Messages saying LIMIT SWITCH HIT

[Chuck Keysor]

Hello Shopbot Friends:

As I continue to nibble away at my railing project, I created a set of cut files, for the left and right halves of my arches. In total, I have 3 right half files, and 3 left half files. The left and right halves are mirror images.

On two of the 6 cut files (generated in Aspire 4 for my Shopbot), after the cutting has been completed, and the spindle is moving to the home position, (about halfway back home in the x direction), my machine stops, and I get an error message, saying "Limit switch hit". (On the attached file, it said that the Current line was 1225.)

I hit the "Resume" screen button, and then the spindle continues on to its home position, and then stops as it should.

Since I get this message when I am nowhere near any limit switches, and am just traversing an area of my stock that has been heavily machined, this is clearly a bug.

But in the two of the 6 files where this happens (all files are just different tools making different cuts in the same area of the material), the "limit switch hit" message occurs only when all the cutting is done, and the spindle is heading home. It noted the line where execution stopped, but there were not line numbers visible. In any event, I pasted the start and the end of one of the affected files into the attachment.

Machining for each file is taking place across the entire area of my stock. So if in fact, I had a real limit switch error with one file, the error should take place with all 6 cut files, not just 2. And as noted, I am nowhere near any of the limit switches anyway.

I deleted one of my misbehaving cut files, and created a new one. It did the same thing, IE stopped, claiming I had hit a limit switch.

Can anyone tell me what is wrong, that my machine is stopping, with the false error message that the "limit switch hit" has occurred? I have looked at this file, and can't guess or figure why anything is going wrong.

Thank you very much, Chuck

[bleeth]

Chuck:
There is nothing in the file that should cause that. I assume this is SB 3.8xx control software? If so, someone wrote that the latest version seems to have taken quite a few of the bugs out.

[ssflyer]

I'd suspect a static electricity issue. Do you have vacuum running? Bad ground can cause this.

[Ernie Balch]

I had the same error from day 1 on my early PRS alpha. I solved it by turning off the proximity limit switches. This solved the limit switch error but I continued to have occasional communication errors. I tried several computers over the years and turned off all other equipment and did all the anti-static things and still had occasional com problems.

Last year I replaced the controller board and usb cable and fixed all the com problems including the limit switch errors. So the problem was either the usb to serial converter or the control board itself.

ernie

balchsigns.com

[nat_wheatley]

I've had the limit switches turned off on my machine for 4 years because I was having this same issue.

[Chuck Keysor]

Thanks everyone for your replies. And thanks for confirming there is not a programming error. I updated my control software about a year to 18 months ago to whatever was newest then. (My Shopbot is in the basement, and I am upstairs eating my oatmeal, so I will check my control software later.)

I still have to cut two more blanks (with 7 arches on each) so I will take careful note of where my spindle is when operations lock up. Right now, it is my firm impression, that the spindle was at the same spot on the table both times it stopped.

And maybe two months ago, when I had a few long railing parts to cut, I started getting phantom error messages, saying I had exceeded my table limits, when in fact I was maybe 3 feet away from the far end of my bed. In those cases, I elected to ignore the warning and hit the resume option, and everything worked fine.

I'll post more clues later today, thanks again so much, Chuck

[Andre.multigraphics]

I have just set up a PRS and am trying to do the table surfacing and I am getting the same "LIMIT SWITCH HIT" and nothing is happening. Can anyone help here

[coryatjohn]

Andre,

Are you actually hitting the limits? Check to make sure your limit switches are:

1. Connected properly
2. Positioned correctly
3. Functioning (LED goes on and off) when tripped

Double check that the limit switches aren't placed too close to the edges of your table. The table surface routine actually goes beyond the table boundaries by 1/2 the width of your surfacing bit.

[erniek]

I had random limit switch triggers happening once in a while too. Then a few months later the limit switch sensor broke in half for no apparent reason. Made me think that the sensor was defective and causing the random triggers.

[Chuck Keysor]

Follow-up from Chuck:

a) I ran three more arch panels (three different cut files for each arch panel). Only one messed up with the error message saying "Limit Switch Hit!" Again, it happened after all the file operations had been completed and the spindle was heading to the home position. While the position at which this occurred was in the generally same area, about 15 inches away from 0,0, it was not in the exact same spot. And this time it happened with the one of three cut files that had not messed up before. So the problem seems random on one level, but consistent in regards to when this will go wrong (heading home after cutting is done).

b) I have SB 3.6.38, control box firmware version 140
speed 4: 460,800
OS = 2; 5.01

c) I use my proximity switches regularly, as I frequently re-zero my gantry on start-up. They seem fine, though that operation does not utilize the proximity switch at the far end of the table.

