Absolute Encoder Questions / SSI via 5i25

Hi Julian,

Did you get this SSI interface working at all?

I was following your progress and then had to leave the country for 3 weeks.

Thanks,

Dave

Hi

I started testing but right now I am moving my shop, so it will take some time till I can get further.

best regards,
Julian

Hi,

What's the current situation with SSI encoders? I consider using Avago absolute encoders www.avagotech.com/pages/en/motion_contro...ers/aeat-9000-1gsh0/

Meanwhile I already have BiSS encoders www.harmonicdrive.net/products/actuators...-biss-c-overview.pdf , which firmware can I use for them? (I have 5i25+7i76 and 5i25+7i77 kits)

I have the SSI interface and Fanuc serial firmware tested.
(with few minor changed made recently)

BISS firmware testing needs to wait until I get my IC-HAUS evaluation card.

You can use a RS-422 interface daughtercard like the 7I74 for 8 channels (or the RS-422 expansion interface connector on the 7I77/7I76 to test 1 channel) for all three serial encoder types since they all use a RS-422 XMIT and RECV pair per encoder.

All still need driver support (which should be able to share a lot of upper level code since all serial encoder types operate is a similar way once you are above the transport layer)

Yes 'read trigger' makes sense
ideally the sequence should be
read trigger
read fast I/O
read slow I/O (read triggered I/O)
This may involve putting the SSI,BISS,FABS (and maybe SPI also)
read after all reads that dont have to wait

I am also working on hardware DPLL read trigger logic (so slow reads can be pre-triggered so the data is available at the beginning of the thread time)

Chaps .... Does this mean that I will be able to set my iC-Haus interpolator to 256 X and run my 3600 count 1VPP spindle encoder at 3000 RPM

Well maybe...
The interpolator would have to do 256x at 150 KHZ input waveforms, and
that may be asking a bit much. The nice thing about the serial encoder interfaces (vs quadrature) is that they have the option (which IC-Haus uses) of dropping position LSbs when the speed is high so you get the high resolution when you need it (when moving slowly) but they can still track high speed rapids

Cheers Peter
I’ll be watching with interest ....
I think my interpolator started to throw frequency errors at anything above 32 X at 3000 RPM but I didn’t fiddle with any settings.
From what you describe, even at 32X it sounds like the best of both worlds.

I’m trying to run a C axis on my lathe (yes that lathe!) and ideally I need the maximum encoder count possible at up to 120 RPM for positioning. At the moment I’m running 16 or 8 X but as Linux CNC is trying to control the spindle RPM form the encoder, it wanders horribly above 1000 RPM, probably due to lost encoder counts.
This is still something I haven’t fixed yet and don’t really fancy, or cant easily add another encoder for spindle velocity.

PCW wrote:

You can use a RS-422 interface daughtercard like the 7I74 for 8 channels (or the RS-422 expansion interface connector on the 7I77/7I76 to test 1 channel) for all three serial encoder types since they all use a RS-422 XMIT and RECV pair per encoder.

Well, I just looked to the manual for Lika SSI encoders that I have right now (not for long). The pinout includes
Clock in +
Clock in -
Data out +
Data out -
While 7i76 TB3 connector has RX+ RX- TX+ TX- pins.
How do I connect them? Need some interface board to transform the signals?

Or it's just the software should provide Clock at TX and receive data from RX?