Modeling of Novel Compound Tendon-Sheath Artificial Muscle Inspired by Hill Muscle Model

Various types of artificial muscles have been developed in recent years. Nevertheless, they are not well suited to robot applications due to the defects of their mechanical properties, such as small output, limited shrinkage, and slow response. Moreover, portable designs are difficult to realize because of the special power-source requirement. For the shortcomings above, the paper presents a motor-driven tendon-sheath artificial muscle inspired by Hill muscle model. The series and parallel elastic elements both made up of linear springs are applied on the tendon-sheath actuation system. Consequently, the tendon-sheath artificial muscle is created with a compliant structure, variable elasticity, and high power transmission capacity. Next, a compound tendon-sheath artificial muscle transmission system similar to the form of antagonist muscles is modeled based on the static Coulomb friction model. The transmission model with a sinusoidal input is simulated and analyzed in detail. And experiments are performed to validate our transmission model. The model shows high accuracy in predicting the system output. At the frequency of 1 Hz, the fidelity of output torque is 92.3% and the output displacement is 94.2%. Moreover, the maximum output force of the tendon-sheath artificial muscle with 0.8 mm tendon (under the safety factor of 4) can reach 80 N.