Shipbuilding Automation

rmg21,

While your own cell referenced "GPS type" system will be fine for overall positioning, when it gets down to specific operations, or precision assembly, I recommend that you employ "fixturing aids" (precision locating points) on the individual parts and a means for for your positioning system to reference off of them. One such technique would involve a separate precision robotic "arm" whose only purpose was to establish the relative positions of the parts to be joined. Another method would be precisely locating optical transducers along the joint on both the stationary part and the part being positioned for joining. Emitters and detectors would be a combination of wide angle and narrow angle devices to provide the required positioning feedback during the critical last phase of locating the part being moved.

I know nothing of your specific project, but in general, positioning parts such as you are describing, relative to each other is much more accurate when you actually reference them against each other, rather than both separately off a "distant" set of references and then calculating their relative positions, which works well only until you get in the "ballpark" where much higher precision is required for final positioning. The accumulation of errors is small in relation to general positioning, but will turn out to be larger than the precision you require for final joining.

Hope this provides some food for thought.

Regards, Greg

RMG21 wrote: I've look at using indoor GPS to guide the robotic arms with reference to relevant drawings. Besides these blocks are put together within sub-milimetre tolerance

REPLY

GPS relies on a very faint RF signal coming from orbiting satellites. Steel structures, especailly grounded steel structures tend to block GPS signals. Even the best survey grade GPS is not intended to work at sub millimeter accuracy. Been there done that with survey grade equipment and a local Differntial signal transmitter for hydrological and land surveys.

Robotic guided factory systems usually rely on positioning information by picking up on signals emitted by buried wires in factory floor. It works much like the digitizing tablets used to digitize a manual drawing or a photograph. Only difference being the larger escale. Another method used for overhead cranes is similar to the linear positioning scales used on milling machines and five axix CNC machining centers. The crane knows the exact position of the hoist point of the hook by referenceing how far along X, Y and Z axis the crane has moved and raised or lowered the hook.

A third method is laser referencing ( range finding) the clamping arms use to hold the parts being assembled.

As Greg mentions, a less expensive method would be a coarse positoning system referenced to the building envelope and a high precision system referenced to mating points of the sub assemblies. It would also be more flexible to accomodate varying assemblies.

Elnav

Thanks for input guys,

........input so far has been rather high level...large shipbuilding plates could be real pain for such automated fabrication, add normal metalwork practices,...gas cutting, grinding etc, and the pre-welding works in cell could pile up, - How do I overcome/rid of these!?

Also, inspection by client inspectors..

Elnav, thanks for your input, but I think indoor GPS is a self contained system;

http://www.qualitydigest.com/feb05/articles/01_article.shtml

You may want to check out some of the techniques utilized in the aerospace industry that have been developed to allow for fixtureless assembly. Basically this involves incorporating features on the various components which allow for self-alignment that is verified using laser trackers.

Good Luck.

Robert