Servo driver selection

Gatesy wrote:

Do these encoders give out a standard encoder output, or is it unique to Fanuc?

All Fanuc "Red Cap" encoders are proprietary to some degree. The original version had standard AB quadrature plus index, but the commutation signals were proprietary. A later version added battery backup and a position memory to the encoder, so the control could set the home position anywhere, and then when the control was powered up, the encoder could send all the quadrature counts from home to wherever it was at power-off (of the control). This includes the number of full turns from the home position. You did not need to perform a home move sequence each time the control was powered up.
These are called the ABS encoders, and have an extra 2-pin connector on the encoder dust cover. The AB quadrature and index signals on these encoders are industry compatible. They are seen a lot on robots, which can be very hard to home due to the collision risk.

Then, they came up with serial encoders. The problem with quadrature encoders is the count rates get very high when they are moved fast. Some of the latest serial encoders give resolutions of one million counts/rev. If such an encoder is spun at 2000 RPM (33.3 revs/second) then it would give 33.3 million counts/second, which few CNC controls could handle. So, they decided to have the encoder send the absolute position, incuding nuber of turns from home, all the time, rather than the incremental counts. This protocol is totally proprietary.

Jon

Gatesy wrote:

The numbers on the encoder casings are A860-0308-T112 And they are 2500P

This exact model is not in my cross reference, but it seems like it must be from the first series, and will have the traditional AB and Z signals, and the 4 commutation signals. So, it is not a serial encoder.

Jon

Thanks Jon

I have often wondered what the difference is between the different types.

I have found the encoders I have are also listed as A290-0521-V542 incremental pulse coder

Gatesy wrote:

Thanks Jon

I have often wondered what the difference is between the different types.

Oh, it is BAD!!! They made THOUSANDS of different types of encoders, drives, motors, it is VERY confusing.

I have found the encoders I have are also listed as A290-0521-V542 incremental pulse coder

Yeah, see, A290 is a "catalog number" which is different from a "reference number". The A860 is the Reference number. I don't have your A290-0521-V542 number in my cross reference. But, I might be able to look it up from the motor number, which also contains the encoder type info.

Jon

Well I've been having a bit of a dig around on the net and found this page

http://www.beisensors.com/crossover-index.html

going then to Fanuc page

http://www.beiied.com/crossover/fanuc.html

it shows the Fanuc A86O replacement is an H29 (The link doesn't work)

but the data sheet can be found here

https://www.yumpu.com/es/document/view/46615791/model-h29-incremental-encoder-pdf

As Jon said looks like standard A B Z output. Are the commutation signals sent from more sensors that are not part of the actual encoder?

Gatesy wrote:

Well I've been having a bit of a dig around on the net and found this page

http://www.beisensors.com/crossover-index.html

going then to Fanuc page

http://www.beiied.com/crossover/fanuc.html

it shows the Fanuc A86O replacement is an H29 (The link doesn't work)

but the data sheet can be found here

https://www.yumpu.com/es/document/view/46615791/model-h29-incremental-encoder-pdf

As Jon said looks like standard A B Z output. Are the commutation signals sent from more sensors that are not part of the actual encoder?

This is a plain quadrature plus index encoder, it provides NO commutation signals. So, it cannot be used with most systems, as they would have no idea which coils to energize to get it moving right at power-on. There are what are called "six channel" encoders, that provide not only ABZ, but "Hall signals" too. But, then these would need to be "phased" to the motor magnets, which is a little tricky.

The Fanuc encoders are quite good, unless you drop the motor they rarely go bad. And, I have the converters for both main flavors of the Fanuc encoders.

Also note that these encoders are mechanically in NO WAY a drop-in replacement for the Fanuc encoders.
You would have to make a mounting adaptor and a shaft coupling.

Jon

Ok thanks.

Time to weigh up the options I think

Many thanks for all the help

Another quick question. Can LinuxCNC be used to provide a closed loop system when it is used with stepper motors? I assume this would be a sort of dumb stepper driver that keeps stepping until LinuxCNC tells it to stop, rather than telling it how many steps to take?

No they're not to replace the servos!!!

I have a little Conect Cadet lathe that needs a control system, so thought I'd put LinuxCNC on that, it has old steppers on it, would like to put servos on it but they would need to be tiny, so just wondered if you can do feedback with steppers. I'll be replacing the steppers with new ones or servos

Gatesy wrote:

Can LinuxCNC be used to provide a closed loop system when it is used with stepper motors? I assume this would be a sort of dumb stepper driver that keeps stepping until LinuxCNC tells it to stop, rather than telling it how many steps to take?

Yes, this can be done. The Pico Systems Universal Stepper Controller can read an encoder to sense position. Normally, it counts it's own step pulses and supplies that back to LinuxCNC - that is the typical open-loop mode.
But, by flipping a DIP switch on the board, it can read an encoder instead. This does not make the stepper unstallable, but will correct occasional lost steps. It will also alert LinuxCNC when a motor stall has ocurred, so ALL axes will stop. When a motor stalls, you would NOT lose your position alignment as would happen in the open-loop mode.

Jon

Jon