Bio-electromechanical Model of the Muscle Spindle

This work offers a biomimetic, mechatronic linear model for the passive behavior of dynamic nuclear bag fibers of the muscle spindle, capable of transducing joint position and velocity into an electrical signal, similar to that of the afferent anulospiral fibers. We built a mechatronic joint system, composed of a dashpot and a spring in series (Maxwell System) and mechanically coupled the spring to a frequency-modulated oscillator via a variable resistor. The system was capable of sensing the speed of the joint and converting it into a frequency modulated signal in a way similar to that reproduced by the dynamic nuclear bag fibers of the muscle spindle. We were able to prove the concept that the dynamic nuclear bag fibers, effectively behave like a Maxwell system. This is a very simple design that can easily be incorporated into biorobotic systems, greatly improving the accurate positioning of a mechanical joint if it is moving at a measurable speed.