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High Accuracy Indoor Location Tracking?
aletterman asks: "I am looking for technology that can allow my company to track the position of a fork lift as it moves around a warehouse. This would allow us to factor out one problem situation - where the lift was when the driver dropped off the product. Based on the width of our warehouse locations, we need a resolution of about +-1ft. Standard GPS can't get that accurate or work well indoors. The fork lifts already have a VT220 terminal running 802.11b, so adding another device would not be difficult. I am currently looking at a product that can triangulate via the RSSI of the 802.11b network, but I am concerned the changes in the product mix and density of the corrugated boxes will change the RSSI and introduce a mis-positioning of the locations. I would prefer that the device transmit a position either serially or via our 802.11b network. Our warehouses are fairly large (300,000+ sqft) and have a large of amount of corrugated boxes. Any suggestions are greatly appreciated!"
Place optical encoders on the left and right front or rear wheels of the fork lift, so that it knows its delta position based on dead reconning. (about 1mm resolution)
Add 'bar codes' that run the width of the major isles, and point optical encoders downward on the fork lift so that as it drives over them, it can 'reset' its position and eliminate any errors that build up while using dead reconing.
Try to place them so that the fork lift is expected to run over a bar code every 5-15 minutes or so (depends on errors that you measure in encoder accuracy, and the resolution that you need).
Hook them up to a PIC that kicks out the counters for dead reconing as well as any known location events via serial to your computer on which the 802.11b is located. An AVR butterfly will do the job.
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Forklifts in warehouses can be difficult creatures. In the summer when I don't have school, I work at a place where sometimes I need to drive a forklift with flat, solid tires on a wet, greasy floor. It's a bit like ice skating at times, so determining the speed of the forklift could be quite difficult.
I assume that a warehouse as large as yours already has a system for numbering all the shelves.
In that case, why don't you just attach barcodes to all shelves and add a barcode reader with a long coilable cord to the forklifts?
When making a drop, the driver would scan the boxes to be dropped, and then the location they were dropped. To make a pickup, he could scan the box to be picked up, and then a special "pick up" barcode on a label somewhere on the forklift.
Ideally with a system such as this, a user interface requiring no user input other than scanning two barcodes.
This is much cheaper and reliable than any soft of positioning technology, and only relies on the tried-and-true technology of barcodes.
Sure, this is still prone to operator error, but no more so than a similar system using some kind of positioning. You're not going to gain any real benifits from positioning either way that you won't have when going with barcodes.
Check out a company called Dust Networks. They've been working on RFIDish localization for warehouse management based time of flight for years. I'm not sure if they've ever gotten it to work, but if anyone has it's these guys.
Otherwise, I think you're going to have to go with a bunch of cameras and some image processing. Maybe by taking pictures of the celing.
Take heart---the problem you're contemplating has been fairly well studied.
I remember a professor here at CMU saying that you could do localization for forklifts by pointing a camera at the floor. Most warehouse floors have enough scratches and marks on them that as you wander around, you can get a pretty good idea of where you are by comparing them to a map (using techniques like Monte Carlo localization---google it!). Combined with encoders on the forklift wheels, you may be able to get the resolution you need.
Here is a paper describing technology like this. In the results they say they get accuracy down to a millimeter.
So, those talking about painting a grid on the floor have the right idea---but perhaps you don't even have to do that!
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centimeter accuracy using indoor differential gps
e tail.jsp?id=3086
http://www.gpsworld.com/gpsworld/article/articleD
So the person running the forklift would know where to place items and where to go for their next pickup.
I assume you want something somewhat off-the-shelf and not ideas for designing one from scratch. Here's a link to a company that specializes in this type of stuff and might be able to provide a ready to use product. http://www.visonictech.com/info_page.asp?info_id=4 16
If you just look at the highlighted words you first get the requirement "track position forklift warehouse" So he wants to know where the forklifts are in a warehouse. Okay. But WHY?
Second set of words is "where driver dropped product. Ah. I was wondering. Who gives a toss where the forklift is? Oh I worked in enough warehouses to know they are sometimes a pain to find if people don't return them or use them as a portable chair to take their break outside BUT it would be cheaper just to buy another one then set up a tracking system.
So we just got a case of a user making it not very clear what he wants. All of the answers so far have focused on trying to keep track of the forklift. Some intresting solutions and some stupid ones (measuring wheel spin on a forklift forgets that these things slip OFTEN).
However none of you have so far questioned why he wants to do this NOR wondered if this was indeed the real requirement.
More likely he wants to keep tracks of the goods. In practice goods are often misplaced in warehouses. If something is in the wrong rack it can be a pain to find it. Or worse you only notice it when the wrong thing is sent to the customer because items were mixed up.
IF this is the real problem, tracking goods, then all the given solutions are at best incomplete and at worst totally and utterly wrong to a degree that explains why so many it projects are overtime and overbudget.
But surely knowing the location of the forklift whill help tracking goods? Nope. Why? Because there is no way to track were an item was dropped by the forklift. Why not? What if the forklift operator drops of his pallet for a moment to shift another pallet out of his way? What if he takes the contents of a pallet off to put them on another pallet?
Basically this has to do with warehouse procedures that aren't followed or don't match the real situation. Ideally every storage place in a warehouse should have a unique identifier. Each storage place is catogorized as to what it can contain. Every item coming in FITS inside the storage place (not 1 item requiring two spaces OR 2 items going into the same space). At receiving the computer assigns an empty storage space. The forklift operator then takes the item to the required location and stores it. Ideally you want some kind of system to verify this BUT in real live all you need is good employees and good managers who allow each other to do their jobs.
If this system is followed then no goods will go missing. Problem is that this often doesn't happen. Neither does it seem to happen in the posters warehouse. If the forklift operators kept track off where they dropped items off OR dropped them off at the pre-assigned location then things wouldn't go missing.
Sadly he seems to go for a tech solution. Nice but it won't work unless he shifts his attention from the forklifts to the items. They are the ones missing in action.
For the most obvious failure and the sure sign that this p
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