Newsgroups: comp.robotics
Path: brunix!sgiblab!news.cs.indiana.edu!lynx.unm.edu!Mr-Hyde.aoc.nrao.edu!news
From: browen@aoc.nrao.edu (Bruce Rowen)
Subject: Re: axis force sensing in software using motor
Message-ID: <1993Dec13.170718.11638@Mr-Hyde.aoc.nrao.edu>
Sender: news@Mr-Hyde.aoc.nrao.edu
Reply-To: browen@aoc.nrao.edu
Organization: National Radio Astronomy Observatory, Socorro NM
References: <2ea0vj$p5t@saturn.haverford.edu>
Date: Mon, 13 Dec 93 17:07:18 GMT
Lines: 50


>I think I have figured out a crude way to sense if a robot has bumped
>into something, without using any sensors.  It is slow, but can be
>implemented in software.  I have not tested the idea.
>
>The idea is to measure the rotational resistance of an axis motor in both
>directions, in order to yield information about the torque (or linear
>force) load that that axis of the robot is working into.  For example, if
>an arm is pushing down on the table, the elbow (or shoulder) axis of that
>arm will experience unequal torque loads in the forward and reverse
>directions.  By subtracting the frictional component from both the
>forward and reverse applications of torque, one could derive (using the
>arm weight and geometry) the force being exerted by the robot hand on the
>table (presumably equal to zero if the hand is not in contact with the
>table).
>
>I believe it possible to measure the torque load on a motor in both
>directions in software, provided the motor has some sort of optical
... [snip]




>
>I would appreciate any comments, and especially references to similar
>ideas.
>


Or you could just measure the armature current (DC brushed motors).

T ~ kI

where k is the magnetic field flux.

sleazy way to do this is to put a small resistor in series w/ the armature
and measure voltage drop.




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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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