My First Problem...

[laserguy]

Ok, before I start, I have read all the posts here that I could find on the problem and I see a few items of contridicting information.

Here's the problem...

Aparently randomly during running some files the Limit switch trips. I don't know if it's x or y, it does it nowhere near the actual limit switches. If I bypass the message the file runs normally, but, it seems like it moves the x,y slightly. (probably from the jog) the system is a PRS Standard with 2.25 spindle.

Questions...

1) are the limit switches supposed to be ON (lit) all the time and go OFF (unlit) when tripped? or the other way around, I have seen people say both ways.

2) What are other causes that may lead to this.

Oh, The dust collector is grounded.

Thanks ever so much in advance for your help.

Mark

[GlenP]

Hey Mark, I have a PRS standard and if I hit my prox switches it will throw my home off bye a slight bit. Your prox switches should be lit (on) all the time. I am talking about the light on the switch not computer screen. They are normally closed switches and go off when hit the switch. Do you have your spindle wiring seperate from your prox wiring when they go across the gantry? I only have a router but I needed to keep the router wiring and the prox switch wiring seperated to avoid problems. I went to the hardware store and bought some plastic split wire cover and ran the prox in one cover and the router in another and then tie wrapped them away from each other. No prox issues. Because it is random it makes me think ground or static from power wiring. Good Luck. Post how you make out. If you need to call Frank at shopbot, they are second to none when it comes to support.

[myxpykalix]

Mark,
I have a PrtAlpha and unless they operate differently I have to disagree with GlenP with the prox switches.

In my setup the light on the end of the wire that is attached to the carriage normally when you operate your bot is NOT lit up unless you hit the limit (the bolt sticking up) that it senses THEN the light comes on and stays on till you back off from the limit.

I believe that that is the normal operating state of the switches. When ever i come to the limit switch the light comes on and the bot stops IMMEDIATELY.
They very well may have changed the setup with the newer bots and we both might be right!

[Gary Campbell]

Mark...

Your problem is usually an electrical noise issue.
The most common reasons for this to happen are: (random order)
1)Insufficient grounding. See this wiki article: http://shopbotwiki.com/index.php?title=Grounding_your_ShopBot

2)Wrapping or looping of the extra wires from spindle and stepper motors near that of the prox & z zero. Neatness may NOT be a plus here. Wire loops become electromagnets that induce current in other loops nearby.

3) In a few cases a proximity switch is bad.

When your machine gets the erroneous stop hit, write down the table coordinates, and look on the console to see if there is an active light on one of the inputs. (probe/zzero is 1, X is 2, Y is 3 and Estop is 4) Look at them prior to running a file to get accustomed to normal color configuration. This will help SB tech supt to track down problem.

You can also try turning the limit checking off. If this makes a difference, try turning on one prox switch at a time. This may narrow the problem down.

Good luck, Gary

[laserguy]

Glen, Thanks, I'll look at those wires, they are running in the "power chain" together, I'll try to pull them apart as far as possible, I'll also double check the ground.

Jack, I am starting to think you're right that they (ShopBot), at some point changed the lit/unlit switches because there are many places in this forum where people contradict each other on this point.


Thanks, I'll keep ya posted.

Mark

[laserguy]

Gary, Thanks that is great info, I'll run through all of that tomorrow.

Very thourough, I think even I can follow that :P

Many Thanks,

Mark

[Gary Campbell]

Mark...
The input section of the control board is very sensitive. The prox wires are long and can act like an antenna ..of sorts. Any kind of electrical noise that is picked up by these wires will be perceived by the control software as a stop hit. There may be dozens of sources of noise in our shops. Many of them caused by us, the "assembler". All with the same result... stop hit. Thats why the conflicting reports.

[dana_swift]

Mark, a simple way to see if you have noise that can get into your proximity switch wiring harness is to take a portable AM radio (remember those?) and tune it between stations. Turn the volume up and move the antenna around the suspect wiring.

If you have noise, it will be blaring out of the radio. Then you can turn off the culprit and it will go away. Then you can try something to "fix" it and see if it really is better.

If you do not get much noise when moving the antenna near the suspect wiring, then you can ground things all day and most likely accomplish nothing.

Its one of those old tricks, doesn't cost much, but can save you a lot.

If that gets nowhere, then I suggest you look at the TTL signals from the prox switches on the control board with an oscilloscope, if you don't have one, borrow one. If the signal is solid when the spindle is running , then noise of any kind is not your problem.

If the voltage on the input line to the card remains above 3.0 volts it doesn't matter how squiggly it is, likewise if it stays below 0.8 volts it can wiggle all it wants. Between 0.8 and 3.0 volts is "bad" and signals are required to traverse this region and stay out of it. If the signal enters this band transiently, something is unacceptable and needs to be located and fixed.

Now days, your problem is finding an AM radio! Any more most of what is in the stores in the way of portable gear is MP3 players, which have no value for this problem. O-Scopes can be found if you ask around.

If you cant find a "standard" am radio, you might try a short wave receiver. Then when you are finished debugging your "noise problem" you can see how fascinating our elections are to folks all around the world!

What a benefit..

D

[dana_swift]

Mark- a footnote.. electrical noise is everywhere, and you should expect "some" 60hz noise when you move the antenna near any power lines. What you are looking for is noise that is "different" than the noise you get when the spindle isn't running. Also see what it is with the control box turned off.

Good luck.

D

[Gary Campbell]

Dana...
Whay didnt someone tell me back in the 60's to keep that "transistor radio"? What do you mean between stations? You mean there are some?

Gary

[laserguy]

Thanks Dana, I don't think I have one, but I'll look :D

I may ask a question or two of you later today after I make my first try just to make sure I followed your directions correctly.

Mark

[dana_swift]

Mark- feel free! Its a simple way to see if you are barking up the right or wrong tree. Focus your efforts on what is provable rather than wild guesses.

You have mail- if you don't show you received it, you might check your spam box.

Gary- yes a lot of us threw those old transistors out a long time ago. Any AM radio will most likely do the job, another option is a hand held CB radio, but they are hard to find unless you visit a truck stop. Short wave is really the ideal choice, standard broadcast AM next, and lastly cb. What really matters is what an oscilloscope shows. If the oscilloscope shows no noise on the input line, the problem is in the prox switches, or from interference getting into the control card. (Ferrite beads may be a possible solution if that should prove to be the trouble)

D

[laserguy]

Well, good news.

I went through all of the wiring and made sure to separate the power leads from all of the other wires including the Limit Switch Sensors.

So far I have had no problems. I seems so far that the magnetic interference was the problem. I hope so at least. :D

Thanks for the help with the problem!

Mark