I don't suppose these observations offer any concrete clues......

Hmmmmmm, Chuck

[gundog]

I have had the same issue and it is on the way at rapid to home and never close to a proximity switch. I am going to try some ground wire through my collector hose from the machine to my metal duct that was suggested by Brady. I am not convinced this is a static issue.

Mike

[Chuck Keysor]

PS: I forgot to mention that I do not have a dust collection system, so in that case I would not expect static to be an issue. Especially since I have my shop in my slightly damp basement......

I have a 5 foot 12 gage wire screwed into my AC power panel (which has a big grounding rod right on the other side of the wall). I had drilled a hole into my PRT's steel frame and had a lug, star washer and a screw and nut, with the paint scraped off of the frame, all tightly secured. Now, I did have a nice beefy alligator to connect my ground lug to the ground wire. But before my last three panels of arches, I removed the ground clip and soldered the ground wire directly to the lug on my PRT frame. And I had one fault occur after I soldered the connection. Chuck

[bleeth]

Chuck:

From your existing main frame ground run another one up to your Y gantry and continue from there to your z slide.

[gerryv]

I think I recall sometime back that some have fixed the problem by going to another brand or brand/style of limit switches. I don't believe they're that expensive even for good quality ones sourced from N. A. based industrial supply houses. Anyone else recall those posts? There may be some good suggestions there.

[bob_dodd]

Chuck ; Maybe try moving the SO,1,0 command to the very end , after Bot reaches 0,0 . Their might be interference with the spindle shutting down

[Chuck Keysor]

Thanks for the replies......!

Dave R.... I will try your suggestion first as it seems to be pretty straight forward. This afternoon, I did implement the grounding you recommended. I soldered a 12 gauge stranded wire onto my original ground lug, and ran it through the X e-chain and then soldered the other end onto a ground lug bolted on to the y-car. And also onto that lug I soldered another 12 gauge stranded wire and ran that through the Y e-chain along with the spindle cable, and with a soldered on lug, terminated the ground under a metric Allen head screw that holds the fan onto the top of my spindle. But all the connections are soldered as noted, and I got good clean connections under each lug. But I haven't had a chance to run any files yet, as I was tied up the rest of the afternoon, and just got home 15 minutes ago.

I still have two panels with 18 arches to shape and cut out on each panel, so hopefully I will get a fair test of my changed ground. I will report back on this tomorrow!

Thanks Dave, and everyone else, Chuck

[Chuck Keysor]

Dave, I ran the affected cut files for about 4 hours today, and in all that time, everything worked perfectly. (I didn't get any messages saying "Limit Switch Hit".) Prior to making the grounding changes you recommended, I could not have run so many cycles without getting an error message. THANK YOU!!!!

a) I was going to attach pictures of the wiring, but my other PC, with Photoshop on it, is all messed up, and I am not having any luck trying to get it to boot......... But what you explained is pretty straight forward, so the pictures may not be very critical.

b) I should know better than to say everything is fixed, because if I say that, it may mess up again....... To be scientific, I should disconnect the newly added ground wires, and see that I start to get "Limit Switch Hit" error messages again..... But I have to work on all the brackets I have cut out (and bang my head in frustration with the other PC that won't boot.....)

But for now, I feel very confident that my "Limit Switch Hit" error message problem has been resolved! Thank you so much Dave!

Chuck

(PS: I'll post pictures IF/after I get my other PC working, and give an update if my Shopbot starts to send "Limit Switch Hit" messages again.........)

[bleeth]

You're welcome Chuck. It was Ron who reminded me of the likelihood of it being grounding and your clear description of your set-up that gave the info for the probable fix.

[Chuck Keysor]

Dave, here are the photos which show how I implemented your grounding suggestions, which seem to have ended my months long plague of false "Limit Switch Hit!" error messages.

As noted on the photos, I originally had a single chassis ground wire going from the bottom of my Shopbot frame to the AC panel. The 12 gauge wire was only 5 feet long, and it was bolted with a solder lug onto my chassis at one end, and then with a lug and screw, attached to my AC panel chassis. The ground for the AC panel was right on the other side of the basement wall.

The change recommended was to ground the Z car and the Y car. The attached photos show how I actually implemented those two grounding changes.

Thanks again Dave! Chuck

[coryatjohn]

Chuck,

You've inspired me to double ground my Y and Z with dedicated cables.

[bleeth]

"Double Ground"? Make sure you don't create a ground loop. That will accomplish the opposite of what you are trying to do.