MEW 203 and motion controllers

[DerryUKParticipant @derryuk]

I was interested in what Marcus had to say about motion controllers (CNC in the ME workshop) but I am a little unsure how they overcome jitter.

Does a motion controller download all the commands from the PC first before starting a machining process?

[DerryUKParticipant @derryuk]

[Michael HornerParticipant @michaelhorner54327]

Hi DerryUK

Had a read of the article and I think what it is saying a command is sent to the contoller and the only function of the controller is to execute that command it's a bit like what he says about the separate display card, it takes the strain of the MPU. The controller may have a buffer(memory) so it can take more than one command at a time. It would come into its own on a slow PC or laptop.

HTH

Cheers Michael.

[Another JohnSParticipant @anotherjohns]

Have not read the article, but my experience with Mesa 5i25 cards and LinuxCNC might help.

Motion Control cards simply step commands, and format them nicely for the stepper motors (via the stepper motor drivers). The "waveforms" are nice and correct.

Now, while LinuxCNC is better at doing "software timing" than many other programmes (from what I read; almost real-time technology is in there that is not available under Windows and I'd love to be proven wrong) it still has trouble making beautiful waveforms required for accurate stepping when going quickly.

The 5I25 cards also have spindle rev input capability – timing software built into the card, so the software timing loop is not required on your main computer.

My little KX1 CNC mill went from "wow" to "WOW" when I put a 5i25 in it – I could speed up rapid moves dramatically – 100mm/sec is what I do, IIRC. (I can verify when near the machine should anyone ask for verification)

Another JohnS

http://cnc-for-model-engineers.blogspot.com

[DerryUKParticipant @derryuk]

I still don't get it really.

<when I put a 5i25 in it>

What were you using instead of the 5i25 previously John?

Derry.

[Another JohnSParticipant @anotherjohns]

I still don't get it really.

<when I put a 5i25 in it>

What were you using instead of the 5i25 previously John?

Derry – good of you to keep asking questions. Don't stop, until it is clear. I asked questions and others helped.

Before the 5i25 Mesa Motion Controller card, I used the old parallel printer port, that is controlled by software running on the main computer.

So, another way of looking at it; adding the 5i25 card gave me another computer, dedicated to taking simple instructions and "getting on with it", just like a manager at work should delegate to their employees.

Most PC based computers USED to have printer ports, some still do, but now sometimes you need to add in a card to the insides to get an old-fashoned printer port.

The printer ports are 25 pin long, thin connectors, pins in 2 rows on the connectors.

When I went to the Mesa 5i25, I unplugged my mill from the old fashoned printer port and plugged it into the 5I25, then reconfigured the software on my computer to use the 5i25.

I won't say "simply reconfigured" because I DID NOT understand what I was doing, but when it all clicked, I saw how the 5i25 delegated a lot of the really timing-critical parts of CNC to the 5i25, which allowed me to speed up the table travel significantly, without it having "timing errors"

Does that help? Coffee still brewing, so I hope it makes sense. If not, ask.

Another JohnS

[Anonymous]

Posted by John Alexander Stewart on 28/05/2013 22:52:52:

My little KX1 CNC mill went from "wow" to "WOW" when I put a 5i25 in it – I could speed up rapid moves dramatically – 100mm/sec is what I do, IIRC.

Blimey, 100mm/sec, that's impressive, 6 metres a minute, better than a Haas TM3.

Andrew

[Another JohnSParticipant @anotherjohns]

Posted by Andrew Johnston on 30/05/2013 15:32:38:

 

Posted by John Alexander Stewart on 28/05/2013 22:52:52:

My little KX1 CNC mill went from "wow" to "WOW" when I put a 5i25 in it – I could speed up rapid moves dramatically – 100mm/sec is what I do, IIRC.

Blimey, 100mm/sec, that's impressive, 6 metres a minute, better than a Haas TM3.

Andrew; Shown below is the Trajectory section of LinuxCNC for this mill. It's a Seig KX1-NU – came without controllers, so now has a Gecko G540, 48v supply, and a 5i25.

The computer running it is an Intel Atom-based D525MW, one core dedicated to the real time thread in LinuxCNC. (Don't think this is possible on a Windows machine???) The other core does UI, and all the other bits and pieces.

[TRAJ]
AXES = 4
COORDINATES = X Y Z A
MAX_ANGULAR_VELOCITY = 120.00
DEFAULT_ANGULAR_VELOCITY = 60.00
LINEAR_UNITS = mm
ANGULAR_UNITS = degree
CYCLE_TIME = 0.010
DEFAULT_VELOCITY = 20.0
MAX_LINEAR_VELOCITY = 100.00
HOME= 0 0 0 0

Yes, that's a max of 100 "machine units per second", which, is (via LINEAR_UNITS) mm.

The machine just flies during G0 moves!

I might tweak the trim pot for the "A" axis on the G540 to get that axis tuned, but it's a bit of a hassle getting into the internals ATM. Still, 120 degrees/sec on a Sherline rotary table is not bad.

I am *really* impressed with LinuxCNC, this little mill now has my confidence that it will "just do as I ask".

Another JohnS.

 

 

 

Edited By John Alexander Stewart on 30/05/2013 19:00:28

[Anonymous]

Hi John,

Thanks for the info. If I've got my sums right that means the table on your mill will cover it's full movement in about 2.5 seconds, and the rotary table will do one turn in 3 seconds? Both of those are way faster than my CNC mill, so I'm really interested in how they are achieved. From memory my CNC mill rapids are about 25mm/s on the axes and 30°/s on the rotary table. I must admit that my axis rapids seem pretty fast when you're driving a tool towards the table, although it can get tedious waitng for the rotary table to get back to zero.

If I'm correct the KX1 has a 4mm pitch leadscrew, so if the motor is direct coupled it's doing about 1500rpm to get 100mm/s? Are you using stepper motors or a servo system?

Regards,

Andrew

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