Design, Fabrication, and Hysteresis Modeling of Soft Microtubule Artificial Muscle (SMAM) for Medical Applications

Robotic artificial muscles (RAMs) are promising power sources for medical fields such as surgical robotics. However, existing RAMs are challenged by scalability, material costs and fabrications. The nonlinear hysteresis in fluid-driven RAMs causes oscillations in open-loop systems. To circumvent these limitations, this letter introduces hydraulically soft microtubule artificial muscle (SMAM) that is low-cost and scalable, yet simple to fabricate. The SMAM, which only requires a flexible silicone microtube and a hollow micro-coil, is elongated or contracted under a fluid pressure. The SMAM presents an ideal candidate for flexible robotic systems such as endoscopic surgical robots. Experiments are conducted to characterize the SMAMs. Results show that the hysteresis profiles between the input syringe plunger position and output position are stable regardless of its configuration, as opposed to the highly variable responses for the tendon-sheath mechanisms. A new nonlinear model is developed to characterize the asymmetric hysteresis phenomena of the SMAM. Compared to the Bouc-Wen hysteresis models, the developed model presents a better capture of hysteresis. To demonstrate the muscle capability, a SMAMs-driven pulley and a flexible surgical arm are given. The new SMAM and its asymmetric hysteresis model are expected to provide a path for the development of rapidly efficient and low-cost soft actuators for use in flexible medical devices and surgical robotic systems.