I’ll do my best to describe our sortation system in-order to better help you understand the issue. We basically have a drop tray sortation system. Tray’s are carried around horizontally by a drive chain and actuated by pneumatic cylinder stationed at each chute. Each chute is a potential drop for any of the carrier trays on this sorter. The chain is driven by two 7.5hp motor on each end. Each motor is controlled by a power flex 40 VFD which each have a set point of 40hz but no feed back loop. There is currently no feedback loop that allows the two VFD’s to keep tabs on each other and insure that they run in sync. Both VFD’s fire up at the same time and run at their 45hz set point. In terms of operating, this set up seems to work fine.
Our system is 5 years old now and the first time we had to tension the drive chain due to slack was about a year ago. A few weeks ago we had to tension the chain again by the same amount. Putting aside the fact that we weren’t sufficiently monitoring chain slack until it started causing us issues, our current feeling is that it seems like the chain might be stretching at an accelerated rate.
I checked the amperage for both VFD’s and each phase averaged about 2.7amps on one of them and 0.2amps on the other one. Theses results randomly alternate between each VFD after we restart the sorter and hold until the next restart. This suggest that the VFD’s aren’t perfectly in sync and only one of the two VFD’s is carrying the load. Also, when the chain is slack you can see the chain pushed outward as it comes of the sprocket at one end to the sorter, suggesting it’s driving the chain into the sprocket downstream (the manual say’s the chain should bend inwards off the sprocket when the chain is slack).
We’re trying to stay ahead of this issue as we would like to get another 5 years life from our sorter chain and of course avoid any potential hazards that could occur from excessive chain slack (we will continue to monitor though).
Here is my question; Is this sync issues were seeing with the VFD’s normal with type of set up? We’ve been exploring the idea of a mater/slave scenario between the two VFD’s by either upgrading the VFD’s or having it written into our PLC logic. One thing we don’t know is if expecting a situation where both motors share the load equally reasonable or even possible. I’d prefer not to spends a lot of resources trying to make our VFD’s perfectly in sync only to find out that those are unreasonable expectations for our system. Does anyone have any experience with this issue? Should we abandon further investigation of this issue and simply continue monitoring chain stretch? Thanks for reading this post. I’m curious to see if anyone has any opinions on this.
Our system is 5 years old now and the first time we had to tension the drive chain due to slack was about a year ago. A few weeks ago we had to tension the chain again by the same amount. Putting aside the fact that we weren’t sufficiently monitoring chain slack until it started causing us issues, our current feeling is that it seems like the chain might be stretching at an accelerated rate.
I checked the amperage for both VFD’s and each phase averaged about 2.7amps on one of them and 0.2amps on the other one. Theses results randomly alternate between each VFD after we restart the sorter and hold until the next restart. This suggest that the VFD’s aren’t perfectly in sync and only one of the two VFD’s is carrying the load. Also, when the chain is slack you can see the chain pushed outward as it comes of the sprocket at one end to the sorter, suggesting it’s driving the chain into the sprocket downstream (the manual say’s the chain should bend inwards off the sprocket when the chain is slack).
We’re trying to stay ahead of this issue as we would like to get another 5 years life from our sorter chain and of course avoid any potential hazards that could occur from excessive chain slack (we will continue to monitor though).
Here is my question; Is this sync issues were seeing with the VFD’s normal with type of set up? We’ve been exploring the idea of a mater/slave scenario between the two VFD’s by either upgrading the VFD’s or having it written into our PLC logic. One thing we don’t know is if expecting a situation where both motors share the load equally reasonable or even possible. I’d prefer not to spends a lot of resources trying to make our VFD’s perfectly in sync only to find out that those are unreasonable expectations for our system. Does anyone have any experience with this issue? Should we abandon further investigation of this issue and simply continue monitoring chain stretch? Thanks for reading this post. I’m curious to see if anyone has any opinions on this.
Last edited: