Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!elroy.jpl.nasa.gov!decwrl!netcomsv!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Constant Force Mechanisms, Counter Balance Mechanisms
Message-ID: <nagleCDqJxv.G4A@netcom.com>
Keywords: anti-gravity, constant force, counter balance
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
References: <27nq2i$dqm@scarecrow.asel.udel.edu>
Date: Wed, 22 Sep 1993 03:20:18 GMT
Lines: 25

ramanath@scarecrow.asel.udel.edu (Ranganathan Ramanathan) writes:
>I am looking for some mechanisms which can take a
>constant force applied to its free end for some small
>range of motion in 3-D space.  (A typical example is 
>the table lamp mechnism which has a lamp at one end 
>and two four bar arms with springs
>and friction to counter the weight).  

       Constant-force springs are available, if you look in catalogs
of mechanical parts.  One form is the rolamite, which is a neat little
mechanical trick.  Weight and pulley schemes are also constant force.  
But I don't think that's what you want.  If you want to balance an 
articulated structure, counterweights will do it.  These tend to push
the moment of inertia up, though.  This leads to efforts to keep the
mass of the system down, especially for parts far from the base.

      It's possible to simulate counterbalancing
by force feedback, and you can even play with simulated inertia.  That's
worth considering if you're doing, say, "teach mode" for a robot, and you
already have the actuators and control gear.

       You don't say what you are building.  A robot arm?  A feeler?
Care to tell us?

					John Nagle
