VFD conveyor stop timing?

Quick question:

Has anyone ever heard of timing a conveyor with a fully loaded pallet to stop based on its start time?

I would use the PE at the end of the conveyor, but have someone telling me it was programmed to stop based on its start time.

I would also assume after some time, that the conveyor wear and tear would cause this "timing" to change over time, either stopping too soon, or too late.

I guess it can be done this way, but why?

Not doing too much with conveyors, my only guess would be that if the PE malfunctioned and didn't sense the pallet, the conveyor would keep running. Dump the pallet.

Programming it to stop based on a start time is an extra means of safety to prevent the above. So one has the PE AND the start time as a means to stop the load. My thought, but what do I know? Good luck.

Doesn't make sense. I would expect timing to be an overtravel limit only, in case the PE missed.

That would make sense. I'm told it was programmed with the sensor used only for displaying if a pallet is present. Sounded rather odd...

Thanks guys!

That may be more related to how the Dynamic Braking Resistor was selected. In gewneral, selecting the right amount of braking torque, and thereby the resistor, requires knowing the inertia of the entire system; motor, gearbox, drive system and load. But on a conveyor moving unknown quantities of product, the total is difficult to determine. So the "cheater rule" is to calculate the torque required by looking at the acceleration time and backing out the VFD/motor torque to get Average Accelerating Torque and using that as the required Braking Torque if you want the Decel time to match the Accel time..

A little peculiar but i guess if they have mapped the timing out reasonably they could use it.. not a great idea as you don't have a way to track/adapt to belt slippage, etc. a PE doesn't care about slippage as the package breaks the beam when it breaks the beam. if you need protection, an extra photoeye on the same spot just above or below it would work.

I wish I still had rs logix. Our company had some good conveyor code. simple, yet amazing.

ganutenator said:

I wish I still had rs logix. Our company had some good conveyor code. simple, yet amazing.

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What do you guys use now?

I think we are looking at the start wrong when they say start time I think they mean run time or travel time. The time it takes the pallet to reach the end of the conveyor and discharge + a little make sure it's cleared the conveyor.
When a pallet enters the conveyor you start the conveyor and a timer every time you put a pallet o the conveyor you reset the timer.
A TOF timer triggered from the entry PH works well in this application
I like to use both photo eyes (one on each end) and the run time of the conveyor
A simple up - down counter works well add 1 when a pallet enters and subtract 1 when a pallet exits. A count greater than 0 the conveyor runs this give you great visibility you can always know the number of pallets by the counter

I use VFD driven roller conveyor but the VFD is just to give a smooth start not to jerk the load stacked on pallet. I use coast to stop not ramp. I can use a timer to place load where it is needed by measuring each load with PE and calculating the center and basing it on 45 fpm travel (that is what we set our conveyor speed at) Doing this lets me center loads for transfer even when they are different lengths.

alive15 said:

What do you guys use now?

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