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Servo to encoder tuning
I have a 1990 Sabre 1250 with an 850MC with an x-axis servo motor that I put new bearings in. I marked the coupler location for the encoder and put it back together successfully however since I've had this machine i've always notices a high pitch coming from this servo when its just sitting still, the y and z do not do this so this leads me to believe the encoder could be tuned in better. After doing the bearings I turned the machine on and loosened the 4 bolts that hold the encoder on and push the slack one way or the other and I can change the tone of the noise so I'm sure there is a procedure for tuning the 4 potentiometers on the encoder. I've been searching but haven't had any luck finding anything yet. Does anyone here know the procedure or have a document they could send my way. Any help would be great.
Thanks, Joe
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Is this a Brushless servo? If so it most likely has the commutation tracks on the encoder and these have to be aligned with the stator windings.
I have posted the method to do this a couple of times here, you need a double beam scope to do it, and a means of powering the encoder on the bench.
Al.
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Thanks for the speedy response Al. Yes it is a brushless. I have a double beam scope and I'm sure I can come up with a way to power the encoder I have a BK Precision 1635 variable power supply. I've been searching on here trying to find the procedure, I'll keep looking, if you could otherwise post a link to one of your previous posts with it.
Thanks,
Joe
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You need to identify the H1,H2,H3 hall effect equivalent outputs of the encoder, and the three stator windings.
The three stator windings are each connected to a 1k -10k resistor whose other ends are connected together to provide a virtual star point for the scope common.
The probe of one channel is connected to the A phase.
The other scope input is connected to the H1 or HA hall output.
You need to back feed the motor around 200rpm, I use a small DC motor for this.
Then you need to align the two traces so that the H1 straddles the A phase positive going peak.
The PDF shows the alignment for all three tracks.
As long as you have identified the right pair, then it should be OK.
Al.
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Al, I have for pots on my encoder board an A-0 B-0 C-0 and Z would u use them to tune each of the hall outputs then I'm assuming not sure what the Z is for.
Thanks,
Joe
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I have never known these to be tunable, or even need to on the drives I have used?
I don't know what they would be?
Al.
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Here is a picture of the 4 pots, I'm making a coupler now to turn the motor with a dc motor I have to do the alignment like you said, got my 10k resistors and scope ready to go, just have to figure out which wires I need to be looking at to see H1, H2, H3 and I will be set.
Attachment 204852
Attachment 204854
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For some reason i took it to be a Siemens 850 control not a Fanuc, this changes the whole picture, they not only are AC sinusoidal powered, they have their own proprietary commutation.
CN1-2-4-8 are the four commutation signals.
These encoders are automatically aligned with the motor by marks on the encoder bracket, there is an alignment check that can be done, it requires a automotive battery to aling the armature and a test jig to monitor the CN signals for all 1's. I made up a little LED powered board to make it simple.
I can see if I can dig it out.
Al.
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Here is the method from the servo manual.
I made a simple board using 4 2N7000 FETs and LED's with 330ohm resistors for checking the CN outputs.
Al.
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The only problem I see with the procedure you have in the book they show the encoder being on a 3 bolt patter that has slotted holes for the adjustment, Mine has 4 with no slots, there is a tiny bit of play with them just cracked loose but not much probably only .010" or so. I wish I had a manual for this servo motor like the one you posted the pages out of that might have the info I need. Is there a place to obtain such a thing?
Joe
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even if you cannot cannot rotate the encoder the bit pattern should be the same when the armature is oriented properly with the battery, you can use a meter to sheck the voltage on the CN-1 to CN-8
Al.
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I finally had time to take the motor and hook it up on the bench to test the output of C1-8 I applied the voltage to the u and vw leads and the motor locked into a postition and I checked the c1-8 outputs and indeed they are not correct. I tried 8 times to take the encoder off and move the coupler on the end of the motor shaft but I cannot get the right output of C1-8. C2 is the one I cannot seem to get to get correct with the others. If anyone has a service book or knows where to get one for this type of servo I'd sure appreciate it or has the procedure to do this. Its a Fanuc A06B-0512-B501#7073 with A860-0315-T101 2000p encoder. Al, thanks for all your help in getting me this far, I wish I had the type of encoder that your book has it sure would simplify this I think.
Joe