What You Need To Know About VLM Trays
Years ago I was working on a project with an integrator and received a phone call late in the evening.
“Tim, we put the parts on the tray and it folded up like a piece of foil!”
Taking a step back I had been working on this project for about 3 years. 3 years since I first met with the client until we received the purchase order. 3 years of relationship building, 3 years of technical meetings, 3 years of conference calls. Normally a vertical lift module sale does not take this long but this was part of a larger, highly technical project. In those meetings we talked about the tray payload capacity and agreed that it would be close to the capacity of our heaviest duty machine at the time. Receiving a call of this magnitude created a little panic in me but years of mechanical troubleshooting took hold. I asked for a picture, videos, and any other information about how they tested the tray. I’ll get to the outcome of this issue shortly but first lets talk about vertical lift module trays.
I learned a lot through this process about trays, or pans, or carriers, or bins, or whatever else you may want to call a surface you place materials on for storage in a vlm. It is my hope that you learn two very important issues related to vertical lift module trays. Deflection and payload distribution.
Deflection with respect to the trays in a vlm is the distance a tray bends downward when a load is placed onto it’s surface.
When it comes to vlms, tray deflection is a design consideration. By allowing a specified amount of tray deflection manufacturers can reduce the thickness of the steel used thereby reducing the weight of the trays AND the cost to manufacture. As the payload of a tray gets closer to the capacity of the tray the tray will deflect further. This doesn’t explain why the tray in my story folded but we’ll get there. I’ve seen numerous vertical lift modules with scrapes across the access opening bottom. Basically where the trays deflected so much that the bottom of the tray scraped it as the tray was being pulled onto the extractor. As you could imagine these were trays that were loaded to the max capacity or even more!
Tray deflection does not have to be a major issue. Often times I would source a unit from a manufacturer and then add stiffeners to the trays. This would hold the tray rigid and almost always eliminate any deflection. An additional benefit to adding tray stiffeners was that the inventory on the tray would no longer vibrate or bounce as much as before.
The other topic to address regarding trays is payload distribution. I have read the user manuals of almost every vlm in the US market and they all make it very clear that the weight must be distributed equally across a tray. Depending on the way the extractor/lift is designed this could be a major or minor issue. The reason why it is important to distribute weight across the surface of the tray is two fold. First, an equal distribution of weight will minimize tray deflection. Second, is that by having equal distribution the extractor/lift will not be unbalanced. If you operate a vlm with trays that are unbalanced you will see premature and possibly excessive wear on the lift rollers, extractor guide, and sometimes even wear on the chains and belts and their associated sprockets and pulleys. Additionally as trays are being placed into position in their storage location the out of balance could cause lifting to occur and creating a jam into a shelf rail.
So getting back to my story! Yes the tray folded up and was turned into a pile of scrap. We did overcome the issue by creating a fixture which spread the load across the tray both front to back and left to right. This fixturing distributed the weight across the center of the tray but more importantly around the inside perimeter of the tray. I do not think I slept at all the night that call came in but pretty quickly with the help of my integrator partner and some backyard engineering we were able to create a solution which is still effective to this day.
If you are in the market for a vertical lift module do not let the issues of deflection or weight distribution be a concern. Instead be prepared to discuss this an understand how your vendor will overcome any challenges posed by your application as well as knowing what the warranty implications are.
For more information about this issue or any regarding vertical lift modules feel free to reach out to met at [email protected] or message me on Linkedin!