<[Bill Leach 940714.20:34 EST(EDT)]
[Paul George 940714 15:00]
Indeed, Paul, as you have mentioned (and others before you, including
myself), how you choose to view a particular control system example
influences how you might "parse" the parts.
In the simplest biological control loops, it appears that a reference
signal can only have magnitude (including zero) but may not change signs
or "go negative". However, it also appears that there are "complementary
control loops" where such bidirectional control is necessary (most all
physical movement can be viewed that way but I am not sure that even that
view is really correct).
Slowing a car and slamming on the brakes can be a considered a different
action, rather than just a difference in the gain of F2.
Yes they could be but probably are not. Then again... there might
actually be two types of situations. I am thinking of the person that
appears to really have two modes of operation of the brakes; Variable
pressure control to slow the vehicle at some controlled rate is one and
the other is "panic" mode where they just "press for all that they are
worth" (hopefully at least on the brake but often not!).
-bill
[Paul George 940715 12:00]
[Bill Leach 940714.20:34 EST(EDT)]
Then again... there might
actually be two types of situations. I am thinking of the person that
appears to really have two modes of operation of the brakes; Variable
pressure control to slow the vehicle at some controlled rate is one and
the other is "panic" mode where they just "press for all that they are
worth" (hopefully at least on the brake but often not!).
That is the situation I had in mind. People often react very differently to
gaining on another vehicle, and seeing a truck stopped in front of them.
Paul
From Tom Bourbon [940718.1739]
Back from the wedding weekend with my credit cards melted down from overuse
-- the true role of the father of the bride!
What a flood of mail on the net!
[Paul George 940715 12:00]
[Bill Leach 940714.20:34 EST(EDT)]
Then again... there might
actually be two types of situations. I am thinking of the person that
appears to really have two modes of operation of the brakes; Variable
pressure control to slow the vehicle at some controlled rate is one and
the other is "panic" mode where they just "press for all that they are
worth" (hopefully at least on the brake but often not!).
That is the situation I had in mind. People often react very differently to
gaining on another vehicle, and seeing a truck stopped in front of them.
Why would those two scenarios call for two different "modes" of control? If
perceived rate of closure is being controlled, with a reference value of
zero, or something very small, then think of how the error signals would be
changing in the two scenarios, prior to the person applying the brakes.
Even if the person's gain did not change, or the "mode" of control remained
the same, the error signal would be much bigger and growing more rapidly in
the one scenario than in the other. Perhaps?
Later,
Tom
<[Bill Leach 940719.00:53 EST(EDT)]
From Tom Bourbon [940718.1739]
Back from the wedding weekend with my credit cards melted ...
Well it sounds as though maybe you, your wife, daughter and groom
survived ok even if it was a financial disaster (what wedding isn't?).
[Bill Leach 940714.20:34 EST(EDT)]
Then again... there might
actually be two types of situations. I am thinking of the person that
appears to really have two modes of operation of the brakes; Variable
pressure control to slow the vehicle at some controlled rate is one and
the other is "panic" mode where they just "press for all that they are
worth" (hopefully at least on the brake but often not!).
Why would those two scenarios call for two different "modes" of control? If
Tom, I don't know that they do "require" two modes of control but my
"feeling" is that two or more different control systems must be involved
here in this example. People really do "stand on the brake" and
essentially "freeze" until the event is over. This is rather radically
different than even braking hard. Indeed, from the view of the vehicle,
it is not control at all!
Now, my intention is not to say that there isn't any control action,
indeed I believe that all of the action is control action but the person
is acting like a controller that has reached maximum output but the error
is still present. This, I suspect is actually the case. The driver has
envoked control actions that are not wholly appropriate to the error
condition but "doesn't know any better." Their only "learned" control
action is to press on the brakes. If this is not sufficient to correct
the perception that they are about to run into something then they don't
know what else to do. I am suggesting that a human control system
confronted with a disturbance that is outside the range of its' control
functions is, at that moment, not controlling (and make that the range of
its' known control loops).
So, I suppose that the answer to your question is no, it does not require
"two different modes of control". Rather, it is what one might observe
when a control failure occurs.
-bill