Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!netnews.upenn.edu!grip.cis.upenn.edu!ulrich
From: ulrich@grip.cis.upenn.edu (Nathan Ulrich)
Newsgroups: comp.robotics
Subject: Re: High Accuracy manipulators
Keywords: accuracy, position control vs. force control
Message-ID: <29196@netnews.upenn.edu>
Date: 5 Sep 90 18:11:47 GMT
References: <J?=%^5|@ads.com> <1990Aug28.234809.15660@portia.Stanford.EDU> <1990Aug30.014817.8794@portia.Stanford.EDU> <141582@sun.Eng.Sun.COM> <5829@hplabsb.HP.COM> <29067@netnews.upenn.edu> <5832@hplabsb.HP.COM>
Sender: news@netnews.upenn.edu
Reply-To: ulrich@grip.cis.upenn.edu (Nathan Ulrich)
Organization: University of Pennsylvania
Lines: 55

In article <29067@netnews.upenn.edu> I write:
    ...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....

In article <5832@hplabsb.HP.COM> mgsmith@hplabsb.UUCP (Michael Smith) responds:
    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.

You must not have had any exposure to mechanical systems, then, or ever spent
*any* time watching a machinist (the size of your company doesn't lend
any credibility to your ignorance, by the way).  This type of task, which has
been generalized into the peg and hole insertion example, is very prevalent
in all types of mechanical assembly.  Shafts and bearings frequently have this
type of tolerance (or tighter).  Bearing housings and bearings commonly have
interference fits (where the housing bore is *smaller* than the OD of the
bearing).  Even the relatively simple task of inserting a screw or bolt into
a clearance hole is an example of peg and hole insertion, although usually
with much lower tolerances.  I could spend pages listing the tasks I'm aware
of that fall into this category (and I'm only a PhD student, not an employee
of a multi-million dollar company :-).

I think one reason the peg and hole insertion has been a prevalent watershed
for robotic assembly is because it is a good measure of either the precision
of the system or its ability to accomplish difficult tasks with force
control or compliance.  And the tolerance of the fit is a good measuring
stick.  Systems that can accomplish tight tolerance peg and hole insertion
are also considered able to handle different geometries (square key in
square hole, etc) although this is not always true.

Michael Smith continues:
>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.

And who will decide what robots "should" be used for?  Just because a
project doesn't seem to have immediate application does not mean that it 
hasn't advanced the state of the art and will not eventually find application
somewhere.  If we only concentrate on immediately-apparent applications then
we will fall behind in broader research, and ten years from now the Japanese
will be laughing at us (again).  This is not to propose that we ignore
applications.  Although I do think robots are most useful outside of 
manufacturing, many of the ideas that have been tossed around in conferences on
robotics could be applied (and have been, but in Japan or Europe) if the US 
manufacturing industry was more concerned with long-range planning than
short-term profits.

Nathan Ulrich                           "If it was easy, someone would have
ulrich@grip.cis.upenn.edu                done it already..."
DoD #0080 - GT750 pilot