Looking for input and ideas

[wdd0422]

Hi everybody, I have a situation where we have a Cartesian robot sitting on top of an injection molding machine. There are 3 cranes in the bay where this cell is located. The problem is the mast (Y axis) on this robot when all the way up @ the 0 position is up high enough that it could collide with the lower part of the crane trolleys. We have many cells like this but on these the masts are not high enough to contact the Trolley. I have suggested that the hook and cable even all the way up could collide with these so its the same difference but they are not buying it and are asking for a way to prevent a collision on this one robot. To be fair they may have a point.


My first idea was to use a Safety Laser Scanner mounted to the crane traverse beam so it was looking above the power rails at the trolley but high enough to be above the mast on the robot and program a zone so that if the crane was in the protected zone it would stop the crane using RF relays. The problem with this is since there are 3 cranes all 3 would have to be stopped so that doesn't work. So I was thinking I could just use a loud alarm and strobe or revolving lights if the crane entered the protected zone. Also since they are two speed cranes I could put the cranes in slow speed as well if they insisted on this. Final problem is on the side I would need to put the scanner on there is 3" wide brace and also power cables going out to the trolley so when the bridge goes by those would be detected in the protected zone. I thought you could teach the scanner to ignore non-stationary objects unless they were over a certain width but apparently I'm wrong about that.

There are other solutions out there using lasers and a proprietary controller but it would be quite expensive since it would have to go on all 3 cranes and i hate to suggest that for just one area. One thing I'm considering is suggesting they that they move the machines to the other side of the bay in which case i wouldn't have the brace or the cables in the way and I could use the scanner. They may not like the idea much but might be the best way to go.


I'm sure somebody here has dealt with this before so I thought id see what you guys suggest. Id appreciate any ideas or input even if its just to let me know I'm way off here. I'll proof read this before I post but i usually still miss something and I hope Ive explained it well enough. If Ive missed something or Ive not presented it clearly I apologize in advance, please bear with me and Ill correct it.


Thanks everybody and Merry Christmas.

 

[Aabeck]

A sensor to know if any one of the cranes is in the "protected zone"

A signal FROM the robot if it is up too high.

A signal TO the robot to know if a crane is in the protected zone, not to raise too far.

A low range radio signal TO the cranes that stops whichever one is in the protected zone if the robot is already up too far, with audio/visual alert. Hopefully the radio signal can be contained within the 10-15 foot area I am thinking would be needed.

 

[GaryS]

I have actually done a project similar to yours
In that case we had 6 cranes and 2 booms rising from the floor both booms were mounted on a rail system they held a large milling head on each but they mover over the rail, the rail was about 80ft long and both booms could be located anyplace along the rail. The clearance between the top of the booms and the bottom of the crane bridge was about 6 in or less. So we had to track the position of the Bridge, trolley and hoist of all 6 cranes and the position of both booms. One other condition was they needed to use one or more cranes to load and unload the work for the mill. The plant was setup to use from 1 to 6 cranes for a single lift depending what they were lifting.
You are correct it is very expensive and needs careful engineering.

Without actually seeing the setup in person I can only put forth some ideas.

First if the boom is retractable and only needs to be at full height to set zero position.
If as you say full extension is 0 position why not just program a lower travel limit in the boom ( The higher the boom the lower the position value ) that way it would never be able to travel into the path of the crane.

Otherwise the best way would us a laser position sensor to monitor the position of each crane and create a travel limit around the boom for each crane
You are talking about at least 3 laser sensors and a controller of some kind and some creative programming. Whatever you do not use an encoder for positioning. Steel wheels on steel rails will never give you an accurate position there is way too much slip.

I hope this helps.

 

[wdd0422]

What we are considering right now is a retro reflective distance measuring laser sensor from Sick. It would be mounted on the trolley to detect the distance from the traverse (Rail beam)and there would be reflective tape along the rail beam to detect the length. The applications engineer from Sick will be visiting Friday so I can test it and see if it will work for this application.


https://cdn.sick.com/media/pdf/9/59/059/dataSheet_DL35-B15552_1057657_en.pdf