Stop/Starve Whiplash at End of Line

Seeing more stop and starve whiplash at end of line when WMS resequences orders or a live load gate time moves. One hour we are starving the palletizer, the next we are blocked to the rafters. The line chases pace and we pay with jams and micro stops. Classic case: erector speeds up, labeler pauses for a reprint, accumulation fills, palletizer faults on a pattern change.

What helped is boring line control. We set a minimum run time after changeover, speed trim bands tied to downstream queue depth, decay timers on start requests, and hard caps on starts per hour to protect drives and clutches. When WMS calls for odd lot sizes, we switch to a degraded mode pattern that clears the lane cleanly. We cut the upstream handshake to three states only: Ready, Running, Blocked, with a 10 second debounce. We pulled fancy start and stop calls out of MES and only accept target rates in 15 minute buckets.

It smoothed flow and operators trust it. Still not perfect when shipping pulls a rush pallet. How are you balancing WMS and WES demands with simple, robust PLC logic on legacy lines like SLC and early ControlLogix? Any buffer and debounce rules of thumb that survive shift changes?