Steve,
At the spindle end of the travel, I provided a "hard" stop, to ensure proper positioning. This consists of just a bolt with a rubber bumper on the end that contacts a small bracket bolted to the side of the head. At the other end of the travel, I just allow the air cylinder to bottom out. I agree a servo or stepper is a more elegant, if more expensive, way to do this, and would allow tuning to get constant-speed motion, or even a motion profile that should negate the need for stops, dampers, etc. I also used prox sensors to ensure each motion fully completes before taking the next step, so if the carousel for any reason doesn't reach the fully engaged position, there;s no harm done, the toolchange simply stops until the jam is cleared manually. Had I not needed such a wide range of travel (140 degrees), I could've certainly made this work better. Were I doing it over again (and I still might....), I'd make the carousel fixed, and use a transfer arm. I have an idea for that which would be quite simple, using a rotating "claw" on the end of the arm, which would articulate such that the claw was pointed towards the pivot when the arm was rotating, allowing the arm to move much faster, with no worries about the tool flying out.
Regards,
Ray L.