glass scales via ethercat?

Hello all!

As the titel says I want to implement glass scales overr EtherCAT.

Has anyone done that before and could give me some hints where to start from?

I'd also apreciate any theory on that topic!

Is it possible to fully close the loop via ethercat?

 

Given the brutal pricing of Encoder modules for Beckhoff, I have opted to not pursue this. For a machine with 3 to 4 glass scales and considering current ebay pricing, this easily exceeds 250€ per channel (plus EK1100) - I rather by a mesa card for that money.
Instead I found that I could very well connect glass scales to my Delta ASDA-A2 (and quite certainly also A3) controllers and send out the signals via Ethercat to LinuxCNC. I have build a closed loop on my test bench, however, I havent tried to tune it yet.

Thanks for your input @GuiHue!

Yeah, the Beckhoff encoder interfaces would probably break my bank as well, even though I already own an EK1100 and two digitL I/O slices.

How would you go about connecting glass scales to the servo drives?

I also thought about a Beckhoff RS485/RS422 module and compatible glass scales, but I'm not sure if that'd work out as hoped?!
What are your thoughts on that approch?

Regarding Servos: Well, the manual is a good first start;). Also, I forgot to mention, that I am using ASDA-A2-E Series with ethercat. Othervise thins would be rather pointless.

RS485/RS422: No opinion, since I never used that. Could potentially be a bit of a nightmare to configure with linuxcnc and ethercat.

@gueee78
HI
with the ASDA 2 E on CN7 you can implement six digital inputs, I don't know if this is your case.

GuiHue wrote:

RS485/RS422: No opinion, since I never used that. Could potentially be a bit of a nightmare to configure with linuxcnc and ethercat.

RS485 to VFD is quite possible via a serial port or USB adapter. I do this.
There are also ethercat compatible VFD's or ethercat interfaces that alloe ethercat connection to some VFD's

If you're wanting to use the scales as part of a closed loop on a machine with typical travel speeds, then ethercat isn't going to be fast enough.

To close a loop, you need cycle times measured in microseconds, whereas ethercat cycle times are measured in milliseconds.
RS485/422 is even slower, so it all depends on what you're actually wanting to achieve. If you're just wanting to measure position, then either method should work, but if you want run closed loop, it's going to be too slow.

You can replace the encoder on the servo motor with a glass scale and let the servo drive do its job. That would typically mean an incremental differential quadrature signal which is what most cheap glass scales have. Maybe you can get the encoder position from the servo drive over ethercat and save the need for a separate encoder.
Ethercat works fine with closed loop in linuxcnc, the servo loop time is 1 millisecond or thereabout.

Edit: this was already tested in an earlier post.
I can add that I searched around out of curiosity and found a few rotary encoders that send absolute position with timed 1 ms intervals  or slower over rs485. Then that communication should be done by an ethercat unit, decode the value and make that available in a pdo. Does such an ethercat unit exist?

For scales you might be able to use one of these buit not much cheaper than Beckhoff
www.icpdas.com/en/product/ECAT-2092T
There are also ethercat specific encoders
www.encoder.com/ethercat

To clarify: I was thinking about using RS482/422 via Ethercat Beckhoff modules. I use RS485 for my VFD via USB as well.