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There should be no more than 1 ms in hal/LinuxCNC lag at a 1 ms servo thread rate.
if the probe signal goes through multiple hal components, they need to be addf'ed to the
servo thread in processing sequence or you will add additional pipeline delays.


That is, the sequence should be:

hardware read
process-0
process-1
process-2
motion
hardware write

PCW wrote:

You would normally choose a latch velocity low enough that the 1 ms (max) sampling uncertainty causes a minimal position error when probing.

I pondered this truth at one point recently, and did some experiments.  I wondered if the "signal lag" due to communications and HAL processing (I needed to add a noise remover[1] and mux[2] to my probe inputs, so I was at around 10ms of lag at the time, assuming each HAL component added at least one servo-loop of lag) was reducing precision here and causing the motion to continue past the actual probe point, and wondering how fast I could probe without destroying my toolsetter (testing delayed while toolsetter repaired) limited by this lag and deceleration limits.

My first findings were that the HAL lag was significant and I had to limit "fast" probing to 6in/m or so, which made me wonder: I have the axis accel limited to reduce overshoot at the tool[3], but is there a way to override that when probing or homing so I can stop faster?  Does homing use the joint accel limit instead of the axis accel?  Can accel be changed by gcode or HAL?

My second findings were thus: if I probe towards and capture the result, then probe away at the same speed and capture *that* result, and average them, I get results that are more consistent and less dependent on probing speed.  If this makes sense, one could drastically reducing probing time, but "probe slow enough" is just so much easier

Does it sound like I understand what's going on?  Is there any value in pursuing the dual-probe-average method?

Is HAL lag impacted by the order in which stuff is listed in the config files?  It would suck if I were calculating the probe signal just *before* reading the 7i76


[1] Aluminum extrusion CNC with 7i76 here, and sometimes the ATC actions vibrate the frame enough to trigger the toolsetter.  Bad for normal operation, good for detecting failed tool releases
[2] I change the noise limits and/or disable the toolsetter based on the machine's XY position, as a "fix" for the above.
[3] the servos can stop on a dime, but the rest of the machine is limited by its strength and momentum.
[4] I really like the Mesa products, and really appreciate the work you folks have put into them
 

There are reasons why brushed DC motor powered machines have two sets of limit switches, one set does normal limiting while the other set is "extreme limits" that will cut all power to motors.
Brushless DC and steppers motors have no need for such measures as if the drive fails it usually causes the motors to lock and burn quietly, if all other safety measures fail.

Hello snowgoer540,

I had a quick question: would it be possible to also set or override the Material Thickness using magic comments in the G-code?

The idea would be to pass the material thickness directly from the CAM/post-processor, to avoid manual input and reduce the risk of forgetting to set it in the UI. This could be especially useful when running multiple materials with different thicknesses in sequence.

Regards

tommylight wrote:

Or on weak machines where any motor can do damage.  I had an accidental "hard stop homing" on my old wooden CNC.  The limit switch failed and the motors ripped the end off the gantry before I could stop it.
 

I should probably mention how it's set up.  You will have a spinbox for Slat Height in the Probing section, and a spinbox for Thickness in the Material section of the Parameters tab.  If you set BOTH the Slat Height AND the Material Thickness, then the probe start height will change based on the material thickness. 

If either Slat Height OR Material Thickness are 0, then it will default to Probe Height.  A high level recommendation I have (I have not tested this in practice, yet) would be to set Probe Height to 0.  When Probe Height is 0, the probe movement will begin at probe speed from the current Z position.  In most, if not all, cases while running a program, this would start a 5mm (0.197") below Z maximum height, as the g-code filter automagically adds these moves by default.  That means that if you forgot to set a material thickness, your probe would start from the highest point possible, and it would probably be obvious that you need to fix it, and it would be the "safest" option.  

 

Sorry, for some reason it wouldn't upload some of my pictures.

I found a Hypertherm PDF on grounding. My conclusion is that I need a grounding rod in the ground. I do not currently have one. I will start there. And I will go through my shielding grounding to make sure that is good.

Ah thanks that might be a better option!

The smart serial error was likely due to a bad cable connection which has been fixed, but my main concern was ensuring motion could stop if something happens to the smart serial connection.

The run pin didn't seem to clear. It makes sense that the 7i84 I/O pins stop updating but I didn't think the smart serial run pin changed either. I'll double check and post back, but it didn't look like the run pin went low when smart serial was interrupted.

Thanks again for the quick reply! Merry Christmas!

Thank you for the explanation.
Just for a short conclusion in other words. LinxCNC "works" together with mesa HW like a "closed loop regulator". Linux "controlles" the executed steps donbe by mesa in the servo thread and corrects if necassary?
If this is the case I can estimate the error during milling and probing.

Line 24, replace this:

with this:
works for me on 2.10:

 

UH, too hard to me, not understand anythink this all code, but need use touch probe tool height setting only.

how install and use if not newer before has understand code, or hal or ini or what all this need and what all have. and were have. not understand code.

It looks like you are still running the old version of ethercat master.
I look at this message in syslogThis means the EoE code is still active in the ethercat master.
When EoE is removed from the master, all messaged with EoE will disappear.

Make sure to remove the debian/apt installed version of the ethercat masterThen re-compile and re-install the new version of ethercat master.
Also, the configure statement I told you was wrong (sorry about that), it should beand continue to install according to INSTALL.md.

When you have the ethercat master up and running again, check the syslog. There should be no EOE mentioned.
This must work, it is all dependent on that EoE is removed.

i used hard stop homing on many machines with mitsubishi/yaskawa servo drives. all of them have a "torque limit" input and a "torque clamped" output. so just connecting

joint.*.homing => servo-*.limit-torque
joint.*.home-sw-in <= servo-*.torque-clamped

does the trick.

and here's the video when i'm using "torque-clamped" for motion.probe-input. with z axis driven by 2mm pitch sync belt on 20 teeth pulley it is able to resolve silkscreen paint thickness on a PCB...

Oh no, something else not quite right with my build. The halrun binary seems to be missing. I will try to find out how that dropped out. I will need it for the project where I plan to use this pi3.