9731
    and three SMD cap + 2 SMD res , so how can i put my figure on the damaged part ??
     
  6. debe

    debe

    255
    65
    Oct 15, 2011
    On pin9 on U1 IC there should be pulses from the opto pickup. I would just power the servo board & check for pulses from the opto first.
     
  7. adel2014

    adel2014

    22
    1
    Dec 1, 2013
    I checked the Optical Encoder Module " HEDS-9731 " , and when i tested it , i connected 5.12v to Vcc and 0v to GND , the output from Channel A and Channel B is always 5.02 v even when i close the LED path , whats the problem please ?
     
  8. debe

    debe

    255
    65
    Oct 15, 2011
    If theres no pulse on pin 9, then I would suspect the opto unit HEDS-9731 is faulty.
     
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