Light Machine Corp. Benchman XTr (retrofit)

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20 Oct 2015 00:27 #63969 by steve_a
The other mill I helped convert uses LinuxCNC in open loop and I would have thought that would be all the Kflop/Kanalog would need to work. I see a lot of Mach3 stuff for this system but you do have me re-thinking again.
I actually don't like the idea of giving the PID task to the computer. I think a better system is to have the closed loop handled by dedicated electronics in the machine with the computer just sending g-code commands for the system to handle. I know the history of closed loop with LinuxCNC is great but as a hardware person, "philosophically" I prefer self contained systems.
The original system tasked the motion controller with running the PID for closed loop and as far as the software was concerned, it was open looped. The real negative with the Kflop is USB communication but because it is just interpreting g-code, that seems pretty safe.
I have yet to successfully tune a PID. It seems " more art then science" , to quote Galaxy Quest. The Ziegler-Nichols Method seems to be the most straight forward but it has you run the controller into an oscillation before you can do any calculations. Can be very scarey! Anyway, the point is, I want to be sure I can actually tune the darned thing and that is driving my concerns with the Mesa. This will be easier once I find out if the PID information is still in the computer and if it closely matches the numbers dynamyte24 posted.
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20 Oct 2015 03:44 #63980 by MacGalempsy
So the only values from Rex's PID numbers I found usable are the P and the following error. Everything else was not so great. Unfortunately, now my x-axis is not functioning, so it will be some time before I am back up and running on that axis. First I thought it was the motor, so swapped it out with a backup and it worked for about 1 minute before going out again. Then I swapped the amplifier over to the a-axis amp and it still does not work... Time to check the wiring agan because the output is working, but the motor is not.

I am seriously considering getting new amplifiers, ones that have a better track record with LinuxCNC. Does anyone have a recommendation?
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20 Oct 2015 12:23 #63990 by steve_a
Well, Good news bad news. I can confirm the information from Dynamyte24. I found the PID information for this machine.

The X-Y-Z

Kp 40
Ki 2
Kd 80 < this is the only difference. Dynamyte24's was 70.
Kv 80
Kvff 80
Follow Error .1
SPU 50,000
Int Range 40
Accel 20
Decel 20


A axis

Kp 40
Ki 2
Kd 80
Kv 80
Kvff 80
Follow Error .1
SPU 40,000
Int Range 40
Accel 20
Decel 20



Spindle (My spindle is 5,000 rpm but the numbers are the same:

Kp 10
Ki 10
Kd 40
Kv 0
Kvff 0
Follow Error .1
SPU 8000
Int Range .1
Accel 50
Decel 50
So the good news is that these are pretty much consistant numbers. the bad news is that it doesn't sound like this helps you Mac. That makes me wonder what the difference might be.
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20 Oct 2015 21:38 - 20 Oct 2015 21:40 #64004 by dynamyte24
Steve, check the machine serial# shown on the software with the actual serial# of your machine.

The software # for mine is: 110-55AE-0176
Machine # is 021-55AE-0184

The configuration files were shipped on 3.5 floppy while the actual CNC program was on a CD.


Rex
Last edit: 20 Oct 2015 21:40 by dynamyte24. Reason: speelage
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20 Oct 2015 22:28 #64007 by PCW
Note that there is no guarantee that the PID parameters are in the same units between systems...

Also if these are velocity mode drives, tuning is 99% getting the FF1 term correct since the drive itself closes
the current and velocity loops. If you scale the PID output correctly (in machine units per second at 10V)
FF1 will be 1.0

Ziegler Nichols is largely useless for velocity mode drives
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21 Oct 2015 09:51 - 21 Oct 2015 09:52 #64030 by steve_a
I checked the serial number in my configuration and on the machine and they matched! The PID numbers are in fact meant for this specific machine. If yours is working (dynamyte24) and those are valid numbers then that is very positive news. As PCW pointed out, the units may be different but I suspect they are similar enough that if one of us manages to get this, then we will all have a valid starting spot.
I'm back to using the Mesa cards. I am contemplating gutting the machine and spent time today looking at the toroids. I was reading the labels and trying to determine what voltages they supply. In the end, I think I might get raw voltages and need to provide regulators. There is a lot of interconnection with the power and the encoder breakout and the larger controller the encoder PCA attaches to. I also noticed that the 24V PS does not provide 24V unless there is sufficient air pressure. This is probably a safety feature to prevent the tool changer from moving if there is not sufficient air pressure. I am sorely tempted to trash all the power supplies and start over with the encoders, servo motors, DDN-019 and servo controllers. I want to look closer but there seems to be a large amount of control exerted by the two PCA that I most want to trash. If I can work around the Power supply interlocks and allow the new controller to take over, I won't have to do that but I'm not sure it is worth the time to figure out what the cards are doing. Unless I can get hold of a schematic , which is very unlikely, I don't want to waste too much time looking at that. I wrote down some wiring information and need to look that over for a bit and decide what to do next. I WOULD like to get some movement but without the motion controller card, that seems like it would be impossible.
Last edit: 21 Oct 2015 09:52 by steve_a. Reason: spelling
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21 Oct 2015 20:45 #64057 by andypugh

steve_a wrote: I WOULD like to get some movement but without the motion controller card, that seems like it would be impossible.


It is fairly common to test a velocity-mode drive with a 1.5v battery.
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22 Oct 2015 02:50 #64107 by steve_a
Mac Do you have a wiring diagram for your current setup? I'm curious as to what you've done so far.
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22 Oct 2015 07:53 - 23 Oct 2015 02:51 #64121 by MacGalempsy
I do have a complete wiring diagram, which took over 6 months of research and testing.

Here is a link to the manuals and such that I have come across.
Link: Dropbox Account

I have detailed pinouts on all connections coming off the factory boards, as well as signals.
I would be happy to provide these for a small fee, or trade for working ATC code.
Last edit: 23 Oct 2015 02:51 by MacGalempsy. Reason: Added info
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24 Oct 2015 07:01 - 24 Oct 2015 11:58 #64200 by steve_a
Mac,
Thanks for posting those files. Some of this is really making sense now. I attempted to move my Z axis with a 12 v Battery last night. I discovered the electric brake. It says 24V so I didn't even try. I am recharging my battery tonight and I might be able to see this beast move with a charged battery,
I also looked at the wiring to the axis encoders and believe I have a good map of the encoder connections. I'm going to assume that they are all the same.
Last edit: 24 Oct 2015 11:58 by steve_a. Reason: spelling
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