Design and Evaluation of Torque
Compensation Controllers for a Lower
Extremity Exoskeleton
Xianlian Zhou
1
and Xinyu Chen
2
1
New Jersey Institute of Technology, Newark, NJ 07102, alexzhou@njit.edu
2
CFD Research Corporation, 2. Huntsville, AL 35806
ABSTRACT
In this paper, we present an integrated human-in-the-loop simulation paradigm for the design and
evaluation of a lower extremity exoskeleton that is elastically strapped onto human lower limbs.
The exoskeleton has 3 rotational DOFs on each side and weighs 23kg. Two torque compensation
controllers of the exoskeleton are introduced, aiming to minimize interference and maximize
assistance to human motions, respectively. Their effects on the wearer’s biomechanical loadings
are studied with a running motion and predicted ground reaction forces. It is found that the added
weight of the passive exoskeleton substantially increases the wearer’s musculoskeletal loadings.
The maximizing assistance controller reduces the knee joint torque by almost a half when
compared to the passive exoskeleton and the resultant torque is only 72% of that from the normal
running without exoskeleton. When compared to the normal running, this controller also reduces
the hip flexion and extension torques by 31% and 38%, respectively. As a result, the peak
activations of the biceps short head, gluteus maximus, and rectus femoris muscles are reduced by
more than a half. Nonetheless, the axial knee joint reaction force increases for all exoskeleton
cases due to the added weight and higher GRFs.
In summary, the results provide sound evidence
of the efficacy of these two controllers on reducing the wearer’s musculoskeletal loadings when
1
Corresponding author
