New Fanuc interface

[andypugh]

Originally Posted by Al_The_Man The problem with these motors is they do not have standard BLDC commutation signals as Fanuc produce a pseudo sine wave from a 4 bit code.

I assume that this pattern is documented somewhere on the 'Zone, but I can't seem to find it.

I am writing a semi-universal motor-feedback to drive-input converter component for EMC2 and I have a feeling that Red-cap input and output might come in handy.

[Al_The_Man]

PDF here.
It is the drives that require this signal converted to commutation for 8 pole motors.
The Encoder is standard 5v TTL differential (in most cases).
Al.

[andypugh]

Originally Posted by Al_The_Man PDF here. It is the drives that require this signal converted to commutation for 8 pole motors. The Encoder is standard 5v TTL differential (in most cases). Al.

Thanks, that looks like a simple 4-bit Gray code, so is a trivial thing to add.
I can convert it to angle, equivalent Hall or individual phase amplitudes pretty easily.

[Al_The_Man]

IIRC the code does not conform to Gray code, the problem I ran into with a simple logic conversion for BLDC commutation is that there is very few points in one cycle of electrical rotation where the code coincides with the required commutation pulse.
Al.

[andypugh]

Originally Posted by Al_The_Man IIRC the code does not conform to Gray code, the problem I ran into with a simple logic conversion for BLDC commutation is that there is very few points in one cycle of electrical rotation where the code coincides with the required commutation pulse. Al.

There is certainly the issue that 6 into 16 doesn't go, so the commutation segments will end up being different lengths. This probably means that the torque ripple will end up being even worse than normal with trapezoidal commutation.
However, the conversion only has to get the motor turning. As soon as the first transition is seen the phase angle is known, and angular feedback can switch to using the quadrature encoder. (or you could wait to see the encoder index, if preferred).
At that point you can switch to fully sinusoidal commutation if the drive supports it, and end up with an even better result than the original Fanuc system.

[Al_The_Man]

OK, although I do believe Fanuc uses 3 phase sinusoidal control rather than BLDC.
Al.

[andypugh]

Originally Posted by Al_The_Man OK, although I do believe Fanuc uses 3 phase sinusoidal control rather than BLDC.

Once the rotor angle data is into the system the system integrator is free to do what they want with it. Using a conventional BLDC drive is only one option, various sinusoidal phase amplitude formats, PWMs and digital angle data are also supported.

In principle I think you could run a Fanuc Red Cap with nothing more than a parallel port, EMC2 and a $15 IRAMS smart power module. Probably not very well.

I guess my next question might need to be about Yellow Cap :-)

[Al_The_Man]

Yellow cap, DC Brushed PM field, pretty straight forward, although some do have a resolver instead of encoder.
Some also have a DC tach which is generally not used or needed now.
Al.

[Al_The_Man]

I thought I would move these posts to its own thread as Jims was becoming hijacked.
Al.