Proxim RangeLAN2 7920 Manual de usuario Pagina 45

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30
Now if we apply a drive signal to the plant that is proportional to E, then we can say that
our feedback mechanism invokes proportional error control in our system. The equation
of motion for such motion is given by:
(5)
meqeq
TJF
θθ
=+
&&&
where
dt
d
θ
θ =
&
and
2
2
dt
d θ
θ =
&&
m
T
is the motor torque,
eqlm
JJJ
=+
, lJ is the inertia of the load reflected through the
gears and
m
J
is the inertia of the motors,
eq
F
is friction and
θ
is angle. We can also say
that:
(6)
mm
TKI
=
where
I
is the motor current and
m
K
is a constant. Equating (4) and (5) gives:
(7)
m
KIJF
θθ
=+
&&&
If we invoke proportional control, we can assume that we will apply a current that is
proportional to the error:
IE
or we can say using equation (3) that
()
d
Ik
θθ
=−
,
where
k
is a constant. Therefore:
(8) θθθθ
&&&
FJk
de
+= )(
Here we have absorbed the constants
m
kk
into
e
k
and rewritten
J
for
eq
J
and
F
for
eq
F
to simplify. Now if we assume that
0
d
θ
=
, then our equation of motion is:
(9) 0=++ θθθ
e
kFJ
&&&
If we assume a solution
qt
e
θ
=
and let kk
e
= then (8) reduces to:
(10)
2
0
JqFqk
++=
Solving for q gives:
(11)
2
4
2
FFJk
q
k
±−
=
We see that if:
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