Detecting different tools

Hi all, great forum.
I have a sensor question. There is a conveyor with carriages on a chain track going into a paint booth with a robot that will spray paint and then it continues into an oven. The robot has a jacket and only peers through a brushed opening the company has deemed the paint area to be ATEX (I don't think they know what ATEX is but they don't want any electricity of any kind in the spray booth. I need to tell the robot what carriage(tool) number to spray there are approx 13 parts.
I had some thoughts about firing a laser (retro reflective) onto targets and reading the binary. I was going to mount the laser on the six axis robot and let it do this before spraying.This would take some time and the sensor is mounted outside the booth peering through brushes the light would be scattered and because it is not on the six axis but the top of the robot 3rd axis limited movement and alignment errors. The jacket on the robot is only the 3 upper axis or upper arm.
That's the idea so far but I am not sure now seems silly and very hard to implement. Maybe others have some sugggestions?

Think outside the box..

..I mean, think outside the spray booth.

The chain conveyor is your friend.

Set up your tool (carrier) ID system outside the spray booth a fixed distance leading into the spray robot. (13 tools) I would suggest (4) lasers shooting at (4) reflectors, this will give you (15) unique ID's. If you have future expansion plans, another laser/reflector added up front will give you (31) different ID capability.

Install some pulse digital input relative to conveyor chain movement. Depending on the resolution required, this can be as complicated as an encoder, or as simple as a proximity switch that sees holes in a sprocket.

Read your tool ID outside the booth, put it into the top of a FIFO. Increment the FIFO every chain "pulse". The FIFO is impervious to line speed as it is a fixed number of "clicks" to the spray robot.

We have done this for years where various parts were loaded onto a line an ID entered, and the paint booths were 20 meters downstream.

A proximity may be too coarse of a resolution, if you use an encoder, you cannot fire a FIFO every encode pulse, you would have to run the FIFO every X number of encoder pulses.

Last caveat, if the line has reverse capability, you will need to run your FIFO in reverse, when the chain conveyor is being command to run reverse.

the paint booth area is class 1 division 1.
outside the srea also has class and division ratings, but i don't know your setup.

your robot must be intrensically safe also for that environment.

we used an omron bar code reader system to read the slots in a piece of steel. while it did get painted, the system detected the barcode and told the robot what to do.

regards,
james

Check out imf vision sensor od2 229 list is $875.00 us good luck.

What about RFID tags on each carrier? I have never used RFID in a hazardous area, so I am not sure if this would be OK. If it were, you could mount your RFID reader at the entrance to the paint booth, and then proceed to track the carraiges as Plastic described above.

I agree that it would be advantageous to have a controller know the sequence of the parts as they enter the paint area and track their positions on the chain.

The question then becomes how are the parts loaded onto the transport chain in the first place?

We have looked into the rfid tag option, but found that the oven temp was greater than the tags could withstand. so we went with the slotted bar code option.

regards,
james

Really depends on what type of conveyor chain you have. If the carriages are dragged along the floor by a chain with "dogs" at evenly spaced intervals, or if it is an overhead chain with carriers attached to it or a "power & free" type chain, you are in luck. Attach an absolute encoder or resolver to the drive sprocket and gear it to turn exactly once per job spacing of the chain. The number of pulses per turn can then be directly related to distance traveled. An absolute device allows you to remember where you are after the power is cycled off and on.

Use this as your heartbeat, read your style outside the booth in a safe area, then use a synchronous shift register to track your data to the robots.

If the conveyor is a "skid" type where the carrier is not attached to the chain and the spacing between jobs is not consistent things will be much more difficult. You will probably be forced to use intrinsically safe or explosion proof sensors in the booth just prior to the robots.

James Mcquade said:

We have looked into the rfid tag option, but found that the oven temp was greater than the tags could withstand.

Click to expand...

Omron has RFID tags that are rated up to 150C. Check part # V600-D23P55

We use the V600-D23P55 (rated for 80C) in Selective Soldering machines that have +200C preheaters for 1 1/2 minutes. Been working fine for years.

I bet the high temp version could withstand just about any curing oven.
http://www.omron247.com/doc/pdfcatal.nsf/C3A5D6AC8C09A23586256D2F006FB092/$FILE/D09V6000503.pdf

I used RFID that can stand paint oven temp. We just mount the tag on parts carriers. Can't remember the part's number, but it was made by Pepperl&Fuchs. I still have the manager's card:

Helmut Hornis, PhD
330 486 0148