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Index Homing
« on: December 15, 2018, 06:31:19 PM »
Hi Guys,

I'm using CSMIO IP/A on my old bridgeport milling machine for a few years now. All has been ok, but index homing has just stopped working. I've reloaded a previous config and get same issue. So I think its a hardware / sensor issue.

The machine references the z axis fine, then starts the y axis, moves the the homing switch, and reverses direction, usually then it starts slow then moves quicker, but it doesn't ever speed up, and doesn't find the index.

any ideas what to check next? If I manually turn the servo the DRO on the mach3 DRO display changes , so I guess the encoder is working?
Re: Index Homing
« Reply #1 on: December 15, 2018, 06:49:53 PM »
Hi,
I presume your encoder is differential?

If that is the case you will have an A channel, a B channel as the two quadrature signals but you should also have an index signal,
commonly called I or Z. Your quadrature signals are working as evidenced by your test of manually turning the servo but that does
not test the presence of the index signal.

You'll have to devise a test for the index signal. The index signal is so brief that measuring with a multimeter is likely to miss it and you
might conclude that the encoder is faulty when it is not. Observing the signal with a scope is the correct procedure.

Craig
My wife left with my best friend...
     and I miss him!
Re: Index Homing
« Reply #2 on: December 15, 2018, 07:03:32 PM »
I think the encoder is differential, I'll need to double check, it was a few years ago since I did the conversion.

is it likely that one channel could go down, or would it more likely be a cabling fault?

maybe this is an excuse to buy myself a cheap scope
Re: Index Homing
« Reply #3 on: December 15, 2018, 07:21:11 PM »
Hi,

Quote
is it likely that one channel could go down, or would it more likely be a cabling fault?

It could be either. The index signal must hook up to the CSMIO/A and that is where I would probe the input. If the signal is present
then the index homing fault is due to the CSMIO/A or Mach, if the signal is not present then either the encoder or cabling is faulty.

The advance of application specific digital technology has resulted in some very cheap scopes becoming available. Being able to use one
to advantage and interpreting the results still requires all the old skills however. By all means get a cheap scope, this might be your first foray
into that experience, just don't expect a scope to magically solve all your problems, intelligent application is still required.

Craig
My wife left with my best friend...
     and I miss him!
Re: Index Homing
« Reply #4 on: December 16, 2018, 06:35:43 AM »
 
Presuming you are using the motor encoders  rather than linear scales, your servo drive may allow you to observe the index pulse via the drive diagnostic facility. This would indicate whether the drive itself was receiving the encoder index signal. If this is OK, either the drive is failing to output the index to CSMIO, the cable between these is faulty, or the CSMIO is not recognising or processing the index.

Allan
Re: Index Homing
« Reply #5 on: December 17, 2018, 10:35:50 AM »
Yes, I'm using servo's with rotary encoders on the back. I'll double check the cabling on them.

Thanks for all the info guys
Re: Index Homing
« Reply #6 on: December 19, 2018, 02:55:41 PM »
I've checked all the cables, and all looks good, I've also tried moving the encoder input to another channel on the encoder, but still have the same issue. I've tried checking the output of the I channel of the encoder with a DVM, but as you say I can't see anything changing, I have a constant 3.5v.

I updated the firmware to the latest version for mach3

Is there anything else I can do??
Re: Index Homing
« Reply #7 on: December 19, 2018, 03:51:54 PM »
The index pulse is very short, so you would need to turn the encoder extremely slowly to check as above, but given care and patience it should be possible to verify it in that way.  Maybe you could verify that you can see the pulse on a channel that is known to be working properly. That would show you just how easy, or otherwise, it was to see the single line transition.

Allan
Re: Index Homing
« Reply #8 on: December 20, 2018, 06:13:33 PM »
ok, so it looks like the encoder was faulty, I've now changed the encoder and index homing is now working.....ish!

Now I have a new problem, The machine doesn't home in the middle of the Y Axis anymore. My thought is this is becuase the new encoder has a different number of pulses per revolution compared to the old one. The old one had a 1250 PPR. This is my new encoder, (which is the same as I use on my z axis, which works perfect) https://www.cui.com/product/resource/amt10.pdf

Where in the software do I change the PPR to the new figure, I assume is 2048 ppr?
Re: Index Homing
« Reply #9 on: December 21, 2018, 05:16:57 AM »
I'm not sure why the axis no longer homes near the home  switch.

You need to change your ppr to 8192 (4 x 2048) as per data sheet:
Quote
All resolutions are listed as pre-quadrature, meaning the final number of counts is PPR x 4.

You do this within the CS Labs plugin.

Allan