Path: utzoo!attcan!uunet!wuarchive!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!ark1!oasys!mimsy!mojo!disney!josip From: josip@ra.src.umd.edu (Josip Loncaric) Newsgroups: comp.robotics Subject: Re: High Accuracy manipulators Keywords: accuracy, position control vs. force control Message-ID: <1990Sep6.145354.1218@ra.src.umd.edu> Date: 6 Sep 90 14:53:54 GMT Expires: 11/1/90 References: <5829@hplabsb.HP.COM> <29067@netnews.upenn.edu> <5832@hplabsb.HP.COM> Sender: news@ra.src.umd.edu (The News System) Organization: Systems Research Center, University of Maryland, College Park Lines: 77 In article <5832@hplabsb.HP.COM> mgsmith@hplabsb.UUCP (Michael Smith) writes: >In article <29067@netnews.upenn.edu> ulrich@grip.cis.upenn.edu (Nathan Ulrich) writes: >> >>But I'm not a pessimist. I think high-accuracy operations can be realized >>with current technology and with serial robot manipulators. But not with >>precise position control and not with "endpoint" control, but with force >>control. This same low-accuracy human manipulation system can locate its >>two hands relative to each other in space with enough accuracy to put a >>0.9995" peg in a 1.0000" hole. How? By using compliance and force control. >>This is better than any robot manipulator can accomplish without huge chamfers >>and the use of a RCC (which is passive compliance). >> >>My opinion only. Now tell me why I'm wrong. >> > >I work for a $10 billion a year company and I have never seen >an application where such a peg is put into a hole! Such an application >is about as realistic as bin picking or stacking legos. It doesn't matter >how well a system does something that is not useful. This is a major >contention of mine. I believe that a great deal of robotics research >is misdirected. Hey, sure such stuff is fun. My first paper was on >bin picking and I have given demonstrations on compliance using a force >sensor because it was technically challenging and interesting but >subsequently I found that it was misguided. I have never seen force >compliance used in an actual application, not because it is unavailable, >but because it is not as needed as other technologies. > >We have been collectively doing research in robotics for many years now >and they are still not widely used in manufacturing. Why? Because they >are not cost effective and because they have been frequently misapplied. >We need to really look at what robots should be used for and then work >on the problems that specifically prevent them from being used in >those applications. > >Mike "my favorite project was a robotic bartender" Smith >HP Labs Well, perhaps you never had to put that size peg into that size hole... but if you never had to deal with closely fit parts, I'd be very surprised. The key point I'd like to make is that in assembling parts with very tight tolerances (finer than the positional accuracy of the robot) you CAN and SHOULD use force-based strategies. Assembling parts by feel is much easier than assembling them without force feedback. This is another example where designing parts so that their shape guides the assembly process through force feedback can be helpful... Anyway, the reason people have not used active force control much have to do with the technical difficulties of attaching this gadget to a commercial robot - it's very hard to get high enough bandwidth - but passive RCC devices are widely used. Your second point (that robotics research is not being directly applied to manufacturing) is well taken. A classic example (from an MIT robotics course) has students designing an elaborate two-handed dishwashing robot, while dishwashing robots can be bought at Sears for $300. So, what manufacturing needs are better manufacturing machines, and not "robots" in the Capek's R.U.R. sense. Many researchers, however, are motivated by the problem of designing machines capable of functioning in unstructured environments. This has little importance in a highly structured production process, but will be of great significance 10-20 years from now, as robot applications become truly widespread. These future robots may also help reduce the complexity of learning production tasks in a factory (less precise programming will be needed). Summary: robotics research serves more goals than just manufacturing. Force feedback (pasive and/or active) is a valuable technique in assembling close fit parts, which should be designed to help the process along. A final comment: HP probably uses robots mainly to stuff PCBs, which may explain why you've never dealt with peg-in-hole type problems. But, if you assemble VCRs, Walkmans, servomotors, etc., this type of problem quickly shows up. -- Josip Loncaric / SRC / U. of Maryland / -------------------------------------------------------------- ! Today's Special: Opinions....$0.02 each ! --------------------------------------------------------------