Homing process for 5i25/7i76 with 5 axes

tnl.lambert wrote:

It's true - the drives have a built-in homing sequence. The problem is that we then need to program and synchronize 5 different drives with different homing sequences. While that might get us to a 'working product' faster, the end result will be very difficult to modify or tune. We would also then need to write our own homing logic to coordinate all five axes. If we change drives, the same problem applies. My ideal solution would be:

1. Boost the encoder signal into a digital input to get encoder info back from the drive.
2. Connect the signal to the pin of the encoder software component.
3. Rely on the built-in homing interface so that the machinist doesn't have to worry about custom homing sequences or parameters.

I've been fussing around with different variations on this process, but I have never been able to connect to the correct pin combination that will recognize the encoder pulse. There seems to be some issue surrounding the i/o bit (index-enable), and some issue surrounding the connection of the software component to the hardware pins. I'd very much appreciate any insight into this mess that any of you may have.

If your concerned about tuning, then just get a 7i85S and pipe the proper full encoder signal in. Other wise I think the best way would be to let the drive home the motor.

I don't think you would need any special homing logic to do it. When LinuxCNC commands the joint to home the hal pin "axis.N.homing" is set to true, you connect that to the digital input on the drive that starts its sequence, then when its done it sends a signal that it is homed that you would connect to the hal pin "axis.N.home-sw-in". (I am going to assume that the drive will ignore step pulses while it is performing its own home sequence.)

How wide is the index pulse?

If narrower than 1 mS it wont be reliably detected with a 1 ms servo thread
This can perhaps be worked around by using the hardware encoder counter index pins
(I could make a 7I76 config that has 3 hardware index pins on the encoder connector

I'm also not sure about any side effects of homing stepgens to index.
normal encoder homing to index resets the position count but this
does not happen in the stepgen case.

The HostMot2 firmware does support stepgen homing to index (it mimics the encoder logic)
but this is not currently supported by the hostmot2 driver.

It might be easier to use the step/dir with encoder feedback method since that would work with
current driver/linuxcnc and only requires the proper HAL setup.