Question UCCNC and limit-switches, difficulties with

I've only got myself to blame, for I added the T-slot table to an otherwise working Stepcraft, which promptly had an 'attack of the vapours' and now resolutely declines to operate!

The problem is reported as "Reset logic active, etc", which is usually corrected by override/reset in the UCCNC software. This time, despite dismantling to check the x/y/z green limit swtches, and checking their operation mechanically and electrically, I cannot clear the error-code. The x axis limit switch - the bastard right behind the gantry-plate - was mechanicallty stuck, but on freeing, still the error code presents.

I've resistance-tested the limit switches with a multimeter, and am getting some odd results when measuring across the "outside" terminals to which :

The y axis switch reads - half-scale defletion and nil resistance as switch is cycled.
The x axis switch reads - untestable without further dismantling
The Z axis switch reads nil and infinite resistance as switch is cycled

Questions:

1. I believe I have read that these limit switches - which only work in one direction of travel per axis, are only of use in WinPC, and not at all with UCCNC, unless one accidentally "hits the buffers" in the particular direction of travel "protected" by that limit switch. So, if running UCCNC are these switches redundant? (obviously not including the emergency stop button!)

2. If these switches are required for UCCNC, can anyone please suggest a line of enquiry or common-fault, or indeed wiring error, that might account for these values?

Many thanks in advance.

HI

I work with a 420/2 and UCCNC and it works flawlesley

The switches trigger the motorstop on the different axis.

please think that all 3 switches are in serial, so you should measure at the terminals on the stepcraft board and normally measure infinite ohms.. If you trigger one of the switches you should read 0 ohms.

Only measuring the switches does not exclude a pinched cable or something like that.

Good luck

Tom

Huff,

I likely had a similar problem when one of the limit switches in my XZ module went open circuit. Basically the wire had pulled off its connector due to it being too short (a problem "a small percentage of users" have also experienced). This thread might be of use.

https://www.stepcraft-systems.com/en/forum/software2/3646-some-issues-with-limits#38682

You can code them out if you're having problems but they ARE useful.

If all limit switches are active, you can home the machine, drive to the machine bed centre (or other reference point), note down the MACHINE co-ordinates (my spoil board centre is currently X = 298.375 mm, Y = 417.247 mm. Then if your machine loses steps or the software crashes and the workpiece is not ruined, you can re-home the machine then drive back to your fixed reference point on the MACHINE co-ordinates and re-zero.

I soldered the wires onto the XZ axis limit switches after dismantling and discovering what the problem was.

Doug

Hi,

If I may, let me set the record straight on limit switch operation.

All three switches are wired in series through normally closed contacts, so if all is correct there will be 0 ohms across all three when not triggered.

Homing any axis causes the machine to drive towards the associated switch until it is triggered and the circuit is opened. This open circuit situation is monitored by UCCNC/Mach3/WinPC, and when detected reverses the axis motion until the circuit recloses (switch hysteresis). At this point the appropriate preset (in the machine profile) offset parameters are loaded into the axis position stores.

If only one axis homing is commanded, operation of the machine stop there. On the other hand if three axis homing is commanded, the remaining axes will execute the above series of actions and the machine will stop in the "all home" position. The same limit switch line is used in all cases, being sent o/c by each axis switch in turn.

Hope that didn't sound too pedantic, I was trying to make the explanation unambiguous.

Peter

Hi Doug, I believe I've amended the settings in "configuration/x/y/z" axes, but the problem hasn't cleared. Attached are screenshots of the post changes for each axis. All the settings have been applied and saved, and UCCNC restarted, the settings having "stuck".

I've still an obstinately flashing reset button that won't clear. The only noticeable difference from before is that the bar on the over-ride button now no longer goes red when pressed.

Thoughts?

Check the Diagnostic and if you have disabled softlimits:

No limit switch pressed:


One limit switch pressed (here I pressed Y):


Softlimits disabled:


Did you check if the UC100 interface is connented properly?