Palletizer chain driven. Drive 525 RSlogix 5000

We have a pallet dispensing system that's chain driven. The forklift loads10 or so pallets in destaker then all these pallets except the bottom gets picked up to clear the pallet on the very bottom. The long cylinder drags the pallet and pushes it past the lugs. From there two drive chains with outside lugs move it forward. The pallet does not ride on a chain instead it gets pushed by lugs on both sides with two parallel chains to a sensor where the robot starts palletizing. The problem is that when we have a bad pallet that does not transfer properly it gets wedged between lugs and breaks the pallet. This only happens if the pallet is damaged which causes pallet jam. Also, the chain conveyor is mounted to the floor with screws and those get pulled off floor and chain jump the guides and the chain does not stop without wrecking things badly. We have two 525 drives that drive both chains. Is there a simple parameter change that can be done within the drive that would improve the situation. Any advice will be greatly appreciated.

Are the motors the driving force of the wreckage?


Can the motors be configured to limit their torque, so they can move a good pallet but never break a jammed or bad pallet, and instead stall out when a pallet jams? Then you ensure they have enough active cooling and somehow send an alarm when the jam occurs.

As an interim measure you could look at adjusting the overload current (P033) or have a look at the Shear Pin functions (A486-A489). Adjusting these may have little benefit if your motor is smashing away through a gearbox or linkage system that gives it significantly more mechanical advantage, but it might bring the system to causing less harm to itself. Standard hardwood pallets are surprisingly robust.


The better long-term solution would be to put some form of detection in place so out of spec pallets can be recognised prior to entering the system, and then subsequently alarmed and removed. You could also sense the damaging situation on the mechanical assembly before it starts to bend itself in half and tear itself out of the earth.

Wood Pallets Suck

I know these pains all too well. I've been in the bottling industry for awhile now and bad, broken and inconsistent wooden pallets have been a constant source of frustration and heartache. My facility is in the process of making the jump to plastic pallets for a more controlled product carrier. That being said, our palletizer empty pallet magazines are indexed similarly to what you explained, but are conveyed on chains. The parameters that Jeev suggested I think could help, as well as A447/A448 Current Limit. Unfortunately, with wooden pallets it is difficult to ensure you always have a solid consistent material, even if some sort of inspection was installed. Brand new pallets are great, but after they have been 'repaired' a time or two, they are terrible especially if what you are stacking on them needs to stay level. Your fork truck driver ought to pay closer attention. You could have a discussion with your pallet supplier too. While we were using wood pallets, we would occasionally have to call up our supplier and let them know they were sending us garbage (I am putting it mildly). I think our organization also backcharged them for downtime, which may have helped our leverage in the situation.

EDIT: After re-reading your post, you never mentioned if the pallets were wood or not. Guess that was an assumption on my part...sorry.

With the design of these systems I would generally use a mechanical torque limiter which would be designed to slip if the pusher system meets an obstruction. You can simply monitor the time for the pusher to do its cycle and if it takes too long stop the motor and give an alarm. This would protect everything, and they are not expensive.

This is an example.

We use only wood pallets in our plant. We have been pushing back on the supplier in regards to pallets being out of spec but after while we start seeing more and more pallets out of spec. It is a lot of frustration. Would you know by any chance the cost of a single plastic pallet? I ll take a look at that parameter as well today. Thanks

Liam Moran said:

This is an example.

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^^^ This. Is. Sweet.

In general, my view on things like this is that adapting controls to fix mechanical deficiencies is the wrong way to go. Good mechanical design should always factor in what should happen if the material being handled has a problem, like what is described above. Always fix the mechanical problems with mechanical solutions, fix control problems with control solutions.
Only my opinion.

Liam's solution is your best option. We use these on a lot of our machines. They are readily available from a dalton distributor, or if needed now mcmaster stocks a wide range of them.

Also, if you go this route to need to make sure you have some sort of timeout alarm on the axis that the torque limiter is on. You need to monitor a time base from when the pallet gets from A to B. If not, the drive will run and run and wear out the slip disk on the torgue limiter.

Liam Moran said:

In general, my view on things like this is that adapting controls to fix mechanical deficiencies is the wrong way to go. Good mechanical design should always factor in what should happen if the material being handled has a problem, like what is described above. Always fix the mechanical problems with mechanical solutions, fix control problems with control solutions.
Only my opinion.

Click to expand...

What, mechanical solutions for mechanical problems? Heresy! Burn him!

The thing is though, you ALREADY have the VFDs, why not use them first and if it doesn't work to your satisfaction, THEN try something else. Current Limit will in effect cause the drive to alter the commanded speed, so be forewarned because that may have unintended consequences here. I would use Shear Pin (A486) and the Shear Pin Time (A487) parameters to find the right balance of risk vs. reward. Shear Pin generates a SW Over Current Fault if the drive sits at the Shear Pin current level for longer than the Shear Pin time. SW Over Current is a Type 1 fault, so you can have the drive automatically reset if you want to, but given that you would likely want this to detect a jammed pallet, I would think you would want someone to manually clear it.

Its been a few month and only a few intstances where i had to cut the pallet out which is not bad at all. The motors that drive chain stop instantly where i can still safely remove the jammed pallet without cutting it. I really appreciate everyones help in this matter. Thank you so much All!!!

ziyaddin2015 said:

Its been a few month and only a few intstances where i had to cut the pallet out which is not bad at all. The motors that drive chain stop instantly where i can still safely remove the jammed pallet without cutting it. I really appreciate everyones help in this matter. Thank you so much All!!!

Click to expand...

Now you have to convince people that investing in a system that checks the quality of the pallets is worth the uptime