Controll rebuild

Hi,
Admittedly I do not have neither experience in electronics nor specific knowledge of the subject, so I would very much use straightforward advice in simple words.

I need to rebuild control for my 4 axis CNC mill (Damaged in fire). And most likely I will have it ordered for someone to assemble.
But I need at least to know basics.I read about mesa boards and it seems like a solution to go for to connect to PC. 

My PC will be only used to control the CNC and it will be stationed max few meters from the machine.What kind of card and connection you think will be best for me. PCI, PCIe, external, LPT, Ethernet ….. 

Also I do not fully understand how this cards work. I read that they are running some software that takes over generation of step signals.So what is PC communicating to the card?
Is it basically the case that PC sets signal rate that card generates and only sends commands to the card to change this rate.If this is the case how does this work for arcs.

Cris.

Linuxcnc on the PC remains the motion controller.
The step generation is offloaded to the stepgens on the  mesa card
Linuxcnc tells the stepgens to generate steps at a given frequency.
It will continue to generate that frequency forever or until it is told to stop or change frequency.
Which linuxcnc can do 1000 times a second.
Sounds like you need an ethernet Mesa Card. The 7i96s might work for you. The ethernet cable can be up to 100 metres long.
There is a tool called pncconf that will create a Mesa configuation that is included with linuxcnc.

 

Thanks,

So Linux is setting frequency and mese is executing it.

So to have high acuracy in corners or areas where there are accelerations key is still latency of the PC on Linux side.

When CNC software executes arc move is it actually linearised in the motion controller or actually steps are generated based on required acceleration functions? 

Why do you think Ethernet card is will be better than PCI or PCIe? 

Cris.

Cris

So to have high acuracy in corners or areas where there are accelerations key is still latency of the PC on Linux side.

LinuxCNC depends on low latency as it _is_ the motion controller.

The stepgen does linear interpolation between waypoints
but the chord error (difference between arc and polygon) at a 1 KHz
update rate and typical machine tool accelerations is much smaller
than mechanical errors so nothing is really gained by adding parabolic
interpolation between waypoints.

For example say your machine is fairly fast and can cut a 10 mm circle
in 0.1 second, the 100 side polygon created (1000 waypoint/second *0.1 second)
would differ by no more than ~1.6 u from a perfect circle.

For faster devices (for example laser galvanometers) Mesa firmware does
incorporate acceleration (as the effective acceleration of a galvanometer
steered laser spot can be 100s of Gs)




 

OK, 
I have deciced to go with ethernet card as you suggested. 

Now I am not sure what I need to make spindle control. 
It will be powered by 3 phase inverter that accepts 0-10V control signal. 
It is 7,5 kW 18000 rpm, 300 Hz, 400V spindle.

Does mesa board directly supports this function or I need to buy some extension. Was trying to figure this out from description on mesa site but not conclusively. 

Can you please advice. Or perhaps there is some better option to go for.

 

Hi again,

So I have managed to get MESA board and control is being built.

Now I need to source the PC.

I was looking threw hardware specs, but did not figure out what I should look for in terms of computer to control my machine.

Could someone give me a hint here. Any verified spec that works well. 
I can go with used ore new computer. Used will most likely be cheaper, but affordable new computer also has benefits (I do not have to build it and do not have to deal wit things that might not work). 

As a minimum I would like to narrow down CPU brand and type and motherboard. 

Any suggestions please. 

Cris.