Hi learned people, Can anyone provide reference applications where GPS devices have been used to implement anti-collision mechanism for stacker - reclaimer systems? I believe that GPS devices have in-built capability to provide 3-D information (including height from a reference datum level). Any leads and pointers will be much appreciated. Thanks, Raj
Hi Raj, do you have any easier questions?? ;-)
Yes, GPS devices can supply 3D information but it will cost a packet. I know of one instance of a Garmin GPS-35 (
Happy programming! Cameron:-)
I am not sure that you will find GPS to provide data precise enough / in real time for your application
Stackers don't move that fast!! ;-)
Cameron:-)
I worked on a project that had a "CAS" collision avoidance system that controlled the speeds at which the various tools could move across the drill floor on a semi-submersible oil rig.
As the operator moved a piece of equipment closer to another object, the cas program would reduce the maximum speed available to the tool. Tools could collide, they were just limited as to their speed at impact.
That said, the tool plcs used encoders (including angular encoders for the booms) to determine their 3d location. I would be concerned how fast the end of a boom could move under rotation and whether or not a refresh rate of 1 hz would be sufficient for that speed.
Also, the vertical accuracy of gps systems is not as good as the horizontal accuracy. For the Garmin gps 35, with dgps, the horizontal accuracy is ~ 5 m. The question then is, will the error on two or more gps units on two or more machines be the same and cancel each other out? or not? I think you would want to vigorously test that on both vertical and horizontal positions.
Just my two cents, Tom
Why not just use a local radio network. Having sensors embedded throughout the area and transmitters on the stackers could let each know where the other is (relatively), a software map of the area and some exchange of trip data could let them negotiate optimal pathways to prevent them from running into one another.
If you were only after collision avoidance, there are much better (read simpler and cheaper) devices for doing this in an industrial environment - eg. laser scanners from Sick
We've used these gadgets on high-speed process cranes, and once installed, collision avoidance was the least of our troubles..
Cameron:-)
To implement collision avoidance is more involved than implementing a zone management system that absolutely prevents two machines from being in close proximity. It has the benefit of allowing the machines to interact at a slower speed. On the project I was working on, the scale of the machines, and the large freedom of movement ( longitudinal, rotational, both vertical and horizontal boom movement ) would have required a huge number of prox. sensors. The software, also modeled the pipe the cranes were carrying which could range in diameter from 6" to 4' with a length > 100'.
For a stacker system, zone management would probably suffice.
Tom
If you use gyros, compass and accelerometers and reset the integration error with GPS?
Eric Girard
environment -
As Cameron understated, stackers don't move that fast. In fact, stacker/reclaimers are very large machines that travel very, very slowly. I don't expect they need an accuracy better that one meter, probably less. They cost many millions and have proportional budgets available. If they can eliminate a full time operator that would be $500,000 per year. (One full time operator = four people on staff.)
It sounds like Raj is talking about a real-time mapping system. Accurate computerized mapping systems exist. Our company has a subsidiary that deals in such. I doubt anyone ever thought of doing this in real time to track the changing landscape of a reclaimer pile.
Walter.
Now, that's just silly. This is for a stacker/reclaimer, not a rocket!! ;-)
Cameron:-)
As I had stated earlier, the system that I am familiar with, would allow collisions, just at a reduced speed. In fact, one of the customer's client's safety teams wanted a written guarentee that if a collission did occur, nothing would break off any of the machines, fall fifty meters and kill or maim a worker. As no one would sign such a document, the system was modified to actually go to a max speed of 0% at the end of the prox. v. speed curve, giving total collision protection.
My point is, if you are selling someone, an "anti-collision system"(Raj's original query), it better work exactly as advertised, or you better have great liability insurance. As such, I think you would want to test it thoroughly, and document its shortcomings, if any.
Just because a machine is big and slow, doesn't mean you want it getting too intimate with the neighbours. ;-)
Tom
Further to the below, I found an industrial GPS card for Allen-Bradley PLCs (from Hiprom) that claim to be suitable for stacker-reclaimer systems. They provide lat. long. and altitude or Cartesian coordinates as well as velocity vectors to the plc backplane. Kinda neat, but they quote a non dgps Position accuracy of better than 25 metres. A WAAS version would be really good for North American applications.
Hiprom GPS card
Cameron, If I keep posting "easy" questions, then it would not be fun at all. I do value the insights and thoughts provided by all of you over the past few years (since I have been lurking on this newsgroup).
For your information (and other Aussie users), I have moved across from Gladstone, Queensland (north east coast) to Perth, WA (south west coast). The reason for my absence (a fortnight!!!!) is that all the furniture (earthly possessions??) was in transit until now. Regards, Raj
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