Serial Pulse Coders??

[Bruce Griffing]

I have used and understand conventional quadrature encoders. Fanuc has a class of encoders they call "serial pulse coders". Just what is the architecture of a serial pulse coder?

[Al_The_Man]

There is not many Fanuc encoders that are serial, the DC motors used commonly 2k and 2.5k pulse/rev differential as do the AC together with high resolution 10k+ p/rev.
There is also a low signal sine wave type.
The difference in the AC motor encoders is the commutation pulse which is a 4 bit code to produce a pseudo sinusoidal signal for commutation.
On the other hand, Mitsubishi have primarily used serial style encoders where two way communication is over a proprietary two wire serial link up to 100kp/rev.
Al.

[Bruce Griffing]

Al -
Thanks for your reply. Two points. First why do I want to know this?? Well, when I look at the 0 Connection Manual (hardware) on p177 it shows a table of connections for "axis control boards". Based on this table, I have a 4 axis control board that uses "serial pulse coders". This is due to the M1xx or M2xx connector numbers shown in the table that correspond to my axis board.

Second point. I want to run a 4th axis on my machine. I now have a rotary table, Pac Sci servo motor, a US digital encoder to replace the resolver on the motor and a Fanuc servo amp. I was thinking of using a PIC or the like to convert the 10k quadrature encoder to "serial pulse coder" format - that is if I could figure out what "serial pulse coder" format is exactly.

[Bruce Griffing]

Al
OK - I found evidence to support your point about "serial pulse coders" being rare. I looked at the only axis motor that is exposed in my machine - Z. It is an alpha22-3000. By its part number it has an alpha-I64 pulse coder. From what I read, this is an incremental encoder. So my axis board must be able to do incremental as well as serial. Now I just need to determine the details of the incremental interface.

[Bruce Griffing]

The incremental interface appears to have a 1-2-4-8 counter for the low order bits and an A and B channel for a quadrature signal. If that is the case, the I and Q are just a 4 state machine driven by the carry from the low order counter. So can I simulate the Fanuc interface with a 4 bit up/down counter counting the i and q transitions (+ and -) on the encoder with a little logic? Pretty easily implemented in a PIC or otherwise if that is the case.

There is also the matter of the index mark, but that seems straightforward so I won't say more about it.

[Al_The_Man]

If this is a AC servo motor, what is the part number or the encoder part number, see the pdf file I posted for the 4 bit date you mention.
Al.

[Bruce Griffing]

It is an AC motor - A06B-0148-B177. That is the Z motor on my mill. I used it to determine that the axis board will handle a Fanuc style incremental encoder. I want to use this motor (A06B-0373-B169-R) on my 4th axis. My intent was to replace the existing encoder per the discussion above and replace it with an encoder that would work with my control.

[Al_The_Man]

B169 is taper shaft with brake and is a serial encoder, I do not have any info on the serial form, however.
Al.

[Bruce Griffing]

Al-
My intent was to replace the serial encoder with my "homebrew" Fanuc compatible incremental encoder. I just need to learn enough about the Fanuc encoder to emulate it.

[Al_The_Man]

I have been using Fanuc Motors for spindle motors on small lathes etc, Because I was using AMC drives, I had to replace the encoder with a standard BLDC commutation encoder using Renco products.
If your intention is to still interface to Fanuc, you could look at replacing the serial with a standard Fanuc differential type if the mounting is the same.
Apart from the standard encoder pulse, you need the 4 bit commutation pulses as per the PDF.
This is the only proprietary odd ball part of the differential encoder.
Using any other non-Fanuc encoder means aligning the commutation pulses to the stator poles.
I have a couple of Fanuc incremental encoders, but unfortunately they are odd ball low voltage sine wave signal output.
Al.

[Bruce Griffing]

Al-
Thanks for all the help. I now understand what the C1-8 channels are doing. If C1-8 did not need to be aligned to the motor poles, it would be easy to generate them on the encoder with a small microprocessor like a PIC. With a small backup battery to keep the PIC alive, it could be done using the index pulse - but the encoder would then need periodic battery replacement. Also, it would be necessary to understand what the standard alignment of C1-8 should be wrt to the poles and the index pulse, so the index pulse could be correctly aligned to the motor when installed and C1-8 would be generated with the correct phase. I wonder if there is a market for Fanuc compatible encoders...

[Al_The_Man]

Jim Elson has made a cpal interface for the Fanuc commutation to BLDC, with the encoder passed through and used as-is.
The Longer pulse is directly under each pole.
Al.