Miata Mailing List: September 1997, Message #267
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From: 	Tim Mullen <MullenT@gisdbbs.gisd.trw.com>

Subject: Re: NMC: Hysteresis defined & LIDAR followup

Date: 	Tue, 2 Sep 1997 15:21:10 +0000



"Will Brown" <wbrown@comet.net> wrote:



>> In a mechanical system, hysteresis is just exactly what you

>> described. The lag between "input" and "output" ... 



> I would still tend to call that the 'hysteresis dead band' rather 

> than lag - because if you move that input shaft 'just a little' (not 

> enough to get out of the hysteresis dead band) and then *stop* moving 

> it, the output shaft will never change direction.  If it was lag, the 

> output shaft would move after a little while.  



Well, okay, a matter of terminology...



In the rocket (Space Shuttle actually) nossle, the problem was that 

the shuttle would be "off course" and the nossle would be commanded to

move, and it wouldn't (static friction), so on the next cycle of the 

flight control program, the shuttle would be farther "off course", and 

the nossle (the hydraulics actually) would recieve a command for a 

larger deflection, etc. until, finally,  the friction is over come 

and it moves.  The nossle *would* eventually move out of the "dead 

band".  Whatever the cause of the lag, the effect was called hysteresis. 

The problem was predicting it, and anticipating it such that the system 

could minimize it (the smoother/straighter it flys, the more cargo goes 

into space...)



> Team "not an ME or rocket scientist, but I knows hysteresis when I 

> sees it"



Actually, my degree is in Aerospace Engineering, and I never thought 

about it until a year or so ago when my daughter pointed out to me 

that: "Doesn't that mean you're a Rocket Scientist?" - actually, now 

I'm a computer geek...  I haven't done engineering for about 15 years...



>Team "spirited debate, not an argument"



Of course.  Nothing else...



-- 



Tim Mullen