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The vfd has a braking resistor. Now its being controlled, the issue has disappeared.
Think I just read that I should put P to zero and D to 1.

The oddness is possibly due to a VFD overvoltage on rapid decceleration. 
You may need to add a braking resistor to the VFD if you need faster decceleration.

Another  possibility is to limit the spindle speed rate of change by passing
the commanded  RPM through LinuxCNC's limit2 component.

 

Hello everyone!

I am currently investigating a linuxcnc retrofit on a Fadal 4020HT. The machine is a 1996, and I am as of now unsure if it has AC or DC servos. Still figuring out if I am going to go ahead with purchasing it...its potentially a steal!

So background, I am already pretty familiar with linuxcnc. I have a gantry mill that I built from the groundup running linuxcnc/gmoccapy that I make my living with building guitars. Looking to move to something more powerful with an ATC and so I'm shopping VMCs.  Might sound strange but they are a standard for a lot of guitar manufacturers and would greatly improve my workflow.

So this 4020 is from a good sized machine shop, it is under power but hasn't really been used for about a year.  I was able to inspect it and mechanically it is in great shape. There appears to be some sort of problem with the spindle orientation sensing on it. It is running an old 88HS control right now. 

My intention is to potentially purchase this machine and move it over to linuxcnc with probe basic.  Any general guidance or tips from people that have been down a similar road would be greatly appreciated. I also have a few specific questions:

• Since I'm using linuxcnc, is it reasonable or a good idea now or in the future to change the spindle drive over to a modern VFD while retaining the original spindle? I know these spindle drives can be a big cost and difficulty when they go out. I'm also not sure how compatible the existing drive would be with linuxcnc control.
• Related to the above, I am interested in running this conversion on single phase power if that is possible. I believe the servo drivers all ultimately run on DC power, whether they are AC or DC servos, correct? In that case, if I were to also be able to run a VFD from single phase I should be able to avoid the phase converter route. 
• I have not had much luck finding wiring diagrams that give specifics about the lines for the encoders/resolvers on the servos. Does anyone have a good reference for their detailed function to help me figure out how to interface with mesa cards?
• What is the general opinion on homing and limits for fadal conversions? This one, like most or all of them, has that cold start system where you line up the marks on each axis and let the resolvers/encoders do their routine at startup. As far as I understand it has no limit switches or scales or similar. Is it preferable to mimic the same sort of system with linuxcnc or install some sort of homing switches?
• Has anyone had any luck interfacing a jog wheel interface on a VMC with linuxcnc? I would absolutely love to keep that function.

Thank you in advance for any insights you have to offer!

Wie schon gesagt. Das einfachste wären die sserial (smart serial) Karten. Das ist plug n play. Bei der 7i84 zb. hast du s.g. Darlington Ausgänge. Die klnnen kleinere induktive Lasten wie Relaisspulen oder deine Ventile treiben. Haben sogar Freilaufdioden integriert.

Wenn dein Expansionport noch frei ist, kannst du auch die billige Selbstbaulösung fahren. An dem Port liegen 17 IO Pins des Fpgas frei, die du an Relaisboards klemmen kannst. Bzw. an deren Optokopplereingängen natürlich.

Also. Etwas Eigenbau/Gefrickel und du hast Kosten um die 20 Euro. Oder ne 7i84 zum Beispiel die wesentlich mehr kann und plug n play ist. Kosten so um die 100 Euro. Beides ligitim und die Mesakarten sind allesamt tiptop.

P values from 1.5 up to 4 are now controlling, but with an increasing frequency of oscillation the higher the P.
Time to dig out Tommy and JT's tuning guides.

Hallo DG9MDR
Danke für die Info. Werde es Versuchen zu finden.
Gruß Hans (OE6LNG) wenn das ein Amateur Rufzeichen war.

I have now looked at the pid.s values and see that there is no pid.s.feedback
in the hal this is fed from:-
net spindle-vel-cmd-rpm-abs which also has no value when the spindle runs.

So I have changed this to
net spindle-vel-cmd-rpm which is an active value of the current speed.

Nothing changes, so I guess have to set some of the PID values now?

Thanks Peter.
At high speed 3500 gets me 3400, but 300rpm ends up with 500
Also I have an 'oddness'
If I call for too big a jump in speed reduction, say from 3500 to 1000, an internal part of the vfd drops out the enable relay that is set by M3. If I drop the speed in smaller steps, this doesn't happen. (Probably one to sort out with a max rate of deceleration later. ) Acceleration from 0 to 3500 is ok.
I think for now I'd like to concentrate on getting the low speed more precise.

langdons wrote:

Consider using Ubuntu's real-time kernel.

ubuntu.com/real-time

Try installing from the official ISO just to check: www.linuxcnc.org/iso/linuxcnc_2.9.4-amd64.hybrid.iso

Is the package 

linuxcnc-uspace-rtai installed?

Why?????
He is using LinuxCNC 2.5 (probably still named EMC2) with RTAI kernel, while you insist on using RT-Preempt. They are not the same, although they mostly do the same thing.
And your package does not exist. There is linuxcnc-uspace and linuxcnc.
-
Although i admire your will to help, please refrain from dispensing useless information, it is costing us time and effort to fix them and might cost someone dearly.
At least do some checks before posting.

7i84 wurde OK sein, mit 32 eingange und 16 ausgange.
Werbindung zu Mesa 7i96S nur mit ein LAN cable, sehe die manual.
Da gibst noh
7i70 mit 48 eingang
7i71 und 7i72 mit 48 ausgang
-
Das ale kan uber ein bilige BOB gemaht sein, aus die IDC shteckdose im 7i96S, aber total sind 12 ausgange und 5 eingane werfugbar.

What type of PC.

forum.linuxcnc.org/45-espanol

May be helpful.

Try installing from the official ISO just to check: www.linuxcnc.org/iso/linuxcnc_2.9.4-amd64.hybrid.iso

I would make a couple changes in the ini file

OUTPUT_SCALE = 4500

(4500 is 10V/8V * 3600)

And initially I would try open loop
which means P,I,D = 0 and FF0=1

(FF0 should always be 1 regardless
of other PID parameters in a velocity-in/velocity-out
PID control loop like this spindle control )

Hallo was gibt es für die Mesa 7i96s für Erweiterungs   Carden,
Ich bräuchte 9 Ausgänge Für Spindel, Steckdosen (relay),
Pneumatic Ventile  und Zusatzgeräte.

mfg
Hilton