EMC Logo not drawing correctly!

Background on my machine, it's a Milltronics knee mill, purchased with a dead controller. After much work I've finally gotten the machine working on all three axes. Got the 12 wire three phase spindle motor figured out by spinning it and plotting on a o'scope. Last night I went and ran the EMC nc program that default comes up on Axis. My results are attached. I have some issue in varying distance with a commanded move. I put a dial indicator on the x and moved in incremental mode, first positive .100, which I did 3 times, each time I got an additional .120 movement on the indicator, then I moved negative .100 and would get .130 each time in the negative direction. I did this a few times and the error% was not constant. I konw my encoder count/ballscrew/pulley ratio is right. I'm a bit confused as to what would cause the error to change based on direction. Is the 7i43 missing some encoder counts? The distance commanded is correct on the DRO on EMC. I'm using the pre-release v2.5 as I was told that would fix some setup issue I had way back when I couldn't get board communication. Is there any check done in EMC to see that there are the correct number of encoder counts per 1/rev on the encoder to ensure that counts weren't missed? Looking forward to getting this issue sorted out so I can cut some chips soon.


-Scott Flanagan

I've got the 7i43 connected to a 7i33 servo daughter card. I've tried running it slowly w/ the following error down at .005 on a feed move. I haven't spent a ton of time doing my PID tuning on all the axes so I just run it slow and keep it w/in the allowed error. I've also run it w/ .100 following error and it doesn't seem to have any impact. Could this be a servo period issue w/ dropping counts?

-Scott

This really looks like encoder or wiring noise, so a couple questions:

Are your encoders single ended or differential type?

Are the 7I33 inputs jumpered properly to match the encoder type?

Is the 5V at the 7I33 card within 5%? (4.75V to 5.25V)

How are the encoders wired? are the encoder wires shielded? How is the shield terminated?

Encoders are differential, and the 7i33 is jumpered to match. I'll have to check on the 5v when I get home tonight. I do not believe that the wiring is shielded. I am using all of the machine's original wiring, I just terminated it into the 7i33 instead of the Milltronics main board. I guess I should put my scope on the encoder inputs to the 7i33 and look for noise in the signal. I can also count the pulses and relate it to the once per rev as well.

-Scott

Its pretty rare to have this bad a noise situation with differential encoders.

I would re-check the 7I33 jumpering and check that you truly have differential signals
on the 7I33 inputs.

You can do this easily by measuring across the A and /A pins and across the B and /B pins. As you move the motor shaft slightly you should see a equal positive and negative voltage depending on shaft position. This voltage should be between 2.5V and 5V.

Alright, so tonight I checked the 7i33 board out, it is indeed setup for differential input. Then I put my scope on the A and B channels of the encoder. The scope was hooked up in the following way, all grounds common tied to 7i33 ground.



CH1: A+ connected to encoder and 7i33
CH2: A- connected to encoder and 7i33 (look closely for blue channel follows CH2 exactly)
CH3: B+ connected to encoder only
CH4: B- connected to encoder only

As you can see when the encoder is hooked up to the 7i33 board I get the weird almost TTL looking response from the encoder, yet when it's free (i.e. only connected to the encoder) it looks like a proper TTL signal. I originally hooked this up with the B side of the encoder hooked to the 7i33 and the encoder and it looked just like A. Anyone have any ideas? Just for grins I tried swapping the TTL/Differential input jumper on the 7i33 board thinking I interpreted it wrong, but the scope didn't show any difference.

-Scott

Is CH3: B- connected to encoder only supposed to be CH4: B- connected to encoder only
if so it looks to be open

Are you saying the A+ and A- signal are the same? if this is the case, this likely means that the A- lead is unconnected (and being driven through the differential termination resistor on the 7I33)

Both of these things taken together indicate that you really have a TTL encoder with the A- and B- wires unconnected at the encoder or you dont have the actual A- and B- pins connected correctly

For TTL, just connect the A+ and B+ (and perhaps Z+) encoder wires and jumper the 7I33 for TTL inputs

What I'm saying here is that the encoder looks like CH1/2 in the picture when measured in parallel to the 7i33, then it looks like CH3/4 when the encoder is measured w/out being connected to the 7i33 board. Maybe I'm barking up the wrong tree because EMC does read the encoders, I just wanted to verfiy that it was reading them correctly by comparing distance traveled according to EMC vs. # encoder counts. I guess I can ignore this weird error and do my test as I was just w/ the odd looking encoder signal.

-Scott

Yes I understand, and what I am saying is those traces clearly
indicate a wiring or encoder type problem and you will not read
the encoders correctly until this is fixed.

The problem is that either your encoders are not differential
or that the /a and /b wires are not connected