Warehouse sorting gate, swung by a servo drive. The drive supports position, velocity and torque modes. I’ve drawn the sorter in a process diagram and want operators to click the gate symbol to open or close it.
First version: velocity mode, two catalog commands gate.start (with a speed) and gate.stop, on click and on right-click. It worked on the bench. In the warehouse the stop arrived late once and the gate hit its mechanical end stop. Nothing broke, but it scared me.
Which mode should a command from the cloud use? I don’t really get the practical difference between the three either.
Why not torque mode with a low limit? Then hitting the end stop wouldn’t hurt.
Torque mode is for pressing or holding tension, a gate would just drift. And the late stop is the real lesson: never close a fast loop through the cloud.
A command from a symbol can arrive late, the operator can click twice, and a command that gets no answer within 30 s is shown as unknown, not as failed. Only one command runs per diagram card at a time. All fine for «go to open», dangerous for «start moving and wait for stop».
Put the drive in position mode (or let a small PLC next to it do the motion). The cloud only sends targets: one catalog command gate.move with a parameter to of open or closed. The drive does the ramp, the speed limit and the end positions itself, so a late or repeated command still ends in the same place. Make the device ignore a request id it has already run.
On the symbol: Run a command, Basic tier (symbols can’t send anything else), and the confirmation is always asked. Bind the gate symbol’s state to the position the drive reports, so the picture shows where the gate is, not what someone asked for. See Commands on symbols.
Rebuilt it as position mode with gate.move open/closed and the drive’s own limits. Did the double click test on purpose, it just goes to open once. Symbol follows the reported position now. Thanks Ciaran, and Aoife, torque mode had me thinking for a minute.
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