On dynamic control mechanisms of redundant human musculo-skeletal system

This chapter deals with modeling of human-like reaching and pinching movements. For the reaching movements, we construct a two-link planar arm model with six redundant muscles. A simple task-space feedback control scheme, taking into account internal forces induced by the redundant and nonlinear muscles, is proposed for this model. Numerical simulations show that our sensory-motor control can realize human-like reaching movements. The effect of gravity is also studied here and a method for the gravity compensation on the muscle input signal level is introduced. The stability of this method is proved and its effectiveness is shown through numerical simulations. For the pinching movements, realized by the index finger and the thumb, the co-contraction between the flexor and extensor digitorum muscles is analyzed. It is shown that an internal force term can be generated by the redundant muscles to modulate a damping factor in the joint space. Numerical simulations show that the co-contraction of each digitorums makes it possible to realize human-like pinching movements. Our results suggest that the central nervous system (CNS) does not need to calculate complex mathematical models based on the inverse dynamics or on the planning of optimal trajectories. Conversely, the human motor functions can be realized through the sensory-motor control by exploiting the passivity, nonlinearity and the redundancy of the musculo-skeletal systems.