Effect of Fascicle Length Range on Force Generation of Model-Based Biomimetic Controller for Tendon-Driven Prosthetic...

Model-based biomimetic control with neuro-muscular reflex requires accurate representation of muscle fascicle length, which affects both force generation capability of muscle and dynamics of muscle spindle. However, physiological data are insufficient to guide the selection of range of fascicle length for task control. Here a reverse engineering approach was used to investigate the effects of different fascicle length range on controller's force control ability, so as to justify the selection of operating range of muscle length for a grasp force task. We compared 3 different ranges of fascicle length for their effects on force generation, i.e. R₁: 0.5 - 1.0 L_o, R₂: 0.5 - 1.3 Lo and R₃: 0.5 - 1.6 L_o. The rationale to test these range selections was based on both physiological realism and engineering considerations. The steady state force output and transient force responses were evaluated with a range of step inputs as controller input. Results show that the prosthetic finger can produce a linear steady state force response with all 3 ranges of fascicle length. Peak force was the largest with R3. Fascicle length range had no significant effect on the rise time in force generation tasks. Results suggest that a wider range of fascicle length may be more favorable for force capacity, since the contact point of force control may well fall near the optimal length (L_o) region.