Biomedical Engineering Reference
In-Depth Information
Figure 2.3
Schematic of the RUPERT controller structure.
(3) The derivative part of the feedback controller is implemented as a high-pass
filter. A high-pass filter can be regarded of as a differentiator and a low-pass
fiter in series. The low-pass filter attenuates the high frequency noise, and
thus reducing the amplification of high frequency noise by the differentiator.
This will reduce the effect of high frequency noise from corrupting the control
signal, and will ensure a quiet operation from the pressure regulator.
The gains for these IL controllers need to be selected to provide a robust
performance on stability applicable to users of different body sizes and builds
with a large range of parameters and variable impairments. They were obtained
experimentally by trial-and-error through testing the robot on different able-
bodied subjects. Since the application does not demand very accurate control per-
formance, a common set of gains that provides a smooth assistance for overcoming
spasticity, and driving the arm to reach the desired location for different subjects
was taken to be sufficient.
The outer-loop controller consists of two blocks, the 'reference generator' and
controller that contains the logic for the different therapy modes, and also the
reference generator block that generates the reference signals for the inner-loop po-
sition controllers. The 'motion detection' block contains the logic for the different
therapy modes, which enables/disables the 'reference generator' and the inner-
loop controller, thus controlling the activation/deactivation of robotic assistance.
The reference generator when enabled by the 'motion detection' block generates
a smooth reference signals for the inner-loop controller using the minimum jerk
equation.
⎧
⎨
act
j
θ
(
t
)
,
t
<
t
0
re f
j
×
6
3
+
θ
θ
(
t
)=
(2.1)
Tgt
j
⎩
act
j
5
4
act
j
θ
−
θ
(
t
0
)
τ
−
15
τ
+
10
τ
(
t
0
)
,
t
≥
t
0
min
1,
t
.
t
0
T
dur
−
τ
=
where,
t
0
is the time when the reference generator is enabled by the motion detection block
(i.e. output of motion detection block changes from 0 to 1).
