Shopping for a conveyor system

[Paul T]

If you use a fieldbus system you would only need one wire with two conductors, not 119 conductors + the same amount of I/O..?

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With a fieldbus (like DeviceNet) it only takes one fault to take out your whole system. One little bit of forktruck impingement and the day is ruined.

These things look great on an installation budget. They stink for maintainability.

$0.02

Heh. Right. And the multiple cables in the DC or Analog conduit are going to do any better? If you want cable tray in the ceiling, the cost just drove that out of sight especially with the conduit drops to each motor. In any case, on a conveyor system there are all kinds of members to run the conductors and conduit on; the machine frame itself gives more protection than many other systems get.

RoTaTech, I vote for a drive at each motor with DeviceNet. Another possible source for drives is ACTech; they make a good cheap drive. So does Cutler-Hammer, and Automation Direct is selling small cheap drives too.

With only 17 drives, you are probably on the border of bus cost vs. hardwired IO, especially for 350 feet. You will have to buy a node for each drive, or better yet drives with built-in nodes, but that's offset by fewer analog modules in your PLC, a lot less wiring, and much more information on the line (which may or may not be useful to you). Setting up DeviceNet is not that hard and your local vendors will help; even if you've never used it, cost it and see if it helps. And it actually makes maintenance easier as you can monitor both the network and nodes to troubleshoot.

The one thing you want to watch out for with these small discrete drives is their behavior in local/remote mode. You may want to wire your E-Stop into one of the IO points to stop the drive. On some drives, the wired IO is ignored if the drive is in local mode. No more E-Stop. I had this happen a few years ago on a conveyor with about 100 1/2hp drives. In this case, you'll have to use some contactors ahead of the drives to ensure an E-Stop.

 

[allscott]

I have worked on and designed literally DOZENS of this style of conveyor with one drive and multiple motors. I have always used one drive with multiple motors in this application and would never consider anything else, ESPECIALLY a fieldbus run down a conveyor.

It is really quite simple, one drive mounted in the control cabinet or MCC with whatever flavour of control you would like. Run out of the drive to "overload" boxes mounted off of but near to the conveyor. Insided the overload box install a MSP (motor starter protector) for each motor. A MSP for a 1/2HP motor should run you about $30.00

For any maintenance/lock out concerns simply shut off the MSP for whatever motor needs working on and lock the box.

I have also worked with conveyors that had contactors on the output to switch on and off certain parts of the conveyor, drives were AB 1336 and never had a problem. Mostr drive manuals I have ever seen say that if you want to do this consult the manufacturer, so consult the manufacturer and see what they say.

When the solution is this simple, talking about running devicenet or multiple analogs down a conveyor line seems silly IMO. Not to mention the hassle of setting up 17 drives and training plant maintenance about setting up device net nodes and programming a VFD when the bearings go out of a $150.00 motor.

 

[malex]

We have used PowerLogix 4 in this application on many occasions, you might want to check into it.