Touch Sensing and Real Time Path Modification

[jgmell]

Does anyone out there have any experience with Touch Sensing or RTPM. I have an FA20N which I would like to do welding on hand fabricated items. I've been advised to go for laser but the cost is high.

I would like to know an approximate cost and how well it works.  That is what tolerances I can have on my fabrication.

For that matter any advice on laser tracking and vision would be much appreciated also.

[TygerDawg]

I've done it before with Staubli bots.  The old V+ language had a function "ALTER" which allowed one to programmatically make real time changes to TCP position based upon..whatever you wanted.  Analog input signals, whatever.  If I understand Kawa language correctly, it is a derivative of the pre-V+ language VAL.  Maybe some form of ALTER still exists.  If your robot operating system doesn't have something similar to this ALTER function, you're probably out of luck.  Doing this is very tricky anyway.   The advanced programming required to make it work is unlikely to be supportable by Shop Monkeys.

Another way I've done it is to put an independent axis on the end of a bot.  Specifically, a linear servo that made the TCP move perpendicular to the surface of the workpiece so I wouldn't have to try to get the robot to do it.  So it adapted to variations in the workpiece.  Input to the servo controller was a laser displacement sensor with analog output. 

Lasers are great (especially Keyence equipment) but are very particular to the surface condition.  I've explored ultrasonic sensors that are more forgiving, but less accurate.  Baumer Electric makes model UNCK- ultrsonic sensors that are the smallest and most accurate that I have found on the market.  The Banner Engineering units are nice enough, but larger & less accurate.

[rdixiemiller]

 You can use any number of touch or non-contact sensors to locate the part needing to be welded. I guess it would be good to know what configuration parts you are welding. I use sensors and XMOVE TILL (sensor) to locate parts all the time in material handling operations.

[SkyeFire]

Does it have to be realtime?  Or could you use realtime sensing adjustment on a limited number of axes?

I ask b/c years ago, I did a laser-welding system for auto-body roof seam welding using a Kawasaki.  But due to the very tight constraints for the height of the laser above the welding surface (focus length is absolutely critical for laser welding), we used a single-axis compliant head with a pressure wheel that both pressed the layers together (it was a lap join weld) and kept the laser's final optic assembly at exactly the right focus height.

Some companies also sell seam-tracking systems that put a 2-axis servo table on the end effector paired with a video or laser sensor, and let the head perform realtime adjustments to the laser path while the robot just stays "close enough" to the optimum path.

Alternatively, if you don't have to have realtime path adjustment, you might be able to get by using a good vision system -- shoot the part and adjust your path once before welding.  That would work for parts that are presented to the robot inconsistently, but only as long as the parts themselves are very consistent to each other.