Biomedical Engineering Reference
In-Depth Information
act
j
θ
(
)
t
is the actual joint angle for the joint
j
measured by the joint sensor in the
robot at time
t
.
Tgt
j
θ
is the target angle for the joint
j
.
T
dur
is the task duration, i.e. the time taken by the reference signal to reach the
target value
Tgt
j
act
j
(
θ
)
from the initial value
(
θ
(
t
0
))
.
2.5.2 Robot Therapy Modes
The controller shown in
Fig. 2.3
can be used to practice therapy tasks in three
different modes
passive mode, co-operative mode,
and
active-assist mode
.
(1)
Passive Mode
- In this mode of therapy the subject is relaxed and the robot
does all the work in driving the arm to the target location. The output of the
motion detection block is set to 1 from the start of the therapy task (i.e.
t
0
=
0).
Thus, robotic assistance is always enabled. The passive therapy mode helps
to stretch soft tissues to improve range of motion, keep soft tissue compliant,
reduce tone (Reinkensmeyer
et al.
(2001)), preventing contractures (Hogan
et al.
(2006)) and conditioning for further therapy.
(2)
Co-operativeMode
- The co-operative mode stands for a therapy mode where
both the robot and the subject work together to achieve a particular therapy
task. The different blocks of the RUPERT controller function the same in
this mode as they do in the passive mode. However, there is voluntary
participation from the subject in this mode to complete the given therapy task.
The unidirectional actuation of the robot becomes a very useful feature for this
particular therapy mode. In a fully actuated robot, the robot controller will
resist movements from the subject that are faster than the desired movement
of the robot. However, because RUPERT is unidirectionally actuated in each
DOF, the subject will not feel any resistive force from the robot, when his/her
movement is faster than the desired movement of the robot in the direction
of actuation. However, if the subject's movement lags behind the desired
movement, the subject will feel an assistive force from the robot. This type of a
therapy mode was implemented in the MIT MANUS robot where the subject
feels no force if he/she is able to move ahead of the desired trajectory, but
feel an impedance from the robot when his/her movement lags behind the
desired movement (Krebs
et al.
(2003)). The co-operative therapy mode can be
summarized by the following set of equations,
⎧
⎨
k
j
×
θ
error
j
0,
(
t
) <
0
k
j
×
θ
,
τ
j
(
t
)=
(2.2)
⎩
C
IL
j
error
j
k
j
×
θ
error
j
(
t
) ≥
0
where,
τ
j
(
t
)
is the torque applied to the joint
j
.
re f
j
re f
j
error
j
act
j
θ
(
t
)=
θ
(
t
) −
θ
(
t
)
is the error between the reference angle
(
θ
)
and its
act
j
corresponding actual angle
(
θ
)
for the joint
j
at time
t
.
