EMC & EtherCAT

Hi all,
I found some preliminary support for EherCAT in EMC2 - mainly for I/O, not for drives.

Would it be possible to write HAL driver for EtherCAT servo inverter and use this inverter within emc2?

Servo inverter can send: actual position (32bit), actual speed, actual torque/current, bit "in position" etc. - it is fully configurable.
can receive: target position, ramps, max. speed - also it is possible to configure it in nearly any way.

Is it possible to use emc2 with this kind of servo drive?

Well, the drive is possible to configure also in other way, to recieve target speed, ramps etc. and send back to emc actual position, speed....

The question now is, IF is possible (easily) add HAL driver for such a drive.

I looked inside hal_skeleton.c and it is not clear to me how to connect target/actual position inside system, is here any better example? The project is in preliminary stage, we are looking for good CNC software - and emc looks really, really good!

Thanks

Jan

Hello,
thank you for fast reply!

Well, it looks like that this is good way. Driver is Real Time, that's not a problem - I'm planning to use etherlab.org/en/ethercat/ IgH driver with supported Eth. card.

Other way is, how fast can servo drive refresh values on the bus in real life - that's maybe bigger problem than all other future programming issues etc.
With a standard servodrive configuration, we can reach 1ms cycle - within this 1ms interval you cannot get new/updated value and any change you do will be processed after (in the worst case) 1ms.

On the other way, what we need is relatively slow motion in three axis CNC machine - machine for cutting glass tables into parts (with shapes, not only rectangular).

For internal emc2 PID regulator can be this behavior problem, because what I seen from HAL until now is, that every time when is called HAL function with actual position request, HAL driver calculate and send new fresh position.

So, if I set in my .ini file to 1ms period

BASE_PERIOD = 1000000
# Servo task period, in nanoseconds
SERVO_PERIOD =1000000

then it should be OK? Will system ask HAL for actual position (and then set new position) in 1ms intervals with this configuration?

Regards
Jan

Hello,
your assumption is not completely correct, but you are very near - I'm from company which is servo and servo drives manufacturer. My only choices are CANopen and EtherCAT.

Actually, I (personally) would love to have CNC solution under GPL.

Regards
Jan.

Hi Jan
I wrote the ethercat part in the wiki. Sorry for replying this late.

Does your hardware support a closed loop setup? It should.

If so, you can set up the speed loop and the position loop within the ethercat device.
Then you can use the stub I created to send emc's commanded position directy to the device.
Because then you are not in the need of closing the pid loop within the pc and can relax on the settings for BASE_PERIOD and a slow pc would do.

bye
Ulf

Yes, hardware support closed loop - it is primary made for this kind of control.

Actually, I did not find any wiki regarding EtherCAT based servo control, only wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Etherlab - but this is about digital I/O...

Now, we are in phase building testing machine (2D CNC like a plotter - it takes some time).

Regards

Jan

try to bild the ethercat system as described in this wiki.
Then connect the drive controllers directly to the ethercat activated network card of the pc

if you start the realtime and ethercat system you should see transmit all leds blinking
try issuing the "ethercat slaves" command and post the output. Then I can help you to set up the glue module.

/ulf

jan233321 wrote:

Hello,
thank you for fast reply!

Well, it looks like that this is good way. Driver is Real Time, that's not a problem - I'm planning to use etherlab.org/en/ethercat/ IgH driver with supported Eth. card.

Other way is, how fast can servo drive refresh values on the bus in real life - that's maybe bigger problem than all other future programming issues etc.
With a standard servodrive configuration, we can reach 1ms cycle - within this 1ms interval you cannot get new/updated value and any change you do will be processed after (in the worst case) 1ms.

On the other way, what we need is relatively slow motion in three axis CNC machine - machine for cutting glass tables into parts (with shapes, not only rectangular).

For internal emc2 PID regulator can be this behavior problem, because what I seen from HAL until now is, that every time when is called HAL function with actual position request, HAL driver calculate and send new fresh position.

So, if I set in my .ini file to 1ms period

BASE_PERIOD = 1000000
# Servo task period, in nanoseconds
SERVO_PERIOD =1000000

then it should be OK? Will system ask HAL for actual position (and then set new position) in 1ms intervals with this configuration?

Regards
Jan

I would go for speed control over ethercat instead of position control, because the drive would try to move from point A to point B with acceleration and speed parametrized in drive itself. IMHO you should make like this:

velocity_feedforward = derivation of desired_position / or something more stable approach
desired_velocity = Kp* (desired_position - actual_position) + velocity_feedforward;

You have a position loop with P-regulator and velocity feedforward, this is classics.
Faster update - better results as long jitter is not causing problems.