Newsgroups: comp.robotics
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From: browen@lyapunov.aoc.nrao.edu (Bruce Rowen)
Subject: Re: Searching for a passive articulated pointer
In-Reply-To: jonlea@casbah.acns.nwu.edu's message of 14 Nov 1993 20: 20:45 GMT
Message-ID: <BROWEN.93Nov15092605@lyapunov.aoc.nrao.edu>
Sender: news@nrao.edu
Organization: National Radio Astronomy Observatory, Socorro NM
References: <2c63ut$7nj@news.acns.nwu.edu>
Date: Mon, 15 Nov 1993 16:26:05 GMT
Lines: 48

In article <2c63ut$7nj@news.acns.nwu.edu> jonlea@casbah.acns.nwu.edu (Jon Lea) writes:

   I am looking for companies that manufacture a 6-dof articulated pointing
   device.  The device could be catagorized as a 6-dof Coordinate Measuring
   Machine, or a powerless robotic arm.  I have seen them used in medical
   applications (pointing to areas of the brain with respect to MRI images...). 
   They usually consist of slender links connected by rotational joints, and 
   are quite "gangly" in appearance. As I stated, they are essentially used
   for measuring / pointing.

   Given this description, is anyone familiar with companies that produce such
   items?  I struck out in the Thomas Register, so I am looking for any ideas
   on new directions to look.

   Jon Lea
   Northwestern University
   jonlea@nwu.edu

While working for Texas Tech HSC in El Paso, It was one of my projects
to build just such a device for tracking motion of wrist bones during
wrist movements. All the commercial devices available relied on
potentiometers for position feedback and used A/D conversion for the
computer interface. Though compact, they had poor resolution and bad
accuracy. Also quite expensive. The device I built was a 6 DOF open
chain with digital encoders (20,000 PPR) and an 8051 based interface.
The thing was quite inexpensive ( ~$2000) and had a worse case
resolution of 0.08mm. The design was based upon kinematic optimization
of the structure for maximum articulation and a kinimatic based
calibration scheme was used for "self calibration".


FYI. This work was performed in conjunction with New Mexico State
University which has an EXCELLENT robotics program focusing on modern
adaptive and robust control for non-linear systems. (we don't need no
steenkin' dimensions or knowledge of parameters!)

(I know, what a plug for NMSU. Somebody please give Pete Pittman a
job! He be a most excellent robotic control and toxic waste handleing
guy!)


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Bruce Rowen 				National Radio Astronomy Observatory
Scientific Programmer				Array Operations Center
browen@aoc.nrao.edu			  P.O. Box O  Socorro, NM   87801
(505)385-7329					     (505)385-7000
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