joint 0 limit error

good point John, always the simple things that escape me.

Well this is clearly a wire routing issue. I have moved things around and made it much better, but the glitches are still there. Also had forgotten to add the homing_ignore_limits = yes to the x axis. Of course that allows me to at least get homed. Also took out the limits for X, so now I just have a home switch.

Re-connecting for N/C didn't help. I think I will give sheilding a go next, but I don't have anything at home to try that with so it will have to wait. Thanks all for your help.

btvpimill wrote:

According to halscope, you are correct Jon. there are random spikes which sometimes lineup I guess to trip it on limit error. Currently yes the switches are snap action micro's, when hit pulls the line to ground. I do have pull-ups on the line, can't remember the value right now, but prolly 1K on a 5V system. I should note, this is NOT connected directly to the paraport. It goes though a uP which just multiplexes the switch's so I have enough I/O. I suppose this could be my uP screwing up, but I really doubt that since removing the switches removes the problem.

Would I be better to connect them to the NC side and have them always closed?

There are probably 5 reasons why NC is better. There is the noise immunity issue, then
what happens if a wire breaks, or oil gets into the switch and makes the contacts have
poor contact. NC is somewhat more "fail-safe".

You could add some capacitors that slow down transients on the sense wires.

Jon

Hi

If you have noise on your limits circuit(s) there are a couple of things you can do besides checking grounding, shielding etc.

One is to put a debounce component into the limit signal chain. This will have the effect of filtering out very momentary spikes and dips, because the level has to be low for x cycles before a condition is triggered.
I have used this before with a 3 phase motor driven mill which put noise into the power supply despite filters etc.

Another lateral solution, is one I used with a small mill with a particulary 'dirty' DC motor controller, unshielded, just plonked in a ABS housing. It continually triggered limit errors despite cable shielding etc.

Take a small 12v relay and a plugin 12v power supply.
Wire the limits in series to the relay coil, all powered by the 12v supply
Connect the NO relay contacts to your BOB as the signal.

The limits carrying 12v just to power a load coil, are pretty much immune to any noise and the signal pin gets a clean on/off from the relay contacts if a switch goes open circuit.

Unless there is some compelling reason to have separate limit switch inputs, I would chain them together, it saves inputs.
It is immediately apparent which axis triggered just by looking at the machine.

If you set up your soft limits properly and don't get your co-ordinates systems screwed up, you should never get to a limit switch situation anyway (in theory )

regards

debouncing would be perfect. I can debounce it through my I/O card. I was not aware EMC had a debounce component. I may just use it instead.

. This will have the effect of filtering out very momentary spikes and dips, because the level has to be low for x cycles before a condition is triggered.

Note the use of very momentary

Obviously if the debounce were set too high, the axis could overrun and cause damage before a condition registered.

(You could calculate your cycles per second, your max velocity movement per second and see how far the axis could travel in the
time required for activation if concerned)

Extracts from my mill .hal file

## problems with limit switch activation errors due to 3 phase noise
## try a debounce component to iron out momentary spikes

loadrt debounce cfg=2
addf debounce.0 base-thread

setp debounce.0.delay 30

net all-limit-raw <= parport.0.pin-13-in => debounce.0.0.in
net all-limit <= debounce.0.0.out

net all-limit => axis.0.neg-lim-sw-in
net all-limit => axis.0.pos-lim-sw-in
# above repeated for each axis


regards

PS I see I have just duplicated Andys input - should learn to type faster!