Hello Guest it is July 08, 2020, 01:34:30 AM

Author Topic: Homing and limit switches  (Read 1835 times)

0 Members and 1 Guest are viewing this topic.

Homing and limit switches
« on: October 09, 2013, 03:23:00 PM »
Greetings group and Art;

I've been using my DIY CNC for sometime now and recently had to remove my gantry for routine maintenance and change out one or two limit switches.

I've been using the switches as both limit and Home, My issue is, when I Home the axis's they trip on limit each and every time. I've checked all my settings and they appear to be okay. ( I used the auto set feature).

Any idea what is happening? Maybe it's very simple and I'm forgetting the basics or having a brain freeze.

Thanks in advance

Jerry

Offline Hood

*
  •  25,846 25,846
  • Carnoustie, Scotland
    • View Profile
Re: Homing and limit switches
« Reply #1 on: October 09, 2013, 04:29:09 PM »
Likely your switches are not positive snap acton switches and when Mach moves back off them they are closing and opening and closing etc. So what happens is Mach ignores them as limits when homing, hits the switch, backs off and sees the switch close and calls that home. However your switch is just on the edge of being closed/open so Mach sees it open again and this time it is treated as a limit and thus you get the Limit Triggered.
To be sure this is the case have a look at the LED at the side of the axis, if it changes to green when you home then that is your problem. If it is still red then there must be another issue and if you attach your xml I will look through it to see if there are config issues.
Hood
Re: Homing and limit switches
« Reply #2 on: October 09, 2013, 04:52:31 PM »
Thanks Hood,
I'll give that a go and let you know

Jerry
Re: Homing and limit switches
« Reply #3 on: October 09, 2013, 05:39:43 PM »
Hay Hood,

When I clicked on Ref All  the z axis moves first and trips the limit (the LED did not turn green, which if it did, would have indicated  Homed)

I Checked out the switches and discovered that when I activate them manually they appear to click twice and when I release the lever arm it clicks twice again !!!

I have no idea why, but can only guess that when you order a package of twelve switches for approx. $10.00 from china, "you get what you pay for"  :o   LOL

Any way I'm in the process of ordering a new set of quality switches.

Thanks for you help and take care

Jerry

Offline rcaffin

*
  •  1,029 1,029
    • View Profile
Re: Homing and limit switches
« Reply #4 on: October 09, 2013, 11:34:38 PM »
Quote
I Checked out the switches and discovered that when I activate them manually they appear to click twice and when I release the lever arm it clicks twice again !!!

Well known problem in the electronics world. It's callled 'switch bounce', and is exactly that.

cheers