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SmoothStepper plugin noise filtering.
« on: June 08, 2009, 01:55:28 PM »
Afternoon all.

Just a quick query about the noise filtering in the SmoothStepper plugin control menu.  I have connected up all my limit switches today (6 in total) and I have found that my system has become unusable.  Everytime the reset button is pressed in Mach 3, it would immediately trip out again.  On the odd occasion where it didn't trip out, I could jog an axis for a fraction of second, before it tripped out.

I have tried a few things like tidying the cabling up, and re-routing a few wires, but the problem does seem to be down to noise getting onto the limit switch lines.  Some switches are worse than others (I've tried enabling them each indiviually) but they all seem to suffer.

I have also tried the noise filtering in the SmoothStepper plugin control menu.  This seems to have had a good effect.  I tried setting the noise filtering on the "Limits" to 5µs and this didn't really help.  Increasing it to 10µs made things better, and as I incremented it upwards, things got better and better.  I have been tinkering for about an hour now, with it set to 50µs, and have not had one noise problem.

Can anyone tell me if they have had to use this noise filtering, and if so, how much?  Also, are there any negatives of using it at all?  I'm a bit wary of just masking the problem here, but despite re-routing wires, I cannot seem to eliminate it.

Cheers
Andy

Offline Hood

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Re: SmoothStepper plugin noise filtering.
« Reply #1 on: June 08, 2009, 02:17:58 PM »
The SmoothStepper is good at picking up any noise that is about so a lot of people need to use the filtering. On my Mill I occasionally had problems with the E-Stop triggering when I switched on the motor or the air brake was switched off, this was during the Beta testing when there was no filtering. Greg added it to the plugin and I found that I only needed 1.43 in the E-Stop box. The next thing was the MPG was implemented and this again gave me noise problems so again I entered 1.43 and that solved my problems.
 The lathe I dont need any filtering at all.

It will just depend on each individual machine and how noisy the environment is, I have always taken good care with regards shielding and also I try to keep the 5v signal wires as short as possible, I have 24v working all my I/O on the lathe  and convert to 5v just prior to it entering the BOB.

50µs will be fine, just means the SS will ignore any signals that are that or  shorter in  time but as its such a minimal time anyway its not going to cause you problems.

Hood
Re: SmoothStepper plugin noise filtering.
« Reply #2 on: June 08, 2009, 02:28:35 PM »
I did notice that the Estop was being triggered especially when powering up the stepper motor drives, and also when I started an axis moving.  Once the axis was moving (when the noise filtering value was around 10µs) it would carry on fine, but then trigger the Estop when it changed direction.

Thinking about it, I haven't used shielded cable for the limit switches, so I'll have to change that when I get a moment.

Cheers
Andy

Offline Jeff_Birt

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Re: SmoothStepper plugin noise filtering.
« Reply #3 on: June 09, 2009, 11:10:46 AM »
I suspect that you have no optical isolation between the SS and your limits?
Happy machining , Jeff Birt
 
Re: SmoothStepper plugin noise filtering.
« Reply #4 on: June 09, 2009, 01:00:36 PM »
That's correct Jeff, the limit switches are fed straight into the SS (all on Port 2).  I'm using a really basic breakout board that I cobbled together from a small sheet of veroboard (stripboard).  I'm still at the experimenting stage, so I may get around to pruchasing a better breakout board in the near future.

Does opto isolation have any effects on reducing the noise seen?

Cheers
Andy

Offline Jeff_Birt

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Re: SmoothStepper plugin noise filtering.
« Reply #5 on: June 09, 2009, 01:14:41 PM »
I always recommend optical isolation on any machine, whether it has a SS or not. That good wire management and proper (earth)grounding are your first lines of defense. Don't route noisy stepper or VFD lines in parallel with signal lines like encoders or limit switches (if you can avoid it.) It is generally a good idea to use shielded lines for all you input signals as well. Some machines will use shielded cables for the steppers and other won't. The layout will dictate if you need to shield them or not.

The problem come about if the things your driving also have optical isolation built in (like some Gecko stepper drives) you have to be careful not to 'stack' up the optical isolation.

Happy machining , Jeff Birt
 
Re: SmoothStepper plugin noise filtering.
« Reply #6 on: June 09, 2009, 01:37:05 PM »
I know the stepper drives have optical isolation already, it is just the inputs to the SS that are not isolated at present.

My machine is very much "lashed together" electrically at present.  I am intending to construct a little portable trolley type enclosure for it, so I'll tidy up all the wiring, and replace the input signal wires with shielded cables when I do that.

For now though, I am getting results just using the noise filtering options available.

cheers
Andy