Combined feedforward and feedback control of a redundant, nonlinear, dynamic musculoskeletal system

Dimitra Blana, Robert F. Kirsch, Edward K. Chadwick
Received: 6 June 2008 / Accepted: 11 March 2009 / Published online: 3 April 2009
International Federation for Medical and Biological Engineering 2009

Abstract:
A functional electrical stimulation controller is
presented that uses a combination of feedforward and
feedback for arm control in high-level injury. The feedforward
controller generates the muscle activations
nominally required for desired movements, and the feedback
controller corrects for errors caused by muscle fatigue
and external disturbances. The feedforward controller is an
artificial neural network (ANN) which approximates the
inverse dynamics of the arm. The feedback loop includes a
PID controller in series with a second ANN representing
the nonlinear properties and biomechanical interactions of
muscles and joints. The controller was designed and tested
using a two-joint musculoskeletal model of the arm that
includes four mono-articular and two bi-articular muscles.
Its performance during goal-oriented movements of varying
amplitudes and durations showed a tracking error of
less than 4 in ideal conditions, and less than 10 even in
the case of considerable fatigue and external disturbances.