Ground Loops and Missed Steps

[cbcnc]

I'm having some problems with glitched steps and my Porter Cable router. I'ld like to get some of your thoughts on how to fix this.
I can watch the lead screws, on all 3 axes, literally jump around when the router is running. I think that the bugger is in the router switch and that it is noisy.
My machine is Here:
With the exception that I have built a new Y axis out of aluminum and steel guides. (gotta update the pics)
I'm using shielded cable to run from my controller to my motors and have made sure that I have only grounded the controller end of the shield.
I did eliminate a loop in the shielding between the Y and Z axes tonight but haven't been able to test it. The loop was in between the Y and Z ground shielding and had connected the grounds together thru the metal parts.
I need some new ideas, though and was hoping you guys might have some thoughts on how to fix this?

Thanks,
Chris

[cbcnc]

Would ferrite beads help?
I do know that they are used where you want to minimize interference.
But, otherwise I know nothing of their principles or how to use them.

C

[Al_The_Man]

A line filter of some kind might help, Large ferrite toroids are one method, also make sure good grounding practices are carried out, including a good motor ground, preferably to a common system ground plate.
Al.

[cbcnc]

I was checking out 'pminmo's' wiki site and he has an article about grounding.
http://pminmo.com/PMinMOwiki/index.php5?title=Grounding
I think that I have followed what he is suggesting in my controller. I will look closer at it to see if there are any mistakes.
My controller is plugged into a computer grade power strip (the kind w/ a modem plug etc.) and there is an additional line filter where the power line plugs into the controller.

C

[cbcnc]

Another thing about the Porter Cable trim router is that it is a double insulated tool and so only has a 2 wire power cord.
What I have done is replaced the cord with a 3 wire cord. The problem is that it has a plastic body and therefore nowhere to hook up a ground wire. Then I put 3 ceramic capacitors (.001 mfd) between all of the power connections and ground. I was hoping to be able to filter the 120v ac. Don't know if this was proper or if the caps were the right value.
It still doesn't help.


C

[Al_The_Man]

On a double insulated motor, the ground should be tied to the motor mount to ensure the machine gantry is adequately grounded.
Al.

[pminmo]

What does the physical layout of your controller wiring look like and the wire routing? Brushed motors create electrical noise, if they take no precautions to prevent that electrical noise from being radiated or coupled then your system will see it. So the issue becomes how to keep it from affecting your system. Wire routing is extremely important, you want to keep motor wires as much as possible away from signal wires. You want to use limit and home switch in the normally closed positions, and keep those away from motor wires. Using RFI/EMI filters in your controller is a good idea.....

[ger21]

Try plugging the router into a different circuit.

[cbcnc]

Hi Phil,

When you say to keep the motor wires away from the signal wires do you mean stepper motor wires? The 120v cord for the router is not inside my controller box.
My home and limit switches are NO and setup for and active low. In other words, when the switch is closed it takes it to ground. I am also using an unshielded cable for those.

This is the configuration that I have had for a long time. Your 4x72105a interface and my other controllers are still a future project.

Chris

[cbcnc]

I think it's a crappy switch in the router.
Just as an experiment I ran my machine with the router hooked to a speed controller. It has a seperate switch that you can run on full or variable.
I got alot less interference. The axes definitely didn't jump when I turned it on.
So....
Short of an electronic debouncing circuit, would filter caps across the switch help? If so, what kind of values should I try?

C

[tpworks]

What controller are you using?
I had a similar problem back when I bought my first controller (Brewington)
It is similar to the hobby cnc board using SLA7026 3 amp unipolar chips.
I wound up putting filter caps where the db25 connected and it cleared up the problem. caps are marked 741
they are on the step and dir signal lines (6 caps) for three axis.

[cbcnc]

Tom,

Thank you, that's a really good thought. My controller is very basic. It's a Kleinbauer "Piker". I think that it was designed to be very inexpensive. It works and does what it is supposed to but, maybe at the expense of a more sophisticated circuit that might contain better noise immunity.
I'm thinking I will try your idea out.

Chris