| Traditional rigid robots employ electromagnetic actuations and rigid materials to manufacture controllable and precise rigid-linked systems. Unlike those robots, soft robots own multiple freedom of degrees motion and entirely soft structure, which are fabricated by flexible materials, e.g., polyurethane, macromolecular polymers and similar. These materials are soft, non-reactive and stable in extreme environments; therefore, the soft robots made of them have the characteristics of flexibility, adaptability and compatibility. Muscular organs and hydrostats do not possess a rigid skeleton body. However, they generate the dexterous movements of elongating, shortening, bending and torsion, which are produced by the contraction and recovery of their muscles. They are taken as the source of inspiration to establish soft robotic systems. Usually, researchers design and fabricate composite structures in which some smart materials are embedded into them to mimic a muscular function. These smart materials, e.g., SMAs, electroactive polymers and dielectric elastomers not only act as the actuator units but also form the supporting parts of the composite structure. These soft materials integrated with advanced manufacturing technologies and novel structures enable soft robots to possess remarkable dexterity and flexibility even in unstructured and congested environments.In past decades, the term modularity has widely been used to define the assembly of rigid robots to achieve various morphologies for some specific applications. These robots consist of a number of modular components that have independent control loops and standard interfaces. Simultaneously, modularity can be observed in both the structure and vitality of many molluscs, which can inspire the design and manufacture of soft modular robots. The central bodies of bilateral and actinomorphic molluscs are surrounded by a number of homologous structures or arms; such components are analogous to different modules of a soft robotic manipulator. Moreover, molluscs can regenerate their damaged or lost arms, tissues and organs, which are analogous to the replaceable components of a robot. In this paper, we report on the design, fabrication and performance characterization of a smart modular structure (SMS) that has been inspired by the muscular organs and modularity in animals such as mollusk, and use the SMS as the tentacles of a group of soft robots which can crawl, swim and handle fragile objects in the form of a robotic gripper. The SMS has an independent self-feedback control system and standard interface; therefore, it can be used to assemble robots with multiple morphologies and functionalities such as crawling, swimming and grasping, as demonstrated in this study. These robots can be applied in complicated and various environments as the SMS is insulated, waterproof and fireproof.In this article, we proposed a SMA-based soft and smart modular structure (SMS) focusing on modularity, soft actuators and artificial muscle. The SMS have independent self-feedback system, energy unit and standard communication unit, which is capable of planar reciprocal motion. The SMS can be modular assembled multi-modal soft robots, e.g., actinomorphic soft robots and bilateral soft robots. Take the actinomorphic soft robots as example, we presented its adaptability in various environment. To expand the application of the SMS, we designed smart modular finger structure (SMFS) based on the promoting of the SMS. Based on the SMFS, we designed and fabricated the soft hand robots. The main content and results of the article are below:(1) The designation and fabrication of the SMS, the SMFS and the actinomorphic soft robots, soft hand robots. Based on bionic study from muscular organs and modularity in animals, we designed the SMA-based SMS whose fabrication adopted the soft lithograph and layer casting technology. To delay or avoid the overheating of the SMS, we proposed a micro-fluid SMS inspired by the tubes in the plant and animals. Besides, we designed the SFMS based on bionic study on the hand. Based on the SMS and SFMS, we modular assembled the actinomorphic soft robot and soft hand robot, respectively. Moreover, we combined the energy unit, communication unit with the SMS to fabricate an integrated soft actuator, which was capable of independent work.(2) The kinematics and thermodynamics of the SMS. Based on a modified D-H method, we built the kinematic model of the SMS. A model of the three-armed actinomorphic soft robot was built in MATLAB, and its effectiveness was prove by comparing the results between the simulation and experiment. The finite segment method was used to divide the SMS into a number of equivalent annuluses, whose centers locate in the cross section of the SMA wires. Then, the thermodynamic model of the SMS was built in the MATLAB platform by synthesizing the finite segment method and lumped parameter method.(3) The adaptive regulation heating strategy, high frequency reciprocal flapping motion and analysis of the dynamic of the SMS. SMA wires refer to a group of temperature-induced alloys, and its resistance regularly vary with the temperature. Taking advantaging this property, we built a self-feedback control system, which is available both in the heating and cooling processes of the SMS. The control variable of the self-feedback system can be regulated by the extremum of the sampling data in real-time, which avoids the errors caused by the fluctuation of the power supply source. Based on the self-feedback control system, the SMS achieved bending range control both in the heating and cooling processes. An AR heating strategy was proposed to regulate the heating process of the SMS by utilizing the extremum property of the self-feedback control system. Under the AR heating, the heating time of a reciprocal motion SMS decreased continuously, leading to a lower value. We measured the frequency responses of the SMS under the AR heating strategy and the constant heating strategy, respectively. The cut-off frequency under the AR heating was 0.73 Hz, which is approximately 2 times than the one under the constant heating. The above results illustrate that the AR heating strategy can protect the SMS and prolong its work time, and improve its dynamic response as well.(4) Experiments and control strategies of the actinomorphic soft robots. Based on the SMS, we modular assembled a five-armed actinomorphic soft robots to study the multi-function in various environments. At first, we optimizing the gait parameters of the mobility of the robots. Secondly, we adopted the robot to manipulate the objects like a gripper based on the AR-PWM heating strategy. Thirdly, we studied the capability of the robot in jumping by exert high current on the SMS. Finally, we studied the propelling theory of the jellyfish-like robot which is a variant of the actinomorphic soft robot.(5) The designation, fabrication and control strategies of the soft hand robot. Based on the SFMS, we fabricated the soft hand robots by using mold casting technology. Many experiments were conducted to study the capabilities of the soft hand robot. Based on the electromyography, we achieved the interactive control between the human and the soft hand robot. The soft hand robot was capable of man-like hand motion. The most interesting is the soft hand have a huge gap in its dynamic response, which results its finger can slow and fast motion.
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