Meeting Abstract

6.11  Wednesday, Jan. 4  Linear actuator design based on a new hypothesis of muscle contraction KMACK, DA*; YEO, SH; PAI, DK; UYENO, TA; WILKINSON, KC; TESTER, JT; NISHIKAWA, KC; Northern Arizona University; University of British Columbia; University of British Columbia; Valdosta State University; Northern Arizona University; Northern Arizona University; Northern Arizona University

The conventional approach for simulating muscles is to use Hill-type models that include contractile, series elastic, and parallel elastic elements. Under limited conditions, Hill models provide reasonable predictions of muscle force output. However, because they fail to capture the non-linear, history-dependent behavior of active muscle, Hill models perform poorly at predicting muscle force under real-world conditions. Yet, the history-dependent properties of muscle provide intrinsic stability to load perturbations, as well as sustained energy storage. Failure to model these properties has limited the development of devices, such as prostheses, that perform like real muscles. The “winding filament” model solves these problems by incorporating a titin spring that engages mechanically upon activation and winds upon the thin filaments with each cross-bridge cycle. This mechanism was captured in a constitutive “winding ratchet” model. We designed and tested a linear actuator based on the winding ratchet model. The actuator system works by adjusting the center tension between two serial springs with a DC motor. Once the tension stabilizes, a servo latches the ratchet and holds the length between the two springs. A dual-mode force-lever applies forces by adjusting the length of the system, and measures the resulting force output. During isovelocity lengthening and shortening, the actuator replicates history-dependent behavior displayed by muscle in the absence of feedback control. With feedback, these features are enhanced as in real muscles. We plan to develop the actuator system for use in orthotics, prosthetics and robotics, as well as to obtain a better understanding of muscle function.