3axis CNC retrofitting with LinuxCNC

Hello guys&gals,

First of all I would like to thank the LinuxCNC team for a great looking software and site!

I am in the process of retrofitting LinuCNC on an old 3axis woodworking cnc router, however, this being my first time, (both at CNC, and at Linux) I got stuck.

The machine is fitted with servo motors complete with controllers which have speed/direction input +/-10V.
Feedback is given by incremental encoders attached directly to the motors, 500pulses/rev.

Is a PC with 1/2 parports sufficient? Do I need additional hardware?

Any help is appreciated

Thanks!

Hello.

For the analog output that you require, you will need (most easy and effective approach) a board that will process the linuxcnc speed command to the analog voltage that will connect to your drives.
I sell a type of those boards (Mesa brand). Others boards are also available, like those from Pico systems that I have no direct experience.
The most popular product that I sell to achieve what you need is a combination of a 5i25 + 7i77. It also have several inputs and outputs that generally are enough to run a complete machine. I have stock in Europe and you can find my web site in www.eusurplus.com.

Hi

Have a look at these

www.mesanet.com/pdf/parallel/5i25man.pdf‎

www.mesanet.com/pdf/parallel/7i77man.pdf

Argh, emcPT types faster!

regards

terans1085 wrote:

I am in the process of retrofitting LinuCNC on an old 3axis woodworking cnc router, however, this being my first time, (both at CNC, and at Linux) I got stuck.

The machine is fitted with servo motors complete with controllers which have speed/direction input +/-10V.
Feedback is given by incremental encoders attached directly to the motors, 500pulses/rev.

Another option for analog velocity servo interfacing is the Pico Systems PPMC (Parallel Port Motion Control)
which is a set of boards to control the servo amps, read encoder position and handle digital I/O.
It may look more expensive than the Mesa boards, but is an all-in-one package which doesn't
require a number of additional parts to complete the interface.

The basic 4-axis package is US $780.

See pico-systems.com/osc2.5/catalog/index.php?cPath=1

Jon

Thank you for your replies!

I was looking into the MESA option, and was wondering:

What about using just the 5i25, employing two PWM outputs per servo (forward & reverse), low pass filtered to create an analog signal, into an opamp to amlify to 10V max? In theory then each channel can be fed into the differential inputs of the servo driver to allow forward/reverse control.

Would LinuxCNC support such output? Any problems you can think of of using such setup?

thanks & Regards,

You can certainly do that. We use that method on the 7I33 and 7I48 interface cards
note that to be accurate and fast is a bit trickier, we use:

FPGA PWM --> cable
--> cable impedance matched termination
--> fast CMOS buffer powered by accurate reference voltage
--> passive LP filter (to avoid slew limit problems of active filter)
--> multipole active filter/level shift

Hi,

I have acquired Mesa's 5i25 and 7i77 and hooked the drives up. Currently in the process of tuning PID.

Focusing just on X-axis, this is what I've learned so far:

• Increasing P more than 10 makes the drive makes a loud noise
• Increasing I to about 20 reduces following error, but only up to about 0.5mm. Further increasing has no visible effect.
• Increasing D to 1 makes the motor make a very loud vibrating noise.

I do not really understand the concept of FF0, FF1 and FF2.

Any tips on what and what not to do?

Thanks and Regards,

if you have velocity mode drives,

gnipsel.com/linuxcnc/tuning/servo.html

is a good tuning tutorial.

Note that you should have no I or D when doing the preliminary tuning

X axis has 160 encoder pulses / mm so 0.5mm is a lot of pulses of following error.

PCW: I shall be trying this method and keep you posted

Thanks!