Study On Biologically Inspired Design Of Actuator-sensor-structure Integrated SMA-artificial Skeletal Muscle

Natural muscle like skeletal muscle is the most spectacular actuator in the world due toits unique flexibility, versatility and biomechanical behavior. After millions of years ofevolution, animals have shown breathtaking motion performance that artificial technologycan hardly imitate. Researchers increasingly agree that if human technology could mimicnatural muscle, then biological-like performance would follow. Therefore, to design amuscle-like actuator is a worthy endeavor for engineers and natural muscle has providedtremendous biological inspiration for muscle-like actuator design. However, two challengeshamper the development of artificial muscle (AM): biologically inspired design (BID)principle and technology. BID uses analogies to biological systems to develop solutions forengineering problems. BID is not the blind copying of nature but the comprehensiveconsideration of engineering problems, biological system identification and technology.The motivation of this dissertation is to develop a novel AM with muscle-like flexibility,high force-weight ratio and multifunction of actuating, self-sensing and energy-storing.Firstly, BID principle should be solved, i.e. how to guide the AM design. secondly, theselection and processing of biomimetic material, i.e. how to implement the AM design. Inthis dissertation, BID architecture is proposed systematically to guide the AM design. Then,shape memory alloy (SMA) is adopted as the actuating element. In order to imitate musclebiomechanical behavior, an in-depth study is conducted on muscle biomechanics andmaterial properties of SMA. Furthermore, two key technology research regardingself-sensing and hysteresis properties is conducted for SMA actuated artificial skeletalmuscle (SMA-AM). The main research contents and achievements of this dissertation arelisted as follows.1. Biologically inspired design architecture of artificially muscle. BID architecture isproposed systematically. The BID comprises two steps: biologically system identification(BSI) and engineering system realization(ESR), which collectively determine the biomimetic degree (BD). Furthermore, the muscle system identification is carried out according to BIDmethod and the muscle biomechanical model is established as the guideline for AM design.2. The develop of SMA-based actuator-sensor-structure integrated artificial skeletalmuscle. The SMA-AM is designed based on BID architecture and biomechanical model,which comprises parallel SMA wires, surrounded by a custom-made passive composite(CMPC). The SMA wires are arranged in overlapped pattern inspired from sarcomerestructure. The CMPC mainly comprises silicon tube encapsulated by a polyethyleneterephthalate (PET) mesh. Experimental results demonstrate that the SMA-AM can initiallyimitate muscle biomechanical property and actuating and energy storing function. To achievethe integrated design of actuator-sensor-structure, SMA self-sensing properties are exploredand modeled based on the investigation of SMA electrical resistivity (ER). Finally theself-sensing capability is further demonstrated by its application to a novel SMA-AMactuated robotic ankle-foot.3. Hysteresis modeling and compensation control of SMA-AM. SMA presents non-linearsaturated hysteresis behavior during phase transformations, which may cause inaccuraciesand even oscillations in SMA-AM control systems. SMA hysteresis properties are deeplyexplored based on a series of electro-thermo-mechanical experiments under different stressand driving frequency conditions. And then a sigmoid-based hysteresis (SBH) model isproposed to characterize the hysteresis phenomenon. Experimental results demonstrated themodel validity. Then, the hysteresis phenomenon is greatly reduced by utilizing the inverseSBH model based feedforward controller.4. Application exploration SMA-AM actuated ankle-foot rehabilitation system. Todemonstrate the integrated actuating and self-sensing properties, a new SMA-AM actuatedankle foot orthosis (SMA-AFO) system is designed with light and compact, highforce-weight ratio properties. The SMA-AFO is capable to assistant the dorsiflexion andplantarflexion of human ankle-foot joint. In order to deeply characterize the dynamicbehavior of the SMA-AFO system, a general thermal-electrical-mechanical model isproposed, including heat transfer behavior, voltage-displacement hysteresis, self-sensingbehavior frequency response of the system. Furthermore, a model-based sliding mode controllaw is developed for the SMA-AFO system. Finally, a Lyapunov function is proposed toprove the global stability of the SMA-AFO system. Experimental results have demonstrated the correctness the general model and the effectiveness of the controller. The AFO responsespeed and tracking accuracy are greatly improved with frequency increased by up to1Hz andthe RMS tracking error reduced by up to82%, which basically satisfies the initialrequirements of ankle-foot rehabilitation.