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Author Topic: Am I loosing Steps, and what should I do  (Read 13992 times)

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Offline russh

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Am I loosing Steps, and what should I do
« on: July 07, 2016, 05:16:44 PM »
Hello All,

I thought I would restart this thread after a misunderstanding regarding my Mach 3 license which has now been resolved with Tweakie.


As I originally wrote, I seem to be experiencing an issue with my machine that results in it loosing its positioning.

As an example, I have made a video (see below link) in which I set the work offset zero at the surface of the work piece. I then rapidly move the axis around a little, and re position the cutter on the work piece surface. Only to find that it shows up as not being as Zero in Mach 3

https://www.youtube.com/watch?v=gR1-5u9HwIs

Just to give you some detail, the machine uses NEMA 34 Stepper motors, operated via a JNC-40M control board connected to a new PC via USB. All the electronics (Input Transformer, Control Board, Motor Drivers, etc) sit in the same enclosure, all close to each other.

From what I have read (as Tweakie pointed out), the JNC-40M controller has a pretty hit or miss success rate of being stable with Mach 3, so Im wondering if this is the cause of the problem?
Before I go buying a new control board, I guess I would like some feedback from you guys of if this seems to be a case of losing steps, and if there is anything specific I can check (maybe with the electronics such as feedback, etc)?

Any help would be greatly appreciated

Thanks

Offline Mogal

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Re: Am I loosing Steps, and what should I do
« Reply #1 on: July 07, 2016, 09:16:18 PM »
Sounds like this is a NEW setup?

I have no experience with the control board, but lots with grounding issues ;)

You say everything is pretty close together, so control, power and sensor lines are pretty close to?
Did you utilize a star grounding point? If everything is so close together, it can cause cross talk in the lines.

My setup had everything really close together too, and gave me problems until I ripped the wiring apart
and re-wired the works, paying close attention to detail with grounding EVERYTHING to a single point.

I'm not losing steps anymore.

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #2 on: July 08, 2016, 03:48:03 AM »
Thank you for your reply.

Could be a huge bonus having you help if you have loads of grounding experience, as that could be the first starting point.

The following might help
I am in contacted with a chap over in Australia (Im Based in the UK by the way), who also bought one of these machines (by the way, its not a new setup I have made, its an actual CNC bought from a Chinese supplier). I believe the machines are based around the mechanics of the old Makini CNC but with revamped motors, drivers and electronics (apparently!)
Anyway, this other chap has been having issue of a different kind, but possibly all down to the same design problem.

He was finding an issue with the spindle drive that would cause sporadic operation on the spindle speed at low RPM. He found that the problem with the spindle drive was cross talk between the output and input of the axis stepper motor drivers, they were sending noise back into the transformer, then into the motion board and on into the spindle driver.

Best I be honest up front, I am from an electrical engineer (Im a mechanical grease monkey). So if you could share any help and steps in baby talk.....that would be great. But it sounds like this could be a good starting point if you all agree.

Therefore, what do I need to look at doing? Do I need to separate components, separate wires, fit ferrites, etc ??

Thanks again all

Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #3 on: July 08, 2016, 04:11:07 AM »
Watching your video, it shows at the end that you reach the top of your work surface at -0.73mm. If you were to lose steps, you would reach the work surface before the Z axis reads zero. Normally losing steps on the Z axis results in plunging into the work piece. It appears as if you were gaining steps when Z moves up resulting you reach Z zero above your work surface.

I assume that moving Z up is the Z+ direction?

Gaining steps could be a noise issue as Mogal indicated earlier or a PC problem. Is your machine grounded to the mains power outlet, the wall socket?

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #4 on: July 08, 2016, 04:24:00 AM »
Hi,

I think you are right, I am gaining steps more often that loosing, as when I have ran the test other times, even though there are times it looses steps (plunges down), most of the time it results in the tooling being higher (+) than the set zero point.

I need to examine the electrical setup in more detail, but when you say grounded to mains, do you mean to the mains earth or the neutral? (Uk has Live, Neutral and Earth which are Brown, Blue and Green respectively)

I will take some more close up photos of the electronics later to share, but if it helps for now, the following photo is of a similar machine with pretty much that same electronic setup as mine.


Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #5 on: July 08, 2016, 04:44:23 AM »
Yes, Europe has a green or yellow/green wire for ground or earth as you call it. Is your machine connected to a wall socket that has an earth connection or do you just use the 2 power wires Phase and Neutral?

A few pictures of your electronics might help. Is this problem only the Z axis or do the X and Y axis show the same behavior?

What steppers are you sing, what drivers and what power supply set-up?

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #6 on: July 08, 2016, 05:16:15 AM »
Hi,

It connected to a wall socket (well a isolation switch), that includes the earth connection. The cable from the machine (that connects to the wall isolation switch) also has earth. If that earth cable is connect to the actual machine somewhere I can not answer at the moment, but I will check on this.

The issue exists in all the axis (should have mentioned that sorry), but seem more exaggerated in the Z.

I will get some picture of the power supply setup, drivers etc. But there are not labels on the NEMA 34 Stepper motors so I have limited information on them

The earth system of the mains supply to the factory is a TT (Terra-Terra) earthing system with a local earth electrode

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #7 on: July 08, 2016, 11:01:28 AM »
Hi All,

I have taken some pictures of the electronics.

Couple of points I noticed
1) While the machine uses the JNC-40M drivers, the PCB control board seems to be made by the machine manufacturer, so Im not sure he they have done a spin off of it.
2) There are 4 wires going to the stepper motors, not sure if that helps


















« Last Edit: July 08, 2016, 11:13:02 AM by russh »

Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #8 on: July 08, 2016, 11:52:31 AM »
This does not look bad at all. I would start by untangling the wires for the steppers from the USB card, it looks like they are on top of the card. Secondly I would unplug the green connector blocks from the stepper drives and check for lose or bad connectors.

Also check the connectors on top of the USB card for lose wiring.

I would measure the voltage to the stepper drives, should be close to 70VAC but not higher then 80VAC. Measure for some time and see if it spikes up over 80VAC. Your stepper drives are Leadshine drives after I Googled the partnumber in the picture and these are good drives but don't like overvoltage.

Do you have access to another computer to run Mach3 on? Just to see if this makes a difference.

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #9 on: July 08, 2016, 12:37:09 PM »
Thanks G21,

I will do check all the bits you mention

I've actually tried two PCs already with Mach 3, and the same issue occurs (one was an old one I had laying about but good spec, the other one was a brand new built from scratch job)

One out of interested question, as the steppers have 4 wires, does that me they are the better "position feedback" type