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Offline BR549

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Re: Probe
« Reply #10 on: November 21, 2011, 07:01:26 PM »
HUM I have never seen it double write the trip point here. Once the initial trip takes place the G31 is no longer actively waiting for a trip it is already into the record and stop sequence of the code. At least that is how Art explained it a long time ago.

There IS switch travel to account for in the calibration of the simple probes. It may be small with some probes BUT it is there and measurable so you really need to account for it. ALso with a 3 legged circiuit the switch travel may vary around the radial movement of the probe.

Normally in calibaration you add the switch travel into the tip radius as a total tip radius. Mach3 DOES have a tip diam comp built in and it ONLY  comps the Var values of the G31 function.

A normal calibration function would be the ball and post method. It sets the Tip comp AND the axis offsets in the same test.

(;-) TP



Offline Tweakie.CNC

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Re: Probe
« Reply #11 on: November 22, 2011, 02:18:26 AM »
Quote
HOWEVER - if the probe contacts are re-made and then re-broken during that decceleration phase, Mach will RE-WRITE that point as the point of contact.

Quote
HUM I have never seen it double write the trip point here. Once the initial trip takes place the G31 is no longer actively waiting for a trip it is already into the record and stop sequence of the code. At least that is how Art explained it a long time ago.

Perhaps this point needs to be investigated, at least as it applies to the latest lockdown version - does it re-write or not ??

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

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Re: Probe
« Reply #12 on: November 22, 2011, 04:29:14 AM »
HUM I have never seen it double write the trip point here.

Probably because you have decent acceleration and therefore don't notice it. Wind down your accel to a minimum and try it. As it's decelerating after the first trip, trip it again (several times if you like) . The appropriate var will be set to the position of the LAST trip. I've tested this a gazillion times when doing my probing routines with 3.42.20 - can't speak for other versions. Your milage may vary (arf  ;D).

Ian

Offline Tweakie.CNC

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Re: Probe
« Reply #13 on: November 22, 2011, 04:36:56 AM »
Ian,

With version R3.043.022 and using G90 G31 any deceleration settings in motor tuning are totally ignored when the Z Axis comes to a halt.
I am still testing but so far I can find no evidence that the value retrieved from Get Var (2002) is over-written by any subsequent contact, it is just the first trip point that is recorded.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

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Re: Probe
« Reply #14 on: November 22, 2011, 05:32:20 AM »
any deceleration settings in motor tuning are totally ignored when the Z Axis comes to a halt.

Not sure I understand what you mean Tweakie.

Anyway it seems my memory is not what it used to be - time to give it up and grow veg I think. I've mis-described the issue. I'll try again. If the trip (or as many trips as you like as it's decelerating after the first trip) is/are momentary i.e. bounced as per my original description of a "glancing blow", then the value stored is where the axis stops after decelerating and NOT where the trip occurred. HOWEVER if the last trip of several remains made (i.e. does not bounce) then the FIRST trip is what is recorded.

Ian
« Last Edit: November 22, 2011, 05:45:35 AM by stirling »

Offline Tweakie.CNC

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Re: Probe
« Reply #15 on: November 22, 2011, 05:46:44 AM »
Ian,

Quote
Probably because you have decent acceleration and therefore don't notice it. Wind down your accel to a minimum and try it

With version R3.043.022 and using G90 G31 the Z axis comes to a halt after first contact without any regard to acceleration settings, winding down the Acceleration has no effect.

Quote
If the trip (or as many trips as you like as it's decelerating after the first trip) is/are momentary i.e. bounced as per my original description of a "glancing blow", then the value stored is where the axis stops after decelerating and NOT where the trip occurred.

This is not what I am finding from the tests I have done so far. As mentioned the value retrieved from Get Var (2002) is the first contact point not where the axis finished up.
Could you perhaps describe a test method that you have used to support your re-writing of the value please.

Tweakie.



Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Tweakie.CNC

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Re: Probe
« Reply #16 on: November 22, 2011, 06:36:08 AM »
Correction to above ....

By increasing my probing feedrate to a much higher rate than I would normally use the acceleration settings do have an effect on the axis deceleration after a trip has occurred but I can still not see a second contact during that period making any changes to the Get Var (2002) value.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

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Re: Probe
« Reply #17 on: November 22, 2011, 08:21:17 AM »
As you've found, you have to set your feedrate high and your accel low otherwise you can't see what's happening. (It's still happening - you just can't see it). Here's the settings I'm using to show this issue. I use the X axis but it doesn't really matter because it's best done offline if your machine can't actually take the velocity value below.

Max velocity 15000mm/min, Accel 62.5mm/s/s (the lowest I can get Mach to take at that vel). Then run this:

F15000
G31 X5000
M666 (just displays var 2000 i.e. message getVar(2000))
M30

Now if I let it accel and get to approx X=1000 and then trigger AND HOLD the probe, Mach will start the decel ramp and eventually stop around X=1500 or so. The value in var 2000 is correct i.e. approx 1000 i.e. where it was first triggered.

Now do the same again but at approx X=1000 trip AND RELEASE the probe. Mach will again start it's decel ramp but when it stops the value in var 2000 is approx 1500 i.e. the same as the X DRO i.e. where it's come to a stop.

You can do this with no machine "attached" and you can either use a real probe, a switch or even with the keyboard using probe emulation.

Ian

Offline BR549

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Re: Probe
« Reply #18 on: November 22, 2011, 10:16:22 AM »
Something must have changed in the G31. In early testing and argueing with Art about which was the best probe cycle type 1 or 2 it did not do that.

I tested every combination we could think of to test the accuraccy of the cycles. Art ending upbeing right about the accuracy but wrong about the "best" cycle. But it never got added(;-)

Ian do you have a debounce setting that may be blocking the first trip????  I do know the testing I did was before the debounce was added in.

Perhaps the debonce routine that was added played havic on the original code???

Just a thought(;-) TP

(;-) TP

Offline Tweakie.CNC

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Re: Probe
« Reply #19 on: November 22, 2011, 10:34:27 AM »
Thanks for the info Ian.

My machine is busy for the next couple of days but it will be free for the weekend - I will do some more testing then and report back.  :)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.