Best Practice - What controls recommended for a 2-position turntable

[strantor]

Depends what is going to be on the conveyor. Is it a 7ft stack of bagged gelatin or a 1ft cube of dense foam?

The simplest solution that works is usually best, so if it's anything that can handle some jostling then I'd say a couple of mechanical hard stops and motion control by a timer is sufficient. A little slip in the mechanical drive train by a clutch or belt so it can (intentionally, and semi-gracefully) hit the hard stop 5000 times per day without destroying itself. You probably don't even need a VFD; just a reversing contactor pair. There is only one parameter that can be screwed with (timer) and it would only ever need to be screwed with once. After that it should be accurate, repeatable, simple and obvious in its operation, and easy to service. Not very ***y though.

If it's stacked jelly bags though, then you need something more. I would still put in hard stops but they should never be reached except in an over travel event. Ramp profiles based on encoder position. It should gently accelerate, decelerate, and stop based on encoder counts. Prox sensors at both ends (and maybe one in the middle) of travel to confirm/auto-calibrate position and/or generate an error, but not as the signal to actually stop.

 

[parky]

Done many of these for a conveyor company & the simplest & best (in my opinion) is proxies (Slow & Stop) with VFD is the best & most reliable. TBH on many they had hard overtravel stops it was designed so that in the event of failure of the sensors it would come to a hard stop, as extra protection I used timers that had a slight over travel time so in most cases even if it hit the hard stop the motor was about to stop anyway.Have done a couple with encoders but those were multi position systems.

 

[Peter Nachtwey]

I would keep it very simple. Crude and rude. Can you add mechanical stops to the end of travel? That way you don't need over travel switches. This system is moving very slow so just bump into the stops and apply a low amount of torque to hold the turn table at the stop. You said the current system is over designed. Over design the stops. If it can take 56 seconds, then that is less than 2 deg per second. Even at 36 sec the motion is slow. Can you have a "high" speed middle second and then a low speed section at the end of travel and just bump into the stops? Then you only need two limit switches. This is so easy a caveman can figure it out.

If you are going to use an encoder, then use an absolute encoder so you don't need to worry about homing it. You don't need a lot of precision.

My answer would change if you need speed and precision.