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Limit switch being triggered whilst homing?
« on: July 04, 2015, 08:27:00 AM »
Hi guys,

My homing and limit switches are the same and all are wired in series to the same one port.

If I hit a limit switch it is triggered straight away in mach and works great.

My problem is when I am trying to home all the axis. If I have my limit switches enabled when it homes as soon as it hits the limit/home switch Mach3 sees the limit switch triggered and just stops. I thought Mach 3 was set to ignore limit switches when homing?

If I disable the limit switches whilst homing Mach3 does home but it seems to go past the switch trigger by about 1 second before starting to back off, which is odd as when limit switch is turned on as soon as the switch is hit mach sees it and stops.

Any help would be much appreciated!.

Thanks

Offline ger21

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Re: Limit switch being triggered whilst homing?
« Reply #1 on: July 04, 2015, 08:53:56 AM »
You either have a bit of noise, or switch bounce.

Mach3 uses the switches differently for limits and home switches.

For a limit, Mach3 reacts as soon as the switch is tripped.

For a home, Mach3 keeps moving until the switch is tripped, then backs up until the switch opens back up. At this point, it becomes a limit switch again, and any bounce in the switch or noise can trigger it.

Not sure why you're seeing it trigger so slowly? Are you moving at the same speed when you observe the difference?
Gerry

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Re: Limit switch being triggered whilst homing?
« Reply #2 on: July 04, 2015, 08:59:36 AM »
Thanks for the quick reply ger21

I'm a bit confused to be honest.

"For a limit, Mach3 reacts as soon as the switch is tripped.

For a home, Mach3 keeps moving until the switch is tripped"

Is that not the same thing? If the switch is tripped its tripped, its either open or closed I dident think there was any middle ground. I'm not sure why when limit switch's are enabled and I do a refallhome mach3 stops straight away every time showing as limit switch hit, but when they are disabled in homing mode it keeps going for a bit when hitting the same switch before then backing off. :(

Everything ive read online so far says when homing mach 3 should ignore limit switches completely even if they are effectively the same switch as the home switch and on the same pin.
« Last Edit: July 04, 2015, 09:01:32 AM by Tilezzzzz »

Offline BR549

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Re: Limit switch being triggered whilst homing?
« Reply #3 on: July 04, 2015, 10:57:16 AM »
It sounds as if you have very slow acceleration/deaccelleration. THAT would explain the long overtravel to a stop when homing.  ALSO you may have to set a debounce to account for any switch bounce?? Best to fix the switch problem but debounce can help in testing.

IF when homing you get a switch bounce it automatically will set back to limit and IF there is another make of the switch (rebound) it will trip the limit.

(;-) TP
Re: Limit switch being triggered whilst homing?
« Reply #4 on: July 04, 2015, 11:11:33 AM »
Ohh I think I understand now.

Where should i be adjusting the acceleration/decelaration? Should that be edited in general config or somwhere in the motor settings?

Is there a recommended setting?

Thanks guys

Offline ger21

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Re: Limit switch being triggered whilst homing?
« Reply #5 on: July 04, 2015, 11:33:09 AM »
In the motor tuning. Generally, the higher the accel, the better the machine will perform. It usually takes a bit of trial and error to find a reliable value, and all machines are different.

To add to what I said before:
With limits, Mach3 stops as soon as the switch is triggered.
When homing, Mach3 will decelerate when the switch is tripped, then back off the switch until it opens. The home position is the position when the switch opens, not when it's originally tripped.
Gerry

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JointCAM Dovetail and Box Joint software
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Offline BR549

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Re: Limit switch being triggered whilst homing?
« Reply #6 on: July 04, 2015, 12:18:29 PM »
Actually the home position is where the axis comes to a stop after it resets the switch NOT on switch closure. THAT was recently discovered by users.

(;-) TP
Re: Limit switch being triggered whilst homing?
« Reply #7 on: July 05, 2015, 07:08:47 AM »
Thanks guys,

So I have messed with the acceleration settings of the motors and it made a very slight difference I think but it did not solve the problem of going to far after hitting the home switch.

I have also tried adding debounce (up to 4000 from 0) in the general config settings however that dident seem to make any difference to the problem I have when limit switches are enabled.

I have however found a way of homing without my machine trying to destroy itself, that was to turn the homing speed down to 3%, that way it doesn't go far past the switch before it backs off. (This is still with the limit switches turned off)

Im not sure if it makes a difference but the Diver board im using is DDSM4V5.0, which came with a DDream plugin for Mach 3. In the manual it recommends going to the plugin config and adding the following values which is what I currently have set. Should I be changing these settings to something else in the plugin config?

Device Buffer: 400ms

Jog Buffer: 100ms

-----------------

I do however have a new problem though which I dident notice before., My machine wont home Y axis, it does Z, the X and thinks that it is finished. I have checked Y axis is enabled everywhere I can think of and I am able to jog the machine along the Y axis with no problems. Also upon importing Gcode it doesn't show up in the table view so I think the machine must think it cant use Y for some reason? Any ideas? :) -

Thanks guys,

« Last Edit: July 05, 2015, 07:18:14 AM by Tilezzzzz »

Offline ger21

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Re: Limit switch being triggered whilst homing?
« Reply #8 on: July 05, 2015, 08:27:56 AM »
When using an external motion controller, the debounce in general config is not used.

What is your acceleration set to?

The motion controller should be handling the homing, so you should check in the plugin settings to see if there are any homing specific settings.

I don't know anything about that device or it's plugin, so don't really have anything else to offer.

Perhaps contact the manufacturer, or read through the device manual, if there is one.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html