🚀 go-pugleaf

In article <1990Aug30.014817.8794@portia.Stanford.EDU> boehlke@sunrise.stanford.edu (Dan Boehlke) writes:

   I see the next breakthrough in robotics being the 
   introduction of very high accuracy manipulators--
   say an order of magnitude (or more) better than
   any systems of the 80's.  There are plenty of potential
   products that simply cannot be assembled today anywhere 
   outside of a laboratory.

Very high accuracy manipulators are very difficult to design using
today's technologies if they are to be of any general use.  The best
(gp commercial) figures I remember from the 80's are approx. .001"
repeatabilty for a _light duty_ electronic assembly robot (working
envelope ~ 1 cubic foot).  Building a manipulator _accurate_ (not just
repeatable) to .0001" with a similar envelope would probably imply:

  a.  All major joints must be linear slides.  Rotary motion is ruled
out if arms are of interesting lengths, since accuracy and stiffness
requirements go through the roof as arm length increases.  In addition,
kinematic errors due to inaccurate knowledge of zero position are
difficult to reduce at these accuracy levels.

  b.  Temperature controlled environment and workpieces is a must.  Any
sources of heat in the arm itself must also be cooled, or made constant
in effect.  A motor mounted in an arm will cause measurable deflections
as the motor heats up and warms the surrounding structure.

  c.  The tooling (end effectors, part fixturing, etc) costs will be
very high.  The assembly cell should be mounted on a isolated granite 
slab.

  d.  Frequent recalibration and verification would be a must - this
would be a rather delicate device.  

A interesting starting point for such a manipulator would be to look at
Coordinate Measuring Machines and the technology used to build them.

- Bart 

barts@Eng.Sun.Com
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