Biomedical Engineering Reference
In-Depth Information
6.3.4 Control Strategies using Interactive EMG Signals
After the measurements of the MVC EMG signals and finger forces, three different
training modes were provided to the subjects by the hand rehabilitation robot,
namely the (1) continuous passive motion (CPM); (2) EMG-triggered motion
(EMG-TRIG); and (3) continuous EMG-driven motion (cEMG). The first training
mode provides passive motion to each finger for the hand opening and hand grasp
tasks. In this mode, the subject was not required to provide any motor effort.
The actuators would lead all the fingers according to the training task. In the
EMG-triggeredmotion mode and the continuous EMG-drivenmotion mode, EMG
signals are used to identify the intention of the hand opening and grasp from the
subject during training. The EMG levels used in the EMG-TRIG mode and cEMG
mode were normalized to the MVC value, which was defined as:
EMG
i
−
EMG
i
,
rest
EMG
i
,
IMVC
−
EMG
=
(6.1)
EMG
i
,
rest
where, EMG
i
is the EMG of the agonist muscle
i
(ED during the extension, or
APB during the flexion) after the processes of full wave rectification and moving
average with 100ms window, EMG
i
,
rest
is the averaged EMG of muscle
i
during the
resting state, and EMG
i
,
IMVC
is the EMG during maximum isometric contractions.
In the second mode (EMG-TRIG), the hand rehabilitation robot would wait
for the EMG signals from ED or APB to reach above the threshold (commonly set
at the 30% of the maximum voluntary contraction EMG signal strength) before
initiating the motion of the training task. Once the EMG signal from the subject
above the threshold, the robotic system would assist the subject to complete the
training task.
The last training mode (cEMG) uses the EMG as the continuous driven signal
for the training. Subject is required to continuously make voluntary muscle effort
to complete the training task. The system actuates the hand opening or hand
grasp task movements only when the real time EMG signal strength is higher than
the threshold level and the system stops when the EMG signal strength is below
threshold. Thus encourage the subject to continuous make effort to open or grasp
their hands during training.
6.3.5 Hardware and Software Interfaces
All detected EMG signals, force and position feedbacks were sampled at a fre-
quency of 1000 Hz with an USB NI data acquisition system (model: cDAQ-9172),
and a LabView (version 8.5)-based application development platform for real-time
control. The finger position inputs were used as a visual feedback for the subject,
as shown in
Figure 6.10
.
The fingers' positions were displayed by the sliders during the finger tracking
task. The target sliders move back and forward from 0% to 100% of the ROM of
each finger in predefined
t
seconds. When the target sliders move, the subject'
fingers (indicated by the control sliders) need to follow the movement of the target
