Biomedical Engineering Reference
In-Depth Information
k
j
indicates whether the angle at the joint
j
increases or decrease in the direction
of actuation in joint
j
. For example, the shoulder flexion/extension (SFE)
angle increases from 0 deg to 90 deg when the shoulder is flexed. So,
k
SFE
=+
1 for the shoulder. While for the elbow flexion/extension (EFE)
joint, the joint angle decreases from about 110 deg to 0 degwhen the elbow
is extended, thus
k
EFE
= −
1.
C
IL
j
(•)
is a function that combines the inner-loop control law and actuator
dynamics for the joint
j
.
(3)
Active-Assist Mode
- The active-assist therapy mode is implemented in the
form of a triggered assistance mode. When a reaching task is presented to
the subject, the subject starts the task by making a voluntary effort to reach
the target. The output of the motion detection block is 0 at the start of the
therapy task, thus allowing the subject to start the task voluntarily. During
this period of voluntary movement, the motion detection block monitors the
distance between the endpoint of the subject's arm and the target location
(
r
EP
(
t
))
. The robotic assistance remains disabled as long as the rate of change
v
t
EP
(This is
so, because when the subject is moving towards the target
dr
EP
/
dt
of
r
EP
(
t
)
is less than a particular threshold i.e.
dr
EP
/
dt
(
t
) <
will be
negative). The value of
v
t
EP
will determine the sensitivity of the algorithm to
either stops in the subject's movement or a movement away from the target.
Once the value of
dr
EP
/
dt
(
t
)
v
t
EP
)
, the output of the
motion detection block is changed to 1, thus initiating robotic assistance to
assist the subject's arm towards the target. It should be noted that after the
initiation of assistance, the functioning of the robot will be similar to the co-
operative mode if the subject continues to make any voluntary contribution to
the movement.
(
t
)
crosses the threshold
(
The use of these three therapy modes for performing reaching movements by
plots of the three DOFs of the robot involved in reaching movements, shoulder
flexion/extension, elbow flexion/extension and humeral rotation. The figure
consists of a 9 plots arranged in three rows and columns, which correspond to
the three therapy modes, and the three DOFs respectively. In the passive mode
(row 1) the subject was relaxed and the position controller of the robot drives the
three DOFs to their corresponding target angles. While in the co-operative mode
(row 2), the subject provided voluntary contribution to the movement which can
be seen in the section of the movement where the actual angle (blue trace) leads
the corresponding reference angle (red trace). In the active-assist mode, the subject
starts the movement voluntarily, and the robotic assistance is initiated later when
the 'motion detection' block detects either a slow movement or a movement away
from the target. The difference in the initiation of robotic assistance between the
passive and co-operative modes, and the active-assist therapy mode can be seen
as a shift in the point-of-assistance (dashed vertical black line), which is defined as
the time during the therapy task at which robotic assistance is initiated, between
