Unexplained stopping

[chodges]

Ok – I am stumped.

We are running PartWorks version 1.1 and ShopBot Control Software version 3.5.5 on a 2008 model PRS Alpha in a shop with a wood floor. Our machine is grounded directly to an 8’ ground rod embedded in concrete. All of our electrical service is new, with proper grounding.

Our PC is running Windows XP, version 2002, with Service Pack 2. According to Device Manager, I am running the ShopBot Controller (Driver Date: 12/16/04, Version 4.28.0.2700) USB cable mapped to COM3 with the following settings:

Bits Per Second: 115,200
Data Bits: 8
Parity: None
Stop Bits: 1
Flow Control: None
Randomly, either when running a job or when moving the X,Y position of the carriage using the M2 command, our machine makes a very abrupt stop with a hard “thunk” sound, and gives us the Quit or Resume messagebox.

There is no consistency to this. It has happened with numerous job files, and at arbitrary X,Y positions.

The odd thing is that if we move the carriage using the arrow keys, this NEVER happens.

If this happens during a job run, we can Resume the job without losing our coordinates – the machine still knows where it is on the X,Y axis.

If this happens while executing a M2 command, we cannot Resume the move. Even though the red window in the ShopBot Control Software appears to show the coordinates at which the gantry locked up, a Resume will send the gantry to a random (not intended) X,Y point and it moves VERY slowly.

Possibly related to this: We machine mostly plastics, and they tend to develop a lot of static charge. Last week, I was moving the carriage without the spindle turning, and I noticed that plastic debris on the table was following the bit as though it was a magnet.

I have thoroughly grounded every part of this machine I can think of. I even put a large strip of copper under my Sintra (extruded PVC) crash plate and bolted it to the gusset under my rails. The gears on all 3 stepper motors are tight and properly aligned.

Do I need to buy an expensive ionizer to discharge the static? Or does a more recent version of the software address this issue? Has anyone else encountered this?

Any help would be most appreciated – thanks!

[zeykr]

I'm not the best one to address the static or grounding, but I have found the latest version does do a better job of resume. In the past if I paused and resumed when using the CR command, it would move off someplace and go very slowly - with latest version I can resume even in a CR command as when surfacing table. I do seem to have gotten more com errors with latest version though and no other intended changes.

You don't mention what message is stated in the pop up resume message you get - I have had two different machines develop problems with a prox switch where the movement of the machine would randomly cause the prox to trigger. Try running with prox switches disabled for a short time if you can and see if you still have problem. May at least narrow it down to where to look.

[paul_z]

Are chips falling on you Z zero plate? If so, I'd always store the plate with the ground clamped on the plate. (Other discretes such as the prox inputs go into the same chip which could be disrupted by a static discharge.)

[jerry_stanek]

You that it is grounded to an 8’ ground rod embedded in concrete. Concrete is not a proper ground especially if there is a vapor barrier used. Make sure you drive the ground rod to earth there may be several feet of stone under the concrete also.

[Gary Campbell]

Charlie...
Every time I have seen/heard the "stop with a thunk", it has been caused by static. Fixes depended on what actually needed grounding.

Agree with Jerry on the ground rod. They are a safe path to ground for lightning. They are very seldom a good low resistance ground for a computer controlled machine.

Ground your machine to something that is connected to the ground buss bar in your electical panel. Here is some additional grounding info: http://shopbotwiki.com/index.php?title=Grounding_your_ShopBot

None of the version I have seen can help with your problem.

[dana_swift]

One possible suggestion- get a bottle of spray fabric softener, and "spray" your plastics and cutting area to discharge the static buildup. You may have to spray every few minutes. If that stops the problem then you know for certain that the static is the source for your stopping problem.

The solution may not be so simple. There is nothing you can ground to get rid of static on a non-conductor. Increasing the humidity in your shop would be of assistance perhaps, as most of your cut surface is in contact with air.

It would be an interesting thing to run the equations to test Paul's hypothesis. I can imagine a mythbusters style experiment to try to force it fail that way..

The fabric softener is worth a try tho. Much easier/cheaper than stringing copper all over the place, and vastly more likely to work.

[dldalley]

We had a similar situation, and it eneded up being a computer resource issue. Other applications were in use on the machine at the same time it was being used by the CNC machine....it was basically a resource management issue...not sure if this is the same issue that you are experencing, however it did take us awhile to trouble shoot the problem.

Hope this helps

[myxpykalix]

Unless i missed it you don't say if you are using dust collection? If so you need to run a copper wire thru the dust collection and ground it to your dust collector.

I was having the same issues when i first got my bot and after i did that it has never happened again.

[paul_z]

I mention the Zzero plate unprotected as a possible cause because it happened to me. I reached for my Zzero plate as a cut was nearly finished. It was winter and the humidity was very low. I could feel the discharge and my machine stopped and my router shut down. Since then, I always ground my Zzero plate when not in use.

ESD protected inputs are usually designed to prevent hard failures, not operational upsets. (BTW I do not know if ESD protected devices are even used on the bots.)

It is so easy to provide low impedance protection to the input by grounding it with the grounding clamp when not in use.

[signsbyjay]

Another item to consider with an earth ground is the moisture in the ground. I have had similar problems that were solved simply by pouring a bottle of water at the base of my grounding rod(where it enters the floor).

Jay

[dana_swift]

Paul- I can see that happening easily the way you describe, from static built up on your body. I do like the idea of grounding the zzero plate and avoiding the issue.

Thanks for the suggestion. :)

[kubotaman]

I feel that your comment of the plastic chips following the bit as it moves is the key. When I got my Bot I surfaced the MDF table first thing. Of course it shutdown half way thru. My fix was to install a normal hardware small diameter cable thru the dust collector hose which is grounded on my dust collecter by way of a small aligator clip. Has worked for two years now without a hitch. One day I forgot to clip the cable to the dust collector and when I did install it while the Bot was running it just about put me on my keester!!!! Just some thought!!